Simultaneous determination of fluorescent whitening agents (FWAs) and photoinitiators (PIs) in food packaging coated paper products by the UPLC-MS/MS method using ESI positive and negative switching modes

A sensitive ultra-high performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS) method was established for the simultaneous determination of fluorescent whitening agents (FWAs) and photoinitiators (PIs) in food packaging coated paper products. Samples were firstly soaked in water and then ultrasonically extracted by using methanol-trichloromethane. The extraction solution was subsequently separated by using a Phenomenex Luna C18 (2) chromatographic column (50 mm x 2.00 mm, 3 mu m) using methanol-5 mmol L-1 ammonium acetate as the mobile phase. The target analytes were ionized by the ESI positive and negative switching modes and detected using the multiple-reaction monitoring (MRM) mode. The method was validated for linearity and range, accuracy, precision and sensitivity. Under the optimized conditions, the calibration curves were linear over the selected concentration ranges of 10-1000 mu g L-1 and 0.5-50 mu g L-1 for four FWAs (FWA28, FWA85, FWA71 and FWA351) and the rest of the ten compounds, respectively, with calculated coefficients of determination (R-2) greater than 0.99. The instrument limit of quantitation (ILOQ) and the corresponding method limit of quantitation (MLOQ) of fourteen target analytes were in the range of 0.5-10 mu g L-1 and 6-125 mu g kg(-1), respectively. Recoveries were calculated at three levels of concentration spiked into negative samples and the values were found between 79.2% and 115% with relative standard deviation (RSD) values of 3.21-2.3% for intra-day precision (n = 6) and 4.5-11.5% for inter-day precision (n = 5) 2.5-7.2%. The method was successfully applied to analyse twenty-five food packaging coated paper product samples and FWA184 and 4-MBP were detected in only two samples with the concentrations of 151 mu g kg(-1) and 32 mu g kg(-1), respectively.