Available Laboratory Methods for Soil Gas Analysis

Transcription

1 Available Laboratory Methods for Soil Gas Analysis US EPA Soil Gas Sample Collection & Analysis Workshop San Diego, CA March 21-22, 2007 Gina M. Plantz NewFields Environmental Forensics Practice, LLC

2 Presentation Outline Importance of QA/QC Methods Overview QA/QC Considerations Case Study Data

3 Importance of QA/QC The goal of quality assurance and quality control (QA/QC) is to identify and implement sampling and analytical methodologies which limit the introduction of error into analytical data

4 Abbreviations Used CCV = Continuing Calibration Verification GC/MS = Gas Chromatograph/Mass Spectrometer HT = Holding Time ICAL = Initial Calibration ISTDs = Internal Standards LCS = Laboratory Control Sample LCSD = Laboratory Control Sample Duplicate MDL = Method Detection Limit RSD = Relative Standard Deviation RL = Reporting Limit SSTDs = Surrogate Standards TIC = Tentatively Identified Compound

5 Choosing the Correct Method 1. Target Analyte Lists Determined by your contaminants of concern 2. Reporting Limits Determined by RBCs from agency 3. Methodology Determined by answers to 1 & 2 4. Media Certification 5. Laboratory Certification

6 RLs vs. MDLs RLs = lowest point of the ICAL. MDLs = minimum concentration of an analyte that can be measured and reported with 99% confidence that the analyte concentration is >0. Statistical value determined by running a least 7 replicates of the low point in the ICAL. If lab is reporting to MDL, must J flag the data

7 ISTDs vs. SSTDs ISTDs = A known amount of a compound, which is chemically similar to the target compounds, which is added to the sample. The signal from the detection of the ISTD is used to calculate the relative response factor(s) ) (RRF) of the target compound(s). Spiked into samples immediately prior to instrumental analysis. SSTDs = A compound that is chemically similar to the analyte group but not expected to occur in an environmental sample. The recovery of the surrogate standard is used to monitor for unusual matrix effects, gross sample processing errors, etc. Spiked into samples prior to sample preparation.

8 Key Points Your Laboratory must have (and follow) a Standard Operating Procedure (SOP) for each method, which must meet or exceed the method s QA/QC criteria Modified should not equal major deviation from the method

9 Laboratory Certification Many state regulatory agencies across the country require laboratories to be certified (by method or matrix) to conduct air analysis Some states requirements may be more stringent than the method s QA/QC requirements Recommend: if the state does not have the cert. requirement, that the lab at least have NELAP certification for method NELAP= National Environmental Laboratory Accreditation Program

10 Methods Focus on US EPA Toxic Organic (TO) SW-846 QA/QC requirements differ between the methodologies that are available Major difference: TO developed for gas phase samples SW-846 developed for aqueous and solid phase

11 EPA TO Methods (1999)

12 TO-13A: SVOCs TO-13A Utilizes Polyurethane foam (PUF) and XAD-2 resin media for sample collection Lab must certify clean the media before it s sent to the field Media must be pre-spiked with field surrogate standards

13 TO-13A QA/QC HT = 7 days from collection to extract Samples must be <4C Soxhlet extraction (8270) Analysis by GC/MS MS must pass tune criteria every 12 hrs. ICAL: 5 pts. 30% RSD allowed LCS: % Recovery Blank: Targets <RLs ISTDs: -50 to +100% SSTDs: % Recovery

14 TO-17 Applicable to wide variety of VOCs Sorbent tubes Must be applicable to the VOCs of concern Many labs use standard ATD (air toxics desorption) tubes, which are applicable to a wide range of VOCs Lab must certify clean Send out 2-4 tubes per sample location

15 TO-17 Analysis Key steps in sample analysis: 1. Dry purge of the sorbent tube with dry, inert gas before analysis to remove water vapor and air 2. Thermal desorption of the sorbent tube (primary desorption) 3. Analyte refocusing on a secondary trap 4. Rapid desorption of the trap and injection/transfer of target analytes into the GC and analysis by MS

16 Example Thermal Desorption System Thermal desorption system should: - automatically leak check each tube - include a tube conditioning system - automatically add internal standards Graphic from Scientific Instruments Services, Inc. with permission

