SPME for the Extraction of Pharmaceutical Compounds From Water

By: Katherine K. Stenerson, Craig Aurand, and Robert Shirey, Reporter US Vol 27.1


Katherine K. Stenerson, Craig Aurand,
and Robert Shirey
katherine.stenerson@sial.com

In a previous edition of the Supelco Reporter (Reporter 26.4), we presented data showing the use of a new, solvent stable, biocompatible, SPME fiber for the extraction of a common beta-blocker drug and its metabolite from a plasma matrix. The inert fiber was coated with a polar-embedded reversed-phase bonded silica. In a continuation of work with these fibers, we evaluated their use for the extraction of pharmaceutical compounds from water. This topic has recently gained notoriety with the discovery of low levels of pharmaceutical and personal care products in drinking water sources.

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Experimental

The pharmaceutical compounds used for this study (Table 1) were selected to represent commonly used prescription and over-the-counter products. Biocompatible SPME fibers coated with polar-embedded reversedphase bonded silica were used to extract these compounds from both deionized and treated wastewater samples. A summary of the SPME procedure used is presented in Table 2. Samples were buffered to pH=7 with potassium phosphate prior to extraction. The desorbed SPME extracts were then analyzed by LC-MS/TOF.

Table 1. Pharmaceutical Compounds Extracted Using Biocompatible SPME


Table 2. SPME Extraction Conditions

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Reproducibility

To evaluate the reproducibility of the SPME procedure, multiple replicates of deionized water samples spiked at 50 μg/L were extracted, and the average response factors and percent relative standard deviations were determined. As is common in SPME experiments, internal standards were added prior to extraction and used in the calculation of the response factors. Good reproducibility was demonstrated with the exception of ranitidine (Table 3).It was later discovered that a contaminant introduced by the desorption solvent was causing interference with the analysis of this compound.

Table 3. Reproducibility of Relative Response; Extractions from Deionized Water Spiked at 50 μg/L

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Linearity

A linearity experiment was conducted using both spiked deionized water and treated wastewater samples to determine the quantitative ability of the SPME extraction. A comparison of spiked treated wastewater and deionized water samples was performed to evaluate any possible matrix effects on recovery of the compounds. The samples were spiked with the analytes indicated in Table 1 at levels from 5 μg/L to 100 μg/L, and internal standards were added to each sample prior to extraction.

Overall, no matrix effects were observed in the wastewater samples (Figure 1). Very little difference in response and linearity was observed between the two sample matrices, and all compounds were detected down to 5 μg/L. The response of ranitidine was found to be less linear than the other compounds, due to the interference described earlier.

Figure 1. Linearity of Extractions from Deionized Water and Treated Wastewater

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Comparison of Fiber Chemistries

This extraction procedure was then used for a broader range of pharmaceutical compounds. In this study, two different fiber chemistries were evaluated. A biocompatible SPME fiber, coated with C18 bonded silica, was compared to the polarembedded reversed phase fiber. Samples of deionized water spiked at 500 μg/L were extracted, and the absolute responses of each compound were compared for each fiber. The results are summarized in Figures 2 and 3. All compounds were extracted by each stationary phase, but a higher recovery was observed using the C18 than the polar-embedded reversed-phase fiber for a majority of the compounds.

Figure 2. Comparison of Recovery of Extraction of Pharmaceutical Compounds from Deionized Water Using C18 and Polar-embedded Biocompatible SPME Fibers


Figure 3. Comparison of Recovery of Extraction of Pharmaceutical Compounds from Deionized Water Using C18 and Polar-embedded Biocompatible SPME Fibers

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Conclusion

  • Biocompatible SPME fibers can quantitatively extract pharmaceutical compounds from water.
  • Extraction conditions should be optimized for the particular compound list of interest.
  • For the compounds studied, levels down to 5 μg/L were successfully detected. Lower levels may be possible for some compounds, depending on extraction conditions and LC-MS ionization efficiencies.
  • Both the polar-embedded and C18 fibers have utility for this application. Depending on the analytes, the C18 may show better recovery than the polar-embedded reversed-phase fiber chemistry.

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References

  1. US EPA Method 1694: Pharmaceuticals and Personal Care Products in Water, Soil, Sediment, and Biosolids by LC/MS/ MS, Dec. 2007
  2. Batt, M. Kostich, J. Lazorchak. “Analysis of Ecologically Relevant Pharmaceuticals in Wastewater and Surface Water Using Selective Solid Phase Extraction and UPLC-MS/MS.” Anal. Chem. 2008, 80 (13), 5021-5030.
  3. C. Aurand, K. Stenerson, R. Shirey, D. Vuckovic, J. Pawiliszyn, “Extraction of Propranolol and Metabolite from Rat Plasma Using Biocompatible Solid Phase Microextraction (SPME). Supelco Publication T408089, 2008.

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