Determining Total Organic Carbon in Drinking Water

EN 1484, a standard created by the European Committee for Standardization, and ISO 8245, a standard created by the International Organization for Standardization, are two of the worldwide standards utilized for the monitoring of water. These standards utilize combustion oxidation for the determination of total carbon, total organic carbon and total inorganic carbon that is present in a variety of source waters. The standardization of water monitoring greatly improves water quality in drinking water, groundwater, surface water, seawater applications and wastewater.

Due to the variety of organic materials that can be present in source water, it is imperative that a strong oxidation is utilized in order to achieve maximum carbon monoxide (CO) recovery. According to both EN 1484 and ISO 8245, multiple oxidation techniques have been historically capable of achieving this desired recovery. OI Analytical addresses this issue of multiple options through the use of both heated persulfate and combustion. In particular, the Ol Analytical Model 1080, as shown in Figure 1, is a useful instrument utilized for accurately determining the recovery of copper phthalocyanine- tetrasulfonic acid tetrasodium salt as a test material for EN 1484 and ISO 8245 compliance. Analyzing these samples through the use of combustion oxidation is a very thorough process that results in consistently high sample recoveries.

Ol Analytical Model 1080 TOC Analyzer.

Figure 1. Ol Analytical Model 1080 TOC Analyzer.

Experimental Background

Based on the theoretical molecular weight of the tetrasodium salt as stated in both EN 1484 and ISO 8245, the theoretical percent carbon is 39.049%. Therefore, a 100 ppm C solution can be prepared using 0.256 g/L of tetrasodium salt. However, the Certificate of Analysis (COA) for the copper reagent’s lot number states that the measured percent carbon is 53.48%. According to the supplier, the acceptable carbon range for this product is 21.4–56.6%. By utilizing the measured percent carbon value provided by the COA, 0.187 g/L of copper reagent was used to prepare a 100-ppm C solution.

Methodology

Although the Model 1080 supports several different oxidation methods, the non-purgeable organic carbon (NPOC)-Only method was utilized to analyze copper phthalocyanine-tetrasulfonic acid tetrasodium salt. In the NPOC Only mode, the sample is aspirated, transferred into the total inorganic carbon (TIC) chamber, acidified using 2 N hydrochloric acid, heated to 70 °C and sparged.

During the acidification process, carbonate and bicarbonate ions convert CO to CO2. This product, as well as any other dissolved CO2 present within the solution, is then removed from the sample during the sparging process followed by venting it into the atmosphere through the select manifold. An aliquot is then reclaimed by the syringe and injected into the total carbon (TC) furnace onto a quartz bed that is heated up to 680 °C. The sample is then converted into a gaseous phase that is forced through a layer of catalyst to ensure the complete conversion of all carbon-containing compounds to CO2.

Following these procedures, the solid-state non-dispersive infrared (SS-NDIR) detector is used to measure the concentration of the resulting CO2. The response by the SS-NDIR detector does not change as a result in any potential changes in sample pH or temperature, thereby allowing this instrument to avoid any potential interferences that can occur from gases such as chlorine, chlorine dioxide, sulfur dioxide, etc. When the total organic carbon (TOC) concentration present within the sample is determined, the results are reported as either ppm or ppb TOC. The initial removal of the TIC allows for replicates to be injected and processed quickly, thereby expediting the analysis process.

Results and Discussion

The TOC samples analyzed in this study were run on a Model 1080 TOC Analyzer that was calibrated at 0, 1.0, 5.0, 10.0 and 25.0 ppm C through the use of potassium hydrogen phthalate (KHP). The calibration data and method details are listed in Tables 1 and 2, respectively.

Table 1. Calibration Data.

Sample Repetitions Average Area
(counts)
% RSD Calibration R2 Response Factor
(µg C/k-cnt)
0 ppm C KHP 3 2,900 6.41 0.9997 0.1496
1 ppm C KHP 3 13,080 1.59
5 ppm C KHP 3 65,442 1.25
10 ppm C KHP 3 125,450 0.58
25 ppm C KHP 3 303,055 0.64

Table 2. Method Details.

Mode Sample Volume (mL) Acid Volume (mL) System Pressure (psi)
NPOC Only 1.0 0.1 20

Table 3 provides details on the recovery results achieved by Model 1080 in excess of 98% of operating in the combustion mode at both 10 and 100 ppm C levels according to the actual yields. These percentages clearly indicate the excellent oxidation capability provided by the Model 1080 instrument. Additionally, these values also show a more impressive performance of this combustion oxidation technique that is comparable to the wet oxidation technique. The theoretical yields are based on the stoichiometric formula that is used to synthesize the compound, which, in most cases, is higher than the actual yield. The actual yield, which is discussed in the Background section, was obtained from the manufacturer and is an indication of the efficiency of the company’s synthesis procedure.

Table 3. Recovery Results.

Sample Repetitions Average Area (counts) % RSD Calibration R2 Response Factor (µg C/k-cnt)
10 ppm C KHP 3 126,304 0.87 101.80% 135.28%
10 ppm C Theoretical 3 170,865 0.77
10 ppm C Actual 3 128.579 0.69
100 ppm C KHP 3 1,117,078 0.57 98.33% 134.38%
100 ppm C Theoretical 3 1,581,749 1.50
100 ppm C Actual 3 1,157,474 1.15

Conclusion

The COA should always be consulted prior to utilizing the copper phthalocyanine-tetrasodium salt to prepare standards for operational checks. The preparation of reagents should always be based on the percent carbon stated on the COA, rather than that which is determined by theoretical percent carbon of copper phthalocyanine-tetrasodium salt.

The exibility of the Model 1080 TOC Analyzer allows for the optimization of several difficult applications, such as copper phthalocyanine-tetrasulfonic acid, tetrasodium salt.

This information has been sourced, reviewed and adapted from materials provided by OI Analytical.

For more information on this source, please visit OI Analytical.

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