Single reaction chamber (SRC) microwave digestion offers significant benefits over traditional microwave digestion for pharmaceutical samples: higher sample throughput, reduced labor and consumables costs, simplified workflow and superior digestion quality.

	New USP chapters <232> and <233> for the measurement of inorganic contaminants in pharmaceutical samples have been implemented. While samples can be dissolved in aqueous or organic solvents, the large majority will require digestion, and closed-vessel microwave digestion is stipulated by USP. Single reaction chamber (SRC) microwave digestion is a new type of closed vessel digestion that was developed by Milestone and offers many advantages over closed vessel digestion-particularly for pharmaceutical sample types.

	Two sample types, St. John's wort and fish oil, typical of finished product pharmaceuticals, were digested using an SRC digestion system and analyzed for the four toxic USP elements using collision-cell ICP-MS. Since all samples are digested together in a single chamber, duplicates and spike recoveries were performed to confirm the retention of volatile elements and the absence of cross contamination.


	The data above show excellent DLs and recovery-even for the volatile element mercury. There is no loss of volatiles or cross-contamination with the UltraWAVE.

	The Milestone UltraWAVE can digest up to 15 samples simultaneously, at up to 300 °C and 199-bar pressure. Its high temperature and pressure capability enables the complete digestion of virtually every sample type. Samples are weighed into vials and placed in the chamber: and any combination of sample types can be digested together, greatly simplifying the sample prep workflow. Raw materials, excipients, API, and final product can all be digested together in the same run. And the UltraWAVE uses disposable glass vials, eliminating vessel assembly/disassembly and vessel cleaning, which significantly reduces labor and consumables costs. Most pharmaceutical sample types have high organic content, including oils and fats, which are difficult to digest and generate CO

 which increases pressure in the reaction vessel. The high pressure capability of the UltraWAVE enables it to digest entire fish oil gelcaps-not possible with traditional closed vessel microwave.

	The UltraWAVE can digest samples in as little as 3 mL acid which minimizes reagent blank levels – important since ICP-MS will be used predominantly for USP <232>/<233>. The SRC chamber is prepressurized with N

 prior to the start of the run. This prevents sample boiling, eliminating cross-contamination and loss of volatiles.

	Milestone's UltraWAVE SRC microwave digestion system offers multiple benefits for sample preparation and subsequent analysis.

	Due to its higher sample capacity, use of disposable vials, and faster cool down time, the UltraWAVE's sample throughput is 2x–3x higher than closed vessel digestion. Its lower consumables costs, simple operation, and superior digestion quality also make the Milestone UltraWAVE the perfect choice for pharmaceutical sample prep.


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Articles

Application Notes Atomic

Microwave Sample Prep for Heavy Metals Determination in Accordance with USP /

 maximum voltage was increased from 60 kV to 70 kV while maintaining the same size profile. This article highlights the advantages of 70 kV excitation of cadmium, an element of interest for the Restriction of Hazardous Substances Directive (RoHS), at parts per million (ppm) levels. 

	The MAGPRO 12 W miniature source is small and low power, which is an advantage for a number of applications. Our 12 W source has several anode materials available: a tungsten anode for either XRF or in X-ray imaging, as well as Rh, Ag, Cr, Cu, and Mo. The entire X-ray source (tube plus high voltage power supply) weights about 700 g (25.0 oz) and can be controlled by your choice of USB, digital, or analog control, and has an interlock connection for X-ray safety (Figure 1). The increase of high voltage from 60 kV to 70 kV for the MAGPRO was primarily motivated for use in handheld imaging applications. This increase in voltage also shows important benefits for spectroscopy applications as well. This article highlights the advantages of the 70 kV excitation for low levels of cadmium.


	Figure 1: Image of the 12 W X-ray source.

	Experimental Conditions and Results for XRF Detection of Cadmium

	Cadmium detection is of interest because it is a toxic metal that needs to be detected for RoHS/WEEE compliance. Detection of cadmium at low concentrations is particularly difficult because cadmium's 23.2 keV K

 emission line is much higher than that of other toxic elements of interest. An X-ray source with a higher voltage helps to increase the X-ray signal from cadmium. For this experiment, we used a typical XRF setup where the sample is placed at 45° to the tube and detector. The X-ray spot on the sample was 4×6 mm, achieved with a collimator and a tube-to-sample distance of 25 mm. A 200 µm molybdenum foil was placed between the tube and sample to suppress the Compton background scattering roughly between 20 to 30 keV; thereby suppressing the background under the cadmium K

 peak. Figure 2 shows four spectra taken from a polyvinyl chloride sample with 10 ppm of Cd, with the tube set at 40, 50, 60, and 70 kV. A 42 mm

 SDD collected the data with a 15 mm sample-to-detector distance over 180 s live time, with the input count rate ranging from 20 to 100 kcps. It is evident that increasing the voltage also increases the cadmium signal. In this set-up, 10 ppm of cadmium is detectable in a reasonable 3–5 min time frame.


