Multiplexed external calibrator and control for screening and diagnostic assays

1 . A method of quantifying a target analyte in a series of samples by mass spectrometry, the method comprising:

obtaining a mass spectrometer signal for a calibration mixture, wherein the calibration mixture comprises a plurality of calibrants comprising at least a standard of the target analyte at a known target concentration in the calibration mixture, a first isotopic analog of the target analyte at a known first concentration, and a second isotopic analog of the target analyte at a known second concentration, wherein said plurality of calibrants are distinguishable by mass spectrometry from one another and have different, known concentrations from one another in said calibration mixture;

adding an internal standard to the calibration mixture and to each of said series of samples prior to obtaining the mass spectrometer signal for the calibration mixture and each of the series of samples, wherein the internal standard comprises a third isotopic analog at a third known concentration of the target analyte distinguishable by mass spectrometry from the standard of the target analyte, the first isotopic analog, and the second isotopic analog, wherein each of the first, second, and third isotopic analogs of the target analyte has a substantially same physiochemical properties as the target analyte, with at least one atom in each of the first, second, and third isotopic analogs being a different isotope of the corresponding at least one atom of the other isotopic analogs and of the standard of the target analyte;

identifying from the mass spectrometer signal for the calibration mixture a characteristic response of each of said plurality of calibrants, wherein each of the characteristic responses is associated with a different m/z value corresponding to a different one of the plurality of calibrants and being indicative of the concentration of each of the plurality of calibrants in the calibration mixture;

generating a single calibration curve for the calibration mixture based on said characteristic responses of the at least the standard of the target analyte, the first isotopic analog of the target analyte, the second isotopic analog of the target analyte, and the internal standard comprising the third isotopic analog of the target analyte;

obtaining a mass spectrometer signal from each of the series of samples;

identifying from the mass spectrometer signal for each sample a target analyte characteristic response indicative of an unknown concentration of the target analyte in the respective each sample, and a characteristic response indicative of the known third concentration of the internal standard comprising the third isotopic analog of the target analyte added to the respective sample; and

comparing the characteristic response of the target analyte in the each sample to the single calibration curve to quantify the unknown concentration of the target analyte in the respective each sample.

2 . The method of claim 1 , wherein the calibration mixture comprises different, known concentrations of each of the standard, the first isotopic analog, and the second isotopic analog, and wherein each of the standard, the first isotopic analog, and the second isotopic analog is distinguishable by mass spectrometry from the others.

3 . The method of claim 2 , wherein the calibration mixture comprises at least a fourth isotopic analog of the target analyte, wherein the fourth isotopic analog is at a different, known concentration and is distinguishable by mass spectrometry from the standard, the first isotopic analog, the second isotopic analog, and the internal standard comprises the third isotopic analog.

4 . The method of claim 3 , wherein the concentration of the heaviest isotopic analog in the calibration mixture is less than the concentration of the other of said isotopic analogs of said target analyte in the calibration mixture and wherein the concentration of the lightest isotopic analog in the calibration mixture is greater than the concentration of the other of said isotopic analogs of said target analyte in the calibration mixture.

5 . The method of claim 1 , further comprising preparing the calibration mixture by combining a known quantity of each of the plurality of calibrants.

6 . The method of claim 1 , further comprising adding the calibration mixture to a surrogate sample matrix prior to obtaining the mass spectrometer signal for the calibration mixture.

7 . The method of claim 6 , further comprising separating the plurality of calibrants from the surrogate sample matrix prior to obtaining the mass spectrometer signal for the calibration mixture.

8 . The method of claim 7 , wherein the separation comprises at least one of solid phase extraction, liquid-liquid extraction, liquid chromatography, gas chromatography, supercritical fluid chromatography, affinity, immunoaffinity, and capillary electrophoresis.

9 . The method of claim 7 , further comprising derivatizing the plurality of calibrants prior to the separation.

