MSACL 2023 Abstract

INTRODUCTION: Direct mass spectrometry approaches such as paper spray mass spectrometry (PS-MS) are presenting new alternatives as candidate methods for clinical workflows. PS-MS, in particular, offers a facile strategy for chemical measurements in complex samples such as biofluids. Small aliquots (i.e., ≤10µL) of sample are deposited on pointed paper strips with co-deposited internal standards. The strips are moistened with a suitable solvent, and upon the application of high voltage, ions are generated in a manner akin to electrospray, allowing direct analyte quantitation via tandem mass spectrometry. The strips are inexpensive and disposed for each measurement, eliminating carryover, and can be used to conduct ‘on-paper’ derivatization reactions as well as replace the extraction/preconcentration steps necessary in other analytical workflows.

OBJECTIVES: To demonstrate the use and effectiveness of chemically modified PS-MS paper substrates for the rapid, sensitive, and quantitative measurement of proteins in biofluids, including the rapid ‘one instrument’ measurement of albumin/creatinine ratios in urine.

METHODS: All measurements were performed by paper spray tandem mass spectrometry with a high-throughput paper spray ion source (Thermo Scientific™ TSQ Altis™ triple quadrupole mass spectrometer with a VeriSpray™ source). PS-MS paper substrates were modified by grafting polyamidoamine (PAMAM) dendrimers to their surface, increasing protein affinity. The extraction / preconcentration of target proteins from urine and serum was accomplished by vortexing the strips in 150 µL biofluid samples, followed by a short wash. Measurement by PS-MS was accomplished using barcode traceable VeriSpray™ PS-MS sample plates, allowing multiplexed measurements of 24 strips per plate, and the unattended measurement of up to 240 samples. Quantitative calibrations were achieved for both proteins and creatinine utilizing co-deposited internal standards.

RESULTS: The PAMAM functionalized PS-MS paper substrates were characterized for direct protein measurements in human urine and serum sample matrices. This included optimizing sample extraction times, washing protocols and evaluating the storage stability of the modified paper substrate. A 30 second protein vortex extraction followed by a 5 second acetonitrile wash was optimal. Once prepared, PAMAM functionalized PS-MS substrate exhibited no deterioration in performance when stored at ambient conditions over a one month period. As examples, the direct measurement of hemoglobin and albumin in urine and lysozyme and insulin in serum is presented, achieving up to 11 fold sensitivity improvements, dependent upon the charge state of the protein. The analytical performance of the functionalized paper substrate was evaluated for the analysis of albumin in urine, achieving linearity with R2 > 0.99, LOD of 1.1 µg mL-1, LOQ of 3.8 µg mL-1, precision <10%, and recoveries of 70-83%. The direct, simultaneous measurement of urinary albumin and creatinine ratios for anonymous patient samples by PS-MS demonstrates excellent comparison with validated clinical results obtained utilizing immunoturbimetry for albumin and the spectrophotometric Jaffe method for creatinine.

CONCLUSION: The use of PAMAM functionalized PS-MS paper substrate enhances the sensitivity of direct protein quantitation from biofluids. The ‘one instrument’ quantitative measurement of urinary albumin/creatinine ratios by PS-MS shows significant promise as a new candidate method for clinical analyses.