Species-specific sulfur isotope-amount ratios of sulfur-containing amino acids using HPLC and MC ICP-MS

Abstract

Sulfur isotope-amount ratios (generally reported as δ34/32S or δ33/32S) have been used for nutrition and migration studies of humans and animals in various bio-compartments for decades. Especially hair represents a promising chemical archive for sulfur.In contrast to total sulfur, the isotopic composition of the major sulfur-containing amino acids reveal more information about the nutritional status and living conditions of an individual, since they have different original sources and follow different metabolic pathways. Methionine and cysteine are incorporated into proteins (e.g. in hair). Methionine cannot be synthesized by the human and animal organism and therefore has to be supplied by the diet. Cysteine is synthesized by the body, but the process requires a steady supply of sulfur.For this reason, the development and optimization of a species-specific method to assess the isotopic composition of sulfur in these amino acids in hair is a prerequisite to gain more understanding about the underlying fundamental processes. Hence, the aim of this master thesis is to develop an analytical method, both to separate the amino acids from hair and to assess the sulfur isotopic composition in the collected fractions. The methodological approach included the development of a proper sample preparation to clean the hair and a suitable digestion method to obtain the intact amino acids derivatives methionine sulfone and cysteic acid from hair through oxidation and hydrolysis of methionine and cysteine. For separating and collecting fractions of the oxidized sulfur-containing amino acids, a procedure was developed and optimized using high-performance liquid chromatography (HPLC). Finally, sulfur isotope-amount ratios were recorded by multi-collector inductively coupled plasma mass spectrometry (MC ICP-MS).