Standard Operating Procedure for Volatile and Semivolatile Organics Gas Chromatography
Modified SW846 Method 8015
1.0 Scope and Application
1.1 This method is used to determine the concentration of volatile and semivolatile organics (VOC/SVOC) in air samples. The purpose of this SOP is to ensure reliable and reproducible analytical results of the VOC/SVOC(s) in air samples for on-site gas chromatographic (GC) analysis. The VOC/SVOC are 1,1,1-trichloroethane, benzene, trichloroethene, toluene, ethyl benzene, o-xylene, m-xylene, decane, trimethylbenzene, undecane, dichlorobenzene, naphthalene.
2.0 Summary of Method
2.1 This method describes the analytical procedures and the general gas chromatographic conditions necessary for the detection of the VOC/SVOC(s) to be analyzed. Samples are analyzed by using a gas sampling valve. Detection is achieved using an flame ionization detector (FID) and the gas chromatograph is temperature programmed to separate the compounds of interest.
2.2 The gas chromatograph is calibrated using a five point calibration curve for the VOC/SVOC(s) of interest. Verification of the instrument stability is checked every ten samples with a mid-point calibration standard. The method is expected to provide reliable and reproducible quantitation of VOC/SVOC(s) for concentrations to 1 mg analyte per liter of air. This value will be verified in a method detection limit (MDL) study according to Fed. Reg. 40 CFR, Part 136 at the beginning of the precharacteriztion study. The method detection limit study encompasses analyzing seven standard replicates (concentration at three times the expected MDL), calculate the standard deviation and the MDL is three times the standard deviation.
3.0 Sample Collection
3.1 Sample Collection: All samples will be delivered to the gas chromatograph's gas sampling valve via a heated stainless steel transfer line.
4.0 Apparatus and Materials
4.1 Gas Chromatograph System: Hewlett Packard HP5890 Gas Chromatograph, this GC system is capable of temperature programming and has a flow controller that maintains constant column flow rate. The system must be equipped with gas sampling valves and solenoids as detailed in fig. 1, all required accessories including an FID detector, and a packed column insert for the split/splitless injection port. A data system for measuring peak area and/or peak height for data acquisition and processing is essential.
4.2 Gas Capillary Columns
Capillary column: J&W Scientific DB-VRXcapillary column 75m x 0.45mm i.d. film thickness 2.55 mm or equivalent.
The capillary column chosen must meet the needs of the analysis and does not introduce contaminants which interfere with the identification and quantitation of the compounds of interest. Caution should be taken in choosing a column as introduction of air onto a column may damage it. Manufacturers recommendations will be taken into account for column selection.
4.3 Gases: Ultra-high purity nitrogen is used for the carrier gas and FID make-up gas. High purity hydrogen and zero air will be used to generate the flame in the FID.
5.0 Standards
5.1 Analytical Standards: Certified calibration gases are purchased from (??Source??). These concentrations should cover the linear range of the detector which should be approximately 1 mg analyte per liter of air to 10,000 mg analyte per liter of air. There should be five different concentrations of standards. One of the concentration levels should be at a concentration near, but above, the method detection limit. The remaining concentration levels should correspond to the expected range of concentrations found in the real samples or should define the working range of the GC.
5.2 Initial Calibration Analytical Sequence
VIBLK
Level 5 Standard
VIBLK
Level 1 Standard
Level 2 Standard
Level 3 Standard
Level 4 Standard
Level 5 Standard
VIBLK
VIBLK (Volatile instrument blanks) are analyzed to demonstrate that the system is free of contaminants which may interfere with the analysis. A blank is an injection of UHP nitrogen. The VIBLK must not contain target analytes at or above the reporting limit.
5.3 Linearity Requirements: The calibration curve must have a correlation coefficient R >= 0.99 using linear regression for quantitation to be performed.
5.4 Continuing Calibration Check Standards (CC): A calibration check standard is the mid-point concentration (Level 3). In order to ensure instrument stability the CC is analyzed at a minimum of once every four hours and at the close of an analytical run. In order to continue analysis the CC must meet the following quality control criteria
The percent difference (%D) between the calculated concentration and the nominal concentration must be <= 15.0%
%D = Conc. (nominal) - Conc. (calc.) x 100
Conc. (nominal)
The retention times of the GPPT must fall within the established retention time windows (See Section 6.3)
Continuing Calibration Analytical Sequence
ini. Lab ID
morning Initial Calibration
Samples
min. Every 4 hours VIBLK
min. Every 4 hours CC VOC/SVOC standard Level 3
Samples
Closing VIBLK
CC VOC/SVOC standard Level 3
If the above QC criteria are not met, standards and VIBLKs may be injected a second time. If they fail to pass the criteria again, the analysis must end. The GC system must be inspected for problems to determine the cause and perform whatever maintenance is necessary before recalibrating and proceeding with the sample analysis. All samples that were injected after the sample exceeding the criteria must be reinjected.