	Figure 2: The cadmium line at about 23.2 keV gets larger as the voltage on the tube is increased. This is an advantage for cadmium detection in XRF systems looking for toxic metal at low concentrations.

	The MAGPRO source is meant for use in small benchtop systems where small size is valued. It has increased its high voltage range from 60 kV to 70 kV, which is an advantage in detecting higher atomic number elements such as the hazardous substance cadmium.


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Miniature 70 kV, 12W X-ray Source

Many biomedical research applications exploit the natural fluorescence response of amino acids, the essential building blocks of all proteins. These protein fluorescence responses have been used for everything from pharmaceutical manufacturing to biowarfare defense. 

	Proteins, the complex organic compounds made of chains of amino acids, are the most abundant organic molecule in all living things on Earth. They act as catalysts, regulate physiological processes, and they defend the body against disease.

	Three common amino acids, tryptophan, tyrosine, and albumin, responsible for the majority of inherent fluorescence, have a common structure of hydrogen-based rings. These ring structures, called 

 absorb UV radiation and emit a weak fluorescent signal at varying wavelengths.

Fluorescence in Action: Cancer Fighting Weapons

	Spectroscopy has proven to be invaluable in the fight against cancers. In lung cancer detection, for example, use of autofluorescence bronchoscopy employs a narrow probe inserted through the patient's mouth into the upper bronchial tree.

	Autofluorescence has been shown to be far more sensitive than white light bronchoscopy in the detection of carcinomas or dysplastic lesions, but it also has a high rate of false positives. Researchers at the Department of Respiratory Diseases in Rotterdam, the Netherlands (1), are investigating the use of absorbance/reflection optical spectroscopy to improve specificity without losing sensitivity.

	Using a specially designed probe to fit the 2.8 mm bronchoscope channel, the mucosa tissue was irradiated with a tungsten/halogen broadband light source and a blue laser calibrated to 407 nm. The resulting reflectance and fluorescence emissions were collected via a multichannel Avantes spectrometer installation equivalent to two AvaSpec-ULS2048CL-EVOs in parallel.

	The emission peak for autofluorescence of healthy tissue was 500 nm. Areas that display an abnormal fluorescence profile can be rapidly targeted for additional spectral measurements which can be acquired in <1 s. Diseased tissue displayed drastically lower emission intensity at shorter wavelengths compared to healthy tissues. The combined autofluorescence imaging and optical reflectance spectroscopy significantly improved the positive predictive value compared with autofluorescence alone without sacrificing sensitivity.

	The Avantes Engineering team reproduced a series of experiments (2) conducted with samples of tryptophan, tyrosine, and bovine serum albumin to demonstrate our protein detection capabilities. The team used conventional absorbance techniques with a continuous wave (CW) illumination source (AvaLight-DHc) and an AvaSpec-ULS3648-USB2 spectrometer configured for UV (190–400 nm). Absorption measurements, recorded between 190–320 nm, correlated changes in concentration to changes in absorption. Fluorescence was not measured during this experiment.


	Figure 1: Absorption response of amino acids in 0.25 mg concentration solution.

	The team running this experiment prepared three different concentrations for each of the three sample analytes: 1 mg/mL, 0.5 mg/mL, and 0.25 mg/mL, and took broadband absorption spectra profiles for each.

	The absorption profiles of the amino acids correlated directly with the amino acid concentration in solution. As fluorescence is a function of absorbance and quantum yield, the fluorescence can be estimated and would be expected to also correlate with concentration.

	(1) M.P.L. Bard et al., "Improving the specificity of fluorescence bronchoscopy for the analysis of neoplastic lesions of the bronchial tree by combination with optical spectroscopy," 

	(2) P. Held, "Quantitation of peptides and amino acids with a Synergy(tm) HT using UV fluorescence." B.-T. Instruments, Winooski, VT (2003).


