A sensitive method for simultaneous quantitative determination of surfactin and iturin by LC-MS/MS

Surfactin and iturin are antimicrobial lipopeptides produced from Bacillus spp. and have significant prospective applications in many fields. Therefore, accurate analysis of these lipopeptides in the fermented product of some Bacillus strains is important. A sensitive method for simultaneous quantitative determination of surfactin and iturin fermented by Bacillus natto NT-6 was developed and validated using liquid chromatography-tandem mass spectrometry. Crude extracts of antimicrobial lipopeptide samples were dissolved in a mixture of acetonitrile/water (7:3, v/v) in 0.1 % (v/v) formic acid and eluted with acetonitrile/water (7:3, v/v) containing 5 mmol L-1 ammonium acetate and 0.1 % (v/v) formic acid. The target compounds were detected by mass spectrometry (ESI+) using selective ion monitoring. A good linear regression in the range of 0.20-10.0 mg L-1 for both surfactin and iturin (R-2 >= 0.9995) was observed with spiked recoveries of 93.3-108.2 %, RSD values less than 15 %, precision 4.14-13.30 %, and a detection limit of 0.374 mg L-1. This method has a simple preprocessing operation, good repeatability, and provides an accurate quantitative analysis of surfactin and iturin.