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EPA/ORD has recently completed a two-part study of the effect of heating and <br /> acidification on MtBE in groundwater samples (White et al , 2002, 2003) The first part <br /> dealt with the rate of hydrolysis of MtBE at 80°C at pH I and pH 2, using headspace <br /> analysis where the sample is heated statically for 30 minutes (EPA Method 8021) They <br /> found that at pH 2, 6% of the MtBE hydrolyzed to TBA and that 57% of the MtBE <br /> hydrolyzed to TBA at pH I The second part of the study involved analysis of diluted and <br /> undiluted replicate samples from an MTBE plume in California The samples were <br /> acidified in the field to a pH of<2 and analyzed using the same static headspace sampler <br /> As expected, diluted samples with corresponding diluted acid reduced the rate of MtBE <br /> hydrolysis to TBA In undiluted samples, 22 to 89% hydrolysis of MTBE was reported <br /> In diluted samples (1 10 dilution), the fraction of MtBE hydrolyzed ranged from I to <br /> 18% These studies have prompted EPA/ORD to consider proposing addition of <br /> trisodium phosphate (TSP) to raise the pH of groundwater samples for preservation <br /> instead of acid addition No studies have been done to determine potential impact of this <br /> preservation change to analysis of VOAs <br /> In further study (Lin, et al , 2003) acid hydrolysis was identified when samples at pH < 2 <br /> were heated in headspace sampling at 80°C No acid hydrolysis was seen in storage (28 d <br /> at 4°C), and none was seen if the pH of the stored samples was adjusted prior to heating <br /> It is important to state that, to the best of our knowledge, there are no commercial <br /> laboratories that are currently using EPA Methods 5021 (static headspace) for the <br /> analysis of VOAs (including oxygenates) The static headspace method is seldom used <br /> for water samples <br /> All of the California laboratories that we surveyed used purge and trap procedures (EPA <br /> Method 5030) where the samples are either not heated, or are heated to a maximum of <br /> 45°C while purged with helium at 40mL/min for 11 minutes Some labs have a preheat <br /> time which is typically less than 3 minutes The maximum concentration of MtBE that <br /> can be analyzed without dilution is typically X200 gg/L These conditions are markedly <br /> different from the static headspace analysis where the samples are heated at 80°C in the <br /> presence of acid with no purge for 30 minutes <br /> Recent studies using typical field and laboratory conditions indicate that acid hydrolysis <br /> of MtBE in properly handled groundwater samples do not compromise the integrity of <br /> dissolved MtBE and TBA analysis <br /> • A recent study done by Handex using EPA Method 624 (purge and trap with <br /> GC/MS) found no conversion of MtBE to TBA Water samples were spiked with <br /> 200, 2000, 20000 µg/L MtBE, stored at 4"C and acidified to a pH 52 with various <br /> holding times of up to 31 days Unpreserved control samples were also analyzed <br /> No TBA concentrations were detected <br /> • A study done by SPL at the request of Marvin Katz (Shell Oil Products US) <br /> consisted of analysis of 200 gg/L MtBE in HCl preserved, unpreserved and <br /> heated and unheated samples showed no detectable TBA <br /> 21 <br />