ASTM: D6508: Anions in Water by CIE-UV

Summary
Analytes
Revision
Data and Sites

Official Method Name

Standard Test Method for Determination of Dissolved Inorganic Anions in Aqueous Matrices Using Capillary Ion Electrophoresis and Chromate Electrolyte

Current Revision

Current edition approved Jan. 10, 2000. Published April 2000.

Media

WATER

Instrumentation

Capillary Ion Electrophoresis with Indirect UV Detection

Method Subcategory

Inorganic

Method Source

ASTM

Citation

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

Brief Method Summary

Capillary ion electrophoresis is a free zone electrophoretic technique optimized for the determination of anions with molecular weight less than 200. The anions migrate and are separated according to their mobility in the electrolyte when an electrical field is applied through the open tubular fused silica capillary. The electrolyte's electroosmotic flow modifier dynamically coats the inner wall of the capillary changing the surface to a net positive charge. This reversal of wall charge reverses the natural EOF. The modified EOF in combination with a negative power supply augments the mobility of the analyte anions towards the anode and detector achieving rapid analysis times. Cations migrate in the opposite direction towards the cathode and are removed from the sample during analysis. Water and other neutral species move toward the detector at the same rate as the EOF. The neutral species migrate slower than the analyte anions and do not interfere with anion analysis.
The sample is introduced into the capillary using hydrostatic sampling. The inlet of the capillary containing electrolyte is immersed in the sample and the height of the sample raised 10 cm for 30 s where low nanolitre volumes are siphoned into the capillary. After sample loading, the capillary is immediately immersed back into the electrolyte. The voltage is applied initiating the separation process.
Anion detection is based upon the principles of indirect UV detection. The UV-absorbing electrolyte anion is displaced charge-for-charge by the separated analyte anion. The analyte anion zone has a net decrease in background absorbance. This decrease in UV absorbance in quantitatively proportional to analyte anion concentration (see Fig. 9 in the method). Detector output polarity is reversed to provide positive mV response to the data system, and to make the negative absorbance peaks appear positive.
The analysis is complete once the last anion of interest is detected.

Scope and Application

This test method cover the determination of the inorganic anions fluoride, bromide, chloride, nitrite, nitrate, ortho-phosphate, and sulfate in drinking water, wastewater, and other aqueous matrices using capillary ion electrophoresis (CIE) with indirect UV detection. The test method uses a chromate-based electrolyte and indirect UV detection at 254 nm. It is applicable for the determination or inorganic anions in the range of 0.1 to 50 mg/L except for fluoride whose range is 0.1 to 25 mg/L.

Applicable Concentration Range

0.1-50 except fluoride which is 0.1-25 mg/L

Interferences

Analyte identification, quantitation, and possible comigration occur when one anion is in significant excess to other anions in the sample matrix. For two adjacent peaks, reliable quantitation can be achieved when the concentration differential is less than 100:1. As the resolution between two anion peaks increase so does the tolerated concentration differential. In samples containing 1000 mg/L Cl, 1 mg/L SO₄ can be resolved and quantitated, however, the high Cl will interfere with Br and NO₂ quantitation.
Carbonate concentrations greater than 500 mg/L will interfere with PO₄ quantitation.
Formate, a common organic acid found in environmental samples, migrates shortly after fluoride but before phosphate. Formate concentrations greater than 5 mg/L will interfere with fluoride identification and quantitation. Inclusion of 2 mg/L formate into the mixed anion working solution aids in fluoride and formate identification and quantitation.
Divalent organic acids usually found in wastewater migrate after phosphate. At high concentrations, greater than 10 mg/L, they may interfere with phosphate identification and quantitation.
Chlorate also migrates after phosphate and at concentrations greater than 10 mg/L will interfere with phosphate identification and quantitation. Inclusion of 5 mg/L chlorate into the mixed anion working solution aids in phosphate and chlorate identification and quantitation.
As analyte concentration increases, analyte peak shape becomes asymmetrical.

Quality Control Requirements

Minimum quality control requirements are initial demonstration of proficiency, plus calibration verification, 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.