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Application Notes Molecular

Biomedical Fluorescence Applications

	The continued application of engineered nanoparticles (ENPs) raises concerns about their introduction into natural water bodies via wastewater discharge, incorrect disposal, and leaching from outdoor applications. If discharged into surface water, the fate of ENPs in drinking water treatment processes needs to be evaluated. Coagulation is one of the primary treatments used to remove particles from drinking water; thus, understanding the fate of ENPs during typical coagulation processes is required to accurately predict human exposure. Single particle ICP-MS (SP-ICP-MS) is an important advancement in environmental monitoring of ENPs that has the capability to quickly evaluate size, concentration, and dissolved metal concentration simultaneously with minimal sample preparation.

	With many ENPs utilized in consumer products, this work focused on five common varieties: Ag, Au, TiO

. The fate of these particles through coagulation processes in two surface water types was evaluated using SP-ICP-MS. Zone 4 coagulation process (aka 

) was used for these experiments. Sweep floc occurs when coagulant is added past the point of solubility, creating insoluble flocs that aggregate. Other particles in the water are attracted to the coagulant flocs and are removed during sedimentation.

	Citrate-stabilized Ag (40, 70, and 100 nm dia) and Au (50, 80, and 100 nm dia) NPs in 2 mM sodium citrate were purchased from nanoComposix, Inc. (San Diego, CA). Uncoated TiO

 (30–50 nm), and ZnO NPs (80–200 nm) were purchased from US Research Nanomaterials, Inc. (Houston, TX), and prepared in DI water. Dissolved Ag, Au, Ti, Ce, and Zn standards in DI water were used to calibrate the instrument.

	To simulate coagulation processes, the most commonly used coagulants, including aluminum sulfate, ferric chloride and ferric sulfate, were purchased from Thermo Fisher Scientific, Inc. (Pittsburgh, PA). River water and lake water samples were collected from the Missouri River, and Schuman Lake in Rolla, MO, respectively. Samples were taken from just below the surface, two feet from the bank. Precleaned polypropylene bottles were used to collect samples, and stored in the refrigerator until use.

	A NexION® ICP-MS with Syngistix™ Nano Software Module (PerkinElmer Inc., Shelton, CT) was used for sample analysis and data processing, using 

	A six-gang stirrer with 2-L square beakers was used for the coagulation treatments (Phipps and Bird). Following the addition of water, 70 nm Au (5 µg/L), 80 nm Ag (2 µg/L), 100 nm TiO

 (5 µg/L), and 80–200 nm ZnO (6 µg/L) nanoparticles were added to the beakers and dispersed by stirring. Predetermined amounts of coagulants were added to the beakers and stirred at decreasing speeds to simulate flocculation and sedimentation. Samples were taken immediately after dispersion and after sedimentation to evaluate the change in particle size, concentration, and dissolved ion concentration.

	Data demonstrating the change in size distribution histograms of Ag ENPs in river water and lake water after Zone 4 coagulation with three different coagulants are provided in Figure 1. "NO TREATMENT" samples were water matrix with ENPs added and were stirred and underwent sedimentation but did not have coagulant added. "BEFORE TREATMENT" samples were collected from each beaker immediately after the ENPs were dispersed. No obvious shift in size was observed after each treatment. However, the decrease in frequency indicates that the ENPs were removed to some degree after each treatment.


	Figure 1: Change in size distribution histograms for Ag ENPs during various coagulation treatments in (a) river water and (b) lake water.

	The change in ENP particle concentration after various coagulation treatments was studied in river and lake water. Particle-size-distribution histograms were generated for each treatment and each particle type. Combined distributions for each particle type are shown in Figures 2 and 3 for river water and lake water, respectively. Particle concentrations decreased after each treatment for all ENPs. The water matrix impacted size distributions, likely due to differences in dissolved organic carbon (DOC). CeO

 ENPs showed greater stability in high DOC lake water compared to lower DOC river water, as indicated by a mean particle size closer to that of the primary particles in the standard. ZnO is known to be highly soluble in water, thus particle size will vary based on water chemistry. In this case, particles aggregated more in lake water compared to river water. In control samples ("NO TREATMENT"), the particle size and concentration was similar before and after treatment for most particles, showing stability between the time of ENP addition and final sampling. ZnO ENPs exhibited dissolution over time when no treatment was applied due to its known solubility in water.


	Figure 2: Size distribution histograms for (a) Au, (b) TiO

, and (d) ZnO ENPs after Zone 4 coagulation treatments using various coagulants in river water.

