Abstract: A new method for the determination of plant growth regulators including 2-naphthoxyacetic acid, 2,4-dicholrophenoxyacetic acid and 1-naphthlcetic acid in radish was developed by liquid chromatography-electrospray ionization mass spectrometry (LC-ESI/MS). The chromatographic separation was performed on a Diamonsil C18 column (250 mm× 4.6 mm, 5 μm) by using a mobile phase made up of 0.01 mol/L formic acid-ammonium buffer solution (pH 4) and methanol (30:70, V/V) at a flow rate of 0.7 mL/min. The mass spectrometric quantitative analysis was based on selective ionic measurement by electro-spray ionization in the negative ion mode. Baseline separation was achieved for three plant growth regulators within 8 min. Good linearity was observed in the range of 0.01－10 μg/mL for all of them. The detection limit at a signal to noise ratio of 3 was 0.0018 mg/kg for 2-naphthoxyacetic acid, 0.004 mg/kg for 2,4-dicholrophenoxyacetic acid and 0.003 mg/kg for 1-naphthlcetic acid, respectively. Under optimal conditions, the average recovery rate and relative standard deviation were 77.56%－105.08% and 3.48%－15.88% at spike levels of 0.01, 0.05 mg/kg and 0.50 mg/kg, respectively. Therefore, this method is suitable for the determination of plant growth regulators in radish.

Key words: liquid chromatography-electrospray ionization mass spectrometry (LC-ESI/MS), ultrasound-assisted extraction, plant growth regulator, radish