An LC-MS/MS Method to Measure <i>S</i>-Methyl-<span style="font-variant: small-caps">l</span>-Cysteine and <i>S</i>-Methyl-<span style="font-variant: small-caps">l</span>-Cysteine Sulfoxide in Human Specimens Using Isotope Labelled Internal Standards

• Published in: Molecules
• Main Authors: Tharsini Sivapalan, Antonietta Melchini, Jack Coode-Bate, Paul W. Needs, Richard F. Mithen, Shikha Saha
• Format: Article
• Language: English
• Published: MDPI AG 2019-07-01
• Subjects: <i>S</i>-methyl-<span style="font-variant: small-caps">l</span>-cysteine; <i>S</i>-methyl-<span style="font-variant: small-caps">l</span>-cysteine sulfoxide; sulphur compounds; liquid chromatography tandem mass spectrometry; body fluids
• Online Access: https://www.mdpi.com/1420-3049/24/13/2427

This is the first report describing an analytical method for quantitative analysis of two naturally occurring sulphur compounds, <i>S</i>-methyl-<span style="font-variant: small-caps;">l</span>-cysteine (SMC) and <i>S</i>-methyl-<span style="font-variant: small-caps;">l</span>-cysteine sulfoxide (SMCSO), in human body fluids using isotope-labelled internal standards and liquid chromatography-mass spectrometry (LC-MS)/MS techniques. This method was validated according to the guideline of the Royal Society of Chemistry Analytical Methods Committee. It offers significant advantages including simple and fast preparation of human biological samples. The limits of detection of SMC were 0.08 &#181;M for urine and 0.04 &#181;M for plasma. The limits of detection of SMCSO were 0.03 &#181;M for urine and 0.02 &#181;M for plasma. The calibration curves of all matrices showed linearity with correlation coefficients r² &gt; 0.9987. The intra and inter day precisions in three levels of known concentrations were &gt;10% and &gt;20%, respectively. The quantification accuracy was 98.28 &#177; 5.66%. The proposed method would be beneficial for the rapid and accurate determination of the SMC and SMCSO in human plasma and urine samples using by isotope labelled internal standards.