Determination of UV Absorbers from Sunscreens by UHPLC with Photodiode Array Detection

Measure UV-absorbing compounds in consumer products and characterize the UV absorption spectra of the individual components by employing high-speed liquid chromatography with photodiode array detection.

Sunscreens are topical lotions that disperse UV absorbing compounds in an oily base that may also contain emollients, skin moisturizers, and light reflecting particles of zinc oxide. Common UV-absorbers added to sunscreens include oxybenzone (benzophenone), avobenzone, octinoxate (octyl methoxycinnamate), octisalate (octylsalicylate), homosalate, and octocrylene.

The oily matrix of sunscreen lotions coupled with the high UV absorbance of the analytes makes HPLC the method of choice for analysis of sunscreens, and by using photodiode array detection, the complete absorption spectrum of each compound is obtained as it elutes. The sensitivity of HPLC/PDA is also sufficient to measure these compounds in environmental water samples, which facilitates research on exposure and environmental fate. In this application, an HPLC method used by a commercial analytical laboratory is improved by using ultra high performance liquid chromatography (UHPLC) on a Hypersil GOLD 1.9-μm column. The resolution of adjacent peaks is improved even as method run time is reduced from 45 to 7 min. Applications include determination of UV absorbers in three consumer products and in water from a public swimming pool. Also documented is chromatographic method performance including resolution, calibration range, method detection limits, and precision of retention time and peak area.

Experimental Conditions

Samples

Samples of three commercially available sunscreens were prepared for UHPLC analysis and a sample of swimming pool water was collected from a local public pool and prepared by using solid phase extraction. The sample was reconstituted in 200 μL of mobile phase, filtered into an autosampler vial, and injected.

Instrumentation

Thermo Scientific Accela High-Speed Liquid Chromatography system with PDA Detector Thermo Scientific ChromQuest 5.0 Chromatography Data System (CDS).

Chromatographic conditions

Columns: Thermo Scientific Hypersil GOLD, 1.9 μm, 100 × 2.1 mm (Thermo Scientific 25002-102130)

Mobile phase: A: Water

B: Acetonitrile

Isocratic: 40:60

Flow rate: 1000 μL/min

Run time: 7 min

Detector: PDA, D2, and W lamps, 10-mm flow cell, 20Hz, 0s rise time

Scans: 200-500 nm, 1Hz, 1nm bandwidth, Step1

Discrete: 313 nm, 20Hz, 11nm bandwidth

Column temp.: 45 °C

Injection: 1 μL "no waste" injection from 25 μL sample loop, 4 μL/s 1 mL Flush and 1 mL Wash, using 90:10 acetonitrile: water from Flush Reservoir

Results

The UHPLC separation of sunscreen agents provided by this application (Figure 1) provides better resolution, peak shape, and run time compared to the original method used by the commercial laboratory. Particularly noteworthy is the 6-fold improvement in run time and sample throughput.

Figure 1

Conclusion

A fast HPLC separation performed on the Accela high speed chromatography system equipped with a PDA detector resolves six UV-absorbing components of sunscreens in about six min with retention time and peak area precision better than 1% RSD. The UV absorbance spectrum of each compound is acquired as it elutes and can be matched against a stored spectral library to aid in compound identification.

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