Stability of volatile organic compounds in environmental water samples during transport and storage

Abstract

The stability of volatile organic compounds in environmental water samples has been studied, particularly with respect to the establishment of preanalytical holding times. Methods have been developed for the preparation of standard samples containing known concentrations of volatile organics. Three water samples were used: distilled water, surface water, and groundwater. Samples were stored at both room temperature and under refrigeration. Data were collected over a 365-day period by gas chromatography /mass spectrometry. In water samples containing low chloride content (distilled water), rapid dehydrohalogenation of tetrachloroethane to trichloroethylene occurred. Such degradation was also evident in the surface water and groundwater samples stored at room temperature. A less rapid conversion of trichloroethane to dichloroethylene occurred in distilled water samples stored at 25 °C. Reduced concentrations of aromatic volatiles were observed in both surface and groundwater matrices after 28 days. Loss of carbon tetrachloride was also apparent in surface water samples stored at room temperature. Subsequently, experiments were conducted to determine the value of reduced pH in sample preservation. It was shown that acidification with hydrochloric acid effectively prevented degradation and allowed indefinite storage. However, sampling and analytical considerations make the use of HC1 impractical. Therefore, a study was carried out using sodium bisulfate and ascorbic acid as preservatives. Both substances effectively preserved the samples, but sodium bisulfate proved to have several advantages over ascorbic acid. Samples preserved with either acid were stable over the 112-day experimental period.The implication is that with preservation the maximum holding times for such samples will be limited only by the need for sample turnaround.

Preliminary evaluation of selected in situ remediation technologies for Volatile Organic Compound contamination at Arid sites

“…As a general rule, the reaction rates in solutions near room temperature increase approximately 2.5 times for an increase in solution temperature of I0°C. This trend was observed by Maskarinec et al (1990) for the hydrolysis of several alkyl halides in distilled water and surface-water samples at 4°C and 25°C. Similar experiments by these investigators with groundwater samples, however, did not produce conclusive trends,…”

“…For example, the HMCRI (1987) summary confirms that chloroform hydrolysis is accelerated by increasing pH but methylene chloride hydrolysis is not. Conversely, the addition of hydrochloric acid or sodium bisulfate to achieve a pH of 2 consistently decreased the hydrolysis rate for the alkyl halides studied by Maskarinec et al (1990).…”

“…hydrolysis of organic compounds results in the formation of intermediate products rather than a complete decomposition to innocuous compounds.All the alkyl-halide compounds of the ID host site are susceptible to hydrolysis to varying extent Maskarinec et al (1990). conducted experiments to determine the maximum length of time that ground-and surface-water samples could be held prior to analysis without significant changes in concentrations of various contaminants, including alkyl-" halide VOCs.…”

Performance Evaluation of a Thermal Desorption/Gas Chromatographic/ Mass Spectrometric Method for the Characterization of Waste Tank Headspace Samples

“…A holding time study was conducted on a representative subset of the target analytes (Table 4) using the practical reporting time (PRT) method developed by Bayne et al (28,29). A holding time study was conducted on a representative subset of the target analytes (Table 4) using the practical reporting time (PRT) method developed by Bayne et al (28,29).…”

An automated purge and trap gas chromatography-mass spectrometry system for the sensitive shipboard analysis of volatile organic compounds in seawater

“…Typically, seawater samples collected for the analysis of VOCs must be preserved and analyzed later in a land-based laboratory. Although halocarbons have reportedly remained stable for many months in environmental water that has been acidified and stored under refrigeration [11], the stability of halocarbons has not been confirmed within a few hours after sampling. The concentration of DMS is less stable, as DMS can be produced by the decomposition of dimethylsulfoniopropionate (DMSP) generated by marine organisms, particularly phytoplankton [12].…”