Adduct Formation-Supported Two-Way Electrospray Ionization Strategy for the Determination of Urinary Creatinine Concentration with LC-MS-MS in Abstinence Control.

In this work, an alternative LC-MS-MS strategy for the analysis of urinary creatinine in abstinence control was presented and discussed. The two-way electrospray ionization consisted of two different precursor ions in which fragmentation was used in multiple reaction monitoring experiments. A creatinine adduct ion with sodium and sodium acetate together with the conventional analyte protonation was investigated. Adduct formation and fragmentation was explored by appropriate infusion experiments performed with analyte solutions prepared in different concentrations. The analytical signal was compensated by the application of appropriate isotopically labeled internal standard. The advantages of information carried by precursor ions separated in the mass spectra were pointed out. Sample preparation based solely on sample dilution performed in the final HPLC vial directly. A Luna 5 μm C18 (2) 100 A, 150 mm × 2 mm analytical column together with a mobile phase consisted of H2O/methanol = 3%/97% (v/v) with 10 mmol/L ammonium acetate and 0.1% acetic acid (flow = 0.4 mL/min) were used for the separation performed during a run of 5 min. The linearity was examined in the range of 100-3,000 mg/L. The limit of detection (13 mg/L), limit of quantification (43 mg/L) together with method precision/accuracy, selectivity, stability and matrix effect were tested to be appropriate for forensic applications. The applicability of water as surrogate matrix for method calibration was also examined successfully. The presented strategy was used in the analysis of real samples. No interferences with the creatinine peak eluted at about 1.0 min could be recorded.