Comparison of positive and negative ion detection of tea catechins using tandem mass spectrometry and ultra high performance liquid chromatography

Tea catechins are an important group of natural compounds associated with health promoting effects and desired commodities for the growing market of dietary supplements and functional foods. Consequently these compounds attract more interest of research groups worldwide. A reliable quantitative analysis of tea catechins is essential for human intervention studies, manufacturers of dietary supplements and quality control by authorities. UHPLC–ESI-MS/MS analytical method was chosen due to rapid runtime, high sensitivity and selectivity. The chromatographic separation of eight tea catechins was achieved within 2.5 min on C₁₈ BEH analytical column (100 mm × 2.1 mm i.d.; 1.7 μm), whilst the gradient elution mode was employed using water:methanol mobile phase with addition of volatile organic acid. The concentration of organic acids in the mobile phase was optimised within the range of 0.01–0.1% (v/v). High sensitivities were achieved in positive (10.2-16.8 fmol/inj.) and negative ion detection mode (102.1-168.1 fmol/inj.), through accurate and complex tuning of MS parameters. The UHPLC-ESI-MS/MS method was validated in terms of linearity (>0.9997; >0.9990), range (0.02–2.40 mg L⁻¹; 0.15-24.00 mg L⁻¹), LOD (3.0–4.8 μg L⁻¹; 30.1–48.0 μg L⁻¹), LOQ (9.9–15.8 μg L⁻¹; 150.5-240.0 μg L⁻¹), intra-day precision (4.4-7.1% RSD; 3.3-5.1% RSD), accuracy (94.06-113.7%; 89.5-108.4%), retention time repeatability (0.0-0.5% RSD; 0.0-0.6% RSD), and peak area repeatability (1.2-4.0% RSD; 2.4-3.5% RSD) for positive and negative ion detection modes, respectively. The statistical comparison of the quantitative results obtained in positive and negative ion detection mode was performed.