Special Issues-05-01-2017

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.

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).

High resolution mass spectrometry with nano-LC is used for protein identification and quantification in both top-down and bottom-up proteome analysis. Reliable instrumentation in combination with ultrapure mobile phases is essential for data integrity. Premixed 80% acetonitrile with 0.1% formic acid (LS122-500) and water with 0.1% formic acid (LS118-500) were designed to produce a consistent chromatographic performance using this instrument system. In this study, these mobile phases were used extensively to evaluate several factors which can affect separation of protein digests such as peak retention, peak repeatability, and sample carryover. Our results demonstrated excellent chromatographic performance using Thermo Scientific EASY-nLC 1200 LC system and Thermo Scientific LTQLX ™ ion trap mass spectrometer with the specialized premixed mobile phases.

By switching to a Raptor C18 column, labs can process more samples per hour while still meeting fluorochemical method requirements.

Determination of PBDE congeners can be performed at high sensitivity with good accuracy using the GCMS-TQ8050.

Drinking water is an important part of environmental exposure, especially for small children. Countries around the world have put regulations in place to monitor drinking water quality for a wide range of hazardous compounds.

Click the title above to open the May 2017 issue of Current Trends in Mass Spectrometry, Volume 15, Number 2, in an interactive PDF format.