DART-HRMS analysis of gossypol and theobromine in feed samples

Abstract

DART (Direct Analysis in Real Time) is a relatively new ionization technique that belongs to the so-called Ambient techniques, which ionize analytes from sample surface and in their own environment without the need of any sample treatment or chromatographic separation. The combination of DART with high-resolution mass spectrometry and tandem (quadrupole-Orbitrap) provides the sensitivity and selectivity needed for a fast and direct analysis of analytes in complex samples. The presence of gossypol and theobromine in feed is regulated to 20 mg/kg and 50 mg/kg, respectively. Generally, the analysis of these compounds in feed requires a long and tedious sample treatment before the LC-MS/MS analysis, which usually becomes the bottleneck of food control laboratories. In this project, a new DART-HRMS method has been developed for the direct analysis of gossypol and theobromine in feed samples. The most critical DART parameters (ionization gas, temperature, analysis mode, etc.) were optimized to effectively ionize these analytes. Nitrogen gave better results than helium as ionization gas, and temperatures of or above 400 °C were needed for the effective thermal desorption of both compounds, having been previously deposited in a QuickStripTM rack with their extraction solvent and totally or partially dried. Scanning mode gave better results than pulsing mode. Fragmentation pathways were also studied for both compounds using MS/MS in order to obtain structural information and to identify the most characteristic product ions. The DART-HRMS/MS method developed was fast, selective and sensitive enough to detect both regulated compounds 50 and 8 times, theobromine and gossypol respectively, below the legislated level using a simple extraction of 0.5-1 g of feed samples before the DART-HRMS/MS analysis. Positive samples previously analysed by UHPLC-MS were easily detected applying the new DART-HRMS/MS. Results obtained demonstrate the good performance of the proposed method