In this two-part article, the authors take a look at the major factors affecting background contamination in inductively coupled plasma-mass spectrometry (ICP-MS), particularly when measuring ultratrace elements in specialty applications such as aerosol matrices from electronic cigarettes and electronic nicotine delivery systems (ENDS). In order to obtain meaningful data, the analyst must understand and address the magnitude and variability of environmental contamination by ubiquitous trace metals during the sample preparation procedure. The impact of these contaminants on the procedural blank and the associated impact on the accuracy and precision of sample results can unfortunately lead to false positive results.

Liquid introduction with flow injection is the most widely used sample introduction method for inductively coupled plasma-mass spectrometry (ICP-MS). Nevertheless, background contamination issues are problematic for determinating trace or ultratrace analyte concentrations that are commonly investigated. This is particularly important in specialty applications such as aerosol matrices from electronic cigarettes (also known as vapes, electronic nicotine delivery systems [ENDS]). To obtain meaningful data, the analyst must understand and address the magnitude and variability of environmental contamination by ubiquitous trace metals during sample preparation for trace analyses. The impact of these contaminants on the procedural blank and the associated impact on the accuracy and precision of sample results can lead to false positive results. Part 1 of this tutorial addresses address how environmental contamination may be minimized by using good personal analytical practices, avoidance of glass and low purity quartz during sample collection and preparation, and choices of high purity solvents during sample collection and preparation.

Part 2 will discuss the use of high purity polymer materials during sample collection and preparation, elemental carryover during sample preparation, and how the inorganic analyst can avoid approaches and procedures that may cause unforeseen problems.

Preparation for Analysis of Organic Substances Versus Inorganic Substances

Sample preparation and analysis of samples for many organic substances may be based on the assumption that the organic analytes are not environmentally ubiquitous. For example, if an analyst is required to analyze nicotine in tobacco, tobacco smoke, liquids, or aerosols from ENDS, the analyst may reasonably assume that extractable nicotine concentrations on glass surfaces of clean beakers, flasks, impingers, filter materials, pipet tips, glass or polymer sample vials, and other ancillary materials are negligible. In such cases, any analytical signal detected in procedural blanks is likely due to poorly cleaned glassware, the presence of other compounds with the same nominal mass, or from instrumental electronic noise. This assumption, however, is not valid for sample preparation for analysis of trace metals in tobacco, tobacco smoke, liquids, or aerosols from ENDS with inductively coupled plasma-optical emission spectrometry (ICP-OES) or ICP-MS. Metals are ubiquitous in many, if not most, commonly used laboratory set-up and supplies, including (but not limited to) glassware, hood surfaces, dust particles, filter paper, tubing, and pipette tips. Different ancillary materials and a different skillset are required for sample preparation for analysis of trace metals in any matrix by ICP-OES or ICP-MS.

Factors That Interfere with Accuracy in Analyses for Inorganic Substances

The relative ease or difficulty of a given analysis depends on several factors, including concentration of the analyte relative to the sensitivity of the analytical instrumentation, the chemistry of the analyte, the matrix, isotopic interferences from other elements that have the same mass as the analyte (1), polyatomic ionic interferences formed in the plasma during the analysis that have the same mass as the analyte (2), and the potential for environmental contamination by extractable metals that are present to various degrees on all surfaces and most materials.

The following suggestions can be an effective means to reduce the background contamination issues, make a difference in levels of contamination associated with environmentally ubiquitous metals, and yield lower procedural blanks and method limits of detection (LOD), as well as false positive results:

Use powder-free gloves, nitrile if possible. Powder particles can contaminate samples.

Do not pick up sample tubes with a fingertip inside the tube opening.

Avoid contact of fingers or gloves with surfaces near the opening or inside the cap of any sample tube or solvent container.

Use pipets with polypropylene or fluoropolymer pipet tips, never glass pipets.

Use pipets that do not have external stainless steel tip ejectors (Figure 1; all figure images are CDC sourced). It is easy to touch a drop of liquid with the tip ejector and contaminate a sample with iron, chromium, nickel, and other metals. If pipets have external steel tip ejectors, it is advisable to remove the tip ejectors and remove the tips manually after use in sample preparation.

Never turn a pipet sideways while liquid is in the tip. Acid will corrode the pipet piston and degrade it, resulting in contaminated samples.

If a pipet tip touches skin or a laboratory surface, assume that it is contaminated. Learning not to lean back against a countertop in a laboratory also prevents contact and contamination of tips that may have been left protruding over the side of the countertop by a fellow laboratory worker who did not want the tip to touch the countertop surface.

Do not purchase acid in glass containers. Ultrahigh purity acids for analysis of metals are double distilled from fluoropolymer or high purity quartz stills and sold in perfluoroalkoxy (PFA) or fluorinated ethylene propylene (FEP) fluoropolymer bottles (Figure 2). Less expensive intermediate purity acids are available in polyethylene or polypropylene containers. Several purity grades can be obtained in polyethylene or polypropylene containers that are still higher purity than acids from glass bottles. The acids may be further purified by distillation in PFA or high purity quartz stills sold by some vendors. Depending on acid consumption in a laboratory, these stills can pay for themselves with savings on ultrahigh purity acids in approximately a year.

If using bottle top acid dispensers, avoid glass entirely. Use empty PFA, FEP, or polypropylene containers that have been well rinsed with dilute ultrahigh purity acid. Use dispensers with fluoropolymer only exposed to the path of liquid flow (Figure 2). A dispenser that has glass parts or that has a platinum coated valve ball is unsuitable for dispensing acids for trace metals analysis. For example, one of our team members obtained a dispenser that had an “inert” platinum coated valve ball in an otherwise all-fluoropolymer liquid path. This dispenser ruined several of our analyses before we realized that multiple metal impurities were leaching into acid from the platinum coated valve ball. The first few liquid pumps were low in metals concentrations, followed by metals concentrations that reached a peak as the acid that was in contact with the platinum reached the dispenser outlet, then declined again as subsequent pumps rinsed the metals out.

