Wednesday, November 10, 2010

NCASI METHOD COLOR 71.01 (Color Detection)

Scope and Application

This method has been validated at the single and inter-laboratory level in wastewater treatment plant influents, biologically treated effluents from kraft pulp and paper mills, and receiving waters.


A. A spectrophotometer with a tungsten lamp source and a 10 nanometer (nm) spectral slit width is required. The instrument must be capable of emitting light at a selectable wavelength of 465 nm with an operating range of 400 to 700 nm.

B. Glassware should be washed with detergent, rinsed with tap water, then rinsed with reagent grade water prior to use.

Equipment for sample preparation

A. Filtration apparatus consisting of a flask, a vacuum source, and a filtration holder that will accommodate a 47-mm filter.

B. Pasteur pipettes.

C. 50-mL graduated cylinder

D. 100-mL beaker.

E. 47-mm, 1.0-μm glass fiber filters for pre-filtration

F. 47-mm, 0.8-μm membrane filters

Other apparatus

A. pH meter calibrated using a two-point calibration procedure at pH 7 and pH 8 using the appropriate buffer solutions

B. Magnetic stirrer

C. Sample cuvettes (absorption cell) for the measurement of absorbance,

Reagents and Standards


A.  Metrepak pHydrion buffer capsules, or an equivalent supplier (dibasic sodium phosphate and monobasic potassium phosphate, pH 7.0), to stabilize sample pH.

B. Organic-free reagent water in which color is not detected by this method.

Reagents for Standards

A. Potassium hexachloroplatinate, K2PtCl6 (Aldrich or an equivalent supplier),

B. Crystallized cobalt (II) chloride hexahydrate, CoCl2•6 H2O (Aldrich or and equivalent supplier)

C. Concentrated HCl.

D. Organic free reagent water.

Reagents for Sample

A. Sodium hydroxide (20%), ACS reagent grade. For pH adjustment.

B. Hydrochloric Acid (10%), ACS reagent grade. For pH adjustment.

Detail Procedure

A. Preparation of standard
1. Dissolve 1.246 g of potassium hexachloroplatinate, K2PtCl6 (Aldrich or an equivalent supplier), and 1.00 g of crystallized cobalt (II) chloride hexahydrate, CoCl2•6 H2O (Aldrich or an equivalent supplier), in a portion of organic free reagent water containing 100 mL of concentrated HCl. Dilute this solution with distilled water to the desired color value. For example, dilution to 1000 mL will provide a standard with a color value of 500 PCU. Dilution to 500 mL will provide a standard with a color value of 1000 PCU.

2. Prepare a five-point calibration curve encompassing the sample concentration range. Prepare a calibration curve by diluting 5, 10, 20, and 50 mL of 500 color unit stock solution of platinum cobalt in 100 mL of deionized water. Include the absorbance measurement of the 500 color unit stock solution of platinum cobalt in the curve. The prepared calibration standards will have color units of 25, 50, 100, 250, and 500. Take OD at 465 ηm. It is necessary to prepare a calibration curve that brackets the expected values of color in the samples.

3. Prepare a Standard Curve. Show R square equation on the chart.   y = mx + b
Where  y = absorbance of standard
            m = slope
            b = y intercept
            x = is the calculated color values

 B.  Preparation of Sample.

1. Shake the sample to ensure homogeneity and immediately measure 50 mL of the sample using a 50-mL graduated cylinder. For method blanks, measure 50 mL of reagent grade water.

2. Measure and record the sample pH (initial pH).

3. Gently open a pH 7 Metripak pHydrion (or equivalent) buffer capsule and add approximately one-half of the contents (powder only) to the sample. Stir until all of the buffer has dissolved.

4. Adjust the sample pH to 7.6 ±0.05 by adding a small volume of sodium hydroxide solution (preferably 20%) dropwise. If the pH is adjusted slightly too high, hydrochloric acid (preferably 10%) may be added dropwise to readjust the sample pH. The volume of the sample not increases more than 1%.

5. Record the adjusted pH.

6. Assemble an aspiration-type filtering apparatus and pre-wet a 0.8-μm membrane filter with approximately 1 mL of deionized and/or distilled water on each side of the membrane.

8. Gently shake off the excess water, place the filter onto the filter support, secure the filter holder/funnel in place, turn the aspirator on, and slowly add the sample.

9. Transfer the sample filtrate to a 100 mL beaker equipped with a Teflon stir bar. Place the beaker on a mechanical stir plate and gently stir the sample. And once again check pH of the sample. If adjustment required than the sample will again filtered through 0.8-μm membrane filter.

10. Take OD at 465 ηm.

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