	Though it won't be discussed in detail here, total ENP removal was improved when polymer was added as a coagulant aid. This result was expected due to the cross-linking nature of the polymer during floc formation. Compared to citrate-stabilized ENPs, uncoated TiO

, and ZnO ENPs were more efficiently removed across all treatments in river water, likely due to the lower average surface charge resulting in more charge neutralization and aggregation.


	Figure 3: Size distribution histograms for (a) Au, (b) TiO

, and (d) ZnO ENPs after Zone 4 coagulation treatments using various coagulants in lake water.

	Monitoring ENPs during drinking water treatment is important as their use in consumer and commercial products continues to rise. This work has demonstrated SP-ICP-MS, using PerkinElmer's NexION ICP-MS with Syngistix Nano Software Module, to be a good technique to monitor the particle size and concentration of ENPs in surface waters. This study has also shown that the efficacy of coagulation to remove ENPs from surface waters is an important parameter to consider for risk assessments.


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The Benefits of SP-ICP-MS to Assess the Fate of Nanoparticles During the Coagulation of Drinking Water

	There are two primary methods of blending ethanol into gasoline: match blending and splash blending. Match blending aims to achieve some specified boiling point for the mixture and is primarily done with aromatics, resulting in a dirtier emission profile versus splash blending. Splash blending is the primary method used in the United States and is based on percent volume, specifically aiming to achieve 10% ethanol by volume in the final mix (Environmental and Energy Study Institute, 2014). In this study, we look at the Ocean Optics MZ5 MIR Spectrometer's ability to determine volume fraction of ethanol in a splash-blended fuel mixture using MIR spectroscopy.

	In the world of fuel octane ratings, the 0-mark is set by 

-octane, also known as 2,2,4-trimethylpentane (Compound Interest, 2016). Focusing on the latter, mixtures were made using 

-octane (99.8%) and 200-proof ethanol from Millipore Sigma. The following volume fractions were prepared:

	Sample fluids were placed onto the crystal and measured. The MZ5's Mirror software saved the processed absorbance spectra.

	The MZ5-MIR-ATR spectrometer offers excellent spectral response from 910-1810 cm

 and is a robust measurement system for petroleum products and general process organics. Its simplified fixed-crystal design eliminates fiber connections and the movement/vibrational issues that come with their use.

	Figure 1 shows the resulting spectra for the ethanol mixtures described in Table I, along with some explanations for the activities and how they relate to the organic structures.


	Figure 1: Absorbance of i-octane/EtOH mixtures.

	The ethanol activity is clearly the dominant influencer to these spectra, which is highly useful in determining its concentration both in the lab and on the process line. While there are two regions of large alcohol activity, the C-O stretch band is both the largest and the most independent of the 

-octane profile. Plotting the volume fraction versus this absorbance trend provides a strong correlation (Figure 2).


	Figure 2: Absorbance trend of C-O stretch band.

	The MZ5 is more than a spectrometer-it is a window into the molecular structures and concentrations of the chemicals in your process stream. In addition, Ocean Optics can provide users with algorithm development and machine learning tools that derive additional insight from the spectral data the MZ5 collects. Tools can be developed and refined to handle complex fuel mixtures and account for interference issues to provide readings that are robust and trusted.


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Volume Fraction Determination of Ethanol in Splash-Blended Fuel Mixture

This application note demonstrates the measurement by X-ray diffraction (XRD) of positive electrode material from lithium ion batteries during the charge/discharge process.

	Lithium ion secondary batteries are widely used in small portable devices such as mobile phones. Research and development of lithium ion batteries for use in automobiles and larger machines is an active field. To develop lithium ion secondary batteries with high capacity, high stability and long life, it is essential to evaluate the stability of the positive electrode material during the charge/discharge process. Operando X-ray diffraction measurements using an attachment that reproduces the charge/discharge environment and a 2D detector that can perform high-speed measurements enables detailed observation of crystal phase changes while a battery is in use, making it suitable for studying battery performance and life.


	Figure 1: Figure 1 shows a picture and an illustration of the cross-sectional structure of a battery cell attachment. The positive electrode material was LiMn

. Measurement using an exposure time of 15 s was repeated while charging/discharging the electrode at a charge and discharge rate 1C = 132 mAh/g. Changes to the X-ray diffraction profile over time were investigated.

	X-ray diffraction measurements of the positive electrode material during high-speed charging and discharging were carried out with a battery cell attachment and a HyPix-3000 2D detector on a Rigaku SmartLab X-ray diffractometer.


