STANDARD OPERATING PROCEDURE FOR ANALYSIS OF
ANALYTES WITH COSOLVENT FLUSHING
SCOPE AND APPLICATION
1. This SOP describes the analytical procedures utilized by the University of Florida (UF) for analysis of select constituents of non-aqueous phase liquids (NAPLs) in both lab and field cosolvent flushing studies.
2. This SOP was written by D. P. Dai and P.S.C. Rao at the University of Florida. This version (v.2) was updated on July 27, 1995.
3. The selected constituents were l,1,1-trichloroethane (TCA), p+m-xylene, o-xylene, 1,3,5-trimethylbenzene, n-decane, 1 ,2-dichlorobenzene, n-undecane and naphthalene.
4. The method involves gas chromatography (GC) techniques for estimation of the concentrations of above constituents in cosolvent samples; a flame-ionization detector (FID) is used to quantify the analyte concentrations in the sample. The method has been found to provide reliable and reproducible quantitation of all constituents, except TCA, for concentrations >0.10 mg/mL. This value is then considered to be the method detection level (MDL). The standards calibration curve for FID response was found to be linear up to 200 mg/mL. For concentrations beyond this value, sample dilution was required.
5. Samples selected for GC-FID analysis were chosen on the basis of preliminary screening to determine approximate concentration ranges, and select appropriate GC parameters (e.g., sample injection volumes; concentration range for standard curves, etc.). However, the strategies for sample screening are not within the scope of this SOP.
6. Cosolvent flushing samples from lab and field experiments are sub-sampled in to 2-mL GC vials for analysis.
PURPOSE
The purpose of this SOP is to insure reliable and reproducible analytical results of NAPL constituents in cosolvent flushing samples for laboratory-based or on-site (field-based) OC-FID analyses, and to permit traceability of possible causes of error in analytical results.
PROCEDURES
A. Sample Containers, Collection, Transportation and Storage
Sample Containers
Water samples are contained in 5-mL glass sample vials (Fisher Catalog # 06406-19F) with Teflon-faced septa caps. The glass vials and the caps are not reused.
Sample Collection
Each sample vial is completely filled with sample, such that no headspace exists, and capped. The vials are not opened until the time of sub-sampling or analysis.
Transportation and Storage
For field studies, the samples are 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 are 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 Celsius, until they are ready for GC analysis. After sub-sampling, the samples are returned to cold storage.
For lab studies, the samples are stored in a refrigerator if analysis is expected to take more than eight hours.
B. Sub-Sampling and Dilution
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.
Sample may need to be diluted with cosolvent prior to GC analysis. The dilution (usually lOx) necessary is determined from preliminary screening analysis.
C. 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-niL) with Teflon-faced caps (Fisher Catalog # 03-375-16A) are required for GC analysis.
Volumetric Class A pipets (0.5, 1, 2,5, 10 mL) are required for preparations of the calibration standards.
Gas Chromatograph System
An analytical GC system is required, complete with a temperature-programmable oven, an auto-injector suitable for on~olumn injection, and either an integrator or a PC-based data acquisition/analysis software. Also required are other accessories, including analytical columns and the gases required for GC-FID operation.
Two types of GC systems were used at UF; a Shimadzu 14-A system equipped with an
autosampler and FID was used to analyze samples in lab and on site, while a Perkin Elmer Autosystem with an FID and an integrated autosampler was used for some lab analysis. The Shimadzu GC was linked to Shimadzu CR-601 Chromatopac integrator, while the Perkin Elmer system was linked to a IBM-compatible PC loaded with Turbochrom (version 4.01) software.
1. Column
The capillary column used was a Restek R'IX 624 column (75-m long, 0.53-mm i.d.) with a 3.0-mm film thickness Restek Catalog # 10974), and a J & W BD-5 column, 30-m long, 0.53-mm i.d. with 1.5-mm film thickness.
2. Gases
Zero-grade air, and ultra-high purity hydrogen are used for the FID, and ultra-high purity helium is used as the carrier gas.
D. Reagents
Reagent Water
Reagent solvent is defined here as the solvent in which an interferant is not observed at the method detection level (MDL) of the parameters of interest.
Laboratory reagent water used is HPLC-grade or OPTIMA-grade water (Fisher Catalog # W5-4 and W7-4).
Reagent Ethanol
Absolute ethyl alcohol or food grade ethanol were used as wash solvents on GC and for making 70/10/20 ethanol/pentanol/water mixed solvent for standard preparation and sample dilution and as a blank.
Reagent Pentanol
Reagent grade pentanol Fisher Catalog # A394-4) is required for preparing 70/10/20 ethanol/pentanol/water mixed solvent for standard preparation, sample dilution and as a blank.
E. Standard Solutions
Stock Standard Solution
Analytical standard solutions are prepared from pure materials by the laboratory. Stock standard solutions, at 1000 mg/mL of each analyte, are prepared in 70/10/20 ethanol/pentanol/water mixed solvent, kept in 22-mL glass vials (Fisher Catalog #03-393-D) with Teflon-lined caps; with minimal headspace ensures no volatile losses. These stock solutions are stored at 4 deg Celsius.