If the laboratory has high airborne particulate, use a plastic autosampler cover. This is a good idea even if the air particulate is not very high. Covers may be purchased with or without high efficiency particulate air (HEPA) filtered air units that blow filtered air over open sample containers.

Unless it is the only way to avoid inhalation of acid vapors, use a hood for diluting or transferring concentrated acids, but do not leave samples in a hood unless it has little or no corrosion and laminar flow with HEPA filtered air. If laboratory air has high particulate levels, a standard hood protects the analyst, but pulls contaminated laboratory air over open sample or solvent containers faster than air outside the hood. Polypropylene hoods with HEPA or ultra-low particulate air (ULPA) filtered air are available (Figure 2), but they require sufficient dedicated air flow. If the analyst works with hydrofluoric acid, a hood absolutely must be used for safety.

Choice of Materials Used for Sample Collection, Preparation, and Analysis 

An analyst must consider and choose appropriate types of ancillary materials that will be used for transfer, containment, and digestion for dissolution of metals and elimination of organic substances before developing an analytical method for analysis of trace metals. As previously discussed, glass containers and transfer devices are appropriate choices for preparation of samples for the analysis of organic substances. Even though some glass microparticles and trace inorganic substances from glass may be extracted into the standard or sample solution, they are often eliminated during further organic sample preparation steps, or not detected during common chromatographic or mass spectrometric analyses. However, the use of glassware is a very poor analytical practice for analysis of trace metals with very few exceptions.

Mercury is a rare exception to the rule of avoiding glass for analysis of trace metals. Mercury compounds may adhere to glass silicate surfaces on the basis of polar attractions, but mercury is a Pearson soft acid cation metal (3,4) and is not strongly coordinated to surface oxygen atoms of glass silicate containers in the presence of a polar or acidic solvent. Mercury halides are readily extracted from some aqueous solvents into polar organic solvents in glass vessels (5). Because mercury is not strongly coordinated to silicates, it is usually found at very low concentrations in glass. Thus, glass tends to have very low mercury concentrations. Therefore, mercury standards may be prepared in glass volumetric flasks for analysis with a direct mercury analyzer (6,7). Low ng/L concentration mercury standards prepared in 0.2% v/v ultrapure nitric acid and 0.01% w/v high metals purity L-cysteine were stable when kept refrigerated in glass flasks for more than a year (Figure 1). Refrigeration was used between analyses to slow cysteine thiol oxidation beyond the disulfide form of sulfur that can coordinate soft acid cation metals like mercury to prolong the stability of mercury in oxidized form in solution.

Mercury is an exception to the common good analytical practice of avoiding sample and solvent exposure to glass when it is the lone analyte with a direct mercury analyzer. If mercury is not the lone analyte, the general good inorganic analytical practice of avoiding glass always applies, because other metal contaminants are likely to be extracted from glass by acidic solvents. Avoiding glass during trace metals analyses has been recognized as a good inorganic analytical practice for decades. We have found it necessary to briefly review the chemistry of glass related to metals analysis since the development of ENDS devices, and availability of grant funding to study their emissions has attracted many scientists with limited experience in the analysis of metals. In some states, regulatory requirements for aerosol de- vices include the analysis of toxic metals in liquids and aerosols of some devices. This has increased the demand for inorganic analytical chemists in commercial compliance laboratories as well, resulting in a shortage of competent inorganic analytical chemists. Often this demand is filled with analysts who may have experience performing analyses of organic substances but may benefit from a review of good inorganic analytical practices that differ from good organic analytical practices.

Avoidance of Glass for Inorganic Sample Collection, Preparation, and Analysis

Murphy (8) discussed the need to avoid glass during sample preparation for accuracy in trace element analyses in 1976, before greater sensitivity made possible by instrumentation developments since that time made lower contaminant concentrations even more apparent. In 1984, Knapp stated, “Glass is usually not suitable...” for trace element determinations (9). In 1996, Dulski discussed the avoidance of glass during analysis of metals (10). The inorganic analytical chemist needs to be aware of why these highly experienced chemists discussed the need to avoid glass during sample preparation and inorganic analysis.

The first reason is the mobile nature of ions in glass. Glass is manufactured from substances with low elemental purity, so glass is not a pure silicate substance. Thin glass membrane electrode glass is known to contain other impurities but is manufactured with high concentrations of some ions, such as sodium from soda ash. Whether the analyte intended to be measured is hydronium ion with a pH meter electrode or a specific metal with a selective ion electrode, the thin glass membrane analytical design is based on different potentials for two or more different hydronium or metal ions to migrate to and from the glass membrane silicate matrix (11). There are numerous selective glass electrode designs based on different glass membrane potential combinations for different metal ions, but the application of the pH meter demonstrates the migration of acid hydronium ions into the glass membrane in exchange for metal ions from glass silicate matrix. This is one reason that acidic samples are contaminated by metal impurities from glass.

If pure water were a sufficiently strong solvent for all metal ions, inorganic analytical chemistry would be much easier. However, most metals other than alkali metals require acids to prevent hydrolysis of the metal ions to the respective oxides or hydroxides, nearly all of which are insoluble in water at neutral pH (4). To illustrate problems with the use of acids in glass flasks as impingers for collection of aerosols for metals, four borosilicate glass laboratory flasks were rigorously precleaned overnight with ultrapure acid, and shaken with 10% v/v ultrapure concentrated nitric acid and 1% v/v hydrochloric acid that was discarded before five hour leaching periods in the same acid mix, corresponding to a procedure for trapping metals for aerosol analysis over a period of 5 d. Although five analyses in 5 d is insufficient for establishing a legitimate method limit of detection, the day-to-day variability and ranges of concentrations observed from leaching chromium, nickel, copper, zinc, tin, and lead were higher than sample results reported in the literature, with the exception of copper at elevated concentrations in some aerosols from a few devices (12). It is apparent that the use of glass vessels for sample collection for smoke or aerosol analysis will result in samples contaminated by metals leached from glass by acid, and produce unreliable results.

