High-pressure liquid chromatography separation, comparison

The GC is often connected to a mass spectrometer. Mass spectrometry (MS) breaks samples apart and separates the ionized fragments by mass and charge. Vast libraries of comparison fragments make computer-aided identification of materials possible even when the sample is very small. Most forensic laboratories have access to a combined gas chromatograph/mass spectrometer (GC/MS). High pressure liquid chromatography (HPLC) separates many types of drugs and may also be combined with MS. 

Preferably, high pressure liquid chromatography (hplc) is used to separate the active pre- and cis-isomers of vitamin D3 from other isomers and allows theic analysis by comparison with the chromatograph of a sample of pure reference j-vitamin D3, which is equilibrated to a mixture of pre- and cis-isomers (82,84,85). This method is more sensitive and provides information on isomer distribution as well as the active pre- and cis-isomer content of a vitamin D sample. It is applicable to most forms of vitamin D, including the more dilute formulations, ie, multivitamin preparations containing at least 1 lU/g (AOAC Methods 979.24 980.26 981.17 982.29 985.27) (82). The practical problem of isolation of the vitamin material from interfering and extraneous components is the limiting factor in the assay of low level formulations. 

We have evidenced the difference between the reactivity of the MD and CE by measuring the reaction rate of I with CE and MD separately. We have shown the existence of a supplementary synergetic effect due to which, in the case of the reaction between I with the mixture MD-CE, the reactivity of the glycol increases in comparison to that of MD [44—46,89]. With this aim, high pressure liquid chromatography (HPLC) measurements where employed to monitor the evolution of every molecular species which can appear in the reaction, on the model reaction which employs a monoisocyanate instead of the diisocyanate [89]. 

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