How to determine copper in industrial water
Copper Photometric Method (0-5 ppm)
The main purpose for determining copper in industrial water is an indication of corrosion somewhere in the system. Chemical factors that cause corrosion of the copper alloys include low pH, ammonia, cyanides, hydrogen sulfide, sulfur and compounds. Although the corrosion rates of copper alloys in industrial waters are usually not high enough to produce significant degradation of the copper components themselves, dissolved copper can cause other operational problems. For example, dissolved copper tends to plate out on steel components in a system; this creates cell action that can cause serious pitting of the steel in both cooling and boiler systems. For these reasons the copper test is designed to give accurate low level measurements.
Theory of Test
This test is based on the development of a brown-yellow color produced by the reaction of cupric ion with sodium diethyl-dithiocarbamate at a pH of 8.
Apparatus Required
Filter photometer complete with assorted laboratory glassware.
Chemicals Required
Copper Reagent P 1
Copper Reagent P 2
Copper Standard
Nitric Acid, 10%
Procedure for Test
This procedure uses a wavelength of 415 nm and a light path of 20 mm. Prepare a calibration curve for the photometer using successive dilutions of the copper standard to adequately cover the anticipated range of copper in the samples to be tested. The dilutions of the standard should be treated in exactly the same manner as that discussed below for the analysis of the water samples.
Each time a determination is made, the calibration curve should be checked with a dilution of the standard to establish a correction factor. This procedure is necessary to insure that the results are accurate, since reagent age and stability as well as the sample temperature, can affect the results. To minimize the temperature effect, all reagents and samples should be analyzed at the same temperature. Transfer 2.0 ml of 10 per cent nitric acid to a flask containing 20.0 ml of samples. Evaporate the sample to approximately 1 ml (do not evaporate to dryness). Bring the volume back up to 20.0 ml by adding copper-free water. Add 20 ml of the copper reagent P1 to the prepared sample, mix and divide it into two equal portions. Add 10 ml of copper-free water to one portion. Use this solutions as a reference blank to set the meter to zero absorbance immediately prior to the test. Discard this solution.
Add 10.0 ml of the copper reagent P2 to the remaining portion of the prepared solution. Mix the solutions, wait for two minutes to allow for complete color development, and measure the absorbance on the photometer.
Calculation of Results
Compare the absorbance reading with the calibration curve and read the results directly in parts per million of copper.
Limitations of Test
This method is subject to interference from the presence of iron, manganese, nickel, cobalt, vanadium, zinc, lead and cyanide. The copper reagent P1 reduces the interference from these ions to an acceptable level by controlling the pH of the solution. Samples containing cyanides, must be pre-treated or serious interference will result due to the formation of copper cyanide complexes.
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