Chemical ionization mass analyzers

GC/MS has been employed by Demeter et al. (1978) to quantitatively detect low-ppb levels of a- and P-endosulfan in human serum, urine, and liver. This technique could not separate a- and P-isomers, and limited sensitivity confined its use to toxicological analysis following exposures to high levels of endosulfan. More recently, Le Bel and Williams (1986) and Williams et al. (1988) employed GC/MS to confirm qualitatively the presence of a-endosulfan in adipose tissue previously analyzed quantitatively by GC/ECD. These studies indicate that GC/MS is not as sensitive as GC/ECD. Mariani et al. (1995) have used GC in conjunction with negative ion chemical ionization mass spectrometry to determine alpha- and beta-endosulfan in plasma and brain samples with limits of detection reported to be 5 ppb in each matrix. Details of commonly used analytical methods for several types of biological media are presented in Table 6-1. 

HPLC - Beckman 125 binary gradient pumps, 168 diode-array detector, 507 autosampler MS - Ion-trap mass spectrometer Finnigan LCQ equipped by APCI (atmospheric pressure chemical ionization), data analyzed in negative mode, spectra confirming found compounds were obtained from tandem mass spectromectry (MS/MS). 

The most suitable and effective method to date that is capable of analyzing several neurosteroids simultaneously is gas chromatography/electron capture-negative chemical ionization/mass spectrometry (GC/EC-NCI/MS) with selected ion monitoring (SIM). This technique allows a focus on a few specific ions bearing structural information. 

This system was studied by Schwartz. Toluene at 10 ppm, nitric oxide at 1 ppm, and nitrogen dioxide at 1.2 ppm were irradiated with ultraviolet lamps in a 17-m batch reactor for 270 min. Collected aerosols were successively extracted with methylene chloride and then methanol. The methylene chloride extract was fractionated into water-soluble and water-insoluble material, and the latter fraction was further divided into acidic, neutral, and basic fractions. The acidic and neutral fractions were analyzed by gas chromatography and chemical-ionization mass spectrometry the compounds identified are shown in Figure 3-7. The two analyzed fractions represented only about 5.5% of the total aerosol mass. It is noteworthy that classical nitration of an aromatic ring appears to... 

The fatty acid composition of lipids is usually analyzed by gas chromatography following transesterification into methyl esters. Unmodified lipids can be analyzed by HPLC or by soft chemical ionization mass spectrometry. In the course of sample preparation it is often necessary to separate the various membrane fractions (plasma membrane, thylakoid, microsomal, mitochondrial, etc.) by sophisticated gradient centrifugations, as well as the individual lipid classes within a membrane fraction, usually by thin-layer chromatography (TLC). 

Ma CY, Bayne CK. 1993. Differentiation of Aroclors using linear discrimination for environmental samples analyzed by electron capture negative ion chemical ionization mass spectrometry. Anal Chem... 

Derivatization is also useful to detect volatile metabolites. Liu et al. [282] described a specific, rapid, and sensitive in situ derivatization solid-phase microextraction (SPME) method for determination of volatile trichloroethylene (TCE) metabolites, trichloroacetic acid (TCA), dichloroacetic acid (DCA), and trichloroethanol (TCOH), in rat blood. The metabolites were derivatized to their ethyl esters with acidic ethanol, extracted by SPME and then analyzed by gas chromatography/negative chemical ionization mass spectrometry (GC-NCI-MS). After validation, the method was successfully applied to investigate the toxicokinetic behavior of TCE metabolites following an oral dose of TCE. Some of the common derivatization reagents include acetyl chloride and TV-methyl-iV- ft-b u (y Idi methyl si I y I) tro (1 uoroacctam i nc (MTBSTFA) for phenols and aliphatic alcohols and amines, dansyl chloride and diazomethane for phenols, dansyl chloride for amines, acidic ethanol and diazomethane for carboxylic acids, and hydrazine for aldehydes. 

In order to determine ureas and metabolites of triazines and ureas in agricultural soils, reverse-phase liquid chromatography was used with atmospheric pressure chemical ionization/mass spectrometry (APCI/MS), in positive mode. Gas chromatography/ion trap mass spectrometry was used in MS/MS mode to analyze the parent compounds of the triazines and chloroacetanilides. Method performance was much better in GC-MS/MS than in LC-MS, and acetochlor LOQ was dramatically improved by using GC-MS/MS, this herbicide being very poorly ionized into the APCI interface. 

The formation of SO2, COS and H2S was also studied during exhaust conditions. Chemical Ionization Mass Spectrometry (CIMS) was used for on-line exhaust gas analysis (11). In the CIMS instnunent (CIMS 500, V F) the exhaust gas is soft ionized by a pre-ionized Xe gas. SO2, H2S and COS in the exhaust gas was continously analyzed. The exhaust gas was generated by a Volvo 234 FT engine, with a fuel containing 629 ppm sulfur. The engine speed was 2700 rpm with a load of about 15 Nm and the outlet temperature was 873 K. The engine was run with... 

A chemical ionization mass spectrometer (MS), from V F named Air-sense 500, an electron pulse ionization mass spectrometer, fi-om V F named H-sense, and Fourier-transformed infrared spectrometer (FTIR), from MKS named MultiGas 2030 Model, are used simultaneously to analyze the product composition. FI2O is calculated via the oxygen mass balance. 

NMR spectra were measured with a Varian Unity 300 FT-NMR spectrometer. Liquid chromatography-atmospheric chemical ionization-mass spectrometry (LC-APCl-MS) in positive and negative ion modes was performed using a Hitachi M-1000 spectrometer. Unknown metabolites were isolated and purified from the grape fruits extracts with solid phase extraction method (Porapak Q) and HPLC. Isolated metabolites were analyzed by free form or derivatized (methylated, acetylated) form for identification. All of the non-radiolabelled reference standards 1-6 are synthesized in our laboratory and their chemical structures are shown in Figure 2. 

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