Determining Diesel and Oil Range Organics in Water using Automated Solid Phase Extraction

Transcription

1 Determining Diesel and Oil Range Organics in Water using Automated Solid Phase Extraction David Gallagher, Horizon Technology, Inc. Key Words Diesel, Oil, Organics in Water, Seawater, Solid Phase Extraction, SPE, method 8015, ISO-9377 Introduction Although not frequently a problem, recent incidents at sea have led to large amounts of crude oil being released and dispersed throughout the Gulf of Mexico, such as in the Deepwater Horizon Gulf oil spill of 2010 (NASA photo above). Originally presumed to be Louisiana Sweet Crude, sample testing later revealed a harsher form of crude containing a high amount of asphaltenes was actually being released. The differences are substantial, as Louisiana Sweet degrades more readily in nature than crude oil containing asphaltenes. While data is still mixed as to what type of oil has been released, the need for a fast and reliable method of testing still exists within the environmental industry of the Gulf Coast states. One of the most frequently used methods of testing for petroleum products in water is EPA Method (ISO 9377). 2 This method provides for the detection of non-halogenated diesel range organics (DRO) from C10 to C28 using a gas chromatograph with flame ionizing detectors or GC-FID. In more recent history, Method 8015 has been built up to also include Oil Range Organics (ORO) up to C40. Traditional techniques used for the extraction of 8015 samples, such as liquid-liquid extraction (LLE), can be problematic. Emulsions and corrosives may form, requiring the use of costly chemicals such as biocides, emulsion breakers, and corrosion inhibitors. Errors may occur, as the efficient and accurate use of these chemicals is reliant on factors such as the amount of oil in the water and droplet size, which are not always known. As an alternative procedure, the use of automated solid phase extraction (SPE) simplifies and reduces the amount of analyst interaction with a given sample. SPE involves filtering a water sample through a disk in which analytes are concentrated and, later, eluted using a variety of solvents. Due to the nature of SPE, emulsions cannot form and the amount of solvent needed for a given extraction is a fraction of traditional techniques. This application note will highlight the use of the Horizon Technology SPE-DEX 4790 Automated Extraction Systems. This fully automated extraction system makes use of SPE technology to reduce costs associated with the extraction procedure and to increase the throughput of a laboratory. It is designed to extract a wide range of target analytes from both influent and effluent sample matrices and can handle a high amount of suspended solids. Its Envision controller is a user-friendly, web-based interface which provides a simple, yet elegant method of interacting with up to eight extraction units. For the analytes of

2 interest in this study, the Atlantic DVB SPE disk is used due to the nature of its reverse phase interactions. After the extraction procedure is complete, it becomes necessary to both dry and concentrate a sample. Traditional techniques for these processes include the use of sodium sulfate, which must first have a significant amount of time invested in it to ensure cleanliness, and a water bath, which can very easily bring a sample to complete dryness. This study will make use of the Horizon Technology DryVap Concentrator System with DryDisk Separation Membrane. This union of steps provides for automated drying and concentrating at the push of a button. The DryDisk is a physical separation membrane which will allow solvent through, but not water. There is no pre-cleaning necessary and very little physical waste. The DryVap allows for up to six samples to be dried and concentrated at a time. It applies heat and sparge while under vacuum for a fast concentration with end point detection. When used in conjunction with the Reclaimer Solvent Recovery System, (now replaced with the SolventTrap SVOC ) up to 95% of the DryVap vapors can be reclaimed. Instrumentation Horizon Technology SPE-DEX 4790 Automated Extraction System Envision Controller Atlantic DVB SPE Disk DryVap Concentrator System DryDisk Separation Membrane Reclaimer Solvent Recovery System Agilent 6890N GC-FID HP5890 Series II GC-FID #2 Diesel Fuel Standard 5W-30 Motor Oil Standard Mineral Oil Standard Florida Total Recoverable Petroleum Hydrocarbon (TRPH) Mix (C10 C40) 1-Chlorooctadecane Surrogate Spike O-Terphenyl Surrogate Spike Method Summary 1. Make a solution with a concentration of 5 µg/ml of the Florida TRPH Mix and 10 µg/ml of O-Terphenyl surrogate 2. Inject this solution into the GC-FID systems to determine the retention times of the individual analytes C10 C40 for later reference. Table 1: Purge Method 3. Purge the SPE-DEX 4790 extractors using the method shown in Table 1. Step Solvent Soak Time Dry Time Prewet 1 Methanol 0 s 15 s Prewet 2 MeCl 0 s 15 s Prewet 3 MeCl 0 s 15 s Rinse 1 Acetone 0 s 5 s Rinse 2 Acetone 0 s 5 s Rinse 3 MeCl 0 s 10 s Rinse 4 MeCl 0 s 10 s P a ge 2

