Gas-phase Derivatization by Chemical Ionization

Mateo-Vivaracho, L., Ferreira, V. and Cacho, J. (2006) Automated analysis of 2-methyl-3-furanethiol and 3-mercaptohexyl acetate at ng L 1 level by headspace solid phase microextraction with on-fibre derivatization and gas chromatography-negative chemical ionization mass spectrometric determination,/. Chromatogr. A, 1121(1), 1-9. 

Biological specimen extraction can be accomplished by liquid-liquid, solid-phase or solid-phase microextraction with subsequent detection of GHB or GBL by gas chromatography-mass spectrometry (GC-MS) using electron ionization (El), positive or negative chemical ionization (CI) or gas chromatography with flame ionization detection (GC-FID). LeBeau et al. (1999) describes a method that employs two ahquots of specimen. The first is converted to GBL with concentrated sulfuric acid while the second is extracted without conversion. A simple liquid-liquid methylene chloride extraction was utilized, and the ahquots were then screened by GC-FID without derivatization. Specimens that screened positive by this method were then re-aliquoted and subjected to the same extraction with the addition of the deuterated analog of GBL. The extract was then analyzed by headspace GC-MS in the full-scan mode. Quantitation was performed by comparison of the area of the... 

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. 

MSTFA was also the derivatizing agent of choice for the direct derivatization of flutroline in plasma extracts on the tip of a moving needle injector prior to GC-MS selected ion monitoring (SIM) assay [22]. TMS derivatives of formaldehyde condensates, formed in a gas phase reaction with BSTFA, were used for the separation and quantification of methylal (dimethoxymethane), methylene glycol and a series of poly(oxymethylene) glycol monomethyl ethers by capillary GC-MS using ammonia chemical ionization [23]. The possibility of accelerated... 

GC is a separation technique which is based on partition principles between the stationary liquid phase and the mobile gas phase. The derivatization of substances such as auxins and auxin conjugates is needed to increase their volatility and to improve the chromatographic characteristics of the analyte. It is also used to enhance the detector response, then the sensitivity of the assay. The selection of the derivative for MS depends on the method of ionization. A derivative with favorable El characteristics could be useless for measurements by negative chemical ionization (NCI). Semi-quantitative data were obtained from lAA derivatives mass spectra and their respective merits to GC behaviour and MS ionization are compared in Table 1. 

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