Analytical Method: Color, ADMI as per APHA 2120 F

Instruments and reagents:

Cat.No. 100706  Spectroquant® Spectrophotometer Pharo 100 or
Cat.No. 100707  Spectroquant® Spectrophotometer Pharo 300
Cat.No. 114946  Rectangular cells 10 mm and/or
Cat.No. 114944  Rectangular cells 50 mm
Cat.No. 116754  Water for analysis
Cat.No. 100716  Sulfuric acid 25 % for analysis
Cat.No. 105588  Sodium hydroxide solution min. 10 % for analysis 
Cat.No. 100246  Platinum Cobalt Color Reference Solution (HAZEN 500) with 500 mgl/l Pt
Membrane filter, max. pore size 0.45 µm

 
Method:
Spectrophotometric measurement in the range 400 – 700 nm at 10-nm intervals. Evaluation acc. to (see the literature 1)).

 
Measuring range:

10  – 500    units Pt-Co in the 10-mm rectangular cell (method No. 2517)
2.0 – 100.0 units Pt-Co in the 50-mm rectangular cell (method No. 2518)

 
Working instructions:

Sample preparation:
Filter turbid sample solutions over a membrane filter.
To do this, first pre-rinse the membrane filter with approx. 50 ml of water GR, subsequently re-rinse with approx. 50 ml of sample, and discard the filtrate.
Filter a further 50 ml of sample over the pre-rinsed membrane filter and collect the filtrate for analysis.
 
Zeroing the photometer:
The photometer must be zeroed prior to the measurement of the sample. To do this call up the respective stored method (No. 2517 or 2518) and fill the corresponding cell (10-mm or 50-mm cell) with water GR.
Subsequently press the BLANK ZERO key of the photometer and select “Zero photometer”. Insert the cell into the compartment to start the zeroing procedure.
Zeroing the photometer immediately prior to the analysis of the sample enhances the accuracy of the measurement.

Measurement at the original pH:
Fill the sample into the rectangular cell. Insert the cell into the compartment to start the measurement procedure. The measurement result is subsequently shown in the photometer display.

Measurement at pH 7.0:
Check the pH of the sample and adjust, if necessary, to pH 7.0 with sulfuric acid or sodium hydroxide solution. Fill the pH 7.0 sample into the rectangular cell. Insert the cell into the compartment to start the measurement procedure. The measurement result is subsequently shown in the photometer display.

Note:
When performing serial measurements, the measurement accuracy can be enhanced by re-zeroing the photometer prior to each separate sample measurement.

Calibration:
The user can recalibrate the method by means of one-point calibration. A platinum-cobalt color-reference solution is used for the calibration. This original concentration of use (500 units Pt-Co [500 Hazen]) must be diluted to a value in the middle of the selected measurement range using water GR.

The method is calibrated in the following manner:
1. Press the BLANK ZERO key and select “Calibrate method”.
The message “Zero necessary” appears in the display. Acknowledge by pressing the START/ENTER key.
2. Fill the corresponding cell with water GR and insert the cell. The zeroing operation starts automatically. After the operation is complete, the message “Zeroing successful” appears. Acknowledge by pressing key F4 “OK”.
3. The message “Please key in value of standard” appears. Press key F2 “Standard”, use the alphanumeric keyboard to key in the Pt-Co value of the standard, and acknowledge by pressing the START/ENTER key.
4. Fill diluted calibration solution into the cell. Subsequently press the BLANK ZERO key of the photometer and select “Calibrate method”. Insert the cell into the compartment to start the calibration procedure.
5. The message “Calibration successfully completed” appears, as do also the keyed-in values of the standard and the calculated factor.
Acknowledge the calibration by pressing the F4 key. The calculated factor overwrites the default factor of 1400.

 
 
Results of comparative measurements of the ADMI color measurement:
Measurement of Pt-Co standards on various spectrophotometers:
 
 

10 mm cell
units Pt-Co
Merck
Pharo 100
Merck
Pharo 300
Hach
DR 5000
0 < 10 < 10 1
10 11 11 10
15 15 19 14
20 20 22 20
50 51 49 47
100 101 102 95
175 179 174 169
250 250 251 240
325 323 328 out of range
400 397 397 out of range
500 499 495 out of range

 

 

 

 

55 mm cell
units Pt-Co
Merck
Pharo 100
Merck
Pharo 300
Hach
DR 5000
0.0 < 2.0 < 2.0 0
2.5 2.5 3.7 3
5.0 5.1 5.0 5
10.0 9.9 11.1 10
15.0 14.5 14.6 20
20.0 20.1 20.4 20
50.0 49.9 51.9 51
100.0 97.5 97.5 97

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 
Literature:
1. Allen, W.; Prescott, W. B.; Derby, R. E.; Garland, C. E.; Peret, J. M.; Saltzman, M.; 1973. Determination of color of water and wastewater by means of ADMI color values. Proc. 28th Ind. Waste Conf., Purdue Univ., Eng. Ext. Ser. No. 142:661ff
2. Standard Methods for the Examination of Water and Wastewater, 21th Edition,
APHA 2120 F
3. McClaren; The Adams-Nickerson Color Difference Formula; J. of the Society of Dyers and Columnists; 86, 354ff
4. Bridgeman; Inversion of the Munsell value equation; J. of Optical Society of America; 1953; 499ff

 

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