Quantitative analysis of UV filter chemicals in water using large volume injection

Sabarinathan¹, Sashank Pillai¹, Craig M. Butt^2
1SCIEX, India; 2 SCIEX, USA

Abstract
 

This technical note describes a simple direct dilution method for the trace-level analysis of 10 UV filter chemicals in water. Using the QTRAP 4500 system and 100 µL injection volume, the method achieved in-sample limits of quantitation (LOQs) between 0.005 and 0.1 µg/L (see Figure 1 for oxybenzone). Benzophenone exhibited high background levels and the LOQ was set to 1 µg/L. Quantitative performance was evaluated in matrix spikes (n=5) at 0.1, 0.5, and 5 µg/L in 3 different water samples, including Milli-Q, reverse-osmosis (RO), and tap water. Recoveries ranged from 82% to 114% across the spiking levels in all 3 water types, except for benzophenone-10, which showed accuracies of ~60%. At the lowest spike level of 0.1 µg/L, 5 of the 9 compounds were detected with good recoveries, while all UV filters were subsequently detected in the 0.5 and 5 µg/L spikes. Precision in all matrix spikes was <14%CV.

Key benefits of UV filter analysis in water using the QTRAP 4500 system with large volume injection
 

• Rapid sample preparation. A simple direct injection method with 100 µL injection volume reduced solvent consumption and the overall sample preparation time as compared to conventional SPE methods
  
  
• Sensitive quantitation using the QTRAP 4500 system. LOQs ranged from 0.005 to 0.1 µg/L for all of the targeted UV filter compounds except benzophenone (1 µg/L)
  
  
• Accurate and precise quantitation in various water matrices. Matrix spikes at 0.1, 0.5, and 5 µg/L in Milli-Q, RO, and tap water demonstrated recoveries between 82-114% with precision <14%CV  

Introduction

Ultraviolet (UV) filters are commonly used in cosmetics and personal care products, including sunscreens, soaps and shampoos, to protect against the harmful effects of UV radiation¹. However, these chemicals can enter the environment during wash-off from skin and clothing, and they have been found worldwide in fresh and salt water, sediments and wildlife². The US Food and Drug Administration (FDA) has removed some sunscreens from the market, and recent data suggests that some UV filters may possess potential endocrine-disrupting properties³. Further, certain UV filters, especially in sunscreens, can be toxic to corals². Several governments around the world have banned UV filters to protect coastal waters. Oxybenzone, octocrylene, homosalate, avobenzone, and octinoxate typically show the highest measured environmental concentrations in water at levels ranging from 1 to 10 µg/L, whereas other UV filters detected are typically below 1 µg/L⁴. Therefore, a sensitive, precise and accurate method is needed to quantify UV filters in water to protect human and environmental health. Here, we developed a simple direct injection method to analyze ten UV filters in water using the QTRAP 4500 system.

Methods  

Reagents and standard preparation: Standards were purchased from Sigma Aldrich, and individual 1 g/L stock solutions were initially prepared in methanol except for 2-phenyl-5-benzimazole sulfonic acid (2-PBSA), which was prepared at 0.5 g/L due to its lower solubility. Calibration standards were prepared in the diluent (60: 40: 0.1, v/v/v, methanol/water/formic acid) at concentrations ranging from 0.005 to 100 µg/L.

Pre-spiked water sample preparation: Matrix spikes were prepared by aliquoting 980 µL of the water sample (Milli-Q water, RO lab water, and tap water) and 20 µL of the respective spiking solution (5, 25, and 250 µg/L) to yield the final volume of 1 mL (n=5 replicate samples per spiking level). Samples were vortexed and centrifuged at 15,000 rpm for 20 minutes. After centrifugation, the samples were diluted with 0.1% (v/v) formic acid in methanol at a ratio of 60:40 (v/v) diluent/sample and vortexed to obtain the in-vial concentrations of 0.04, 0.2, and 2 µg/L respectively. The samples were transferred to autosampler vials for instrumental analysis.

LC chromatography: Chromatographic separation was performed using an ExionAD LC system and a Phenomenex Kinetex Biphenyl column (2.6 µm, 100 x 3.0 mm, P/N: 00D4622-Y0). Mobile phase A was water with 10mM ammonium acetate and 0.1% (v/v) acetic acid, and mobile phase B was methanol. The runtime was 16 min using the gradient conditions presented in Table 1. The flow rate was 600 µL/min, the injection volume was 100 µL, and the column oven was 40^oC.

Mass spectrometry: Samples were analyzed using the QTRAP 4500 system with electrospray ionization operating in polarity switching mode. Data was acquired with multiple reaction monitoring (MRM) using optimized source and gas conditions (Table 2) and compound-specific parameters (Table 7 in the Appendix). 2 MRMs per compound were monitored.

Data processing: Data acquisition and processing were performed using SCIEX OS software (version 3.3.1). 