Before more advanced sample preparation devices became available, automated pipettors with glass barrels were used for dilution of samples such as urine into acids containing internal standard metal ions for analysis. The sample and internal standard solution uptake and delivery tubing were made from ultrahigh metals purity fluoropolymers such as PFA. However, the syringe barrels were made of glass and later from low purity quartz. When an analytical chemist began the workday, the syringe barrels were set to maximum volume and 10 to 20 syringe barrel volumes of dilute ultrapure acid solution were passed through the barrels to rinse out the metal ion contaminants that had accumulated from the glass barrels. When the analyst monitored the selected ions, they decreased with each barrel rinse. The acid-extracted metals were significant relative to metal concentrations in urine samples until the syringe barrels were well rinsed with acid, thus necessitating the daily preanalytical acid rinses of the glass barrels. Although the metal concentrations decreased by about half over a period of six months to a year, they never completely diminished. To make matters worse, the kinetics of ion exchange from the glass silicate matrix to the acid were fast. The analyst had to have all samples ready for dilution and continuously dilute one sample after another without stopping. If the sample preparation was stopped for even 5 min, the analyst would see an increase in metal concentrations that came from the glass barrels and contaminated the samples. Even after a 5 min delay, the analyst had to again rinse the barrel contents with the acid solution before resuming sample preparation. One manufacturer was aware of this problem and manufactured some quartz barrels for trial purposes. Unfortunately, the manufacturer used less expensive low purity quartz to manufacture the barrels rather than high purity fused silica quartz. The low purity quartz barrels had lower concentrations of metals leaching from the quartz silica matrix than from glass barrels over time, but the metals concentrations were still significant relative to metals concentrations in urine samples. Over a six-month period, the metals leached from low purity quartz barrels also diminished to concentrations lower than metals concentrations from glass barrels after six months, but the metals concentrations were still sufficiently high that the barrels still had to be daily rinsed out with acid prior to use and after any sample preparation delay. After years of intentional leaching from glass syringe barrels, leaching of metals by acids was still observed. This illustrates that glass cannot be “cleaned” sufficiently for use in trace metals analysis. The avoidance of contact of acidic solutions with glass is not limited to inorganic acids but applies to organic acids as well (13).

Glass fiber filters are commonly used for trapping mainstream smoke particulate for analyses of organic substances. These filters have high acid leachable metals concentrations and are inappropriate for aerosol sample collection from ENDS devices and from mainstream smoke for metals analyses. Low purity quartz filters (14) also released unacceptably high metal concentrations unless subjected to extensive soaking and elimination of fine particles with multiple hot acid rinses. Even after extensive soaking in dilute ultrahigh purity acids, only cadmium, lead, and thallium could be observed in mainstream smoke at concentrations sufficiently above the acid extractable metals backgrounds that remained in the “precleaned” quartz filters (14). Many metal ion concentrations are lower in ENDS aerosols than in mainstream smoke since no combustion occurs; and because ENDS devices are not constructed from some toxic metals and metalloids that are commonly present in tobacco, such as cobalt, arsenic, cadmium, and mercury. The metals concentrations obtained from using dilute acid to extract metals from ENDS aerosols trapped with low purity quartz fiber filters were too high and too variable from sheet to sheet of quartz filter material for use as ENDS aerosol traps (15). Metals that are used in manufacture of ENDS devices are often below sensitive analytical method limits of detection in liquids and aerosols from newly manufactured devices (16), but the metals become more elevated with age and use of the devices due to corrosion (17). Since most mainstream smoke metals concentrations and ENDS aerosol metals concentrations after device corrosion remain at trace or ultratrace levels, glass or low purity quartz fiber filters contribute significantly to aerosol background levels because of metals leached by acid from the glass or low purity quartz filters. Thus, such filter materials are not suitable for use as mainstream smoke and ENDS aerosol sample collection or preparation materials. Extraction of metals from glass is not limited to acidic solutions. A group affili- ated with Schott AG recently published a white paper on delamination of pharma- ceutical grade glass vials in basic solution (18). They discussed their work to produce glass vials that are more resistant to delamination, as well as earlier work on delamination of glasses of various compositions in alkaline solution. Delamination of glass is not unexpected, since silicates are more soluble in alkaline solution, permitting small flakes of glass (along with metals in the glass silicate matrix) to become liberated from glass surfaces as the silicate is dissolved. Significant solubilization of molded glass component surface elements was also determined when vials were stored containing neutral aqueous 15% w/v KCl solutions or other alkali metal salts (19). For the inorganic analytical chemist, this data on glass and metal contaminants in acidic, basic, and neutral high ionic strength solutions confirm that complete avoidance of the use of glass flasks, impingers, watch glasses, sample tubes, vials, glass fiber filters, and other ancillary glass materials is good inorganic analytical practice for avoiding sample contamination from metals in glass.

In Part 1 of this article, we have discussed good sample handling practices that will help minimize sample contamination during preparation for inorganic analyses. We reviewed the background and gave specific examples of sample contamination caused using glass and low purity quartz during sample collection and preparation.

In our next column, we will discuss the use of ancillary polymer and fluoropolymer materials that may be obtained with very low acid-leachable metals and that may be further cleaned for use in inorganic sample collection and preparation.

The findings and conclusions in this report are those of the authors and do not necessarily represent the views of the Centers for Disease Control and Prevention.

(1) Neubauer, K. Reducing the Effects of Interferences in Quadrupole ICP-MS. 

