Rapid Screening of 19 UV Filters in Cosmetics Using Swab Touch Spray Ionization Coupled with Quadrupole/Orbitrap High-Resolution Mass Spectrometry

An analytical method combining swab touch spray ionization and quadrupole/Orbitrap high-resolution mass spectrometry (Q/Orbitrap HRMS) was developed for rapid screening of nineteen UV filters in cosmetics. Upon investigation of various spray solvents such as methanol, acetonitrile, tetrahydrofuran, acetone and isopropanol, methanol and acetonitrile were found to be the optimal solvents for positive and negative ionization modes, respectively. For further optimization, methanol-acetonitrile mixture solvents with different volumetric ratios (4∶1, 3∶2, 2∶3, 1∶4, V/V) were compared. A methanol-acetonitrile mixture solvent (4∶1, V/V) was selected as the spray solvent. Moreover, the spray voltages ranging from 3.5 to 6.5 kV were optimized, among which 5.0 kV was found to be the optimum voltage. The position of the swab was another critical parameter. If the swab was placed too close to the MS inlet, electric discharge could occur. On the other hand, a distant swab position may result in unstable or even no signals. The position of the swab was optimized to be 0.8 cm horizontally and 0.5 cm vertically from the MS inlet. Under the optimized experimental conditions, the cosmetic samples were gently picked up using the swab and mounted in front of the MS inlet without the need of sample pretreatment. 30 μL methanol-acetonitrile mixture solvent (4∶1, V/V) was added to the swab. Afterwards, a high voltage of 5.0 kV was applied to the metallic swab handle. In this way, the charged droplets produced from the swab tip were subjected to the Q/Orbitrap HRMS analysis under the full-scan/parallel reaction monitoring acquisition mode. Experimental results showed that the limits of detection of the nineteen UV filters were between 0.01 and 2.0 mg/kg. Satisfactory repeatability was obtained ranging from 1.4% to 9.9% (n=6). The analysis of a single sample could be completed within 1 min. The established method is simple, fast, accurate, reliable, and suitable for the rapid screening of UV filters in cosmetics.