LC-MS is a technique routinely used in sample analysis that combines liquid chromatography (LC) with mass spectrometry (MS). Extremely sensitive modern MS has helped LC-MS replace several immunoassays. LC-MS has helped improve the efficiency of drug discovery due to its excellent sensitivity and specificity. The technique can be combined with stable isotope dilution for precise and reproducible assays.
The LC-MS technique is useful for the detection of steroid drugs in body fluids and in profiling endogenous steroids. Steroid sulfates have been detected with high sensitivity using this method. Plasmaspray has been used to test saliva for steroid hormones in patients suffering from congenital adrenal hyperplasia.
Amino acids were one of the first compounds analyzed using LC-MS coupled with laser desorption and thermospray. Nucleosides, nucleotides, saccharides, peptides, and proteins were all analyzed and their molecular weights were determined using LC-MS coupled with electrospray. Bile acids have also been determined using LC-MS and thermospray.
Ultra-pure additives and solvents such as acetic acid, acetonitrile, ammonium acetate, ammonium bicarbonate, ammonium fluoride, and ammonium hydroxide are available from Sigma Aldrich for use in LC-MS systems.
LC-MS is used in the analysis of diverse samples such as soil, drinking water or waste water, air, and sludge. The samples may belong to many different chemical species ranging from non-polar hydrocarbons to ionic organometallic species.
Several pesticides and herbicides including triazine derivatives, chlorophenols, phenoxyalkanoic acids, and sulfonylurea herbicides can be analyzed using LC-MS. Separation of polycyclic aromatic hydrocarbons and organometallic compounds is also possible using the technique.
Biochemical Screening for Genetic Disorders
Blood samples of newborn babies are analyzed using LC-MS to detect metabolic disorders. Second-tier LC-MS testing has been used for confirming the results of first-tier immunoassays in newborn screening.
LC-MS is widely used in the determination of pharmaceutical compounds and especially in the separation of optically active drugs. Antibiotics and potential antimalarials have been studied using thermospray. The use of LC-MS in the identification of bromazepam and similar drugs in case of intoxication has been successfully demonstrated.
Detection, isolation, and purification of drug metabolites is another major application of LC-MS, as they are chemically or thermally labile, and need liquid chromatography. Separation and characterization of components in a crude mixture of natural products such as complex lipids, alkaloids, and hydroxylated or unsaturated fatty acids has been achieved using LC-MS.
LC-MS systems from Shimadzu feature high sensitivity, provide precise quantification, and improve analytical throughput in food, pharmaceutical, chemical, and environmental analysis.
Therapeutic Drug Monitoring and Toxicology
In drug monitoring, LC-MS assays have been developed for immunosuppressants including tacrolimus, cyclosporin, everolimus, sirolimus, and mycophenolic acid. Similar assays for aminoglycosides, anticancer drugs, and antiretrovirals have also been described.
LC-MS assays can be multiplexed to measure several drugs and metabolites in a single run, thus simplifying lab workflows and providing additional information such as metabolite profiles in clinical biochemistry labs. LC-tandem MS is used in toxicology screening for the detection of a wide range of toxins, drugs, and metabolites.
Thermo Fischer provides a range of LC-MS systems including ion trap LC-MS, triple and single quadrupole LC-MS solutions. This is in addition to LC-MS software and accessories suitable for the analysis of environmental pollutants, complex proteins, and drug metabolites.
LC-MS analysis has been helpful in steroid biochemistry studies where traditional immunoassays have not proved very effective. Highly sensitive LC-MS assays have been developed for the measurement of low dihydrotestosterone and testosterone levels in women and children.
Urinary steroid profiling has been simplified using LC-MS methods as these steroids are excreted as glucuronide or sulfate conjugates which will need to be hydrolyzed and derivatized for GC-MS analysis.
Vitamins and Related Metabolites
LC-MS is a preferred method for the measurement of vitamin D and its metabolites. LC-MS assays have been developed for 25-hydroxyvitamin D2 and D3 in plasma and serum. Similar assays are also available for fat-soluble vitamins such as vitamin K15 and Vitamin E13,15.
Reviewed by Afsaneh Khetrapal BSc (Hons)