Mass Spectrometry

A simple analytical method, requiring no sample pretreatment, was developed for determination of chromium, iron, nickel, and zinc in mouthwash by inductively coupled plasma‒optical emission spectrometry (ICP-OES). This method allowed the study of potential migration by iron, chromium, and nickel from stainless steel containers.

Our annual review of products introduced at Pittcon or during the previous year

Complex isobaric and polyatomic spectral interferences can be mitigated using triple quadrupole ICP-MS (ICP-MS/MS) with a collision–reaction cell (CRC). This configuration allows for the multielement characterization and detection of smaller nanoparticle sizes.

The structural complexity of monoclonal antibodies (mAbs) challenges the capabilities of even the most advanced chromatography and mass spectrometry techniques. This study examines the use of micro-pillar array columns in combination with mass spectrometry for peptide mapping of both mAbs and antibody–drug conjugates (ADCs).

Under a suitable thermal oxidation regime, vegetable oils yield a mixture of volatile and semivolatile organics that exhibit very high antimicrobial activities against a variety of microbial species. Volatile and semivolatile products were characterized with GC–MS using electron ionization and chemical ionization. The thermal oxidation of vegetable oils resulted in the formation of an array of shortand medium-chain acids, aldehydes, and ketones that act synergistically to yield a potent antimicrobial disinfectant.

Since glycans are responsible for bioactivity, solubility, immunogenicity, and clearance rate from circulation, it is vital to have a detailed map of glycans in therapeutic glycoproteins. Detailed glycoprotein structural analysis must be able to identify the peptide sequence where the glycans are attached as well as the structure of the glycan portion, including oligosaccharide sequence and glycosyl linkages. This article details methods for mass spectrometry experiments on both released glycans (“glycomics”), as well as on intact glycopeptides (“glycoproteomics”) using electron transfer dissociation, high-energy collision dissociation, and collisioninduced dissociation fragmentation pathways, which are needed to fully elucidate the structure of glycoproteins.

In this study, general extract screening of food storage materials was done with nontargeted analytical methods to understand what analytes could potentially leach into food or beverages. GC and mass spectral deconvolution effectively separated analytes within the complex mixture and TOF-MS provided full mass range spectral data for identification. This workflow can be used for confident characterization of components present as extractables from food packaging materials.

There is growing interest in the determination of endogenous proteins in biological samples for diagnostic purposes, because a concentration increase or decrease of such proteins can allows us to monitor the state of a pathological condition such as cancer. Immunocapture LC–MS/MS analysis combines the workflow of conventional immunological assays with LC–MS analysis. This article describes typical challenges, such as cross reactivity and the mass spectrometer’s dynamic range, as well as the advantages of isoform differentiation and multiplexing.

Interest in connecting ion mobility spectrometry (IMS) to GC and especially to LC is now growing. One favorable property of IMS is that it can work with ambient pressure and can be easily connected to a gas or liquid chromatograph. Analytical applications of GC–MS and LC–MS are very different and encompass investigations into food, medical science, environment, drugs of abuse, chemical warfare agents, and explosives.

In drug development, quantitative determination of a candidate drug and its metabolites in biofluids is an important step. The standard technique for quantitative metabolite profiling is radiolabeling followed by HPLC with radiodetection, but there are disadvantages to this approach, including cost and time, as well as safety and ethical concerns related to administering radiolabeled compounds to humans. Frank Vanhaecke and his research group at Ghent University have been developing an alternative technique, and he recently spoke to us about this work.

We present a brief review of this year’s ASMS conference, which took place June 4–8 in Indianapolis, Indiana.

Simultaneous, enantiomer-specific identification of chiral molecules in multi-component mixtures is extremely challenging. Many established techniques for single-component analysis fail to provide selectivity in multi-component mixtures and lack sensitivity for dilute samples. Mass spectrometry is chirally blind, and so cannot directly distinguish the two enantiomers of chiral molecules. Here we discuss how enantiomers may be differentiated by Mass Spectrometry correlated with PhotoElectron Circular Dichroism (MS-PECD) using an electron–ion coincidence imaging spectrometer. Following an ionizing circular polarized laser pulse, ions and electrons are detected in coincidence on their respective time- and position sensitive detectors. The MS-PECD asymmetry measured on electrons tagged by the mass of their corresponding parent ion directly reveals that the compound with identified mass is chiral without the need for any prior enantiomeric separation or enantiomer-selective complexation. MS-PECD enables direct enantiomeric excess measurement of multi-component chiral samples in a table-top mass spectrometer.

