Determining organic compounds in drinking water utilizing the Biotage® Horizon 5000 and TurboVap® II

Introduction

This application note will outline a procedure for the extraction and concentration of organic compounds in drinking water utilizing the Biotage® Horizon 5000, TurboVap® II with End-Point Sensors, and Atlantic® C18 SPE Disks. To demonstrate compliance, the limits set in EPA Method 525.21 were used as a guideline and an initial demonstration of capability (IDOC) as well as method detection limit (MDL) study was performed.

When SPE is performed manually, unintentional errors can occur throughout the process. The same can be said when concentrating extracts, such as inconsistent final volumes or uneven nitrogen delivery into sample tubes. These factors can end up in skewed results and relative standard deviations, resulting in possible method criteria failures.

The proposed solution outlined below will eliminate manual intervention throughout the extraction process while delivering a very reliable, efficient and consistent means of concentrating while demonstrating its ability to comply to the EPA Method
525.2 guidelines.

Instrumentation

Biotage instruments and consumables

»    Biotage® Horizon 5000 Automated Extraction System (P/N SPE-DEX 5000)
»   TurboVap® II (P/N 415100)
»    TurboVap® II Rack with End-Point Sensors, 6 positions, 200 mL tubes (P/N: 415100)
»    Atlantic® C-18 SPE Disk, 47 mm (P/N 47-2346-02)
»    Evaporation Tube TurboVap® II, 200 mL, 1 mL End-Point (P/N C42567)

GC/MS

»    Agilent 6890 GC
»    Agilent 5793 MSD
 

Method summary

1. Purge the extractor with the method listed in table 1.
2. Obtain 1 L water samples and adjust to pH 2 using HCl.
3. Add 0.05 g of sodium sulphite (Na2SO3) and 5 mL of methanol to each sample.
4. Spike each sample with the appropriate amount of 525.2 Internal Standard Mix that has been diluted to 500 µg/mL.
5. Spike any laboratory control or matrix spike samples with the appropriate amount of standard.
6. Place the sample bottle on the Biotage® Horizon 5000 Extractor System and place the Atlantic C-18 disk in the standard 47mm disk holder. Attach collection vessels to the system.
7.  Extract the samples using the method in table 2 and collect the final sample extract.
8. Dry the final sample extract by passing it through sodium sulphate (Na2SO4) and transfer to a clean 200 mL TurboVap® 1 mL End-Point tube.
9. Concentrate the extract to a final volume of 1 mL using the TurboVap® II and the settings in table 3.
10. Spike each extract with the appropriate amount of 525.2 External Standard Mix that has been diluted to 500 µg/mL.
11. Transfer the extract to a 2.0 mL GC vial and analyze via GC/MS in scan mode. The conditions in table 4 were used for analysis, however any GC/MS and cartridge capable of producing results equivalent to or better may be used. See manufacturer information for suggested settings specific to the GC/MS or cartridge that is used for analysis.

Table 1. Purge Method for Biotage® Horizon 5000.

Table 2. Extraction Method for Biotage® Horizon 5000

Table 3. TurboVap® II Settings.

Table 4. GC Settings

Results and discussion

To demonstrate compliance, the limits set in EPA Method 525.2 were used as a guideline and an initial demonstration of capability (IDOC) as well as method detection limit (MDL) study was completed. The IDOC consisted of four replicates spiked at a concentration of 5.0 ppb where percent recovery must fall within 70–130% and the RSD must be ≤ 30%.
The MDL consisted of seven replicates spiked at 0.5 ppb which are used to calculate the minimum amount that can be measured with 99% confidence that the reported value is greater than zero. These values are all found within table 5 below.

Excluding hexachlorocyclopentadiene, carboxin, atraton and prometon, all results observed in table 5 fall within a range of 70–130%. Even including the trouble compounds, the average percent recovery for all compounds across the study was 96.9%. The relative standard deviation is < 20%, with a majority of compounds under 5% RSD. The calculated MDLs were all roughly comparable to the MDL values outlined in EPA method 525.2 which this application is based upon.

Table 5. Extraction Results (4 IDOC samples @ 5.0 ppb, 7 MDL samples @ 0.5 ppb).

Hexachlorocyclopentadiene’s low recovery can be attributed to the compound’s sensitivity to thermal and photochemical degradation. The recovery of carboxin can be attributed to its significant instability in water. The low recoveries for atraton and prometon likely stem from inefficient extraction from the water at pH 2, which causes ionization in solution under acidic conditions.

Conclusion

The results in table 5 demonstrate the Biotage workflow solution is capable of fully automating the extraction of organic compounds from drinking water. The resulting data is both accurate and precise while achieving EPA 525.2 method limits. This solution not only eliminated the sample to sample variation that is experienced with manual techniques, but it frees up time for users to perform other tasks within the laboratory.
The Biotage solution including the Biotage® Horizon 5000, TurboVap® II, and Atlantic® C18 SPE Disks reduce analyst labour, solvent usage, turnaround time, and improves accuracy and precision when compared to manual SPE extraction methods. All of these qualities improved method performance while reducing the total cost of a sample to a laboratory.

References

1. United States Environmental Protection Agency, Method 525.2, Revision 2.0: Determination of Organic Compounds in Drinking Water by Liquid-Solid Extraction and Capillary Cartridge Gas Chromatography/Mass Spectrometry.
   
   

Literature number: AN950