Sample Handling

Collect samples in accordance with Practice D 3370. Rinse sample containers with sample and discard to eliminate any contamination from the container. Fill to overflowing and cap to exclude air.
Analyze samples, as soon as possible, after collection. For nitrite, nitrate, and phosphate refrigerate the sample at 4^oC after collection. Warm to room temperature before dilution and analysis.
At the laboratory, filter samples containing suspended solids through a prerinsed 0.45 um aqueous compatible membrane filter before analysis.
If sample dilution is required to remain within the scope of this test method, dilute with water only.

Maximum Holding Time

Relative Cost

$201 to $400

Sample Preparation Methods

This method has 8 analytes associated with it.

Analyte	Detection Level	Bias	Precision	Spiking Level
Bromide(24959-67-9) Bromide Bromide (9CI) Bromide ion (-1)	0.132 mg/L	103% Rec (ML)	6.60	2.00 mg/L
Chloride(16887-00-6) Chloride Chloride ion	0.073 mg/L	99% Rec (ML)	6.80	2.00 mg/L
Fluoride(16984-48-8) Fluoride	0.032 mg/L	103% Rec (ML)	3.70	2.00 mg/L
Nitrate(14797-55-8) Nitrate Nitrate ion Nitrate-N Nitrates/nitrites Nitrogen, nitrate	0.082 mg/L	142% Rec (ML)	8.10	1.99 mg/L
Nitrate/nitrite(E-10128) NO2+NO3 NO2/NO3 NO3+NO2 Nitrate + nitrite Nitrate plus nitrite Nitrate+nitrite Nitrate/nitrite Nitrite + nitrate Nitrite+nitrate	N/A	N/A	N/A
Nitrite(14797-65-0) Nitrite Nitrite (as ion) Nitrite nitrogen Nitrite-N Nitrites Nitrogen, nitrite	0.102 mg/L	66% Rec (ML)	19.20	2.00 mg/L
Phosphate(14265-44-2) Orthophosphate Orthophosphate, total Phosphate Phosphorus (as phosphate) Phosphorus, phosphate, ortho Reactive phosphorus Total orthophosphate Total phosphorus	0.102 mg/L	95% Rec (ML)	8.30	1.99 mg/L
Sulfate(14808-79-8) Sulfate Sulfate (as ion) Sulphate (as ion)	0.066 mg/L	103% Rec (ML)	9.70	1.98 mg/L

Precision Descriptor Notes:	This test method interlaboratory collaborative was performed by 11 laboratories using one operator each. Four Youden-Pair spike concentrations for the seven analytes anions yielding eight analyte concentration levels. Test data were submitted for eleven reagent waters, eleven substitute wastewaters, 15 drinking waters, and 13 wastewater sample matrices. The precision, bias, and matrix recovery of this test method per anion analyte in four tested sample matrices are based upon the analyte true value, calculated using weight, volume, and purity. All collaborative participants used the premade chromate electrolyte. Ten laboratories used a Waters CIA Analyzer with Millennium Data Processing Software, and one laboratory used a Agilent CE System with Diode Array Detector that provided equivalent results.
Detection Level Note:	Spiking Solution No. 9, containing 10 mg/L of each analyte, was diluted 1:50 with water and was used for detection limit calculations. Seven replicate samplings were run, and the mean and standard deviation were calculated.

Precision Descriptor Notes:

This test method interlaboratory collaborative was performed by 11 laboratories using one operator each. Four Youden-Pair spike concentrations for the seven analytes anions yielding eight analyte concentration levels. Test data were submitted for eleven reagent waters, eleven substitute wastewaters, 15 drinking waters, and 13 wastewater sample matrices. The precision, bias, and matrix recovery of this test method per anion analyte in four tested sample matrices are based upon the analyte true value, calculated using weight, volume, and purity. All collaborative participants used the premade chromate electrolyte. Ten laboratories used a Waters CIA Analyzer with Millennium Data Processing Software, and one laboratory used a Agilent CE System with Diode Array Detector that provided equivalent results.

Detection Level Note:

Spiking Solution No. 9, containing 10 mg/L of each analyte, was diluted 1:50 with water and was used for detection limit calculations. Seven replicate samplings were run, and the mean and standard deviation were calculated.

Revision	PDF/Link
Current edition approved Jan. 10, 2000. Published April 2000.

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ASTM: D6508: Anions in Water by CIE-UV

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