(2) May, T. W.; Wiedmeyer, R. H. A Table of Polyatomic Interferences in ICP-MS. 

; University Science Books, 2000, 191–228.

(4) Pappas, R. S. Sample Preparation Problem Solving for Inductively Coupled Plasma-Mass Spectrometry with Liquid Introduction Systems I. Solubility, Chelation, and Memory Effects. 

(5) Tandon, S. N.; Gupta, C. B. Liquid-Liquid Extraction Behaviour of Mercury (II) as Chloride. 

(6) Fresquez, M. R.; Gonzalez-Jimenez, N.; Gray, N.; Watson, C. W.; Pappas, R. S. High Throughput Determination of Mercury in Tobacco and Mainstream Smoke from Little Cigars. 

(7) Fresquez, M. R.; Pappas, R. S.; Watson, C. H. Establishment of Toxic Metal Reference Range in Tobacco from U.S. Cigarettes. 

Accuracy in Trace Analysis: Sampling, Sample Handling, Analysis. Volume I, Publication 422; National Bureau of Standards

(9) Knapp, G. Decomposition Methods in Elemental Trace Analysis. 

A Manual for the Chemical Analysis of Metals

. Analytical Sciences Library, Electrochemical Analytical Chemical Methods, 2023, 7.1. 

https://chem.libretexts.org/Bookshelves/Analytical_Chemistry/Supplemental_Modules_(Analytical_Chemistry)/Analytical_Sciences_Digital_Library/In_Class_Activities/Electrochemical_Methods_of_Analysis/02_Text/7%3A_Electrochemical_Analytical_Methods/7.1%3A_Ion-Selective_Electrodes#:~:text=The%20glass%20used%20in%20a%20pH%20electrode%20contains,distance%20into%20the%20glass%20and%20displace%20 sodium%20ions

(12) Ahmed, A, A.; Youssof, I. M. Attack on Soda-Lime-Silica Glass Bottles by Acetic, Citric, and Oxalic Acids. 

Measurement of Elemental Constituents of Cannabis Vaping Liquids and Aerosols with ICP-MS

Measuring Heavy Metal Contaminants in Cannabis and Hemp

(14) Pappas, R. S.; Polzin, G. M.; Zhang, L.; Watson, C. H.; Paschal, D. C.; Ashley, D. L. Cadmium, Lead, and Thallium in Mainstream Tobacco Smoke Particulate. 

(15) Lisko, J. G.; Hearn, B.; Pappas, R. S.; Stanfill, S.; Tyx, R.; Keong, L., et al. “Factors to Consider when Analyzing Electronic Cigarettes: Challenges and Solutions.” Society for Research on Nicotine and Tobacco Annual Meeting 2018, POS4–13. 

https://cdn.ymaws.com/www.srnt.org/resource/resmgr/conferences/2018_annual_meeting/65388_srnt_2018_abstract_fin.pdf

(16) Gray, N.; Halstead, M.; Valentin-Blasini, L.; Watson, C.; Pappas, R. S. Toxic Metals in Liquid and Aerosol from Pod-Type Electronic Cigarettes. 

 (4), 337–347. DOI: 10.1093/jat/bkaa185

(17) Halstead, M.; Gray, N.; Gonzalez-Jimenez, N.; Fresquez, M.; Valentin-Blasini, L.; Watson, C.; Pappas, R. S. Analysis of Toxic Metals in Electronic Cigarette Aerosols Using a Novel Trap Design. 

(18) Ennis, R. D.; Pritchard, R.; Nakamura, C.; Coulon, M.; Yang, T.; Visor, G. C.; Lee, W. A. Glass Vials for Small Volume Parenterals: Influence of Drug and Manufacturing Processes on Glass Delamination. 

(19) Haines, D.; Gober-Mangan, E.; Klause, M.; Rothhaar, U. Comparative Predictive Glass Delamination Study. 

Articles

Columns: Atomic Perspectives

Good sample handling practices that minimize sample contamination during preparation of inorganic analyses are discussed, using glass and low purity quartz as examples.

Contamination Control During Sample Preparation for Trace Element Analysis of Electronic Cigarette Aerosol with Inductively Coupled Plasma-Mass Spectrometry, Part 1

After introducing organic nitrogen polymers in the last column, we continue this theme by studying an important family of polymers—polyaramids. In this column, we examine the spectra of polyaramids, which are polyamides that contain an aromatic ring in their chain. Included in this family is Kevlar, which is an important polymer many are familiar with. We also examine the spectra of “slip agents,” which are small molecule amides used to lubricate injection molds and are oftentimes found as contaminants in polymer products.

A common way of forming polymers into useful products is called 

 (1). In this process, melted polymer is injected into a cavity or mold in the shape of a desired product. The melted plastic conforms to the shape of the mold; once the plastic cools, the mold is opened and the newly made product is ejected. The process is then repeated. Injection molding is a fast and inexpensive way of making many plastic items (1).

However, a problem with injection molding is that the manufactured product can sometimes stick to the surface of the mold, meaning the process must be shut down and the stuck piece removed, which wastes time and money. A trick injection molders use to solve this problem is to coat the inside of the mold with a slip agent, a material that lubricates the surface of the mold, allowing formed plastic products to be ejected from the mold more easily.

Small molecule amides are frequently used as slip agents. The reason I am including these in a discussion of polymers is that slip agents can be found as surface contaminants on some types of polymers, and their spectra can interfere with determining the structure of the polymer itself. For example, a polyethylene-based product with an amide slip agent on its surface will exhibit peaks from the polymer and the amide, adding confusion as to whether the product is made from a polyamide, polyethylene, or both. This confusion is a problem with surface sensitive infrared (IR) sampling techniques, such as attenuated total reflectance (ATR), where the slip agent on the surface is more readily sampled than the underlying polymer because of the small depth of penetration of the technique (2). A way around this problem is to simply clean the surface of the polymer with a paper towel soaked in solvent before taking the spectrum of the sample.

