Determination of Organic Acids in Cucumber Leaves by Solid Phase Extraction–Electrospray Ionization–Ion Mobility Spectrometry (SPE-ESI-IMS)

Abstract

A solid phase extraction-electrospray ionization-ion mobility spectrometry (SPE-ESI-IMS) method was developed to determine six organic acids in cucumber leaves. The multiplexing IMS using correlation technique was adopted to optimize the signal-to-noise ratio (SNR) and resolution. 90% methanol/water was selected to be the solvent, the flow rate was 120 µL·h−1, the stop frequency of ion gate was 5000 Hz, the ion gate opening period was 0.1 ms, the air flow velocity was 2.0 L·min−1, the electrospray voltage was 3.5 kV, and the drift tube temperature was 90 °C. The cucumber leaves were treated with ultrasound in 50% methanol/water. The analytes were subsequently eluted from an SPE cartridge with 0.1 mol·L−1 HCl, and the extract was neutralized to pH 2–3 with ammonia before freeze-drying. SPE-ESI-IMS enabled the effective determination of citric acid, fumaric acid, lactic acid, malic acid, pyruvic acid, and succinic acid based upon the drift time. The limits of detection were from 0.008 µg·mL−1 to 0.2 µg·mL−1, and the recoveries of spiked samples were from 87.00% to 107.20%. The convenient, sensitive, and efficient developed SPE-ESI-IMS method may be applicable for the determination of organic acids in leaves.