6.0 Instrumental Procedures
6.1 Gas Chromatographic Configuration
6.1.1 A capillary column chosen to meet the needs of the analysis is installed into the FID of the HP 5890 GC system, as shown in fig. 1.
6.2 Recommended operating conditions are as follows: (dependent upon capillary column chosen)
Injection port temperature 250 deg. C
FID detector temperature 260 deg. C
Initial column temperature 35 deg. C
Initial hold time 3 min.
Ramp rate 6 deg. C/min
Final column temperature 170 deg C
Final hold time 2 min.
Carrier: nitrogen 20-30 cm/sec (set at 35-60 deg C)
Make-up gas: nitrogen to yield a total nitrogen flow through detector of 40 ml/min
6.3 Retention time windows (Reference SW846 Method 8000, Section 7.5)
Before establishing windows, make sure the GC system is within optimum operating conditions. Make three injections of a mid-level standard containing all compounds of interest throughout a 72-hour period. Note: serial injections over less than a 72-hour period result in retention time windows that are too tight. Calculate the standard deviation of the three absolute retention times for each analyte. Plus or minus three times the standard deviation of the absolute retention times of each standard will be used to define the retention time window; however the experience of the analyst would weigh heavily in the interpretation of chromatograms. The laboratory must calculate new retention time windows for each standard on each GC column and whenever a new GC column is installed. The data must be retained by the laboratory.
6.4 Gas Chromatographic analysis
6.4.1 Direct Injection: 2.0 ml of the sample is injected into the GC using an automatic gas sampling valve. Sample injections are properly documented in the analytical runlog.
6.4.2 Sample dilutions: If the responses for any analyte exceed the linear range of the system, a smaller injection volume may be used on future samples. Use the results from the original analysis to determine the appropriate injection volume required to get the largest analyte peak within the upper half of the calibrated range. Quantities injected used must be documented. In the event that a sample, such as the influent, can not be analyzed by reducing the injection volume dilution using a Tedlar gas sampling bag may be used, see USEPA Reference Method 23 for use of Tedlar gas sampling bags.
6.4.3 Contamination by carryover can occur whenever high level and low level samples are sequentially analyzed. To reduce carryover, the sampling valve should be flushed with at least 100 volumes of sample prior to injection. A sample analyzed after a sample with a response outside the calibrated range will be inspected for carryover and flagged as suspect. If a sample is anticipated to be of a level close to or exceeding the calibration range, a VIBLK should be methodically analyzed.
6.5 Analyte Identification: Analyte identification is based on absolute retention time as established in Section 5.3. Establish daily retention time windows for each analyte using the absolute retention time for each analyte in the initial mid-level CC standard for that day. The daily retention time window equals the retention time plus or minus three times the standard deviation determined in Section 5.3.
6.6 Analyte Concentration: When an analyte has been identified, the concentration will be based on peak area, which is converted to concentration using the linear standard calibration curve (External standard calibration).
Concentration (mg/ml) = Calculated conc. (mg/ml) from calibration curve * D.F.
D.F. = dilution factor = Final diluted volume
Volume of sample added
7.0 Quality Control
7.1 Injector liner must be cleaned or changed if any related problems occur (i.e. increase base line, noise, integration or signal deviations)
7.2 A VIBLK must be analyzed every four hours and before the closing CC standard. This blank is taken from a zero air cylinder and analyzed by the same gas sampling valve as is used to analyze the samples. In order for the VIBLK analysis to be acceptable the blank must not have any target analytes detected at or above the reporting limit. If a VIBLK fails to meet this criteria analysis should not continue until an acceptable blank is analyzed.
7.3 Initial standard calibration must be conducted daily or for each analytical batch,, whichever is more frequent. An analytical batch is defined as a spiked soil.
7.4 For each analytical sequence, the continuing calibration check standard should be evaluated (Refer to Section 4.0) to determine if the chromatographic system is operating properly. Careful examination of the standard chromatogram can indicate whether the column is still good, the column is leaking, or the gas sampling valve is leaking or contaminated. If any changes are made to the system (e.g. column changed), and the CC standard does not met the continuing calibration criteria as outlined in Section 5.4, recalibration of the system must take place.
8.0 Compound List and Reporting Limits
8.1 Compound List given in Section 1.1
8.2. Reporting Limits
Compound reporting limits as established from the Method Detection Limit Study are (3 x MDL). Reporting limits are also evaluated based on the chromatography of the compound.