ASTM: D5997: Carbon (all forms), On-Line Measurement in Water

Summary
Analytes
Revision
Data and Sites

Official Method Name

Standard Test Method for On-Line Monitoring of Total Carbon, Inorganic Carbon in Water by Ultraviolet, Persulfate Oxidation, and Membrane Conductivity Detection

Current Revision

Reapproved 2000. Current edition approved July 10, 1996.

Media

WATER

Instrumentation

Membrane Conductivity Detection

Method Subcategory

Organic

Method Source

ASTM

Citation

Annual Book of ASTM Standards, Section 11, Water and Environmental Technology, Volume 11.01, Water (I)

Brief Method Summary

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 between TC and IC. If IC is high relative to TOC, it is desirable to use a vacuum degassing unit to reduce the IC concentration to obtain meaningful TOC values by difference.
The basic steps of this test method are:1) Conversion of remaining IC to CO₂ by action of acid, 2) Removal of IC, if desired, by vacuum degassing, 3) Split of flow into two streams to provide for separate IC and TC measurements, 4) Oxidation of TC to CO₂ by action of acid-persulfate aided by ultraviolet (UV) radiation in the TC channel, 5) Detection of CO₂ by passing each liquid stream over membranes that allow the specific passage of CO₂ to high-purity water where change in conductivity is measured, and 6) Conversion of the conductivity detector signal to a display of carbon concentration in parts per million (ppm = mg/L) or parts per billion (ppb = ug/L). The IC channel reading is subtracted from the TC channel reading to give a TOC reading.

Scope and Application

This test method covers the on-line determination of total carbon (TC), inorganic carbon (IC), and total organic carbon (TOC) in water in the range from 0.5 g/L to 50 000 g/L of carbon.

Applicable Concentration Range

0.5-50,000 ug/L

Interferences

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. Not all suspended or refractory material may be oxidized under these conditions.
Other interferences have been investigated and found to be minimal under most conditions. The membrane is hydrophobic in nature and passes only gaseous materials. Potential interferences are nitrite, sulfide, and high levels of hypochlorite or iodine.
Use of the vacuum degassing unit or sparging the sample renders the IC reading meaningless and 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.

Quality Control Requirements

Instrument calibration must be performed according to the manufacturer's schedule and instructions.
Instrument calibration and blank readings must be checked whenever reagents or UV lamps are changed. The calibration check should be carried out with a different calibration material and concentration than that used for the instrument calibration.
Resin quality should be checked at the same frequency as UV lamp replacement. In the on-line mode with the UV lamp off, measure low TOC water (< 100 mg/L) that has been deionized to a resistivity of > 18 Mohm-cm. If either the TC or IC channel measures > 10 ug/L, the resin may need replacement.
The user should confirm that the unit is giving proper response using the sample matrix with compound types of interest and operating under the environmental extremes of interest.

Sample Handling

Collect the sample in accordance with Specification D 1192 and Practices D 3370.

Maximum Holding Time

Relative Cost

Unknown

Sample Preparation Methods

This method has 1 analyte associated with it.

Analyte	Detection Level	Bias	Precision	Pct False Positive	Pct False Negative	Spiking Level
Carbon(7440-44-0) Carbon	0.060 ug/L	97	1.00			15.00 ug/L

Precision Descriptor Notes:
Detection Level Note:	The limit of detection (LOD) for this test method was estimated by plotting the standard deviation for each of the three lowest concentrations against the analyzed concentration. From this data the y-intercept is considered to be the best estimate of the precision at zero concentration (S₀). The S₀ value was determined to be 0.020 mg/L. The LOD is assigned as three times S₀ or 0.060 mg/L. This data supports the assigned limit of quantitations (LOQ) of 0.5 mg/L.

Precision Descriptor Notes:

Detection Level Note:

The limit of detection (LOD) for this test method was estimated by plotting the standard deviation for each of the three lowest concentrations against the analyzed concentration. From this data the y-intercept is considered to be the best estimate of the precision at zero concentration (S₀). The S₀ value was determined to be 0.020 mg/L. The LOD is assigned as three times S₀ or 0.060 mg/L. This data supports the assigned limit of quantitations (LOQ) of 0.5 mg/L.

Revision	PDF/Link
Reapproved 2000. Current edition approved July 10, 1996.

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ASTM: D5997: Carbon (all forms), On-Line Measurement in Water

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