DOI: 10.5061/dryad.g1jwstr34
title: Unwanted loss of volatile organic compounds (VOCs) during in situ chemical oxidation sample preservation: Mechanisms and solutions

description: 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.
description: # Unwanted loss of volatile organic compounds (VOCs) during in situ
 chemical oxidation sample preservation: Mechanisms and solutions Dataset
 DOI: [10.5061/dryad.g1jwstr34](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.