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EPA DESCRIPTION REVISIONS(DATE) COMMENTS introduction(i.e.,direct injection,purge-and-trap,vacuum distillation,automated METHOD static headspace and cartridge desorption),none of which were designed for soil Method added was a new as. For soil as samples,modifications of the introduction step are needed. Volatile Organic Compounds(VOCs)in method added[o the"Second g g P P Air Collected In Specialty-Prepared Edition'of the'Compendlum of Based on surveys conducted by DTSC of fixed and mobile laboratories that TO-15 Canisters and Analyzed By Gas "Second Edition" Methods for the Determination analyze$OII gas samples,there are two basic techniques that are current) being Chromatography/Mass Spectrometry (January 1999) of Toxic Organic Compounds In Y g P q Y g (GC/MS) Ambient Air It Is a spin-off of employed for soil gas analysis using Method 8260B/C: purge-and-trap and direct Method TO-14A. injection. Each sample introduction technique has its own advantages and disadvantages. The advantages and disadvantages of each sample introduction Method TO-17 was anew technique are summarized in Table 2. method added to the'Second Volatile Organic Compounds(VOCs)In Edition"of the'Compendium of - 'Second Edition' Methods for the Determination Table F-2: Advantages and Disadvantages of Sample Introduction Techniques TO-17 Ambient Air Using Active Sampling Onto 9 9 P q Sorbent Tubes (January 1999) of Toxic Organic Compounds In .:Ambient Air'It Is an update of Sample Introduction Advantages Disadvantages Comments Methods TO-1 and TO-2 from Technique the fust compendium(1989). A volume of soil gas Larger volumes of soil Analytes are faced into a Not recommended for sample is Injected gas sample may be water matrix and purged out polarlwater soluble (forced)into a purge-and- faced Into water to Into trap before entering into compounds. trap sparger containing achieve lower reporting GC column.Loss of target Surrogates(liquid- water.Analytes are limits with limitations. analytes possible. phased)are used but purged out of sparger into • Surrogates,Internal Depending on the type of Introduced separately the sorbent trap using standards and spikes sample container/vessel in Into sparger.Does not ;�' Helium gas.Analytes in are added Into the which the sample is actually provide true F- MODIFIED GC/MS METHODS the trap are thermally sparger before sample collected,sample may need QA/OC Info.on soil gas. desorbed Into the GC introduction and to be transferred before Ideal for higher column for separation. purging. injection Into sparger- concentration samples. A. EPA Method 8260 Soil gas volumes can potential sample loss in Not recommended for be changed by using a transfer process. low level(low smaller syringe or Law recovery of polar/water concentration)samples. EPA Method 8260(Volatile Organic Compounds by Gas Chromatography/Mass concentrated soil gas soluble compounds. Recommended for S ectromet GC/MS Is designed to determine VOCs in a varlet of solid and samples can be diluted Calibration curve not screening of oxygenates P ry( )) 9 Y In glass bulb before matrix-matched if liquid &chlorinated liquid matrices(SW-846,1996). There are two basic technical modifications made Injecting Into sparger: standards are used. compounds due to poor to this analytical method for soil gas sampling. In the first technique,a volume of soil purging efficiency. Direct Injection of soil gas Technique is quick with Limited sample size; • Recommended for gas sample is injected into the`sparge vessel(sparger)containing water and then sample Into GC column limited sample handling. threshold limit on how much screening purposes VOCs are purged out of.the sparger with helium gas onto a sorbent trap. VOCs in for separation. Holding time not an sample can be Injected into (qualitative data)and .Issue:provided samples GC column. routine monitoring of the sorbent trap are thermally desorbed into the GC column for separation and are injected immediately Lower reporting limits may limited number of known analysis. This is equivalent to EPA Method 5030(Purge-and-Trap for Aqueous after collection. hot be possible and data compounds. Samples). In the second technique,a small volume of the soil as sample is direct) No transfer ofanalytesto es may not meet the DQOs s. Calibration standards q g P y from one phase to risk assessment purposes. prepared by expansion Injected Into the GC. - another(i.e.,gas to Calibration not matrix- of liquid standards in liquid to gas). matched. vialsibulb may not be • Can handle high level amenable to all Laboratories employing a modification of EPA Method 8260 to analyze soil gas (concentrated)samples. compounds. samples should adhere to all the basic analytical requirements of the original method including purge time,calibration and Quality Assurance/Quality Control(QA/QC). Modifications for soil gas samples are outlined in the following sections. 2; Calibration EI hhtr EPA 82608 or 8260C is acceptable, 8260C is an updated version of 82606. a. One of the limitations of using EPA Method 82608 for soil gas analysis is Because the California certification program(ELAP)does not currently certify labs to the calibration technique. The current practice in most laboratories is to do 8260C,labs are certified for 82608 only. use liquid-phase standards to prepare the calibration curve. For logistical 1. Sample Introduction and economic reasons,soil gas calibration curves are prepared with liquid-phase standards. The use of liquid-phase standards may create The original EPA Method 8260 outlines five specific methods for sample biases which are undetermined. The chemical dynamics(vapor pressure, solubility,etc.)of each compound is different. The"behavior'of a 12/10/2009 -71 - 12/10/2009 -72-