Unwanted loss of volatile organic compounds (VOCs) during in situ chemical oxidation sample preservation: Mechanisms and solutions
Data files
May 06, 2025 version files 8.62 KB
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JHML_Tae_Scavenger_Rawfile_FIgure_2.csv
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JHML_Tae_Scavenger_Rawfile_Figure1.csv
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README.md
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Abstract
To assess the performance of hazardous waste sites remediation technologies like in situ chemical oxidation (ISCO) with persulfate (S2O82−) researchers must periodically measure concentrations of target contaminants. Due to the presence of relatively high concentrations of the residual oxidant expected in many samples, the standard analytical method requires the addition of a relatively high concentration of ascorbic acid to prevent the oxidation process from continuing after sample collection. We discovered that addition of ascorbic acid quencher results in a radical chain reaction that transforms two common halogenated solvents (i.e., tetrachloroethene and hexachloroethane). To avoid the artifact associated with the radical chain reaction, a small quantity of n-hexane can be added to aqueous samples to extract target compounds and protect them from the radical chain reaction initiated by addition of the quencher. We recommend the use of this alternative sample preservation method whenever high concentrations of residual S2O82− are expected to be present in water samples that are contaminated with halogenated solvents.
Dataset DOI: 10.5061/dryad.g1jwstr34
Description of the data and file structure
This dataset contains raw and processed GC/MS data supporting Figures 1 and 2 in the associated manuscript, which examine unintended transformations of volatile organic compounds (VOCs) during sample preservation in in situ chemical oxidation (ISCO) experiments using persulfate and ascorbic acid. There are no blank cells in the data column. All values represent either detected signals.
Files and variables
File: JHML_Tae_Scavenger_Rawfile.xlsx
Figure 1 data: Artifact Formation During Preservation with Ascorbic Acid
The csv sheet titled “Figure 1” presents the experimental data demonstrating how the addition of ascorbic acid as a preservative in the presence of residual persulfate initiates a radical chain reaction that degrades halogenated solvents.
- Columns A–I: Time series data (in minutes; 0, 0.083, 15, 30, 45, 60 min) and GC/MS peak areas of tetrachloroethene (PCE) and hexachloroethane (PCA), and persulfate concentration which was measured by colorimetric method (KI/KIO3 actinometry) normalized to initial concentration and replicate data for compariosn to check the reproducibility as a function of time.
- Columns K–S: Normalized concentration levels of compounds (PCE, PCA, and persulfate) as a function of time.
- Columns U–AC: Final normalized values of compounds (PCE, PCA, and persulfate) (e.g., averages and standard deviations of normalized concentration level at each time points) used in plotting Figure 1.
- Columns I, S, and AC: Standard deviations were calculated from duplicate experimental runs. A value of zero indicates that the two measurements were identical.
This figure illustrates the mechanism by which target analytes are unintentionally transformed after sample collection, emphasizing the risks of artifact formation when high concentrations of oxidant and quenching agent are both present.
Figure 2 data: Effectiveness of n-Hexane Extraction as a Preservation Strategy
The “Figure 2” csv sheet evaluates the use of n-hexane extraction as a protective measure to prevent radical-driven loss of halogenated solvents during sample preservation.
- Columns A–E: GC/MS peak area data for tetrachloroethene (PCE) and hexachloroethane (HCA) at low (5 µM) and high (50 µM) concentrations over time (0, 3, 7, and 14 days) after n-hexane extraction of synthetic ISCO site samples.
- Columns F–O: Final normalized values and their averages and standard deviations used in plotting Figure 2.
The results show that pre-extracting aqueous samples with n-hexane effectively isolates VOCs and prevents their transformation, offering a practical solution to avoid false degradation artifacts in samples with residual oxidant and unexpected artifacts which might be occured during the conventional U.S. EPA oxidant scavenging procedure (injecting ascorbate solution).
Code/software
We do not have any code/software.
Access information
Data was derived from the following sources:
- Our data was generated through experimental procedures.