Rapid analysis of urine using mass spectrometry with atmospheric pressure laser plasma ionization

Abstract

Atmospheric pressure laser plasma ionization (APLPI) technique was studied in application to the problem of rapid determination of physiologically active substances in urine. The objectives of this study included investigation by APLPI method of urine samples obtained from treated patients; determination of analytical characteristics of the method; comparative studies of APLPI and HPLC-MS/MS methods in terms of signal-to-noise ratio and evaluation of the possibility of screening urine samples without sample preparation by APLPI method. The instrumental implementation of the method is based on the use of a high-resolution mass analyzer "Orbitrap", in which the standard ion source was replaced by the in-lab developed APLPI source, combined with thermal desorption sample introduction. Urine samples, in which physiologically active substances, in particular barbiturates, carbаmazepine, thiapride, sulpiride, psilocin, amphetamine, tramadol, diphenhydramine, and others were preliminarily detected by HPLC-MS/MS, were investigated. The APLPI method was found to be capable of detecting all these analytes. The duration of the analysis of one sample does not exceed one minute. Using the "dilution in matrix" method calibration curves for a number of compounds were constructed and the analytical characteristics of the method determined. The calibration curves are linear in the range of three orders of magnitude. The mean value of the relative standard deviation of the ion signal in this range was 24%. The limits of detection found for the determination of diphenhydramine, lidocaine and phenobarbital in urine extracts were 0.7 ng/ml, 0.5 ng/ml and 10 ng/ml, respectively. Comparative studies showed that APLPI and HPLC-MS/MS methods were characterized by close values of signal-to-noise ratios. The advantages of the APLPI method are in the rapidity, retrospective analysis, and small sample volume. The limitation of the method is the necessity of desorption of the determined compounds into the gas phase. The possibility of using the APLPI method for screening physiologically active substances in urine without sample preparation has been demonstrated.