Detection sensitivity, 8 glycerol

A further method for estimation of sialic acid using periodic acid has been reported by Massamiri and coworkers.121 Fonnaldehyde produced by mild, oxidative cleavage of the D-en/f/iro-glycerol-l-yl side-chain of Neu can be detected by 3-methyl-2-benzothiazolinone hydrazone, which yields a green-blue color (absorbance maximum 625 nm). This test, which is slightly more sensitive than the thiobarbi-... 

The emission of molecular ions in organic SIMS is discussed with respect to the method of ionization and the various sample preparation and matrix-assisted procedures used. The matrices include various solid-state and liquid matrices such as ammonium chloride, charcoal, glycerol, and galliun. A neutral beam source is described to analyze thick insulating films. Various chemical derivatization procedures have been developed to enhance the sensitivity of molecular SIMS and to selectively detect components in mixtures. 

A refractive index detector was also constructed on-chip to detect glycerol (743 pM). An improved sensitivity was achieved in the backscatter format, rather than in the forward scatter format, because the probe beam passed the detector channel more than once in the backscatter format. This multiple pass advantage was enhanced in the unique hemi-cylindrical shape of the channel. When the channel was irradiated by a He/Ne laser with a beam diameter of 0.8 mm, a series of backscatter fringes was produced. When the solution was changed from water to glycerol, there was a change in the refractive index, and the position of the fringes shifted (191 pm/mRIU) [151]. 

Fig. 5. Biosynthesis of membrane phospholipids from alkyldihydroxyacetone-P (alkyl-DHAP), the first detectable intermediate formed in the biosynthetic pathway for ether-linked glycerolipids. Enzymes catalyzing the reactions are (1) NADPH alkyl-DHAP oxidoreductase, (II) acyl-CoA 1 -alkyl-2-lyso-sn-glycero-3-phosphate acyltransferase, (III) l-alkyl-2-acyl-in-glycero-3-phosphate phosphohydrolase, (IV) ATP 1-alkyl- /i-glycerol phosphotransferase, (V) CDP-choline l-alkyl-2-acyl-sn-glycerol cholinephosphotransferase (dithiothreitol-sensitive), (VI) CDP-ethanolamine l-alkyl-2-acyI-sn-glycerol ethanolaminephosphotransferase, and (VII) acyl-CoA 1 -alkyl-2-acy 1-OT-glycerol acyltransferase.

Direct inlet probe FAB-MS is an important tool in the analysis of compounds that are thermolabile and/or lack volatility [102]. Lack of sensitivity was initially a limiting factor but detection limits have been enhanced 10-100 fold, because of reduced suppression effects [103], with the use of a dynamic system in which the HPLC effluent is passed continuously into the ion source of the MS [104,105]. In the case of a frit-FAB HPLC interface, which is available commercially, reverse phase HPLC mobile phase, containing 1% glycerol as a matrix, is introduced into the ion source via a steel frit. The sample and matrix are then ionised on the inner surface of the frit with a beam of accelerated xenon atoms (Fig. 9). The optimum rate at which the HPLC mobile phase can be introduced into the ion source is 5 p.1 min and this necessitates the use of a reliable splitter when a conventional 2-5 mm bore HPLC column is used. Although a commercial post-column splitter is available, it is of limited value in the analysis of traee quantities of compounds. 

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