Carbon isotopic ratio analysis by gas chromatography/combustion/isotope ratio mass spectrometry for the detection of gamma‐hydroxybutyric acid (GHB) administration to humans

Abstract

Since GHB (gamma-hydroxybutyric acid) is naturally produced in the human body, clinical and forensic toxicologists must be able to discriminate between endogenous levels and a concentration resulting from exposure. To suggest an alternative to the use of interpretative concentration cut-offs, the detection of exogenous GHB in urine specimens was investigated by means of gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS). GHB was isolated from urinary matrix by successive purification on Oasis MCX and Bond Elute SAX solid-phase extraction (SPE) cartridges prior to high-performance liquid chromatography (HPLC) fractioning using an Atlantis dC18 column eluted with a mixture of formic acid and methanol. Subsequent intramolecular esterification of GHB leading to the formation of gamma-butyrolactone (GBL) was carried out to avoid introduction of additional carbon atoms for carbon isotopic ratio analysis. A precision of 0.3 per thousand was determined using this IRMS method for samples at GHB concentrations of 10 mg/L. The (13)C/(12)C ratios of GHB in samples of subjects exposed to the drug ranged from -32.1 to -42.1 per thousand, whereas the results obtained for samples containing GHB of endogenous origin at concentration levels less than 10 mg/L were in the range -23.5 to -27.0 per thousand. Therefore, these preliminary results show that a possible discrimination between endogenous and exogenous GHB can be made using carbon isotopic ratio analyses.

Current challenges in compound-specific stable isotope analysis of environmental organic contaminants

“…modifications are decarboxylation [108,109], reduction of fatty acid esters to alcohols [110], reduction of organometal (loid) oxides to the corresponding hydrides [111], intramolecular esterification [112], or selective fragmentation [89]. Besides enabling carbon-isotope analysis, the latter approach has been shown to facilitate isotope analysis of nitrogen and hydrogen also [65,89].…”

Potential of IRMS technology for tracing gamma-butyrolactone (GBL)

“…Based on previous work, GBL may be analysed by means of GC/C/IRMS using a moderately polar column and hence does not require a chemical modification to provide acceptable chromatographic characteristics [31]. In that study, it is worth to note that each sample preparation was spiked with ecaprolactone and tetradecanoic acid methyl ester.…”

Forensic Mass Spectrometry

“…Several reviews have discussed forensic applications of IRMS (105)(106)(107)(108), and Meier-Augenstein (109) provided even more comprehensive coverage in his recent book Stable Isotope Forensics. In forensic applications, isotope ratio analysis provides information about the natural or synthetic origins of scheduled drugs (110)(111)(112)(113)(114)(115)(116)(117)(118)(119)(120), organic and inorganic explosives (76,121,122), petroleum hydrocarbons (such as in ignitable liquids) (65,66,(123)(124)(125)(126), and various other forensic materials (such as fibers, matches, and paint chips) (127)(128)(129)(130)(131). The ability to analyze hard and soft human tissue has also provided helpful investigative leads about the geographic origins of humans, especially in John Doe and Jane Doe cases where fingerprints, DNA, and dental records are not found in databases (132)(133)(134)(135)(136)(137)(138)(139).…”