	Figure 2: Figure 2 shows the multiple 1D XRD profiles, 2D profile maps and voltage graphs. Two steps of a two-phase coexistence reaction occurred with charging and discharging. After charging and discharging, the electrode material returned to the same crystal phase as before the measurement started.

	The Rigaku SmartLab Automated multipurpose X-ray diffractometer with HyPix-3000Hybrid pixel array multi-dimensional detector can perform high-speed Operando measurements of crystal phase changes of lithium ion batteries to evaluate battery performance and life.


	Figure 3: Rigaku SmartLab automated multipurpose X-ray diffractometer (XRD) with Guidance software.


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Operando Measurement of Li Ion Battery Positive Electrode in Charge/Discharge Process by X-ray Diffraction

Confocal Raman imaging is well suited to investigating biological specimens. The inverted beam path of the Raman microscope alpha300 R

 is especially useful for imaging samples in liquids such as cells and tissues.

	Optical microscopy using fluorescence labeling cannot employ more than a handful of labels in one experiment, restricting the number of molecules that can be analyzed. This limitation does not apply to the label-free Raman imaging as the Raman effect is caused by the inelastic scattering of monochromatic light by the sample's molecules. Each type of molecule in a sample can be identified unambiguously by its individual Raman spectrum. By combining Raman spectroscopy with confocal microscopy the spatial distribution of the compounds within a sample can be visualized (1). It has been successfully applied for the investigation of organic materials (2–6).

	The confocal microscope setup enables the generation of 3D Raman images by stacking 2D images of a series of focal planes. Here, a pressed piece of banana pulp mixed with water was investigated with an alpha300 R

 inverted confocal Raman microscope (WITec). The scan range was 300 × 200 × 90 µm

 with 450 × 300 × 45 pixels. At each pixel a complete Raman spectrum was acquired. The integration time was 34 ms/spectrum. The 3D reconstruction of the Raman image stack (Figure 1) shows starch grains (green) and cell wall components (red).


	Figure 1: Raman image of banana pulp with starch grain marked in green, cell wall material in red.

	Correlative Fluorescence and Raman Imaging of Eukaryotic Cells

	Though strong fluorescence is the "natural enemy" of the weaker Raman signal, correlative fluorescence–Raman imaging using one microscope is possible by choosing a suitable laser wavelength, to avoid signal overlap. Kidney cells (Vero ATCC CCL-81) were grown in a petri dish. Nuclei were stained with DAPI. Cells were imaged in aqueous solution under the alpha300 R

 microscope with a laser wavelength of 532 nm. An image of 50 × 40 µm

 with 150 × 120 pixels was generated. The acquisition time was 0.2 s/spectrum. The resulting correlative Raman–fluorescence image shows the nuclei (blue) imaged by fluorescence microscopy and the nucleoli (green) and endoplasmic reticula (red) imaged by confocal Raman microscopy based on their Raman spectra (Figure 2). The fluorescent dye does not interfere with the Raman measurement.


	Figure 2: Correlative Raman-fluorescence image showing DAPI-stained nuclei (blue). Nucleoli (green) and endoplasmic reticula (red) were identified by their Raman spectra.

	(1) J. Toporski, T. Dieing and O. Hollricher (eds.), 

 Springer International Publishing (2018).

	(2) S. Richter, J. Müssig and N. Gierlinger, 


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Inverted Confocal Raman Imaging for Life Sciences

Using an automated ATR accessory, mid-infrared spectra were collected on 24 individual ATR crystals. Spectra were compared to a spectrum collected using a single bounce diamond ATR crystal. Advantages of implementing automated measurements and benefits of automation in laboratory environments are discussed.

	ATR is one of the most popular mid-infrared sampling techniques because minimal to no sample preparation is required due to the short effective pathlength. Until now, automating ATR methods to improve workflow in high-throughput laboratories has been elusive because of the typical need to clean and dry the ATR sampling surface in between each measurement. By taking advantage of unique Si wafers functionalized with multiple microprisms optimized to perform as ATR elements, ATR automation is available as a commercial macroscale accessory. This application note explores automated ATR measurements in the evaluation of an organic solvent.

	The model sample was propanol-2. Using the AutoATR Accessory by PIKE Technologies, a microtiter style platform for automated ATR measurements, 24 unique sample measurements were made on individual ATR crystals from IRUBIS GmbH. The accessory is suitable for measuring liquids, gels, pastes, and casted films. The AutoATR stage is controlled and data collection is initialized by PIKE AutoPRO7 software. Spectra collected with the AutoATR were compared with a single reflection diamond ATR. Spectral resolution was 8 cm

 and 16 scans were co-added. Before the automated sample measurements an individual background was acquired for each well.

