Zeev Karpas

Flow injection method for determination of uranium in urine and serum by inductively coupled plasma mass spectrometry

The uranium concentration in urine of a population that is not occupationally exposed to uranium compounds is in the range 1–40 ng l−1 with a median around 10 ng l−1. This is analytically challenging for routine analysis because at such low levels it is difficult to prevent contamination during sample preparation. The method presented here is based on sample introduction via a flow injection analysis system and inductively coupled plasma mass spectrometric detection, and requires virtually no sample preparation, except for acidification of the urine sample with a few drops of HNO3 The analysis is fully automated and fast with an analysis time of 60 s per sample. The lower limit of detection is 1.5ng l−1. Memory and matrix effects may be decreased by adding 1 g l−1 of a surfactant (Triton-X 100) to the carrier stream. The validity of the results is demonstrated through measurement of standard reference materials, standard dilution experiments and, at higher concentrations, by comparison with results obtained by an independent method based on laser induced fluorescence.

Atmospheric pressure chemical ionization of alkanes, alkenes, and cycloalkanes

Normal and cyclic alkanes and alkenes form stable gas-phase ions in air at atmospheric pressure from 40 to 200°C when moisture is below 1 ppm. Ionization of alkanes in a 63Ni source favored charge transfer over proton transfer through pathways involving [M−1]+ and [M−3]+ ions. Ion mobility spectra for alkanes showed sharp and symmetrical profiles while spectra for alkenes suggested fragmentation. Ion identifications were made by using mass spectrometry, and ionization pathways were supported by using deuterated analogs of alkanes and alkenes. Alkanes were ionized seemingly through a hydrogen abstraction pathway and did not proceed through an alkene intermediate. New methods for interpretation of mobility spectra utilizing ion mobility spectrometry, atmospheric pressure chemical ionization mass spectrometry, chemical ionization mass spectrometry, and ion mobility spectrometry-mass spectrometry data were demonstrated.

Trace elements in cocoa solids and chocolate: an ICPMS study.

The concentrations of eight trace elements: lead (Pb), cadmium (Cd), chromium (Cr), manganese (Mn), cobalt (Co), arsenic (As), bismuth (Bi) and molybdenum (Mo), in chocolate, cocoa beans and products were studied by ICPMS. The study examined chocolate samples from different brands and countries with different concentrations of cocoa solids from each brand. The samples were digested and filtered to remove lipids and indium was used as an internal standard to correct matrix effects. A linear correlation was found between the level of several trace elements in chocolate and the cocoa solids content. Significant levels of Bi and As were found in the cocoa bean shells but not in the cocoa bean and chocolate. This may be attributed to environmental contamination. The presence of other elements was attributed to the manufacturing processes of cocoa and chocolate products. Children, who are big consumers of chocolates, may be at risk of exceeding the daily limit of lead; whereas one 10 g cube of dark chocolate may contain as much as 20% of the daily lead oral limit. Moreover chocolate may not be the only source of lead in their nutrition. For adults there is almost no risk of exceeding daily limits for trace metals ingestion because their digestive absorption of metals is very poor.

Ion mobility spectrometric studies of organophosphorus compounds

Abstract The mobility spectra of several organophosphorus compounds were measured by ion mobility spectrometric methods. The correlation between the mass and structure of the ions formed and their mobility was investigated. It was found that compounds in which the phosphorus atom is trivalent had higher mobilities than their phosphonate isomers. It was also found that substitution of an alkoxy group by chlorine had little effect on the mass-mobility correlation. The tendency of these compounds to form protonated dimers was studied, and the protonated monomer to dimer ratio in dimethylmethylphosphonate as a function of concentration was measured.

Use of Neural Networks for Quantitative Measurements in Ion Mobility Spectrometry (IMS)

The use of a neural network (NN) to derive quantitative information from the mobility spectra of dimethylformamide, bromine, and hydrogen fluoride is described. Unlike traditional methods, where the areas or heights of known and identified peaks are used for calibration, employment of N N does not require detailed knowledge of the ion chemistry of the measured system. Efficient N N training algorithms were employed, allowing quick learning with hundreds of input channels. It was also found that the size of the required training set was much smaller than expected from theoretical considerations, due to the interactions between input channels. Thus, this technique may be easily implemented in online or offline analysis of IMS spectra.

Application of neural networks for interpretation of ion mobility and x-ray fluorescence spectra

Abstract Neural networks (NN) have been successfully used to interpret spectral data, and to derive qualitative and quantitative information from ion mobility spectrometry (IMS) and x-ray fluorescence (XRF). It is shown that components of complex mixtures of up to six aliphatic amines may be automatically identified by NN methods from their ion mobility spectra with reasonable accuracy. The ability of NN to identify compounds even under low signal-to-noise conditions of IMS spectra is demonstrated. The use of XRF technique for quantitative determination of parts per million (ppm) amounts of mixtures of Re, Os, Ir and Pt in a polyethylene matrix, which could not be done successfully by conventional methods, was made possible by application of NN, with a root mean square error of a few ppm. The networks could be trained on a personal computer, in less than 10 min, from a surprisingly small data set of training samples to perform these tasks.

