PAH analysis in drinking water using disk SPE automated with the Biotage® Horizon 5000

Introduction

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous pollutants introduced into the environment from anthropogenic activities such as combustion of fossil fuels, tobacco smoking and even during food preparation. These compounds strongly adsorb to sediment or particulate matter, causing them to slowly biodegrade while remaining present in drinking water sources; mostly as leachates from water storage and distribution systems. Exposure to PAHs over time can lead to increased health risks including developmental and reproductive issues. This class of compounds has also been identified as a carcinogen. As a result, PAH’s in drinking water must be monitored.
US EPA method 550.1 is a method used by regulatory agencies to determine PAH’s in drinking water by liquid-solid extraction (LSE) and high performance liquid chromatography (HPLC).1 The method outlines the steps needed to perform extractions of PAHs from drinking water sources and finished drinking water; as well as the quality control (QC) program requirements to ensure the method is operated under control.
 
Figure 1: Biotage® Horizon 5000 Automated Extractor
 

Automation of the extraction process allows more hands-off time for the operator and ensures better precision between operators. US EPA drinking water methods have embraced the use of SPE, yielding smaller extracts that require less evaporation time and require less solvent recovery. Use of Biotage’s automated sample preparation product line allows users to achieve the precise and consistent data needed to comply with EPA method 550.1 QC specifications as stated in method, section 10.3.2., for Initial Demonstration of Capability (IDC); while at the same time, streamlining laboratory practices to increase lab productivity.

Experimental

The instrumentation used in the method included the Biotage® Horizon 5000 disk extraction system. This is a three-position extraction system that automates disk conditioning, sample loading and elution of the disk. Atlantic® C18 disks were used for sorption of the analytes. The eluent was dried of residual water using DryDisk® membrane drying with the DryVap™. In-line drying and evaporations system. Analysis of the prepared extracts was accomplished with the Prominence i-Series HPLC (Shimadzu Scientific Instruments).
 

Method summary

1. Obtain 1-liter samples of DI water.

2. Acidify each sample with hydrochloric acid until pH <2.

3. Add surrogate compounds to the samples at a concentra- tion of 5 μg/L.

4. Extract the samples using the Biotage® Horizon 5000 with 47-mm Atlantic® C18 SPE Disks using the method shown in Table 1.

5. Dry and concentrate the extracts using the DryVap™ with a DryDisk® to 0.5-mL final volume. See Table 2 for DryVap™ conditions.

6. Analyze the samples using conditions used in HPLC Table 3.
 
Table 1: Extrction method

Table 2: DryVap™ conditions

Table 3: HPLC conditions

Results and Discussion

Figure 2 shows a chromatogram of the analytes of interest in a standard mix. Resolution is good under the conditions specified.
Nine samples were extracted on the Biotage® Horizon 5000, spiked at a concentration of 5.0 μg/L. Three samples were run simultaneously, with each run taking 35-40 minutes to complete. Extracts were then dried and concentrated, taking approximately 1 hour to 1 hour 15 minutes to achieve a 0.5-mL final end volume. Final extracts were prepared and ready for HPLC analysis in under 2 hours.

Figure 2: Chromatogram of the 16 compounds of interest, identified in the key table.

The results for nine replicate samples are shown in Table 4. QC requirements set forth in EPA Method 550.1 Section 10.3, Initial Demonstration of Capability (IDC) state that the recovery value for at least three out of four consecutively analysed samples must fall in the range of R ±30% (or within R ±3 Sr if broader) using the values of R (mean recovery) and Sr (standard deviation of the %) for reagent water in Table 2 of the method. Table 2 of EPA Method 550.1 shows compound recoveries ranging from 70.5 % - 93.6 %. While analysing 9 samples using the Biotage® Horizon 5000, Atlantic® C18 Disk and the DryVap™, the mean compound recovery (R) was found to range from 80.2 % - 95.7 % recovery throughout each run. The relative standard deviation (Sr) of the mean recovery throughout these runs was calculated to be 5.1-6.3, meeting the method IDC criteria of ±30%.

Table 4: The results for nine replicate samples

Conclusion

Automated SPE for preparation of PAHs in drinking water gave excellent results, meeting the requirements set forth in US EPA method 550.1. In addition, the time for preparation was efficient and samples were prepared and ready for HPLC analysis in less than 2 hours. This is a powerful combination for laboratory efficiency.

References

1. US EPA Method 550.1, US EPA https://www.o2si.com/ docs/epa-method-550.1.pdf (1990).

Literature number: AN119