Apparatus for Improved Immunosuppressant Drug Monitoring

Abstract

A liquid chromatography/mass spectrometry system includes: a source of a first mobile phase solvent consisting essentially of water plus 10 mM ammonium formate plus 0.05% formic acid; a source of a second mobile phase solvent consisting essentially of methanol plus 10 mM ammonium formate plus 0.05% formic acid; a chromatography column comprising a length of 30 mm or less of a stationary phase comprising an 8-carbon alkyl chain material bonded to 2.6 μm diameter particles having solid silica cores surrounded by porous silica outer layers; an electrospray ion source of a mass spectrometer fluidically coupled to the chromatography column so as to generate ions therefrom; a mass analyzer of the mass spectrometer operable to quantitatively detect the ions; and a programmable processor electronically coupled to the mass analyzer and comprising instructions operable to determine, based on the ion detection, a concentration of everolimus, sirolimus, tacrolimus, or cyclosporin A.

What is claimed is: 
     
         1 . A liquid chromatography/mass spectrometry system, comprising:
 a source of a first mobile phase solvent (MPA) consisting essentially of water plus 10 mM ammonium formate plus 0.05% formic acid;   a source of a second mobile phase solvent (MPB) consisting essentially of methanol plus 10 mM ammonium formate plus 0.05% formic acid;   a length of tubing operable to receive a liquid sample therein;   a chromatography column comprising a length of 30 mm or less of a stationary phase comprising an 8-carbon alkyl chain material bonded to 2.6 μm diameter particles having solid silica cores surrounded by porous silica outer layers;   a first and a second fluidic pump operable to respectively propel a first flow of the MPA solvent and a first flow of the MPB solvent through, in sequence, a first fluidic junction, the length of tubing and the chromatography column;   a third and a fourth fluidic pump operable to respectively propel a second flow of the MPA solvent and a second flow of the MPB solvent through, in sequence, a second fluidic junction and the chromatography column;   a valve operable to transfer either the flows propelled by the first and second fluidic pumps or the third and fourth fluidic pumps or a mixture thereof to the chromatography column;   an electrospray ion source of a mass spectrometer fluidically coupled to the chromatography column so as to receive compounds eluting from the chromatography column and to generate ions therefrom;   a mass analyzer of the mass spectrometer operable to separate the generated ions according to their mass-to-charge (m/z) ratios and to quantitatively detect ions of each m/z ratio within a range of such ratios; and   a programmable processor electronically coupled to the mass analyzer and comprising instructions operable to determine, based on the ion detection, a concentration of everolimus, sirolimus, tacrolimus, or cyclosporin A in the sample.   
     
     
         2 . A liquid chromatography/mass spectrometry system as recited in  claim 1 , wherein each of the first, second, third and fourth pumps comprises a syringe pump. 
     
     
         3 . A liquid chromatography/mass spectrometry system as recited in  claim 2 , wherein the first fluidic junction is operable to mix the first flow of the MPA solvent and the first flow of the MPB solvent, wherein relative proportions of the MPA and MPB solvents in the mixture are determined by relative dispensing rates of the first and second syringe pumps. 
     
     
         4 . A liquid chromatography/mass spectrometry system as recited in  claim 3 , wherein the second fluidic junction is operable to mix the second flow of the MPA solvent and the second flow of the MPB solvent, wherein relative proportions of the second MPA and second MPB solvent flows in the mixture are determined by relative dispensing rates of the third and fourth syringe pumps. 
     
     
         5 . A liquid chromatography/mass spectrometry system as recited in  claim 4 , wherein the programmable processor is electronically coupled to the first, second, third and fourth syringe pumps and wherein the programmable processor further comprises instructions operable to cause the third and fourth syringe pumps to progressively vary the proportion of the second MPA and second MPB solvent flows that are mixed at the second fluidic junction. 
     
     
         6 . A liquid chromatography/mass spectrometry system as recited in  claim 4 , wherein the instructions are operable to cause the proportion of the MPB flow to progressively vary from 30% to 100%. 
     
     
         7 . A liquid chromatography/mass spectrometry system as recited in  claim 1 , further comprising:
 a selection valve fluidically coupled between the chromatography column and the mass spectrometer; and   a second chromatography column fluidically coupled to the selection valve,   wherein the selection valve is operable to direct compounds eluting from either the chromatography column or the second chromatography column to the mass spectrometer.