Rapid and reliable analysis of underivatized amino acids in urine using tandem mass spectrometry

Analysis Profiling of 48 Endogenous Amino Acids and Related Compounds in Human Plasma Using Hydrophilic Interaction Liquid Chromatography-Tandem Mass Spectrometry

Analyzing and detecting endogenous amino acids in blood is of crucial importance for the diagnosis of medical conditions and scientific research. Considering the lack of UV chromophores in most of these analytes and the presence of several interfering substances in plasma, the quantification of quite a few amino acids and related compounds presents certain technical challenges. As a blank plasma matrix lacking these endogenous substances does not exist, the surrogate matrix method is used, as well as isotopic internal standards for calibration, to ensure the accuracy and reliability of the study. Method validation was conducted for 48 target analytes, giving the following results: linearity (R2 at least 0.99), limit of quantification (from 0.65 to 173.44 μM), precision (intra-day and inter-day RSD for LQC ranged from 3.2% to 14.2%, for MQC from 2.0% to 13.6%, and for HQC from 1.6% to 11.3%), accuracy, recovery, and stability of the method (all complied with the guidelines). To further investigate the applicability of this method to large-scale sample analysis, the method was successfully applied to the analysis of amino acids in plasma samples collected from 20 control individuals, demonstrating its wide application scope for clinical diagnosis and metabolic research.

Use of a guard column coupled to mass spectrometry as a fast semi-quantitative methodology for the determination of plasticizer metabolites in urine

For the first time, a very simple and fast method combining the use of a guard column coupled to tandem mass spectrometry (guard column-MS/MS) has been proposed for the determination of plasticizer metabolites in urine. Briefly, samples (1.0 mL) were submitted to enzymatic hydrolysis for 10 min, filtered, diluted 1/10 v/v with ultrapure water and directly injected into the system. A fast run of only 2 min (3 min including the injection cycle) allowed the determination of 19 analytes. Enzymatic hydrolysis, filtering material, and guard column-MS/MS conditions were optimized. Intra-day precision at the low-level concentration (expressed as relative standard deviation, %RSD) obtained from the analysis of synthetic urine samples varied between 11 and 20%. Limits of quantification ranged from 2.8 to 60 ng/mL. Trueness values, calculated as apparent recoveries, ranged from 70 to 135%. To correct for matrix effects, analyte concentrations in real urine were quantified by the standard addition method. To confirm the results obtained by guard column-MS/MS, an ultra(high)-performance liquid chromatography tandem mass spectrometry (UHPLC-MS/MS) method was also applied (total chromatographic run time 17 min, including column re-equilibration). Concentrations measured with both methods were in good agreement. Hence, we propose the use of guard column-MS/MS to analyse a large number samples in a very short time (semi-quantification), and apply the chromatographic analysis only to those samples with levels close to/higher than the concentrations equivalent to the safe maximum daily intakes of the parent compounds (confirmation). This double strategy (semi-quantification by guard column-MS/MS and confirmation-when needed-by UHPLC-MS/MS) implies important savings in time and money.

Underivatized Amino Acid Chromatographic Separation: Optimized Conditions for HPLC-UV Simultaneous Quantification of Isoleucine, Leucine, Lysine, Threonine, Histidine, Valine, Methionine, Phenylalanine, Tryptophan, and Tyrosine in Dietary Supplements

Amino acids (AAs) are considered as the building blocks of life. Unlike nonessential AAs, the human body cannot synthesize essential AAs and should be supplied in food or dietary supplements. The aim of the work is simultaneous HPLC-UV determination of 10 structurally related AAs without pre- or postderivatization in powdered dietary supplements (PDSs). This was challenging, especially because PDS has no standardized procedures for its quality control. HPLC-UV chromatograms of the 10 AAs were recorded using a gradient elution of the mobile phase on a CLC-C18 column at 225 nm. The elution started with 100% of phosphate buffer (pH 7.4, 10 mM) for 10 min; then, the concentration of acetonitrile increased linearly to reach 50% for another 15 min at room temperature. Good separation was achieved within a 25 min run time without pre- or postderivatization. The method was carefully validated according to the ICH guidelines over the linearity range of 100-200, 50-200, 20-150, 50-400, 20-250, 75-175, 50-250, 50-250, 50-300, and 5-100 μg/mL for l-lysine, l-threonine, l-histidine, l-valine, l-methionine, l-isoleucine, l-leucine, l-tyrosine, l-phenylalanine, and l-tryptophan, respectively, with mean recoveries ranges between 98.91 and 100.77. The method was found to be precise, and the relative standard deviation (RSD) was found to be between 0.28 and 1.92 with recoveries between 97.91 and 101.11. The method was found to be robust that resists deliberate changes in pH, flow rate, and mobile-phase percentages. It was successfully applied for the analysis of PDSs. The proposed method could be very useful for the quality control of the 10 structurally related AAs during their synthesis and for testing raw materials and pharmaceutical preparations.