APPLICATION OF LIQUID CHROMATOGRAPHY/ELECTROCHEMISTRY TO THE DETERMINATION OF COMMON ANALGESICS AND METABOLITES (ASPIRIN, ACETOMINOPHEN, CODEINE)
Abstract
The objective of my research has been to enhance the analytical capability available for investigations involving common analgesics and related compounds. Acetaminophen, aspirin, phenacetin, methyl salicylate, salicylamide, codeine, and naproxen represent widely consumed analgesics whose disposition, metabolism, toxicity, and interaction are of ongoing concern. Liquid chromatography and electrochemistry have been used to illuminate valuable new analytical approaches to the relevant research studies. The aforementioned analgesics were all found to yield oxidation potentials sufficiently low to enable sensitive determination by liquid chromatography with electrochemical detection (LCEC). After characterizing their electrochemical and chromatographic properties, sensitive and convenient methods of determination in serum and urine were demonstrated by LCEC with single- and dual-electrode detection. Codeine represents a whole family of important drugs, narcotic analgesics, which pose significant analytical challenge for in vivo determination. Therefore, codeine was well characterized electrochemically and chromatographically before demonstrating sensitive LCEC determination in serum and urine. Ion-pair LC was used to overcome poor peak symmetry and provide low detection limits. Direct enzymatic two-electron oxidation of acetaminophen (APAP) to N-acetyl-p-quinoneimine (NAPQI) as a reactive, toxic metabolite has been proposed. Synthesis and electrochemical characterization of some 2- and 3-(S)-thioether conjugates of APAP enabled an LCEC comparison of microsomal incubation products versus synthetic NAPQI-thiol reaction products. Relative yield of 2-isomer conjugate decreased as the size of attacking thiol increased. No detectable amount of 2-(S)-N-acetylcysteine conjugate was found even at trace levels in vivo to indicate probable steric hindrance of 2-isomer formation via conjugation with glutathione. An APAP dimer was confirmed as a synthetic reaction product and appeared to be formed in vitro as well. LCEC was shown to be an excellent technique for in vivo determination of major and minor aspirin metabolites. Dual-electrode detection in both series and parallel configurations greatly facilitates metabolite determination. Unique electrochemical properties of trace metabolites offer sensitive detection and even tentative identification.
Degree
Ph.D.
Subject Area
Analytical chemistry
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