Desorption derivatization after

Derivatization After Desorption. Alkanolamines, highly polar basic compounds, present a difficult analytical problem. Although direct gas chromatographic separations can be achieved, this technique is not applicable to trace analysis due to sorption problems at trace concentrations. A derivatization/gas chromatographic procedure has been developed for the determination of alkanolamines in air as low as 100 ppb (54,55). The samples are collected on activated alumina and desorbed with an aqueous solution of 1-octanesulfonic acid. The... 

Formaldehyde is an airborne contaminant from various environmental sources. Acceptable concentration limits of formaldehyde in ambient air are in the range of 20-100 ppbv. It is not possible to sample formaldehyde directly by SPME. However, a unique SPME headspace sampling approach has been developed to quantitatively sample formaldehyde (22). This method involves first exposing the fiber to o-pentafluorobenzyl-hydroxylamine hydrochloride and then to the product headspace. The formaldehyde is derivatized directly on the fiber and after desorption in the GC is quantitated as the derivative. This methodology is... 

The mode of operation in SBSE resembles that in SPME but with a few distinctive differences. For instance, after carrying out an SBSE procedure, two Twisters (dual SBSE extraction) can be simultaneously desorbed in one thermal desorption tube in order to further enhance the sensitivity. In the so-called multishot mode, up to five Twisters were desorbed in one desorption tube with in situ derivatization for quantification of estrogens in river water.46... 

Mass spectrometry is another detection technique widely used in neuropeptide analysis. Concentration sensitivities in CE-MS do not reach those obtained by CE-LIF nevertheless, tedious derivatization procedures are avoided. In addition, CE-MS has proven to be a powerful tool for structure elucidation as illustrated by the investigation of the in vivo metabolic fate of peptide E by Caprioli s group [12]. After microdialysis and in-line SPE, neuropeptides migrating out of the electrophoresis capillary were deposited directly onto a precoated cellulose target used in matrix-assisted laser desorption-time of flight (MALDI-TOF) MS subsequently. Structural information is then obtained along with the mass of the peptide(s). 

Derivatization of 4mL of wine is carried out at 70 °C for lmin in a 20-mL sealed vial after addition of 140 pi, of acetic anhydride, 1 mL of K2C03 5.5% solution, and 0.9 g NaCl. Sampling is performed by exposing the fiber at 70°C for 70min (desorption at 270°C for 7min). A PEG fused-silica capillary column was used for GC/MS-IT El (70 eV)... 

Perhaps the main reason for MS success is its ability to detect and characterize organic compounds, giving definite structural information from minute amounts of material. The combination of gas chromatography (GC) and mass spectrometry (GC-MS) is particularly useful for lipid studies because of the ease with which complex mixtures may be separated and identified. In general, any compounds which are volatile enough for GC separation are sufficiently volatile for MS analysis. Compounds which are not sufficiently volatile for GC-MS analysis can usually be studied either after derivatization or with the help of new techniques, such as field-desorption MS. 

Meuldermans et al. [12] presented a complete study on the metabolic pathways of SUF and ALF from the excreta of rats and dogs. Among other techniques, they used GC MS in El and PCI modes for the characterization of major metabo lites after derivatization by silylation or acylation. The same laboratory [13] has identified the two major metabolites of ALF in human urine. Lavrijsen et al. [14] have studied the biotransformation of SUF in vitro in different species using GC-MS in El mode, but also with desorption Cl and Townsend discharge ionization. Several metabolites were identified unambiguously on the basis of their MS data, in comparison with the mass spectra of authentic reference compounds. 

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