PROPOSED STANDARD OPERATING PROCEDURE FOR ANALYSIS OF ANALYTES WITH SPME FLUSHING (November 15, 1995)
SCOPE AND APPLICATION
1. This SOP describes the analytical procedures to be utilized by the Soil and Water Science Department, University of Florida, IFAS, for analysis of select constituents of non-aqueous phase liquids (NAPLs) in both lab and field SPME flushing studies for the purpose of quantifying the amount and distribution of residual non-aqueous phase liquids (NAPLs) present in the saturated zone. The matrix for these samples will be an aqueous solution containing a surfactant and an alcohol. The maximum surfactant concentration should be around 3 weight percent; that of the alcohol should be between 1 and 3 weight percent, depending on the surfactant chosen. It should be understood that minor changes in this operating procedure may be necessary depending on the surfactant and alcohol that are chosen for the laboratory and field studies. It is assumed for the purpose of this procedure that an ethoxylated alcohol and pentanol will be the surfactant and alcohol used.
2. This SOP was written by R.D. Rhue, Soil and Water Science Department, University of Florida, Gainesville, Fl. It is a modification of SOP-UF-Hill-95-07-0012-v.2, prepared by D.P. Dai and P.S.C. Rao, Soil and Water Science Department, University of Florida.
3. The selected constituents are n-decane, n-undecane, n-dodecane, n-tridecane, l,2,4,-trimethylbenzene, l,2-dichlorobenzene, and 1,2, 4-trichlorobenzene.
4. The method involves gas chromatography (GC) analysis for concentrations of above constituents in aqueous surfactant samples. A flame-ionization detector (FID) is used to quantify the analyte concentrations in the sample. Gas chromatography has been found to provide reliable and reproducible quantitation of the above constituents in organic solvents for concentrations > 0.10 mg/ml. The standard calibration curve for FID response is linear to greater than 200 mg/ml. For concentrations beyond this value, sample dilution is generally required.
5. Samples selected for GC-FID analysis may be chosen on the basis of preliminary screening which will provide approximate concentration ranges and appropriate sample injection volumes, standard concentrations, etc.
PURPOSE
The purpose of this SOP is to insure reliable and reproducible analytical results of NAPL constituents in aqueous surfactant and alcohol flushing solutions for laboratory-based or on-site (fieldbased) GC-FID analyses, and to permit tracing sources of error in analytical results.
PROCEDURES
1. Sample Containers, Collection, Transportation and Storage
Sample Containers: Field samples will be collected in 5-mL glass sample vials (Fisher Catalog * 06-406-19F) with teflon-faced septa caps. Glass vials and caps are not reused.
Sample Collection: Each field sample vial will be completely filled with liquid, such that no gas headspace exists, and capped. The vials will not be opened until time for analysis.
Transportation and Storage: Field samples will be stored in coolers containing "blue ice", and later stored in refrigerators in a trailer located on the site. Samples may be subjected to on-site GC analysis, and/or shipped back to UF labs; samples will be packed in coolers and shipped via overnight air express (e.g., FedEx). The samples will be stored in the cold storage room or refrigerator at 4ºC, until GC analysis. After sub-sampling, the samples will be returned to cold storage.
For lab studies, samples will be collected directly in 2 mL GC vials when possible and stored in a refrigerator if analysis is expected to take more than a day.
2. Sub-sampling and Dilution
SPME samples from field experiments will be sub-sampled into 2-ml vials for automated GC analysis. Disposable, Pasture glass pipets (Fisher Catalog # 13-678-20B) are used to transfer samples from 5-mL sample vials to the 2-mL GC vials.
For samples needing dilution prior to GC analysis, dilution is usually 1:10 in aqueous surfactant/alcohol solution but the best dilution ratio can be determined following a preliminary screening analysis.
3. Apparatus and Materials
Glassware: Disposable micro-pipets (100 mL; Fisher Catalog # 21-175B; 21-175F) and Class A volumetric pipets (1 or 2 mL) are required for sample dilution.
Disposable Pasteur glass pipets (Fisher Catalog # 13-678-20B) are required for sub-sampling.
GC vials (2-mL) with Teflon-faced caps (Fisher Catalog # 03-375-16A) are required for GC analysis.
Volumetric class A pipets and volumetric class A flasks are required for preparations of the calibration standards.
Gas Chromatograph System: A Perkin Elmer Autosystem XL with an FID and an integrated autosampler will be used for analysis of field and laboratory samples. The Perkin Elmer system will be linked to an IBM-compatible PC loaded with Turbochrom (version 4.01) software.
A J&W Scientific DB-624 capillary column (30m X 0.53mm, 3pm film thickness) will be used. Zero-grade air and ultra-high purity hydrogen will be used for the FID. Ultra-high purity nitrogen or helium will be used for carrier gas.
4. Reagents
Deionized, Double-Distilled Water: Deionized, double distilled water is prepared by double distillation of deionized water in a quartz still. This water will be referred to as reagent water.
n-Hexane: High purity, Pro Analysi grade hexane will be purchased from Fisher Scientific and used as received.
Alcohols: Certified ACS grade n-pentanol and n-butanol will be purchased from Fisher Scientific and used as received.
Surfactants: Commercial grade surfactants will be used in the field studies. Therefore, samples of these same commercial grade materials will be obtained from the manufacturers and used in laboratory and field samples. These surfactants will be identified by the manufacturer's trade name and will be used as received without purification.