The mid-IR spectrum of a slip agent containing a primary amide group, and the structural framework of the primary amide group, are seen in Figure 1.

Remember from our last article that amides come in three varieties: primary; secondary; and tertiary (3). The quantity being counted is the number of C-N bonds, and we saw that a primary amide has one C-N bond, a secondary amide has two C-N bonds, and a tertiary amide has three C-N bonds (3). Additionally, as the number of C-N bonds goes up, the number of N-H bonds goes down. Thus, a primary amide contains an NH

 group, a secondary amide contains a N-H group, and tertiary amides have no N-H bonds. We have also seen that most polyamides contain secondary amide linkages in their backbones (3).

We have discussed the IR spectra of primary amides previously (4). The group wavenumbers for primary amides are shown in Table I.

Briefly, primary amides exhibit two N-H stretching peaks between 3370 and 3170 cm

 (going forward, all peak positions will be in cm

 units even if not so noted), a carbonyl stretch from 1680 to 1630 as exhibited by all amides, a NH

 scissors peak from 1650 to 1620, and a N-H wag from 750 to 600 (4).

We know the slip agent whose spectrum appears in Figure 1 is a primary amide, because of the two N-H stretches at 3358 and 3192, and the C=O stretch at 1659. These three peaks comprise the diagnostic group wavenumber pattern for primary amides. Note that the N-H stretches in Figure 1 fall in the same range as O-H stretches, but are narrower and less intense than the O-H stretches we are used to seeing. This is because hydrogen bonding for N-H bonds is weaker than for O-H bonds, ultimately because of the fact that O-H bonds are more polar than N-H bonds (5). The NH

 scissors peak in Figure 1 is seen at 1633. There should be a primary amide NH

 wagging peak in Figure 1. However, the spectrum in Figure 1 was measured using an ATR crystal that cut off at 750—thus, we cannot see this peak.

, then, is a polymer with an aromatic amide in its backbone. If the polymer chain contains a para linkage, it is called a 

, whereas, if the chain contains a meta linkage, it is called a 

A well-known para-polyaramid is Kevlar, which is a tough, light, and strong polymer made into bulletproof vests and body armor, among other things. The key to the strength of aramids is that adjacent polymer chains can hydrogen bond through the N-H and C=O functional groups, as illustrated in Figure 2.

A single hydrogen bond may not be very strong, but moles upon moles of them are, which gives materials like Kevlar their strength. Similarly, cellulose chains interact via OH/OH hydrogen bonds, strengthening their fibers and allowing such magnificent structures as trees to rise hundreds of feet into the air (7).

The IR spectrum of Kevlar, whose proper chemical name is 

Similar to most polyamides, the Kevlar backbone contains secondary amide linkages. Recall from last time that diagnostic group wavenumber pattern of peaks for secondary amides are one N-H stretching peak from 3370 to 3170, a C=O stretching peak from 1680 to 1630, and an unusually intense N-H in-plane bending peak from 1570 to 1515 (3). Table II shows the group wavenumbers for secondary amides.

In Figure 3, there is a single N-H stretching peak labeled A at 3320, as expected for a secondary amide (3). Note that this peak is of medium width and intensity, and it is much smaller and narrower than a typical O-H stretching peak. The C=O stretch for Kevlar is labeled B at 1650, in the correct carbonyl stretching range for all amides. I assign the neighboring peak labeled C at 1543 as the N-H in-plane bending peak. Now, there is also an intense peak at 1516 that could also be assigned as the N-H in-plane bend. I assigned the peak at 1543 as the N-H in-plane bend based on experience; it has been my observation for a large variety of polyamides, including nylons, that the N-H in-plane bend falls approximately at 1540. We saw this last time in the spectrum of Nylon-6,6 (3). My assignment of the 1516 peak is a benzene ring “ring mode” (8). The broadened envelope labeled D in Figure 3 is the N-H out-of-plane bend or wag. The sharp peak on top of this envelope at 824 is a para-ring out-of-plane C-H bending vibration (9).

The IR spectrum and structure of a meta-polyaramid, Nomex, is seen in Figure 4. Nomex is used to make fireproof suits, among other things (10). Note that in the structure in Figure 4, there is one hydrogen separating the bonds attached to the benzene ring, making this a metagroup (9).

Like all the other polyamides whose spectra we have examined, Nomex contains a secondary amide linkage in its backbone. Consulting Table II, we find that the expected single N-H stretch labeled A is at 3309, the C=O stretch labeled B is at 1657, and the N-H in-plane is at 1537, sticking to my idea that many that many polyamides exhibit their N-H in plane bend around 1540. The N-H wagging envelope is seen as a rise at the end of the spectrum, with some sharp peaks on top of it that we will discuss below.

The intense peak at 1608 is noteworthy, and I assign it as a benzene ring mode vibration, similar to the peak at 1516 in Figure 3. Recall that metasubstituted benzene rings have a ring mode peak at 690±10, and a C-H wagging peak from 810 to 750 (9). In Figure 4, the ring mode is at 686 and the C-H wag is at 782. Both of these sharp peaks are riding on top of the broader N-H wagging envelope.

Slip agents are commonly used amide small molecules that lubricate the molds in injection molding processes. We studied the spectra of one of these, a primary amide, and discussed how they can contaminate the spectra of polymeric materials. Polyaramids are polyamides with aromatic rings in their backbones. We studied the spectrum of a para-polyamide, the well-known polymer Kevlar, and of a meta-polyaramid, Nomex. All these materials follow the group wavenumber rules for primary and secondary amides we have discussed previously.

https://en.wikipedia.org/wiki/Injection_moulding

(2) Smith, B. C. Fundamentals of Fourier Transform Infrared Spectroscopy, 2nd Ed., CRC Press, Boca Raton, 2011.