17 TO-17 Performance Criteria Four performance criteria which must be met: 1. A method detection limit of 0.5 ppbv 2. Duplicate (analytical) precision within 20% on synthetic samples of a given target gas or vapor in a typical target gas or vapor mix in humidified zero air 3. Agreement within 25% for distributed volume pairs of tubes taken in each sampling set 4. Audit accuracy within 30 percent for concentrations normally expected Field QC check

18 TO-17 QA/QC HT = 14 days from collection Samples must be <4C Analysis by GC/MS MS must pass tune criteria every 24 hrs. ICAL: 5 pts. 30% RSD allowed CCV: 30%D Blank: Targets <RLs ISTDs: +/-40% Recommend- 2 nd source standard as an LCS with % criteria LCSD to determine %RPD

19 TO-15 Sampling & Analysis for subsets of the 97 hazardous VOCs listed in Title III of the 1990 Clean Air Act. Lab must demonstrate capability of stability & recovery of all analytes Reporting limits : Full scan: 0.2 to 0.5 ppbv (~1 ug/m 3 ) SIM: to ppbv (0.011 to 0.02 ug/m 3 ) Calibration standards: NIST traceable gaseous standards Primary standards (from supplier) must have stability guarantee certificate Secondary standards (prepped by lab) are allowed a 30 day HT Samples collected in canisters Holding times: VOCs stable for up to 30 days

20 TO-15 Versus TO-14A Both canister based sampling methods TO-15 is an extended version of TO-14A with additional QA/QC TO-14A allows for non-specific detector (e.g. FID, PID, ECD) TO-15 is MS only TO-15 has additional analytes TO-15 Addendum for lower RLs (pptv levels)

21 TO-15 Prep Canister & Flow Controllers One One of the most critical QA/QC pieces for the method is the media certification

22 Media Certification & Management All canisters & flow controllers must have a unique ID and be tracked from day one Canisters should be segregated Low level (ambient & indoor) Source level (soil gas) Canister cleaning Evacuated, heated, pressurized w/humidified zero air Certification requirements No detections above RLs Leak free

23 Batch vs. Individual Batch certification: 10% check of batch cleaned together dirtiest canister is analyzed; if <RLs, then the batch is certified clean Individual certification: 100% canisters are analyzed before certified clean What do you need for your project?? A lab that has a bullet proof tracking system If you have that, then batch cert. is appropriate for most soil gas investigations Individual certs. often needed for sites which may go to litigation

24 TO-15 Analysis Entech Instruments

25 TO-15 Performance Criteria Three performance criteria which must be met: 1. A method detection limit of 0.5 ppbv 2. Duplicate (analytical) precision within 25% on synthetic samples of a given target gas or vapor in a typical target gas or vapor mix in humidified zero air 3. Audit accuracy within 30 percent for concentrations normally expected

26 TO-15 QA/QC HT = 30 days from collection Analysis by GC/MS MS must pass tune criteria every 24 hrs. ICAL: 5 pts. 30% RSD allowed (2 compounds <40%) CCV: 30%D Blank: Targets <RLs ISTDs: +/-40% Recommend: 2 nd source standard as an LCS with % criteria LCSD to determine %RPD Notice SSTDs not required

27 TO-15 QA/QC cont. Trip Blanks = evacuated canister which travels to the field & back unused Only gives information regarding that one canister and if it leaked Equipment blank = useful information Caution on use of ambient air

28 Using SW-846 Methods The EPA publication SW-846, entitled Test Methods for Evaluating Solid Waste, Physical/Chemical Methods, is OSW's official compendium of analytical and sampling methods that have been evaluated and approved for use in complying with the RCRA regulations Some SW-846 methods are allowed for soil gas analysis by some regulatory agencies Methods commonly utilized: 8260 and 8021 Can be quite useful for real-time data

29 SW-846 Sample Prep Syringes, tedlar bags, vials or glass bulbs are used for sample collection Caution: The sample media should be certified clean if site RLs are low HTs: have demonstration that vapor is stable in the media (holding time study)