10 . The method of claim 1 , wherein the calibration mixture further comprises a set of second calibrants for a second target analyte different from the target analyte, wherein the set of second calibrants comprise at least two of a standard of the second target analyte, a first isotopic analog of the second target analyte, and a second isotopic analog of the second target analyte, wherein said second calibrants are distinguishable by mass spectrometry from one another and have different, known concentrations from one another in said calibration mixture and wherein each of said second calibrants are distinguishable by mass spectrometry from said plurality of calibrants, the method further comprising:

identifying from the mass spectrometer signal for the calibration mixture a characteristic response of each of said second calibrants, wherein each of the characteristic responses correspond to a different one of the second calibrants and is indicative of the concentration of the second calibrants in the calibration mixture;

generating a second calibration curve based on said characteristic responses of said second calibrants;

identifying from the mass spectrometer signal for each sample a characteristic response indicative of the concentration of the second target analyte in each sample; and

comparing the characteristic response of the second target analyte in each sample to the second calibration curve to quantify the second target analyte in each sample.

11 . The method of claim 1 , wherein each characteristic response comprises a cumulative intensity of the mass spectrometer signal.

12 . The method of claim 1 , wherein the mass spectrometer signal exhibits an intensity for each m/z, and wherein each characteristic response comprises a separate intensity peak of the mass spectrometer signal for at least one unique m/z corresponding to each of the plurality of calibrants.

13 . The method of claim 1 , wherein obtaining a mass spectrometer signal for the calibration mixture comprises:

ionizing the calibrants or derivatives thereof;

separating the ionized calibrants or derivatives thereof based on their mass-to-charge ratios (m/z); and

detecting the m/z-separated ionized calibrants or derivatives thereof, wherein each of the ionized calibrants or derivatives thereof exhibit a unique m/z ratio relative to the other of the ionized calibrants or derivatives thereof.

14 . The method of claim 1 , wherein obtaining a mass spectrometer signal for the calibration mixture comprises:

ionizing the calibrants or derivatives thereof within the calibration mixture;

fragmenting each of the ionized calibrants or derivatives thereof; and

detecting at least one fragment of each of the ionized calibrants or derivatives thereof, wherein each of the ionized calibrants or derivatives thereof exhibit at least one unique MRM transition relative to the other of said ionized calibrants or derivatives thereof.

15 . The method of claim 1 wherein at least one of the series of samples comprises a quality control, the quality control comprising a second plurality of calibrants selected from the group comprising a standard of the target analyte, a first isotopic analog of the target analyte, and a second isotopic analog of the target analyte, wherein said second plurality of calibrants are distinguishable by mass spectrometry from one another and have different, known concentrations from one another in said quality control.

16 . A method of quantifying a target analyte in a series of samples by mass spectrometry, the method comprising:

obtaining a mass spectrometer signal for a calibration mixture, wherein the calibration mixture comprises a plurality of calibrants comprising at least a standard of the target analyte reacted with a first derivatizing agent, the target analyte reacted with a second derivatizing agent, and the target analyte reacted with a third derivatizing agent, the first, second and third derivatizing agents being isotopic analogues of one another and wherein said plurality of calibrants are distinguishable by mass spectrometry from one another and have different, known concentrations from one another in said calibration mixture;

adding an internal standard to the calibration mixture and each of said series of samples prior to obtaining the mass spectrometer signal for the calibration mixture and each of the series of samples, wherein the internal standard comprises the target analyte reacted with a fourth derivatizing agent comprising a fourth isotopic analog of the first, second, and third derivatizing agents distinguishable by mass spectrometry from the first derivatizing agent, the second derivatizing agent, and the third derivatizing agent, with the internal standard of the target analyte having a fourth concentration different than the respective concentrations of the plurality of calibrants, wherein each of the first, second, third, and fourth derivatizing agents has a substantially same physiochemical properties, with at least one atom in each of the first, second, third, and fourth derivatizing agents being a different isotope of the corresponding at least one atom of the other derivatizing agents;