(3) Smith, B. C. Infrared Spectroscopy of Polymers, XI: Introduction to Organic Nitrogen Polymers. 

(4) Smith, B. C. Organic Nitrogen Compounds, VII: Amides—The Rest of the Story. 

(5) Smith, B. C. Organic Nitrogen Compounds, Part I: Introduction. 

(7) Smith, B. C. The Infrared Spectra of Polymers, VI: Polymers With C-O Bonds. 

(8) Smith, B. C. Group Wavenumbers and an Introduction to the Spectroscopy of Benzene Rings. 

(9) Smith, B. C. Distinguishing Structural Isomers: Mono- and Disubstituted Benzene Rings. 

Column: IR Spectral Interpretation Workshop

Slip agents are commonly used amide small molecules that lubricate the molds in injection molding processes. By studying the spectra of a primary amide, we can see how they can contaminate the spectra of polymeric materials.

Infrared Spectroscopy of Polymers XII: Polyaramids and Slip Agents

This article presents our annual review of spectroscopy products introduced since May of 2022. Some of the products were introduced at Pittcon 2023, which was live in Philadelphia, Pennsylvania, and some were introduced prior to that. The products introduced and described here illustrate that analytical chemistry is a diverse and thriving field, and that device manufacturers respond to the changing demands of the discipline.

After a two-year hiatus because of the Covid-19 pandemic, Pittcon was once again hosted in-person. The 2023 conference took place in Philadelphia, Pennsylvania, and it attracted approximately 5000 attendees and 2500 exhibitor personnel representing almost 500 exhibitors. Exhibitors ranged from major instrument companies to supplies and consumables, service laboratories, professional societies, and publications.

It was evident in the exhibit hall that everyone was interested in connecting in person. Whether it was professional colleagues that have worked together virtually over the past two years, or exhibitors and conference attendees being able to connect in-person for the first time, it was obvious that people missed the interpersonal communication and camaraderie that in-person conferences facilitated, and were glad to reunite with old personal friends and colleagues, while connecting with new conference attendees.

In addition to writing this article, one of my reasons for attending Pittcon was because of my role as an officer of a professional society. Something I noted while spending time in the booth was that there were a large number of students and new scientists who were stopping by and asking questions. It reinforces the general consensus that a live conference benefits young researchers, because it offers them the opportunity to become more engaged with the analytical community.

However, not everything was completely back to normal. A colleague who was scheduled to present in a session found himself chairing the session because the chair was unable to travel, due to his institution’s rules. That was also true of two speakers in the same session; as a result, the number of speakers in the session was reduced. This instance is only one example that highlights the point that, although it may seem like the world is back to a pre-Covid normality, it is not quite there yet.

There were some companies that had traditionally exhibited at Pittcon that were missing, but also new (to me) companies with interesting products. The trends noted last year—more dedicated analyzers and software that is fully integrated into laboratory operations—continues to be a theme in instrument development in 2023.

In particular, engineering teams were hard at work in the last year. There are new products in all the categories we usually review, and many of them are designed to perform important functions critical to the analytical laboratory application the products are meant to be used for. In particular, the Pittcon Today Excellence awardees appear to have some exciting engineering behind their recent developments.

Another interesting theme observed with the new products launched this year was that many instrument manufacturers were focused on shrinking the footprint of traditional instruments. Some of the products described this year are highlighted as having reduced footprints, which is in keeping with the demands to make laboratories and laboratory space more efficient.

At the small end of footprint reduction, handheld instruments are becoming increasingly common and being developed to solve more problems in the field.

This article will be broken into four sections: instrumentation; accessories; components; and software. In this review, a clear distinction between an accessory and component was made to avoid confusion. For this product review, an 

 is defined as a product that is designed to be used with a completed instrument, whereas a 

 is defined as a product that can be used to construct the instrument

With Pittcon being live this year rather than virtual, the Pittcon Today Excellence Awards returned as well. The awards criteria are based on true innovation. In each of the two categories based on company size, there were three awards: gold; silver; and bronze. This year, three spectroscopy products won awards.

In the annual sales over $10 million category, two of the three awards were in infrared (IR) spectroscopy, and both were microscopes. Bruker’s Hyperion II, an imaging microscope with the capability to combine laser imaging using quantum-cascade lasers (QCLs) with Fourier transform infrared (FT-IR) spectroscopy, took the Gold Award. The system is equipped with a focal plane array detector, but the novel aspect of this microscope is the optional QCL module that also relies on patented technology to eliminate artifacts that can be produced by typical laser sources.

The Silver Award went to Shimadzu for the AIRsight FT-IR/Raman combination microscope. The combination provides complementary spectroscopic information, and is designed to minimize the bench space that is used. The concept of having a microscope capable of performing both the FT-IR and Raman techniques is not novel, and academic publications, as well as patents and at least one semi-commercial product, have been described as possessing this capability in the past. But Shimadzu has made a commercial product, which also should appeal to the customer base, both for its functionality and for its smaller footprint than two instruments would produce. Also, of course, this approach allows the user to get complementary spectra from exactly the same spot.

In the under $10 million in annual sales category, ST Japan won the Gold Award for their LC-CollectIR product, an accessory that provided efficient analysis of components separated by liquid chromatography (LC). In a two-step process, the system eliminates the solvent from the LC, and deposits the eluent on a rotating germanium plate. The plate is then analyzed using IR.

As we did last year, we are providing tables with information on the products. We will not describe every entry in detail, but refer the reader to the information in the tables.

Table I lists those companies that submitted product descriptions and the categories where the new products are listed. There were almost 50 new products that are described in this roundup, and the first major category we will cover is instrumentation.