30 8260 QA/QC Analysis by GC/MS MS must pass tune criteria every 12 hrs. ICAL: 5 pts. 15% RSD allowed ICV: 20%D LCS: % Blank: Targets <RLs ISTDs: % Matrix Spike (MS)/MSD: 25% RPD Recommend: to calibrate instrument (if not using gas standards), create headspace over liquid standards and inject aliquot of headspace after equilibration

31 8021 QA/QC Analysis by GC (non-specific detector) ICAL: 5 pts. 15% RSD allowed ICV: 20%D LCS: % Blank: Targets <RLs ISTDs: % Matrix Spike (MS)/MSD: 25% RPD Recommend: to calibrate instrument (if not using gas standards), create headspace over liquid standards and inject aliquot of headspace after equilibration

32 TO-15 vs. 8260B Similarities GC/MS Analysis Concentration of compounds on multi sorbent trap (but different traps and different trapping techniques) Uses ISTDs for accuracy/qc 5 point ICAL Daily CCV Quantitation by RFs

33 TO-15 vs. 8260B Differences TO-15 Standards in Air (N2) Standards in Air (N2) Sample pulled from canister using vacuum pump 3 step trapping process involving cryotrapping and refocusing before introduction onto GC/MS. Typical Calibration ug/m3 benzene ( ppbv) 8260B Standards in liquid (MeOH( MeOH) Purge and trap introduction Sample is purged from sample headspace using He or dry purging Desorption direct to GC/MS Typical Calibration ,000 ug/m3 ( ppbv for benzene)

34 RL Ranges TO B 8260B SIM TO-15 SIM Reporting Limits (ug/m 3)

35 TO-15 vs. 8021(on-site) 1,1,1-TCA, 1,1-DCE, TCE, c-1,2-dce DiGiulio 2006

36 TO-15 vs. 8260B Benzene Hayes et al. 2006

37 TO-15 vs. 8260B TCE Hayes et al. 2006

38 TO-15 vs. 8260B Naphthalene Hayes et al. 2006

39 MSRAS Data TO-15 vs TCE concentrations R 2 = TCE (ppbv) TO-15 TCE (ppbv)

40 Summary of Analytical Methods (excerpt from ITRC 2007, Table D-3) Parameter Method Sample Media/ Storage Description Method Holding Time Reporting Limit VOCs BTEX, MTBE, TPH TO-3 Tedlar Bag or Canister/Ambient Temperature GC/FID 30 days for Canister 1-3 ug/m 3 Non-Polar VOCs TO-14A Canister/ Ambient Temperature GC/ECD/FID or GC/MS 30 days for Canister 1-3 ug/m 3 Polar & Non-Polar VOCs TO-15 Canister/ Ambient Temperature GC/MS 30 days for Canister 1-3 ug/m 3 Low Level VOCs TO-15 SIM Canister/ Ambient Temperature GC/MS 30 Days ug/m 3 Polar & Non-Polar VOCs TO-17 Sorbent Tube/Chilled <4C GC/MS 30 Days 1-3 ug/m 3 VOCs 8021B modified Syringe, Tedlar bag, Glass Vial/ Ambient Temperature GC/PID On-site analysis or up to 30 days (depending on container) ug/m 3 VOCs 8260B modified Syringe, Tedlar bag, Glass Vial/ Ambient Temperature GC/MS On-site analysis or up to 30 days (depending on container) ug/m 3 SVOCs SVOCs TO-13A High volume collection (may require large sample volume; e.g. 300m 3 )/PUF/XAD media/chilled <4C GC/MS Extracted within 7 days of collection & analyzed within 40 days of extraction 5-10 ug/sample Low Level PAHs TO-13A SIM High volume collection (may require large sample volume; e.g. 300m 3 )/PUF/XAD media/chilled <4C GC/MS Extracted within 7 days of collection & analyzed within 40 days of extraction ug/sample

41 Summary Choosing the method: Many options being offered & method QA/QC criteria vary; so how do you decide??? 1. Does the regulatory agency have a method requirement? 2. Can the method meet your RL and target analyte needs? Choosing the lab: 1. Certification for method &/or matrix 2. Meet RL & target analyte needs 3. Running appropriate QA/QC for valid, defensible data