Good chromatographic retention using the Phenomenex Kinetex Biphenyl column

The chromatographic conditions were optimized for good retention and void volume separation for the 10 UV filter analytes (Figure 2). The extended 16 min gradient runtime was optimized to improve analyte separation and avoid analyte coelution with matrix interferences. Good peak shape and retention were achieved using the Phenomenex Kinetex Biphenyl column and the mobile phases comprised of water modified with ammonium acetate and acetic acid, and methanol. The most polar analytes (2-PBSA and sulisobenzone) eluted after the void volume, as shown by the retention factor (k’) of 3.8 for 2-PBSA and 4.1 for sulisobenzone, respectively. Separation from the void volume was important to reduce potential matrix suppression or peak shape interferences.

Sensitivity, accuracy, precision, and linear dynamic range of the solvent-based calibration standards

The solvent-based calibration standards (n=3 injections) were used to evaluate the sensitivity, accuracy, precision, and linear performance of the QTRAP 4500 system for UV filter analysis. The in-vial LOQs were at sub-µg/L levels, ranging from 0.005 to 0.1 µg/L (Table 3) except for benzophenone. An unknown contamination source for benzophenone caused elevated background levels in the diluent, which impacted quantitative performance in standards below 1 µg/L and the LOQ was set as 1 µg/L. Further, benzophenone was not evaluated during the matrix spikes since the spiking levels would have been much higher than the environmentally relevant concentrations. A potential contamination source may have been from the plastic consumables or components in the LC system due to the application of some UV filters in polymer materials to prevent photo-degradation. XICs of the solvent-based calibration standards are shown in Figure 3.  

The LOQ mean accuracy was between 96% and 104%, and the mean precision ranged from 1.9%CV to 23%CV. The LOQ was selected based on the 2 MRM transitions achieving a signal-to-noise (S/N) ratio of ≥10, accuracy ±30%, precision %CV <15% and ion ratio tolerance of ±30%. Across the entire calibration range, each compound's mean accuracy was between 75 and 127%. The observed linear dynamic range was between 3 and 4 orders with r² values >0.992 using a weighting factor of 1/x². 

Quantitative performance in various spiked water samples

The method performance was evaluated in aqueous spikes comprised of Milli-Q, RO and tap water at 0.1 µg/L, 0.5 µg/L and 5 µg/L (n=5 per spiking level). The complete data set is presented in Tables 4-6. These matrix spikes were analyzed by direct injection and quantified using solvent-based calibration on the QTRAP 4500 system.

Unspiked water samples were processed and analyzed against the solvent calibration curve to evaluate potential background contaminant levels. Except for benzophenone, none of the analytes were detected, confirming negligible background levels. The high benzophenone background prevented the evaluation of this compound.

In the 0.1 µg/L spike, 5 of the 9 evaluated UV filters were detected (dioxybenzone, oxybenzone, benzophenone-6, benzophenone-1 and benzophenone-10). Across all 3 water matrices, the mean recovery was between 82.4% and 112%, except for benzophenone-10 which showed recoveries of ~60% in all three water types (Table 4). Further, the method recovery was similar across the water samples, indicating no matrix bias. Good precision was observed with a mean precision of <14%CV for all detected compounds.

In the 0.5 µg/L and 5 µg/L spikes, all 9 of the evaluated UV filters were detected. Similar to the 0.1 µg/L spike, good recovery and precision were shown in all three water matrices except for benzophenone-10 (Tables 5 and 6). Overall, the recovery was between 80% and 120% for the compounds, whilebenzophenone-10 exhibited a slightly lower recovery of ~60%. The mean precision was <10%CV for all UV filters.  

Conclusions
 

The method showed:

• A simple direct injection method with 100 µL injection volume to analyze 10 UV filter compounds in water using the QTRAP 4500 system
  
  
• Good retention and chromatographic separation of the 10 targeted UV filters using the Phenomenex Kinetex Biphenyl column
  
  
• Method sensitivity with the in-vial LOQs ranging from 0.005 to 0.1 µg/L, except for benzophenone.
  
  
• Good linearity in the solvent-based calibration curve with r² values >0.992 for all the analytes.
  
  
• Method applicability with matrix spikes at 0.1, 0.5, and 5 µg/L in Milli-Q, RO, and tap water, recoveries were between 82- 114% with precision <14%CV 

References
 

1. Sharifan, H; Klein, D; Morse, N. UV filters are an environmental threat in the Gulf of Mexico: a case study of Texas coastal zones. Oceanologia 2016, 58, 327-335. DOI: 10.1016/j.oceano.2016.07.002.
   
   
2. Mitchelmore, C.L.; Burns, E.E.; Conway, A.; Heyes, A.; Davies, I.A. A critical review of organic ultraviolet filter exposure, hazard, and risk to corals. Environ. Toxicol. Chem. 2021, 40, 967-988. DOI: 10.1002/etc.4948.
   
   
3. Kwon, B.; Choi, K. Occurrence of major organic UV filters in aquatic environments and their endocrine disruption potentials: a mini-review. Integr. Environ. Assess. Manag. 2021, 17, 940-950: DOI: 10.1002/ieam.4449.
   
   
4. National Academies of Sciences, Engineering, and Medicine. Review of fate, exposure, and effects of sunscreens in aquatic environments and implications for sunscreen usage and human health. 2022. DOI: 10.17226/26381

Appendix