In the atomic instrumentation category, we highlight five interesting products (Table II). Following the trend in all instrumentation, the products are all billed as easy to use. Two are sample digestion systems from 

The one that is most interesting to me is the Radom 

 instrument. The MICAP-OES instrument does not require either argon or cooling water, because the instrument uses a microwave-generated plasma. The most appealing point about this instrument is that it is portable, and does not need any special support, making it ideal for those applications where a traditional instrument may not be appropriate.

Molecular spectroscopy encompasses UV-visible (UV-vis), near-infrared (NIR), mid-infrared (Mid-IR), and Raman. It is among these four categories we find the bulk of the new instrument offerings.

Starting with the UV-vis category (Table III), we find both traditional laboratory-based instruments and miniature instruments.

, a lab-based UV-vis spectrophotometer with a very large sample compartment for flexibility. The instrument seems to have as large a sample compartment as the Cary research instruments, but this instrument is designed with a small footprint.

 is a laboratory-based instrument designed to simplify analyses and be used by operators without extensive training. This is following a trend in laboratory instruments to design the software so that useful data is obtained without the operator being an expert.

The shrinking footprints trend we have seen in instrumentation is also the main feature of the other product introductions. All fall into the category of miniature spectrometers.

 is a fiber-coupled spectrometer that can be integrated into various systems.

Ocean Insight has introduced two instruments into this space. One is the 

, which can cover from the UV (200 nm) to the very NIR (1100 nm), and it is designed to provide thermal wavelength stability, which is a challenge for small instruments that might be used in non-ideal environments. The other Ocean offering, 

, has a similar spectral range and thermal stability, but it is designed to provide a higher spectral resolution.

An interesting new instrument from Open Instruments in Australia also falls into the UV-vis category. This instrument, 

, was originally designed for use in characterizing solar cells, but may present some interesting features making it applicable to other technical areas.

In the fluorescence category, one new product (see Table IV) entered the market. Applied NanoFluorescence introduced the 

, an instrument based on near-infrared fluorescence detected circular dichroism. According to the company, this instrument came out of developments for the National Institute of Standards and Technology (NIST) to measure the enantiomers of single-walled carbon nanotubes.

In the vibrational spectroscopy category, we saw some noteworthy products that were introduced. Two of the three microscopes were discussed when we covered the Pittcon Today Excellence Awards, but there were a number of other interesting introductions.

Table V features the NIR products that were introduced over the past year. In particular, Metrohm has been busy with a number of introductions in the category. Metrohm has introduced a family of analyzers designed for process control, and have the option of sampling for solids or liquids. The 

In addition to the two analyzers mentioned above, Metrohm has also introduced the 

, which is a NIR instrument designed for inline process applications. It can monitor a variety of parameters at the same time, and has up to five sampling points.

The past year has brought some interesting devices to the market in the workhorse category of mid-infrared (see Table VI). We commented on the Bruker 

 in the discussion of the Pittcon awards, but Shimadzu also introduced the 

ABB has introduced a process instrument, the 

, for online measurements of contaminants in natural gas streams. The instrument is based on ABB’s unique laser absorption technology called Integrated Cavity Output Spectroscopy (ICOS).

Edinburgh Instruments has put a new entry into the crowded FT-IR area by introducing the 

 instrument. The specifications as noted on the Edinburgh website put this instrument right in the category of the midrange instruments, but what makes this instrument unique is the ability to do photoluminescence in the IR region.

, that is a photo-induced force microscope, and it provides high spatial resolution. This instrument is a new entry into the rapidly growing field of nano IR spectroscopy, which is designed to address the spot or feature size versus diffraction limit problem of traditional infrared microscopy.

Finally, for this category, Thermo Fisher Scientific has a new product, the 

. This device follows the trend to make footprints smaller and instruments more intuitive for the user, and is described as portable. The application space is the same as most other FT-IR instruments in polymers, pharmaceuticals, and materials.

Introductions in the Raman category, shown in Table VII, mirror those in the UV-vis category in that both laboratory-based research instruments and miniature instruments were introduced.

 integrated with a cryostat system from Montana Instruments to study material at low temperatures.

Another research instrument introduced this past year is the Thermo Fisher Scientific 

, a laboratory instrument with a reduced footprint that is designed to integrate with other analytical techniques.

Wasatch Photonics has two new offerings. The first, the 

 instruments, are small footprint devices that are user configurable and deliver research level performance. It can be configured with a variety of excitation wavelengths. Wasatch has also introduced the 

, a family of similar devices designed for OEM applications

, which joins the family of other IndiGo devices. This Raman instrument is designed with either 532 or 785 excitation, and fits in the palm of the user’s hand. It connects wirelessly to smartphones and tablets for field applications.

Imaging has become a general term to describe systems that produce a multidimensional data set regardless of how the sample is interrogated. That definition certainly applies to the instrument in this year’s category described in Table VIII.

 a family of X-ray analytical microscopes to address areas, such as archaeology and geology, where nondestructive analysis is necessary.

Another imaging instrument using an entirely different technology, the Phocuscan, is from 

, and it offers a standalone photocurrent microscope for applications in areas such as, but not limited to, nanotechnology and semiconductors.

The third imaging instrument—this one from Klar Scientific—is a photo-luminescent spectroscopic 

 with excitation from the deep UV to the NIR. It is modular in design, and allows the researcher to quickly change the configuration to meet the needs of the experiment.

Last year, we stated that the definition of an 

 was that it was designed to be used with a complete instrument compared to a component that becomes part of the instrument. We are continuing with that definition for this year, and Table IX describes the products in the accessory category.

Three of the accessories introduced in the past year are designed for FT-IR. The 

 from Jackfish SEC is a spectro-electrochemical cell and allows researchers to study electrochemical systems under flow. It is well-suited for surface-enhanced infrared reflection absorption spectroscopy (SERIAS) applications. Pike Technologies has introduced a Peltier heated and cooled version of the 

 to study systems at elevated and reduced temperatures or in situations where precise temperature stability is needed. The third FT-IT accessory is the 

 from ST Japan that was described earlier when we discussed the Pittcon Excellence awards.

 have introduced the Apex 400 Automatic Hydraulic Pellet press. To round out the accessory category, Milestone has introduced an 

 to automate reagent addition and dilution and is especially useful to reduce operator exposure and provide consistency of results.

