Vitamin D plays a vital role not only in bone health but also in pathophysiology of many other body functions. In recent years, there has been significant increase in testing of 25-hydroxyvitamin D (25-OH vitamin D), a marker of vitamin D deficiency. The most commonly used methods for the measurement of 25-OH vitamin D are immunoassays and liquid chromatography tandem mass spectrometry (LC-MS-MS). Since immunoassays suffer from inaccuracies and interferences, LC-MS-MS is a preferred method. In LC-MS-MS methods, 25-OH vitamin D is extracted from serum or plasma by solid-phase or liquid-phase extraction. Because these extraction methods are time consuming, we developed an easy method that uses simple protein precipitation followed by injection of the supernatant to LC-MS-MS. Several mass-to-charge (m/z) ratio transitions, including commonly used transitions based on water loss, were evaluated and several tube types were tested. The optimal transitions for 25-OH vitamin D2 and D3 were 395.5 > 269.5 and 383.4 > 257.3, respectively. The reportable range of the method was 1-100 ng/mL, and repeatability (within-run) and within-laboratory imprecision were <4% and <6%, respectively. The method agreed well with the solid-phase extraction methods.

The decomposed body of a 45-year-old female was found, face down, in a mobile home, along with a suicide note and two antifreeze containers. Analysis of the body fluid collected from the decedent showed the presence of 58 mg/dL ethanol, but suspected ethylene glycol was not found in the sample. However, an unusually large peak of internal standard, 1,3-propanediol, was found in the sample. Gas chromatography-mass spectrometry analysis confirmed the presence of 1,3-propanediol in the sample. Using gas chromatography-flame-ionization detection, the concentration of 1,3-propanediol was determined to be 445 mg/dL. To our knowledge, this is the first report involving 1,3-propanediol as the cause of death. The study also highlights the importance for the close scrutiny of data, as 1,3-propanediol is a frequently used internal standard for the assay of glycols.

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Mycophenolic acid (MPA) is an immunosuppressant that is used in renal, liver, and heart transplantation. Due to its narrow therapeutic range, monitoring of MPA levels is essential to avoid toxicity and organ rejection. Although immunoassays are available for the determination of MPA, due to their higher specificity, mass spectrometry methods are preferred. In this unit, we describe a liquid chromatography tandem mass spectrometry (LC/MS/MS) method utilizing positive ionization electrospray and multiple reaction monitoring (MRM) for the quantification of levels of MPA and its conjugate MPA glucuronide (MPAG). Blood collected in a plain, EDTA, or heparin-containing tube is centrifuged to separate the serum or plasma. Proteins are precipitated using a solution containing zinc sulfate and acetonitrile that has been spiked with deuterated internal standards. The resulting protein-free supernatant is injected into the LC/MS/MS system for analysis. The chromatography involves the use of a C18 column and ammonium acetate/water/formic acid and ammonium acetate/methanol/formic acid mobile phases. Quantification of MPA and MPAG levels is achieved by comparing the MRM peak area ratios of analytes and internal standards, consisting of specific precursor/product pairs, with those of calibrators at various concentrations. Calibration curves are constructed from the MRM peak area ratios of calibrators and internal standards versus concentration. © 2018 by John Wiley & Sons, Inc.

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