The two main matrices for screening are urine or serum and heparinized plasma. Whereas urine has the advantage of usually higher concentrations and longer detection windows, serum or heparinized plasma represent the current systemic drug exposure of a patient.
MATERIALS AND METHODS:
An online extraction LC-MS(n) method using a MS(2) and MS(3) spectral library for the identification of substances has been developed and validated to screen serum and heparinized plasma. Extraction was performed by online turbulent flow chromatography under alkaline conditions. Chromatographic separation was achieved using a phenyl/hexyl column with acidic eluents. For detection, a linear ion trap, equipped with an APCI interface, was used and the different compounds were identified using a MS(2) and MS(3) spectral library containing 453 compounds. From 47 patients, urine and heparinized plasma samples were analyzed and the results compared.
The validation of the method gave satisfactory results. Only 3% of the compounds showed a matrix effect>10% in serum. For all other substances and heparinized plasma, the quantitative matrix effect was <10%. 78% of the compounds where a therapeutic range was described in the literature had a limit of identification below the therapeutic range in heparinized plasma and 77% in serum, respectively. In urine and heparinized plasma samples, a total of 168 substances (identified as 86 different compounds) could be identified. In 20 out of 47 cases (43%), the results were identical. On a substance level, the agreement between urine and heparinized plasma was in average 71% with a range of 0-100%.
The presented method allows a fast identification of 453 substances in serum and heparinized plasma. If plasma or serum is used for toxicological screening, the current systemic exposure of a patient can be monitored.