Old stock solutions should be discarded, and a fresh batch prepared every three months. Anytime a comparison with the check standards indicates a problem, a new batch of standards must be prepared.
Working Calibration Standards (Secondary Dilution Standards)
Working calibration standards are prepared by diluting stock standard solutions in mixed solvent (70/10/20 ethanol/pentanol/water).
Calibration Check Standards
Calibration check standards are prepared by diluting stock standard solution in mixed solvent (70/10/20 ethanol/pentanol/water).
F. Calibration
Calibration Standards
Six standards are prepared by dilution of a stock solution (e.g., 1000 g m/mL). As an example, add 0.5, 1, and 2 mL of the calibration standard (1000 mg/mL) solution into 50 mL mixed solvent (70/10/20 ethanol/pentanol/water). This gives six calibration levels (mg/ml) as follows:
Level 1 Level 2 Level 3 Level 4 Level 5 Level6
Analyte Conc. .6 2 10 20 100 200
G. QC Blank Spike/Matrix Spike
1. A 100 mg/ml blank spike is created by adding 10 mL of a stock spiking solution having
a concentration of 10 mg/mL in mixed solvent into 1 mL mixed solvent (70/10/20
ethanol/pentanol/water).
2. A sample (1 mL size) is spiked in duplicate by adding 10 mL of stock spiking solution having a concentration of 10 mg/mL in mixed solvent (70/10/20 ethanol/pentanol/water).
3. The spiking solution is from an independent source relative to the calibration solution.
G. Quality Control
1. GC injector septa must be changed every 60 to 80 injections, or sooner if any related problems occur.
2. Injector liner must be cleaned or changed every 60-80 injection or sooner if any related problems occur.
3. An acceptable method blank analysis must be performed once for each 10 samples.
4. A calibration standard must be run every time the flame is started.
5. Check standard and blank (reagent water) should be run every 10 to 12 samples.
6. A sample spiking should be made every 10 sample along with blank spike.
H. Instrumental Procedures
Gas Chromatography Condition
Recommended operating conditions are as follows:
For RTX-624 Column on Shimadzo:
Injection port temperature 220 C
FID detector temperature 240 C
Initial column temperature 60 C
Initial hold time 2 min
Final column temperature 240 C
Final hold time 2 min
Ramp rate 30 C/min
Linear flow velocity 100/sec at 40 C
For DB-5 Column on Perkin-Elmer
Injection port temperature 240 C
FID detector temperature 265 C
Initial column temperature 60 C
Initial hold time 2 min
Step 1: Final column temperature 200 C
Hold time 5 min
Ramp rate 5 C/min
Step 2: Final column temperature 265 C
Hold time 5 min
Ramp rate 20 C/min
Linear flow velocity 100/sec at 40 C
A typical chromatogram for a mixture of several alcohol tracers in aqueous samples analyzed using the Shimadzu GC system with the above parameters is attached here as Figure 1.
I. Sample Preparation
Sub-sanpling
Samples are transferred from sample vials to GC vials and capped with open-top, Teflon-lined septa caps.
Dilution
Prepare a sample dilution if responses for any peaks in the sample exceed the calibration ranges. The dilution should allow the analyst to obtain a good response within the analytical range, or refer to screen results to determine if initial dilution is required.
J. Sample Analysis
Analysis
The samples are allowed to reach ambient temperature prior to GC analysis.
The vials with sub-sampled (and diluted, if necessary) samples are loaded on the GC auto-injector; l-mL sample size is suggested for all samples and standards. Note that on certain makes of GC, the FID flame may be extinguished if 1 mL aqueous sample is directly injected, thus requiring a split-sample injector or dilution with a non-aqueous solvent. Both options may result in decreased level of detection.
Analyte Identification
The analyte identification is not based on absolute retention time. A relative retention time for each analyte of interest is established by comparison to a specific "standard" peak (e.g., the solvent peak; a major component peak; a spiked internal standard or reference). The analyte of interest must elute at the same relative retention time as the standard; small changes in the absolute retention times might be expected due to variations in flow rate, or column temperature, or other operational parameters. The primary criterion is that the relative retention time of the sample component must be within +/- .01 min of the standard.
Analyte Quantitation
When an analyte has been identified, concentration will be based on the peak area, which is converted to concentration using a linear standard calibration curve.
K. Interferences
Contamination by carry over can occur whenever high-level and low-level samples are sequentially analyzed.
1. To reduce carry over, the injector syringe should be rinsed with a blank (20/10/70, ethanol/pentanol/water mixture) between analyses.
2. Whenever a sample with unusually-high concentration is encountered it should be followed by an analysis of a blank to check for cross contamination.
L. Safety
The main safety issue concerning the use of the GC at a field site relates to the compressed gases in use. 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 must be properly leak-tested at installation.
High-pressure compressed-gas cylinders must 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 the GC. The gas that will 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. It may be worth having a reserve cylinder of air.
If it is not possible to arrange external siting 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.
Refer to the Materials Safety Data Sheets (MSDS) for additional information on environmental toxicity data; and for safety information, procedures and regulations, etc.