Qualitative and quantitative response characteristics of a capillary gas chromatograph/ion mobility spectrometer to halogenated compounds

Abstract The response of a capillary column gas chromatograph/ion mobility spectrometer (GC/IMS) system to chlorinated and brominated alkanes and alkenes in nitrogen, air and nitrogen/CO 2 mixtures was studied. Product ions were formed through dissociative electron capture processes or charge transfer reactions, yielding chloride or bromide ions. The quantitative response was shown to depend on the composition of the carrier gas in which atmospheric pressure ionization processes occurred as well as on the IMS cell temperature. Large variations in the quantitative response of the GC/IMS to different halogenated compounds were observed. The results were compared to those reported for the doped electron capture detector (ECD). Practical implications of the GC/IMS system as a monitor and detector for halogenated aliphatic compounds are discussed.

Atmospheric pressure chemical ionization of fluorinated phenols in atmospheric pressure chemical ionization mass spectrometry, tandem mass spectrometry, and ion mobility spectrometry

Atmospheric pressure chemical ionization (APCI)-mass spectrometry (MS) for fluorinated phenols (C6H5−xFxOH where x=0–5) in nitrogen with Cl− as the reagent ion yielded product ions of M·Cl− through ion associations or (M−H)− through proton abstractions. Proton abstraction was controllable by potentials on the orifice and first lens, suggesting that some proton abstraction occurs through collision induced dissociation (CID) in the interface region. This was proven using CID of adduct ions (M·Cl−) with Q2 studies where adduct ions were dissociated to Cl− or proton abstracted to (M−H)−. The extent of proton abstraction depended upon ion energy and structure in order of calculated acidities: pentafluorophenol > tetrafluorophenol > trifluorophenol > difluorophenol. Little or no proton abstraction occurred for fluorophenol, phenol, or benzyl alcohol analogs. Ion mobility spectrometry was used to determine if proton abstraction reactions passed through an adduct intermediate with thermalized ions and mobility spectra for all chemicals were obtained from 25 to 200 °C. Proton abstraction from M·Cl− was not observed at any temperature for phenol, monofluorophenol, or difluorophenol. Mobility spectra for trifluorophenol revealed the kinetic transformations to (M−H)− either from M·Cl− or from M2·Cl− directly. Proton abstraction was the predominant reaction for tetra- and penta-fluorophenols. Consequently, the evidence suggests that proton abstraction occurs from an adduct ion where the reaction barrier is reduced with increasing acidity of the O-H bond in C6H5−xFxOH.

Diagnosing vaginal infections through measurement of biogenic amines by ion mobility spectrometry

OBJECTIVE To compare diagnosis of bacterial vaginosis according to the Amsel criteria with measurement by ion mobility spectrometry (IMS) of the biogenic amines that are present in vaginal discharge fluid. STUDY DESIGN Duplicate samples of vaginal fluid were collected from 115 unselected and consecutive patients in a vaginitis clinic in Detroit. All samples were evaluated using Amsel criteria and the results were compared with the diagnosis based on the IMS results. RESULTS The incidence rate of vaginal infections was assessed on the basis of both tests and the frequency of BV was found to be 17.4%. The sensitivity and specificity for bacterial vaginosis diagnosis using IMS determination were 95.5% and 98.9%, respectively, with an accuracy of 94.4%. CONCLUSIONS The results show that IMS may be used to rapidly diagnose this common vaginal infection with high accuracy.

Monitoring Indoor Ambient Atmospheres for Volatile Organic Compounds Using an Ion Mobility Analyzer Array with Selective Chemical Ionization

Abstract Three ion mobility analyzers with different reagent gases for chemical ionization were interfaced to a single computer and operated with a software package created for simultaneous and continuous monitoring of 1 to 8 analyzers. Mobility spectra were collected and digitized on separate input channels with 200 ms sampling intervals for individual analyzers. Volatile organic compounds (VOCs) in indoor ambient atmospheres were monitored in two scenarios: laboratory air during designed releases of several VOCs and ambient air in a central chemistry storeroom used for undergraduate laboratories. The ion mobility analyzer with reagent ions of H(H2O)+ n (n = 2 – 4) exhibited response toward alcohols, aldehydes, and other VOCs with low proton affinities. However, analyzers with reagent ions of elevated proton affinity including acetone and dimethylsulfoxide showed selective response toward only VOCs with proton affinities greater than that of the reagent ion. Thus, two tiers in selectivity of array respon...