Residual Measurement Of ClO2 –
Determination of residual ClO2 in process or potable water is a tricky situation. As there are several interferences from other oxidants present in water in addition to ClO2 and its disinfection bi-products. The test method for measurement of ClO2 is a normally interfered with its bi-products chlorite & chlorate due to the difficulty in measuring a specific oxidants among other oxidants.
Following are the methods available and selectively used for analytical measurement of ClO2.
Amaranth – Amaranth is a colorimetric indicator that is selectively decolorized by mg/L concentration of ClO2. The method does not have interference by chlorite,chlorate,monochloramine,free chlorine & ferric ion. And the minimum measurement that can be performed is up to 5mg/L. Hence the said is recommened only in the lab level and not in field.
Chlorophenol Red ( CPR). – The method is similar to Amarnath method where in CPR is decolorized by ClO2. The method faces a interference by free chlorine in water. With this method concentration upto 0.1 ppm can be determined. But again the method is operation dependent because of the precise pipetting requirement.
LGB ( Lissamine Green B) – Like amaranth and CPR,ClO2 selectively decolorizes LGB dye. With this method the minimum residue that can be measured is 2.5 mg/L. but again the method is only recommended at laboratory level and not in field.
DPD method –
This is the most commonly used method for testing ClO2 in industrial methods.
DPD forms a pink color & the intensity of the color is proportional to the concentration of ClO2. The problem with the method is chlorine & chlorite ion also reacta with DPD reagents. The system works fairly well in clean water system. But in cases of cooling tower & waste tower there are several interferences from hydrocarbon, SRB etc…
We SVS AQUA TECHNOLOGIES recommend three methods for measuring the residue of ClO2.
The photometry is a method of analysis which is often used. Whether it is a public bathhouse, food and beverage industry, laboratories, or industrial disinfection – are everywhere photometer is used for the determination of concentrations in solutions. We are providing the world’s first photometer for the entire visible color spectrum with only one light source and only one sensor. The unique sensor combined with the several –year’s experience in water analysis, made this innovation possible. In addition, the sensor measures with a hitherto unknown devices with photometer accuracy. The Bluetooth technology (select models) and a programmed specifically for the PC software makes it easy to manage measurement and customer data..
Reagent tablets offer the highest level of assurance that always the exact amount of reagent needed will be used. Most marketed tablet types, such as DPD for determining Chlorine in water, are regulated by strict international standards aimed at guaranteeing that all tablets with that designation (e.g. DPD 1) can also be used in all designated measurement devices made by any manufacturer. Our devices and reagents can therefore be combined with other manufacturer’s reagents, and this is also true the other way around. One of the questions discussed often is the difference between RAPID and Photometer tablets. Basically both detect the same content but are different in one important point: RAPID tablets contain a material which “bursts” the tablet, e.g. chemical pulp that expands upon contact with water. This “burst material” would, however, disrupt the light ray of the photometer (suspended particles) which is why RAPID tablets should never be used with electronic devices such as photometers.