Under components, there are entries in a variety of areas as illustrated in Table X.

Agilent has introduced a number of supplies to simplify maintaining inductively coupled plasma mass spectrometry (ICP-MS) systems. They include a new 

 to assure fixed volume introductions and 

assemblies. All four of these supplies are designed to improve analysis and minimize downtime.

 with a narrow spectral bandwidth especially suited for Raman spectroscopy.

Lumibird has introduced two neodymium-doped yttrium aluminum garnet (Nd:YAG) lasers. The first, the 

, is a high-power pumped laser suitable for dye/OPO pumping or laser induced fluorescence. The other introduction, the 

, is a compact laser, powered by 24 VDC or a battery, and is especially suited to LIBS analysis.

The last product in the laser category is a miniaturized 

 from Block Engineering. This miniaturized laser allows the transition from laboratory to handheld or field instruments.

Reflex Analytical also has an entry in the components category. They have introduced 

 in borosilicate glass, UV quartz, and NIR quartz materials for applications in micro and macro flow systems.

Our final entry in the components space, Spectrum Scientific, has introduced 

 with a vacuum UV optimized coating for use in the 120–200 nm range.

As some will tell you, instrument and data analysis software are more important than the actual hardware. Table XI shows the software packages introduced over the past year. LabVantage Solutions Inc. has introduced a new version of their 

, providing features and enhancements for the user. For industry specific applications, they have also introduced the 

 that creates a seamless platform from evidence collection and storage, laboratory testing, case compilation, and proceedings while providing robust quality management.

The next two software systems are instrument-based and provide capabilities to control and process data. Metrohm has introduced the 

 software to simplify the control and analysis of Metrohm/B&W Tek NIR and Raman instruments. WITec has introduced the 

 for Raman and correlative microscopy. This new package adds user management and the ability to define distinct hardware setups to streamline recurring experiments.

Finally, John Wiley & Sons, Inc. have introduced 

. This release expands the KnowItAll capabilities to include a patented solution to analyze vapor-phase IR spectra of synthetic cannabinoids, adaptive searching and more support for MS and nuclear magnetic resonance (NMR).

The trends in instrumentation and software continue to see products that are smaller, easier to use, and application-specific. Although general purpose instruments still hold a big share of the analytical instrument business, it was evident as I walked the aisles of Pittcon that many of the products were geared toward increasing productivity and ease of use, to the point that specific workflows for particular analyses are provided.

These trends might be pushing the users to treat instruments and software as answer boxes. This presents a problem. If you do not understand how a device works, what the steps in the procedure were, and what to expect, then you may not recognize a problem.

A class of exhibitors at Pittcon, which are not usually described in these reviews, are the professional societies and the publishers. The original name of the conference was The Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy. There were a number of organizations represented at the conference that fall under that banner. They include the American Chemical Society, The Coblentz Society, the Federation of Analytical Chemistry and Spectroscopy Societies, the Royal Society of Chemistry, and the Society for Applied Spectroscopy, all of whom are committed to educating the user base of analytical instruments particularly spectroscopy. These organizations, along with the publishers that were also represented, such as John Wiley & Sons, LabX Media Group, and MJH Life Sciences (the parent organization of this publication) strive to also provide useful and educational information for the instrument user.

I would highly encourage the reader of this article to take advantage of these resources. Yes, follow the instructions provided by an instrument company for the use of the instrument, but tap the professional societies and publishers for resources to gain more information, or become part of a community where everyone speaks the same technical language and is willing to share their expertise.

If your organization introduces a new product in the coming months, please submit the 2024 

https://www.spectroscopyonline.com/view/spectroscopy-new-product-review

. We will be accepting submissions as the products are introduced and include the appropriate products in the 2024 review.

 is a consultant in vibrational spectroscopy and spectroscopy education. She is the past president of both the Coblentz Society and the Society for Applied Spectroscopy, and serves on the 

 Editorial Advisory board. Direct correspondence to: 

Special Feature

Our annual review of new products for atomic and molecular spectroscopy, including details by category and highlights of overarching trends.

2023 Review of  Spectroscopic Instrumentation

This article proposes a method for the determination of thiosulfate by decoloring spectrophotometry with methylene blue as an oxidant. Methylene blue has redox properties. Its oxidized form is blue, and its reduced form is colorless. Thiosulfate is a medium-strength reducing agent. In an acidic medium, the two can undergo redox reactions to reduce methylene blue and cause the solution to exhibit a fading reaction within a certain range, and the degree of fading is proportional to the amount of thiosulfate added. This method measures the change in absorbance (AU) at a fixed wavelength of 664 nm, and ΔAU has a linear relationship with the content of thiosulfate. The linear range is 0–0.3 mmol/L. From this curve, the content of thiosulfate in the desulfurization solution can be accurately measured. This method is not interfered with by other secondary salts in the desulfurization solution during the thiosulfate determination process, and has high sensitivity. The color change can be observed by the naked eye to judge whether there is thiosulfate in the solution. This method is simple to perform and is an improved method for the determination of thiosulfate in a desulfurization solution.

To ensure the stable operation of fuel plant desulfurization systems, it is critical to maintain the content of thiosulfate within an appropriate range. This new method for thiosulfate determination is highly sensitive
and easy to perform.

May 2023

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2023 Review of Spectroscopic Instrumentation

Spectrophotometric Determination of Thiosulfate in Desulfurization Solutions by Decoloration of Methylene Blue

Terahertz Spectral Investigation of L-Cysteine Hydrochloride and its Monohydrate