3 Method Detection Limit Determination 1. Obtain two liters of DI water and acidify to ph<2. 2. Spike the Diesel standard into one liter such that the final concentration is 0.5 mg/l and the Oil standard into another such that it is 0.8 mg/l. 3. Add the 1-Chlorooctadecane surrogate into each. 4. Place a small piece of aluminum foil over the opening of the bottle and screw on the adapter. 5. Load the sample container onto the extractor. 6. Load an Atlantic DVB disk into the holder and install the holder on the extractor. 7. Install a collection vessel on the extractor. 8. Extract the samples using the SPE-DEX 4790 and the method shown below in Table Assemble the DryDisk Reservoir with a separation membrane and place on the DryVap. 10. Place a concentrator tube on the DryVap. 11. Dry and concentrate the extracts using the DryVap settings shown in Table 3 to a final volume of 5 ml. 12. Transfer the extract to a GC vial(s). 13. Perform the final analysis using GC-FID. 14. To complete the MDL study, extract seven replicates of each type using steps one through six over three, non-consecutive, days. Initial Demonstration of Proficiency 1. Obtain eight liters of DI water and acidify to ph<2. 2. Spike four samples with Mineral Oil and Diesel Fuel such that the final concentration of each is 200 µg/ml (400 µg/ml total). 3. Spike four samples with Mineral Oil and Diesel Fuel such that the final concentration of each is 800 µg/ml (1600 µg/ml total). 4. Add the O-Terphenyl surrogate into each. 5. Place a small piece of aluminum foil over the opening of the bottle and screw on the adapter. 6. Load the sample container onto the extractor. 7. Load an Atlantic DVB disk into the holder and install the holder on the extractor. 8. Install a collection vessel on the extractor. 9. Extract the samples using the SPE-DEX 4790 and the method shown below in Table Assemble the DryDisk Reservoir with a separation membrane and place on the DryVap. 11. Place a concentrator tube on the DryVap. 12. Dry and concentrate the extracts using the DryVap settings shown in Table 3 to a final volume of 0.9 ml. 13. Transfer the extract to a GC vial(s). 14. Perform the final analysis using GC-FID. 15. Analyze by GC-FID. P a ge 3

4 Table 2: Extraction Method Step Solvent Soak Time Dry Time Prewet 1 MeCl 2:00 min 0:30 min Prewet 2 MeCl 2:00 min 0:30 min Prewet 3 Methanol 2:00 min 0:05 min Prewet 4 Reagent Water 1:00 min 0:05 min Prewet 5 Reagent Water 1:30 min 0:02 min Process Sample Air Dry 0:30 min Rinse 1 Acetone 3:00 min 0:30 min Rinse 2 MeCl 3:00 min 0:30 min Rinse 3 MeCl 2:00 min 0:30 min Rinse 4 MeCl 2:00 min 0:30 min Rinse 5 MeCl 2:00 min 2:00 min Table 3: DryVap Settings Dry Volume 20 ml Heater 1 Heater Timer Off Autorinse Off Sparge Pressure 20 psi Vacuum -10 in. Hg Results The MDL study shown in Tables 4 and 5 below were produced over three non-consecutive days and includes seven replicates of each spike. They show that the diesel standard is easier to replicate than the oil standard, as indicated by their standard deviations. This is likely caused by the buildup of oil residue within the injection port and column of the GC. Also, Figures 1 and 2 show typical chromatograms from a GC-FID for diesel and oil respectively. These chromatograms were for 5 ppm spikes and showed average surrogate recoveries of 85.5%. Table 4: Diesel MDL Results Replicate Recovery (mg/l) Average Std. Dev.: MDL: Table 5: 5W-30 Motor Oil MDL Results Replicate Recovery (mg/l) Average Std. Dev.: MDL: P a ge 4

5 Figure 1: GC-FID Chromatogram of a 5 ppm Diesel Full Spike (82.8% Diesel recovery, 85% Surrogate recovery). Figure 2: GC-FID Chromatogram of a 5 ppm 5W-30 Motor Oil Spike (75.4% Diesel recovery, 85% Surrogate recovery). Figure 3. GC-FID Chromatogram of a 1600 ppm Diesel Fuel and Mineral Oil Spike

6 Table 6: 400 µg/ml IDP Study Results (µg/ml) OTP Recovery Average RSD% 1 6 Table 7: 1600 µg/ml IDP Study Results (µg/ml) OTP Recovery Average RSD% 3 3 Conclusion In this study, the use of the SPE-DEX 4790 Automated Extraction System along with the Atlantic DVB disk proved to be an effective combination for the extraction of diesel and oil range organics. It was noted however, that the use of heavier molecular weight hydrocarbons will have a tendency leave trace amounts of residue within the GC injection port and column, especially when used in high concentrations. The use of the automated systems from Horizon Technology allows for a laboratory to realize significant improvements in the areas of labor, time per sample, and cost of analysis while maintaining the high levels of precision and accuracy required within any industry. These qualities are especially desired in the time of an environmental tragedy like the one experienced in the Gulf of Mexico when the ensuing sample load associated with cleanup will surely be extreme. References 1. US EPA Method 8015D, Nonhalogenated Organics using GC/FID, US EPA (2003). 2. ISO , Water quality Determination of hydrocarbon oil index -Part 2: Method using Solvent Extraction and Gas Chromatography, First edition AN _02 16 Northwestern Drive, Salem, NH USA Tel: (603) Support-Service@horizontechinc.com