ASTM: D6317: Carbon (all forms) in Water
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Official Method Name
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Standard Test Method for Low Level Determination of Total Carbon, Inorganic Carbon and Organic Carbon in Water by Ultraviolet, Persulfate Oxidation, and Membrane Conductivity Detection |
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Current Revision
| Current edition approved Sept. 10, 1998. Published November 1998. |
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Media
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WATER |
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Instrumentation
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Total Organic Carbon Analyzer |
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Method Subcategory
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Organic |
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Method Source
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Citation
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Brief Method Summary
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Carbon can occur in water as inorganic and organic compounds. This test method can be used to make independent measurements of IC and TC and can also determine TOC as the difference of TC and IC. If IC is high relative to TOC it is desirable to use a vacuum degassing unit to reduce the IC concentration as part of the measurement. Alternatively, the IC can be removed by acidifying and sparging the sample prior to injection into the instrument. The basic steps of the procedure are as follows:(1) Removal of IC, if desired, by vacuum degassing;(2) Conversion of remaining inorganic carbon to CO2 by action of acid in both channels and oxidation of total carbon to CO2 by action of ultraviolet (UV) radiation in the TC channel. (Acid-persulfate can be added but is usually not required at TOC levels below 1 ppm).(3) Detection of CO2 that is swept out of the U.V. reactor and delay coil by the liquid stream and passed through membranes that allow the specific passage of CO2 to high purity water where change in conductivity is measured and;(4) Conversion of the conductivity detector signal to a display of carbon concentration in parts per million (ppm=mg/L) or parts per billion (ppb=mg/L). The IC channel reading is subtracted from the TC channel to give a TOC reading. A diagram of suitable apparatus is given in Fig. 1 of the method. References 1-5 provide additional information on the method. |
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Scope and Application
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This test method covers the determination of total carbon (TC), inorganic carbon (IC), and total organic carbon (TOC) in water in the range from 10 to 1000 ug/L of carbon. This method is for laboratory or grab sample applications. |
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Applicable Concentration Range
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10-1000 ug/L |
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Interferences
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The oxidation of dissolved carbon to CO2 is brought about at relatively low temperatures by the chemical action of reactive species produced by UV-irradiated persulfate ions and water. Not all suspended or refractory material may be oxidized under these conditions; analysts should take steps to determine what recovery is being obtained. Chloride ion above 250 mg/L tends to interfere with oxidative reaction mechanisms in this test method. Note that error will be introduced when the method of difference is used to derive a relatively small level from two large levels. In this case the vacuum degassing unit on the instrument should be used to reduce the concentration of IC prior to measurement. Alternatively, the sample can be acidified and sparged prior to introduction into the instrument. Use of the vacuum degassing unit or sparging the sample may cause loss of volatile organic compounds, thus yielding a value lower than the true TOC level. At low TOC levels, the degassing unit may introduce a measurable TOC and IC background. Contamination of the sample with both CO2 and organic carbon is a severe problem as lower levels of analyte are attempted. |
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Quality Control Requirements
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Minimum quality control requirements are initial demonstration of proficiency, plus analysis of method blanks, quality control samples, and recovery spikes and, duplicate samples. For a general discussion of quality control and good laboratory practices, see Practices D 4210 and D 5789 and Guide D 3856. |
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Sample Handling
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Collect the sample in accordance with Specification D 1192 and Practices D 3370. Samples must be collected in contamination free bottles sealed with a fluoropolymer lined septa. Specially cleaned (for TOC) 40 ml bottles are commercially available. The sample bottle should be rinsed several times with the sample, filled, and then tightly sealed. To preserve samples for this analysis, store samples in glass at 4oC. To aid preservation, acidify the samples to a pH of 2. It should be noted that acidification will enhance loss of inorganic carbon. If the purgeable organic fraction is important, fill the sample bottles to overflowing with a minimum of turbulence and cap them using a fluoropolymer-lined cap, without headspace. For accurate measurements of samples containing < 0.5 mg/L stringent measures must be taken to minimize contamination. Low level samples exposed to ambient air will generally increase in both inorganic and organic carbon. Sample container and all sampling devices must be clean and exposure of the sample to the atmosphere must be minimized. Blanks should be carried through all steps of the sampling and analysis procedure to check for contamination. |
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Maximum Holding Time
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Relative Cost
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$51 to $200 |
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Sample Preparation Methods
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