STANDARD OPERATING PROCEDURE FOR ANALYSIS OF PENTANOL IN AQUEOUS
SURFACTANT SOLUTIONS USED WITH SPME FLUSHING TECHNOLOGY
DEMONSTRATION (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 (UF), IFAS, for analysis of pentanol in lab and field studies of the SPME flushing technology. It is assumed that pentanol will be the cosurfactant selected. However, it should be understood that the microemulsion precursor has not yet been selected and a modification of this operating procedure will be necessary if a different alcohol is selected as the cosurfactant.
2. This SOP was written by R.D. Rhue, Soil and Water Science Department, University of Florida, Gainesville, Fl.
3. This method involves gas chromatography (GC) analysis for pentanol concentrations in aqueous surfactant solutions used to solubilize OU 1 LNAPL. A flame-ionization detector (FID) is used to quantify the pentanol. Gas chromatography has been found to provide reliable and reproducible quantitation of alcohols in aqueous solutions for concentrations > 1 mg/mL. This value may be considered the method detection level (MDL). Samples will be diluted with methanol to give pentanol concentrations within the linear operating range.
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 for pentanol in aqueous surfactant samples for laboratory-based or on-site (field-based) 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: For field studies, the 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 4 deg. C, until they are ready for GC analysis. After sub-sampling, the samples will be returned to cold storage.
For lab studies, samples will be collected in 2 mL GC vials when possible and stored in a refrigerator if analysis is expected to take more than a day.
2. Dilution
Fifty microliters of sample will be diluted with 4 mL of methanol prior to analysis. A portion of the diluted sample will be transferred to 2-ml vials for automated GC analysis. Disposable, Pasture glass pipets (Fisher Catalog # 13-678-20B) are used to transfer samples to the GC vials.
3. Apparatus and Materials
Glassware: Disposable micro-pipets (50 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.
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, 3 mm 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.
Alcohols: Certified ACS grade pentanol and methanol will be purchased from Fisher Scientific and used as received.
5. Standard Solutions
Stock Standard Solution: A stock standard solution will be prepared by dissolving a known amount of pentanol in methanol and storing at 4 deg. C. 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".
Calibration Standards: Calibration standards will be prepared by diluting aliquots of the stock standard in methanol. Five concentrations will be prepared that cover the approximate concentration range from 0 to 500 mg/L.
Stock Spiking Solution: Since the matrix for the field and lab samples is an aqueous surfactant solution, the pentanol standards in methanol are not suitable for spiking samples. The stock spiking solution will be an aqueous surfactant solution containing pentanol at a concentration similar to that used in field and lab experiments. The stock spiking solution will be prepared by dissolving a known amount of pentanol in the aqueous surfactant solution.
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 solution containing no pentanol 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 200C
FID detector temperature 225C
Temp Program: Isothermal at 70C for 8 mm; Ramp to 200C at 3 C/mm.; Hold at 200C for 10 minutes.
9. 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. Pentanol should elute at its 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.
10. 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 rinsed with reagent water 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.
11. 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 hazards.