Determination of 9 Organic Acids in Tobacco Flavors by Liquid Chromatography-Triple Quadrupole Composite Linear Ion Trap Mass Spectrometry

The 9 organic acids, including malic acid, citric acid, lactic acid, malonic acid, succinic acid, maleic acid, tartaric acid, adipic acid and levulinic acid, in tobacco flavor samples were determined qualitatively and quantitatively by liquid chromatography-triple quadrupole composite linear ion trap mass spectrometry. The 0.1 g of tobacco flavor sample was taken, and 20 mL of water was added. After extracting by ultrasound for 10 min, 1 mL of the supernatant was taken, and passed through a 0.22 μm aqueous phase membrane. The solution obtained was diluted 10 times with water for determination according to the optimized instrument operating conditions. Organic acids were separated by gradient elution with mixed solutions of 0.1% (volume fraction, the same below) formic acid solution and methanol solution containing 0.1% formic acid at different volume ratios on the Synergi Hydro-RP chromatographic column, ionized by negative ion mode of electrospray ion source, scanned by the multiple reaction monitoring-information dependent acquisition-enhanced product ion (MRM-IDA-EPI) mode, quantified by MRM mode, and qualitatively analyzed by combining EPI standard secondary mass spectrometry library with retention time. It was shown that linear relationships between values of the mass concentrations of 9 organic acids and peak areas of quantitative daughter ions were kept in definite ranges, with detection limits (3s/k) in the range of 0.003-0.018 mg·L⁻¹. Test for recovery was conducted on actual samples by the standard addition method, with recoveries ranging from 73.3% to 112%. RSDs of the determined values obtained from intra-day (n=6) and inter-day (n=5) precision tests were not exceed 10% or 15%, respectively. The proposed method was applied to the analysis of 142 tobacco flavor samples, and 4 organic acids with the higher detection rates were lactic acid, malic acid, succinic acid and citric acid.