identifying from the mass spectrometer signal for the calibration mixture a characteristic response of each of said plurality of calibrants, wherein each of the characteristic responses is associated with a different m/z value corresponding to a different one of the plurality of calibrants and being indicative of the concentration of each of the plurality of calibrants in the calibration mixture;

generating a single calibration curve for the calibration mixture based on said characteristic responses of the standard of the target analyte reacted with the first derivatizing agent, the target analyte reacted with the second derivatizing agent, the target analyte reacted with the third derivatizing agent, and the internal standard comprising target analyte reacted with the fourth derivatizing agent;

creating a derivatized sample for each of the series of samples by reacting each of the series of samples with one of the first derivatizing agent, the second derivatizing agent, the third derivatizing agent or an isotopic analog thereof;

obtaining a mass spectrometer signal from each of the derivatized samples from the series of samples;

identifying from the mass spectrometer signal for each of the derivatized samples from the series of samples a characteristic response indicative of an unknown concentration of the target analyte in each derivatized sample, and a characteristic response indicative of the known fourth concentration of the internal standard comprising the target analyte reacted with the fourth derivatizing agent; and

comparing the characteristic response of each of the derivatized samples in the series of samples to the single calibration curve to quantify the unknown concentration of the target analyte in each sample.

17 . The method of claim 16 wherein the target analyte is a ketone or carboxylic acid containing analyte and the first, second or third derivatizing agent is selected from the group consisting of:

18 . A method of quantifying an analyte in a series of samples by mass spectrometry, the method comprising:

obtaining a mass spectrometer signal for a calibration mixture, wherein the calibration mixture comprises a plurality of calibrants comprising at least a first compound at a known target concentration in the calibration mixture, a first isotopic analog of the first compound at a known first concentration, and a second isotopic analog of the first compound at a known second concentration, wherein each of the first compound and the first and second isotopic analogs of the first compound are distinguishable by mass spectrometry from one another and have different, known concentrations from one another in said calibration mixture,

adding an internal standard to the calibration mixture and each of said series of samples prior to obtaining the mass spectrometer signal for the calibration mixture and each of the series of samples, wherein the internal standard comprises a third isotopic analog of the first compound at a third known concentration distinguishable by mass spectrometry from the first compound, the first isotopic analog, and the second isotopic analog, wherein each of the first, second, and third isotopic analogs of the first compound has a substantially same physiochemical properties as the first compound, with at least one atom in each of the first, second, and third isotopic analogs being a different isotope of the corresponding at least one atom of the other isotopic analogs and of the standard of the first compound;

identifying from the mass spectrometer signal for the calibration mixture a characteristic response of each of said plurality of calibrants, each of the characteristic responses is associated with a different m/z value corresponding to a different one of the plurality of calibrants and being indicative of the concentration of each of the plurality of calibrants in the calibration mixture;

generating a single calibration curve for the calibration mixture based on said characteristic responses of the at least the first compound, the first isotopic analog of the first compound, the second isotopic analog of the first compound, and the internal standard comprising the third isotopic analog of the first compound;

obtaining a mass spectrometer signal from each of the series of samples, each of the series of samples containing a target analyte having the same structure as the first compound or an isotopic analog of the first compound;

identifying from the mass spectrometer signal for each sample a first compound characteristic response indicative of an unknown concentration of the target analyte in the respective each sample, and a characteristic response indicative of the known third concentration of the internal standard comprising the third isotopic analog of the first compound added to the respective sample; and

comparing the characteristic response of the target analyte in each sample to the single calibration curve to quantify the unknown concentration of the target analyte in the respective each sample.

19 . The method of claim 18 wherein each of the plurality of calibrants comprises a reaction product of a molecule that is being tested for and a derivatizing agent and wherein each of the derivatizing agents utilized for each of the plurality of calibrants is an isotopic analog of the other derivatizing agents, and optionally wherein the molecule that is being tested for is testosterone, a peptide or a hormone.

20 . The method of claim 12 , wherein the unique m/z corresponding to each of the plurality of calibrants comprises the m/z of a fragment ion for each of the plurality of calibrants.