Residual chlorine in water
January 2005
Analytical Instrumentation & Environmental Monitoring
It is important to understand that although the term 'free or residual chlorine' is used commonly, chlorine as such, is not present in water. Except at very low pH values, as in very strong acidic conditions, chlorine exists in water as hypochlorous acid or as the hypochlorite ion. In both cases the OCI group is present.
Free or total or 'available' chlorine may be determined by titration or by colorimetric analysis. In the titrimetric procedure, using Tytronics' FPA 414, the free chlorine reacts with KI in acidic conditions to liberate iodine, which is titrated with sodium thiosulfate. This method is more suitable for the determination of higher levels of 'free or available' chlorine as in bleach solutions.
Free chlorine may be measured colorimetrically using the FPA 814 process colorimeter. The most common method is to use the ortho-toluidine method. Both the titrimetric and colorimetric methods obviously require the addition of reagents and hence increase the requirements for maintenance of the analysers.
Total residual chlorine is also measured colorimetrically using the FPA 814. The first step is to obtain the release of the chlorine associated with nitrogen, as in the chloramines, using the reagent DPD to add KI and sodium arsenite, which in turn liberates the chlorine from the amines. Range of measurement of 'total residual chlorine' is normally 0 to 2,5 ppm.
The direct UV measurement, using the FPA 2014 process UV analyser is therefore most attractive as the very minimal of maintenance is required. As mentioned above, the chlorine in an aqueous solution exists as the hypochlorous acid or hypochlorite. The OCI entity exhibits a very strong characteristic absorption band in the UV region. The additional advantage of the FPA 2014 is that the measurement is continuous as the sample flows through a cell and no sample capture is required. Tytronics is represented locally by Protea Automation Solutions.
For more information contact Keith Guest, Protea Automation Solutions, 011 719 5700, [email protected], www.protea.co.za
Further reading:
Precision in every drop, powered by ICP technology
Wearcheck
Analytical Instrumentation & Environmental Monitoring
Elemental profiling using Inductively Coupled Plasma – Optical Emission spectroscopy provides useful information on the chemical composition of lubricants.
Read more...
A trusted oxygen analyser back in action
Elemental Analytics
Analytical Instrumentation & Environmental Monitoring
After a period of discontinuation, Servomex’s Oxy 1810 oxygen analyser has officially returned.
Read more...
Multi-channel pH and conductivity controller for the water sector
Senseca
Analytical Instrumentation & Environmental Monitoring
The measurement of pH and conductivity plays an integral role in water systems. Senseca South Africa has introduced a multi-channel controller that allows the connection of up to five digital sensors and a frequency-emitting flow sensor.
Read more...
DEKRA Industrial sets new standards for asset integrity in local petrochemical sector
Analytical Instrumentation & Environmental Monitoring
DEKRA Industrial South Africa has strengthened its position as a leader in hydrogen-induced cracking inspections through a strategic combination of advanced non-destructive testing techniques, investment in state-of-the-art inspection equipment and global technical collaboration.
Read more...
ABB leads in emissions monitoring with industry-first data acquisition system proficiency test
ABB South Africa
Analytical Instrumentation & Environmental Monitoring
ABB is the first company to offer a complete package of continuous gas analysis and DAHS systems fully compliant with international standards.
Read more...
Ensuring clean and safe water
Endress+Hauser South Africa
Editor's Choice Analytical Instrumentation & Environmental Monitoring
Endress+Hauser’s comprehensive range of disinfection sensors is designed to monitor and control disinfectant levels in water treatment processes.
Read more...
High-precision measurement of insulating gases
WIKA Instruments
Analytical Instrumentation & Environmental Monitoring
WIKA has launched the next generation of its GA11 gas analyser. It enables switchgear operators, manufacturers and maintenance companies to record the quality of SF6 gas and alternative insulating gases.
Read more...
Say goodbye to missed contamination with real-time colour monitoring
Analytical Instrumentation & Environmental Monitoring
Applied Analytics offers seamless and rapid colour monitoring in processes with an industry-proven analyser that quickly and accurately monitors colour in your sample stream for impurities and inconsistencies.
Read more...
Metrology laboratory is the heart of data-driven production consistency
Analytical Instrumentation & Environmental Monitoring
Pressing and welding have been at the core of Tier 1 automotive supplier, Malben Engineering for 50 years; but it is the company’s investment in its state-of-the-art metrology laboratory which has set it apart.
Read more...
Unlocking precision: The future of inline concentration measurement
Analytical Instrumentation & Environmental Monitoring
[Sponsored] In today’s resource-conscious industrial world, manufacturers are under growing pressure to optimise productivity, ensure consistent product quality and minimise waste. One of the most effective levers for achieving these goals lies in mastering concentration measurement, and Anton Paar is redefining how it is done.
Read more...
printer friendly version