	The AutoATR uses 24 unique Si ATR elements, which have a thickness of 500 microns. Due to the thin profile of the crystal, the absorbance from Si phonon bands is minimal relative to thicker traditional Si ATR crystals. This allows the entire mid-IR spectral range to be accessed from 5000–400 cm

. Si has an extremely inert sampling surface and is suitable for use with substances having a pH between 1–12. The efficiency of the accessory's base optics and Si ATR element coupled with several microprisms results in high energy throughput and reproducibility.

	Figure 1 shows 24 individual spectra of propanol-2 and a comparison spectrum collected using the PIKE MIRacle single reflection diamond ATR. Spectra collected with the AutoATR were exceptionally reproducible. In the fingerprint region the variance was less than 0.007 AU (no baseline correction implemented). Relative to a single reflection diamond ATR, the absorbance bands were almost two times stronger when collected with the AutoATR. Thus, this accessory will result in higher signal-to-noise ratio and greater sensitivity.


	Figure 1: 24 individual ATR spectra of propanol-2 collected using the AutoATR and a spectrum collected with the MIRacle single reflection diamond ATR (red) for comparison.

	The AutoATR high-throughput accessory is ideal for comprehensive larger studies. Fields of biology, medicine, pharmaceutics, and food could benefit from an automated ATR. Additionally, there are ongoing efforts to transfer infrared spectroscopy from academic research into clinics. An automated ATR device fulfills this requirement and enables larger studies, while increasing lab efficiency and minimizing workforce requirements.

	New innovations in ATR elements in conjunction with an automated optical platform has made automated ATR measurements possible. Using the AutoATR, spectral results are more sensitive than a typical single reflection ATR.


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Automated ATR for High-Throughput Laboratories

The major drawback of a potassium dichromate (PDC) reference solution intended for checking the accuracy of the photometric scale of an analytical absorption spectrophotometer is its lack of broad wavelength coverage. Two different PDC reference solutions are required to cover both the ultraviolet and visible regions of the spectrum. This application note describes a cobalt-nickel-nitrate (CNN) reference solution that is permanently sealed in a fused-silica cuvette. In contrast to PDC reference solutions, a single CNN solution/cuvette filter can be used in both the ultraviolet and visible spectral regions of the spectrum. 

	Standard mixtures of cobalt, nickel, and nitrate ions in aqueous perchloric acid were originally formulated in 1972 by Burke and Deardorff. The reference solutions were sealed in glass ampoules and issued in consumable form as SRM 931. Despite its exceptional popularity in today's modern analytical testing laboratories, SRM 931 is limited in its overall use because of the demanding requirements for careful handling, contamination control, and precise and skillful manipulations to ensure accurate transfer of a CNN reference solution into a separate cuvette for analysis. This restrictive feature of SRM 931 could be overcome by simply sealing the CNN solutions in fused-silica cuvettes.

	The CRM 200 reference standard, first introduced in 1994, features many of the same positive attributes of SRM 931, with the added advantage that the reference solutions are permanently sealed in fused-silica cuvettes as shown in Figure 1. Further improvements in CNN solution/cuvette filters resulted with the introduction of the CA2M 706 reference standard in 2014 as part of the company's commemorative MAVRO series, and later again in 2016 with rebranding of the CRM 200 reference standard. The Stranaska® CRM 200 and CA2M 706 reference standards are distinguishable by their differing scopes of calibration and levels of scientific metrological rigor integrated into the calibration models that underpin their respective certifications. A comparison of the different CNN liquid absorbance standards is presented in Table I.

	The major advantage of Stranaska® CRM 200 and CA2M 706 reference standards is that each solution/cuvette filter is individually certified so that it can be used repeatedly over time. However, it is recommended that the reference standards be returned periodically to Stranaska Scientific for science-based recertification in order to clean the cuvettes, and to update the certified reference values and uncertainties.


	Figure 1: CNN solution/cuvette filters from Stranaska Scientific.

	The Stranaska® CRM 200 and CA2M 706 reference standards, which are derived from the SRM 931 series, are proven alternatives to PDC solutions for performance evaluation and qualification of analytical absorption spectrophotometers in FDA-regulated laboratories. The CNN solution/cuvette filters are more convenient to use by metrologists, engineers, and calibration technicians that do not have meaningful experience in common analytical laboratory practices.


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Application Notebook-09-01-2018