Abstract: The invention relates to stable, isotopically labeled compounds for use in mass spectrometry analysis for quantifying methotrexate in a sample. Exemplary compounds include isotopically labeled variants of methotrexate.

Abstract: The invention relates to stable, isotopically labeled variants of methotrexate for use in mass spectrometry analysis for quantifying methotrexate in a sample. The compounds have the structure wherein each of Y1, Y2, Y3, Y4, Y5, Y6, Y7, Y8, Y9, Y10, Y11<Y12-Y13 and Y14 is independently selected from carbon or carbon-13; and wherein at least 5 of Y1, Y2, Y3, Y4, Y5, Y6, Y7, Y8, Y9, Y10, Y11, Y12, Y13 and Y14 are carbon-13.

Abstract: A method of quantifying a target analyte by mass spectrometry includes obtaining a mass spectrometer signal comprising a first calibrator signal, comprising a second calibrator signal, and potentially comprising a target analyte signal from a single sample comprising a first known quantity of a first calibrator, comprising a second known quantity of a second calibrator, and potentially comprising a target analyte. The first known quantity and the second known quantity are different, and wherein the first calibrator, the second calibrator, and the target analyte are each distinguishable in the single sample by mass spectrometry. The method also includes quantifying the target analyte in the single sample using the first calibrator signal, the second calibrator signal, and the target analyte signal.

Abstract: A method of quantifying a target analyte by mass spectrometry includes obtaining a mass spectrometer signal comprising a first calibrator signal, comprising a second calibrator signal, and potentially comprising a target analyte signal from a single sample comprising a first known quantity of a first calibrator, comprising a second known quantity of a second calibrator, and potentially comprising a target analyte. The first known quantity and the second known quantity are different, and wherein the first calibrator, the second calibrator, and the target analyte are each distinguishable in the single sample by mass spectrometry. The method also includes quantifying the target analyte in the single sample using the first calibrator signal, the second calibrator signal, and the target analyte signal.

Abstract: A method of quantifying a target analyte by mass spectrometry includes obtaining a mass spectrometer signal comprising a first calibrator signal, comprising a second calibrator signal, and potentially comprising a target analyte signal from a single sample comprising a first known quantity of a first calibrator, comprising a second known quantity of a second calibrator, and potentially comprising a target analyte. The first known quantity and the second known quantity are different, and wherein the first calibrator, the second calibrator, and the target analyte are each distinguishable in the single sample by mass spectrometry. The method also includes quantifying the target analyte in the single sample using the first calibrator signal, the second calibrator signal, and the target analyte signal.

Abstract: Embodiments of the present invention feature apparatus, kits and methods for detecting the presence or absence of a mineralocorticoid in biological samples. The methods, apparatus and kits feature a high performance liquid chromatography system with a column for receiving one or more biological samples potentially having mineralocorticoid, said chromatography system receiving one or more biological samples at a first time and separating the compounds in retained peaks comprising at least mineral corticoid retained peak for a mineralocorticoid in the event said mineralocorticoid is present at a mineralocorticoid retention time. And, a mass spectrometer in fluid communication with the high performance liquid chromatography system receives one or more of said retained peaks including the mineralocorticoid retained peak at the mineralocorticoid retention time, and produces a signal to allow said mineralocorticoid to be identified by retention peak and mass charge values.