Our annual review of new spectroscopy products introduced at Pittcon, or during the previous year.

A simple method for extraction and concentration of trace organic compounds found in water for gas chromatography-mass spectrometry (GC-MS) analysis was developed. The method used 25 and 45 mL glass vials with a 5-10 µm thick polymer coatings for extraction of analytes from 20 and 40 mL water samples, respectively. Analytes were subsequently transferred from the polymer coating into an organic solvent, which was reduced in volume to 200-400 µL for analysis. A 10-20 µL sample from the vial was transferred to a tiny coiled stainless steel wire filament using a micro-syringe, or by dipping the coil into the sample. After air evaporation of the solvent, the coil was inserted into the heated injection port of a portable GC-MS system where the analytes were desorbed. Injection using the coiled wire filament eliminated sample discrimination of high boiling point compounds, and minimized system contamination caused by sample matrix residues. The GC-MS contained a new resistively heated column bundle that allowed elution of low-volatility compounds in less than 4 min. Analyses of organochlorine pesticides, polycyclic aromatic hydrocarbons, polychlorinated biphenyl congeners, pyrethroid insecticides, phthalate esters, and n-alkanes in water and wastewater samples were accomplished for low ppb concentrations in less than 10 min total analysis time.

Quantum chemistry is capable of calculating a wide range of electronic and thermodynamic properties of interest to a chemist or physicist. Calculations can be used both to predict the results of future experiments and to aid in the interpretation of existing results. This paper will demonstrate some examples where quantum chemistry can aid in the development of mass spectrometric methods. Gas-phase electron affinities (EAs) have been difficult to determine experimentally, so the literature values are often not reliable. Computational methods using quantum chemistry have allowed the compilation of a self-consistent database for the EAs of polynuclear aromatic compounds. Likewise, proton affinities (PAs) and ionization potentials (IPs) have been calculated and compared favorably with experimental results for these molecules.

Ion mobility mass spectrometry (IMMS) is a two-dimensional technique that allows separation of ionized molecules based on molecular size, shape, and mass‑to‑charge ratio (m/z). It has rapidly become a valuable application for analyzing isomeric compounds in a complex matrix (e.g., proteomic and lipidomic samples) or complex mixtures of structurally related and isobaric analytes (e.g., oil samples or polymer blends). IMMS was investigated as a possible technique to compare purported generic products with Copaxone®, a drug for treating relapsing‑remitting multiple sclerosis, which contains a very complex mixture of synthetic peptides. The analysis was performed on 15 randomly chosen batches of Copaxone® and 5 batches of purported generics that are marketed drugs in their country of origin. All samples were compared to a reference batch of Copaxone® (P53961) using Waters HDMS Compare software. The analysis produced heat maps that highlighted significant intensity differences in peptides at various m/z and drift times. A quantitative assessment of these heat maps was also performed by summing all the pixel values to produce a total pixel value (TPV). While the average TPV for the Copaxone® batches was 510811, the TPVs of the purported generics were 8-13 fold higher (2301682 to 4276572).

Over the last few decades, elemental imaging using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) has emerged as an important tool in the study of solid samples from a variety of scientific disciplines, including medicine, biology, and geology. This article highlights recent analytical trends towards high-speed, high-spatial resolution, multi-elemental imaging that became possible with advances in both LA and ICP-MS technology, including the design of fast-washout ablation cells and commercialization of high-speed ICP-MS such as time-of-flight mass analyzers (TOFMS), This study will demonstrate the new imaging approach by coupling LA with an-ICP-TOFMS system (icpTOF from TOFWERK, Thun, Switzerland) on two application areas: quantitative mapping of trace elements in a sulfide mineral (sphalerite), and imaging of the distribution of a chemotherapy drug (Cisplatin) in a rat kidney. High-performance LA-ICP-TOFMS provides researchers with an effective new tool to study biological and geological processes, with much greater speed and in much greater detail than previously possible with conventional ICP-MS instrumental designs.

