Hydropyrolysis as a preparative method for the compound-specific carbon isotope analysis of fatty acids

Hydropyrolysis over a platinum catalyst as a preparative technique for the compound-specific carbon isotope ratio measurement of C27 steroids

Compound-specific stable carbon isotope analysis by gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS) is an important method for the determination of the (13)C/(12)C ratios of biomolecules such as steroids, for a wide range of applications. However, steroids in their natural form exhibit poor chromatographic resolution, while derivatisation adds carbon thereby corrupting the stable isotopic composition. Hydropyrolysis with a sulphided molybdenum catalyst has been shown to defunctionalise the steroids, while leaving their carbon skeleton intact, allowing for the accurate measurement of carbon isotope ratios. The presence of double bonds in unsaturated steroids such as cholesterol resulted in significant rearrangement of the products, but replacing the original catalyst system with one of platinum results in higher conversions and far greater selectivity. The improved chromatographic performance of the products should allow GC/C/IRMS to be applied to more structurally complex steroid hormones and their metabolites.

Analysis of conjugated steroid androgens: deconjugation, derivatisation and associated issues

Gas chromatography/mass spectrometry (GC/MS) is the preferred technique for the detection of urinary steroid androgens for drug testing in athletics. Excreted in either the glucuronide or sulfated conjugated form, steroids must first undergo deconjugation followed by derivatisation to render them suitable for GC analysis. Discussed herein are the deconjugation and the derivatisation preparative options. The analytical challenges surrounding these preparatory approaches, in particular the inability to cleave the sulfate moiety have led to a focus on testing protocols that reply on glucuronide conjugates. Other approaches which alleviate the need for deconjugation and derivatisation are also highlighted.

Biomedical and Forensic Applications of Combined Catalytic Hydrogenation-Stable Isotope Ratio Analysis

Studies of biological molecules such as fatty acids and the steroid hormones have the potential to benefit enormously from stable carbon isotope ratio measurements of individual molecules. In their natural form, however, the body's molecules interact too readily with laboratory equipment designed to separate them for accurate measurements to be made. Some methods overcome this problem by adding carbon to the target molecule, but this can irreversibly overprint the carbon source ‘signal’. Hydropyrolysis is a newly-applied catalytic technique that delicately strips molecules of their functional groups but retains their carbon skeletons and stereochemistries intact, allowing precise determination of the carbon source. By solving analytical problems, the new technique is increasing the ability of scientists to pinpoint molecular indicators of disease, elucidate metabolic pathways and recognise administered substances in forensic investigations.

Hydropyrolysis of steroids: a preparative step for compound-specific carbon isotope ratio analysis

Compound-specific stable carbon isotope analysis by gas chromatography/combustion/isotope ratio mass spectrometry is an important method for the detection of steroid abuse in athletes. However, steroids in their natural form exhibit poor chromatographic resolution, while derivatization adds carbon thereby corrupting the starting stable isotopic composition. Hydropyrolysis is a new approach, which defunctionalizes steroids but leaves their carbon skeleton intact. The process improves chromatography, allowing the faithful measurement of carbon isotope ratios and enabling a more effective apportionment for the source of steroids and their metabolites.