Extraction of semi-volatile compounds from drinking water using automated SPE

Introduction

Drinking water is an important part of environmental exposure, especially for small children. Countries around the world have put regulations in place to monitor drinking water quality for a wide range of hazardous compounds. Methods such as SL 392- 2007 in China, the EN methods in Europe and US methods such as method 525.2 cover a large suite of analytes of concern, extracted using solid phase extraction (SPE) disks and using GC/MS for detection.
 
US EPA method 525.2 may use solid phase extraction (SPE) to extract the analytes of interest from water samples. It includes a variety of quality control measures to ensure the method is under control throughout the analysis.1 The Biotage® Horizon 5000 (previously known as SPE-DEX 5000) was used in this study to extract the EPA Method 525.2 analytes from six prepared water samples as described in section 9.3, Initial Demonstration of Laboratory Accuracy and Precision. The test involves measuring 4-7 samples of reagent water spiked at approximately the mid-point of the calibration curve, 2-5 μg/L of the full suite of analytes. For each analyte and surrogate, the spike recovery, expressed as a percentage of the true value, should be 70–130% and the relative standard deviation (RSD) should be <30% to meet method criteria. All six samples were
extracted using the same procedure and calibration parameters.

•  Biotage
  » Biotage® Horizon 5000 (previously
  known as SPE-DEX 5000)
  » DryVap™* Automated In-line drying and concentration system
  » Drydisk® Separation membranes
  » Atlantic® C18 High Capacity Disk

The Biotage® Horizon 5000 was used for extraction of the analytes from the water samples. The Biotage® Horizon 5000 is an automated system that conditions the solid phase extraction disk, loads the sample through the disk, rinses the sample bottle and elutes the sample all without user intervention. The 47 mm disk holder was used and high capacity C18 disks were chosen. High capacity disks were used because some of the more water soluble compounds are better retained and suffer less breakthrough with this disk. Ethyl acetate and methylene chloride were used for elution.

*The DryVap™ system has been discontinued. We recommend using the TurboVap® evaporation systems for achieving equivalent results.

Figure 1: Biotage® Horizon 5000 (previously known as SPE-DEX 5000) Automated Extractor

The method run on the Biotage® Horizon 5000 is shown in Table 1. The method information, run time, sample identification and other information are stored in a file when the sample is run. This can be printed in a report or exported to the laboratory LIMS for archiving.

Method summary

1. Obtain six 1 litre samples of drinking water.

2. Add dechlorinating agent to each 1 litre sample.

3. Acidify each 1 litre water sample to pH <2 using concentrated HCl.

4. Add surrogate and internal standard compounds into samples.

5. Start extraction method shown in Table 1 and collect extract (≈32 mL).

6. Add extract to the DryDisk® holder and start automated drying and concentration process on the DryVap™ system (the DryVap™ system automatically dries and concentrates extract to 0.9 mL).

7. Quantitatively bring extract volume to 1.0 mL using methy- lene chloride once the extracts are evaporated to less than 1 mL.

8. Add external standard into the 1 mL extract.

9. Transfer the extract to a 2.0 mL GC vial.

10. Analyze by GC/MS.

Gas chromatography mass spectrometry system

Cartridge ZB Semi-volatiles, 30 m x 0.35 mm i.d., 0.25 µm film thickness (Phenomenex)

Flow Rate 9 psig helium ramped up with the oven temperature to maintain a constant flow

The GC/MS used was a 6890 GC with a 5973 MSD (Agilent).

Total Run Time: 23.83 minutes

Injection Method: 1.0 µL injected, Temperature 280oC , Pulsed splitless
• Inlet pulse pressure 25.0 psi for 1.00 min
• Purge flow to split vent 50 mL/min for @2.00 min

Results and discussions

Six replicate laboratory fortified blanks (LFBs) were extracted as described in US EPA Method 525.2, following the procedure in the method summary in this note. Drinking water was spiked with standards and surrogates at a concentration of 5 μg/L.
The results are shown in Table 2 for each of the six replicate samples.

The recoveries are within the 70—130% recovery as specified in the method quality control criteria in all cases for the more than 100 compounds measured. The precision was excellent and the standard deviations ranged for 2-3% for most of the analytes.

Conclusion

The Atlantic® high-capacity C18 disks provided excellent recovery of the large suite of compounds extracted in water. The compounds included in the method had excellent performance and an average recovery of 98.8% was achieved with a 5 µg/L spike. The spike recovery criterion of 70–130% was achieved in all cases. The Biotage® Horizon 5000 system provided uniform performance and a hands-off approach to the extraction step. The reproducibility of the six runs was excellent and the average of the standard deviation values was 2.57%. The Atlantic high-capacity C18 disk allowed even more water soluble compounds, such as caffeine, to be successfully retained with good recovery, demonstrating the utility of solid phase extraction. In combination with the Biotage® Horizon, the samples were reliably extracted with excellent precision.

References

1. Method 525.2, Determination of Organic Compounds in Drinking Water by Liquid-Solid Extraction and CapillaryCartridge Gas Chromatography/Mass Spectrometry, US EPA https://www.epa.gov/sites/production/ files/2015-10/documents/method_525-2_rev-2_1995.pdf, accessed April 12, 2017.

Literature number: AN114