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Standards Development
This document specifies a method for optimizing measurements of the total organic carbon (TOC) content in water samples containing high loads of suspended solids (SSs) with particulate organic carbon (POCsusp) (e.g., waste water, storm water, raw water, surface water, and sea water), following a combined ultrasonic and alkaline extraction (CUAL) sample-pretreatment method. The method shall use a turbidity ratio (i.e., NTU5/NTU0) to evaluate the adequacy the pretreatment for samples containing SSs as an evaluation index of sample homogeneity (10.2). The analysis procedure shall be outperformed instrumentally using a differential method (e.g., TC-TIC) to quantify TOC.
TOC is an organic water pollution index that expresses the total amount of particulate organic carbon (POCsusp) and dissolved organic carbon (DOC) in water. Accurately measuring TOC including POCsusp is crucial for evaluating the environmental impact of various particulate organic matter derived from inside and outside of a water system, as well as evaluating the mass balance with respect to the carbon cycle. Obtaining reliable TOC data for wastewater samples (influent water, process water, discharge water, etc.) containing particulate organic pollutants from various sources is also important for process management and environmental impact evaluation.
However, TOC data are influenced by sample matrices and the content and properties of SSs, including POCsusp. In particular, during the analysis of samples containing large amounts of SSs, sample handling, instrument set, and quantitative method selection considerably influence the accuracy and precision of the TOC measurements.
This NP specifies an optimized analytical procedure that ensures high accuracy and precision in TOC measurements for water samples containing high loads of particulate organic matter and includes a pretreatment, and the measurement steps to follow.
The NP method differs from existing ISO test methods (ISO 8245, ISO 20236, ISO 21793) for TOC analysis in the following ways:
a) A novel sample pretreatment method—combined ultrasonic and alkaline extraction (CUAL) pretreatment—that ensures sample homogeneity via dissolution of the POC components in SSs to DOC and induces a particle size reduction is adopted.
b) Use of the turbidity index (i.e., NTU5/NTU0) makes it easy to evaluate the suitability of the pretreatment for particle samples as an evaluation index of sample homogeneity.
c) The differential method (e.g., TC-TIC) shall be applied for quantifying the TOC of particle-containing water samples following CUAL pretreatment. The TC-TIC method minimizes the loss of POCsuspderived purgeable organic carbon generated during sonication in the CUAL pretreatment process.
d) In addition to using standard cellulose particles, particle samples of environmental origin shall be used for ensuring quality control of samples containing SSs and for particle-processing control.
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