Antibody drug conjugates (ADCs) are an emerging category of biotherapeutic products based on monoclonal antibodies (mAbs) coupled to powerful cytotoxic drugs. The production of ADCs entails the formation of species with different number of conjugates drugs. The heterogeneity of ADCs species add to the complexity originating from the mAbs microvariability. Sheathless capillary electrophoresis-mass spectrometry (sheathless CE-MS) using complementary approaches was used to perform a detail characterization of brentuximab vedotin (Adcetris, Seattle Genetics). Sheathless CE-MS instrument used as nanoESI infusion platform was involved to perform the intact and middle-up analysis in native MS conditions. The nanoESI infusion approaches enabled estimation of the average drug to antibody ratio (DAR) alongside to drug load distribution. Sheathless CZE-MS/MS method developed was used to obtain from a single injection the characterization of the amino acid sequence with complete sequence coverage. In addition glycosylation and drug-loaded peptides could be identified from MS/MS spectra revealing robust information regarding their localizations and abundances. Drug-loaded peptide fragmentation mass spectra study demonstrated drug-specific fragments reinforcing the identifications confidence. Results reveal the ability of sheathless CZE-MS/MS method to characterize ADCs primary structure in a single experiment.

Using examples from our analysis of L-carnitine and acyl-L-carnitines, we give specific guidance for the use of mass spectrometry in quantitative analysis, as applied to clinical research and clinical pharmacology. We focus on quantitative accuracy and analytical selectivity as keys to successful implementation of mass spectrometric methods in clinical applications

Accurate evaluation of chemical modifications such as asparagine deamidation and aspartic acid isomerization is an essential component of comprehensive characterization of therapeutic monoclonal antibodies (mAbs). When located in the complementarity determining regions (CDRs), these modifications can cause a loss of function, impacting product efficacy and safety, resulting in the designation of the modification as a critical quality attribute. However, artifactual modifications can be introduced by analytical procedures, and distinguishing modifications as either critical quality attributes or method-induced artifacts is an important objective for product development. Conventional peptide mapping coupled with ultrahigh-resolution mass spectrometry offers advanced capabilities for definitive characterization of protein therapeutics. However, experimental conditions such as digestion time and pH can influence the observed level of chemical modifications, usually leading to over-estimation. In this work, a new peptide mapping method was developed specifically for mAb characterization that employs optimal enzyme pH for robustness, but short digestion times and time-course elements to minimize and monitor deamidation/isomerization, respectively, allowing a more accurate assessment of potential CDR sequence liabilities.

Chronic kidney disease or kidney complication resulting from another systematic disorder can impact the organ’s blood filtering capability resulting in the passage of blood-born proteins through the kidneys and into urine.  Clinical analyses for blood proteins in urine are performed to assess proper kidney function or to monitor a diagnosed disorder.  Serum albumin is a common target in these clinical assays and detection of elevated SA levels in urine is termed Albuminuria. Because of normal variability in urine content and volume multiple measurements are often made in comparison to creatitine levels within the same urine sample and reported as a ratio (ACR).  Demonstrated here is a novel means for quantifying albumin and creatinine directly from the same urine sample using MALDI-TOF mass spectrometry.  Standard addition of albumin and deuterated creatinine (d3) into control urine produced a linear and quantitative response (R2 = 0.99 and 0.98) and is used to quantify both analytes across their clinically relevant ranges. This MS-based method represents a simple, fast, attractive alternative to currently clinical methods.

This article investigates the use of gas chromatography–time-of-flight mass spectrometry (GC–TOF MS) to fragrance-profile three essential oils (ginger, wintergreen and rosemary). As well as considering the compositional differences between the oils, we will examine the use of peak deconvolution to identify closely-eluting compounds, and explore the use of soft electron ionization, assisted by comparison of ion ratios, to discriminate between isomeric monoterpenes that are difficult to identify at conventional 70 eV ionization energies due to their very similar mass spectra.

Compounds that are added as fragrances to personal care products (PCPs) can also be allergens or skin irritants for some consumers. Knowing whether these compounds are present in a product is important for both consumers with known allergies and for manufacturers in order to be compliant with various regulations related to allergens. Here, a GC-TOFMS method was developed to screen for and quantify regulated allergens in approximately 5 minutes. This method utilized a short and narrow chromatographic column along with mathematical deconvolution of the TOFMS data to separate the target allergens from each other in the standards and from matrix interference in samples. Calibration equations were compiled for standards from 1 ppb to 1 ppm (on-column) with excellent linearity and correlation coefficients. These were applied to various commercially-available perfume and cologne samples to determine quantitative information for the targeted allergens. The full-mass range data acquisition also provided for non-targeted characterization and comparisons to better understand the aroma profile of each sample. The reported method reduced analysis time for allergen screening while simultaneously increasing the acquired information about the PCP samples.

The power of nontargeted metabolite profiling is illustrated in a study focused on the determination of molecular markers in malting barley that are predictive of desirable malting quality for brewing applications. The metabolite extraction, detection, and analysis methods are highthroughput and reproducible, and therefore, this approach represents a practical addition to the plant breeder’s molecular toolbox.