5. Standard Solutions
Stock Standard Solution: Analytical standards will be prepared from reagent chemicals by the laboratory. Stock standards will each contain a single analyte dissolved in hexane and stored in 20 mL glass vials (Fisher Catalog # 03-393-D) with teflon-lined caps. These stock solutions will be kept in a refrigerator at 4 ºC. Fresh stock standards will be prepared every six months. The procedure for making stock standard solutions is essentially that given in the Federal Register, Rules and Regulations, Thursday, November 29, 1979, Part III, Appendix C, Section 5.10, "Standard Stock Solutions". The only modification of the procedure for the current study is that hexane is used as the solvent in place of methanol.
Calibration Standards: Calibration standards will be prepared by diluting the stock standards in hexane. Each calibration standard will contain each of the eight analytes listed above. Five concentrations will be prepared that cover the approximate concentration range from 0 to 200 mg/L.
Stock Spiking Solution: Since the matrix for the field and lab samples is an aqueous surfactant/alcohol solution, the standards in hexane are not suitable for spiking samples. The matrix for the stock spiking solution will be an aqueous surfactant/alcohol solution containing surfactant and alcohol at the same concentrations as those used in the field and lab experiments. The stock spiking solution will be prepared by dissolving a known amount of the eight target analytes in the aqueous surfactant/alcohol solution. The analyte concentrations will reflect the concentrations expected in the samples.
6. QC blank Spike/Matrix Spike
Two 0.5 mL aliquots of the sample to be spiked will be transferred to clean vials. To one vial, 0.5 mL of aqueous surfactant/alcohol solution containing no analytes will be added. To the second vial, 0.5 mL of the stock spiking solution will be added. The spike recovery will be calculated using the difference between the two measured concentrations and the known spike concentration.
7. Quality Control
GC injector septa will be changed every 80 to 100 injections, or sooner if any related problems occur.
Injector liner will be cleaned or changed every 80 to 100 injections or sooner if any related problems occur.
A method blank will be included in every 50 samples
A complete set of calibration standards (5) will be run at the beginning of each day and after every fiftieth sample.
One standard and a blank will be included in every 25 samples.
A sample spike and a blank spike will be included in every 50 samples.
8. Instrumental Procedures
Gas Chromatography: For J&W DB-624 Column:
Injection port temperature 200 C
FID detector temperature 225 C
Temp Program: Isothermal at l00 ºC for 10 min; Ramp to 200ºC at l0ºC/min.
9. Sample Preparation
Sub-sampling: Field samples will be transferred from the 5 mL sample vials to the 2 mL GC vials and capped with open-top teflon-lined septa caps.
Dilution: Samples will be diluted if chromatographic peak areas for any of the eight target analytes exceed those of the calibration standards. One mL of sample will be added to an appropriate amount of stock surfactant solution to make the dilution.
10. Sample Analysis
Analysis: The samples will be allowed to reach ambient temperature prior to GC analysis.
Sample vials (2 mL) will be loaded on the Perking Elmer GC auto-injector. A one mL injection volume will be used for both samples and standards.
Analyte Identification: Analyte identification will be based on absolute retention times. The analytes of interest should elute at their characteristic retention times within +/- 0.1 minute for the automated GC system.
Analyte Quantitation: When an analyte has been identified, the concentration will be based on the peak area, which is converted to concentration using a standard calibration curve
11. Interferences
Contamination by carry-over can occur whenever high-level and low-level samples are sequentially analyzed. To reduce carry over, the injector syringe should be rinsed with a blank surfactant/alcohol solution between samples.
Potential carry-over will be checked by running a highly concentrated sample, but one still within the standard concentration range, followed by a blank. A negligible reading for the blank will insure that carry-over has been minimized.
12. Safety
The main safety issue concerning the use of the GC at a field site relates to the compressed gases. The FID gases (hydrogen and air) form explosive mixtures. It is important to keep this in mind at all times, and be aware of the hazard potential in the event of an undetected hydrogen leak. All gas connections will be properly leak tested at installation.
High-pressure compressed-gas cylinders will be secured to a firm mounting point, whether they are located internally or externally.
Gas cylinders should preferably be located outside the trailer on a flat, level base, and the gas lines run inside through a duct or window opening. If the gases are located outside, then some form of weatherproofing for the gauges will be necessary. As a temporary measure, heavy-duty polyethylene bags, secured with tie-wraps, have been used successfully; this may not be very elegant but it is very effective for short-term use of the GC. A more permanent protective housing must be built if the GC is located at the trailer for an extended time period.
The main operating drawback to locating the gas cylinders externally is that it is not easy to monitor the cylinder contents from inside. The gas which could be used up most quickly is air for the FID, particularly if two instruments are hooked up to the same supply and they are running continuously. A reserve cylinder of air should be available at all times to prevent down time.
If it is not possible to arrange external citing easily, the gas cylinders should be secured to a wall inside the trailer.
It is a good laboratory operating practice to make sure the flame is attended at all times.
When it is necessary to change the injection liner on the GC, the detector gases should be shut off.
The column must be connected to the detector before igniting the flame.
The trailer should be kept well ventilated when using the GC.
Reference to the Materials Safety Data Sheets (MSDS) will be made for information on toxicity, flammability, and other hazard data.