Colorimetric testingis a widely used method of water testing. A chemical reagent (eg. DPD tablets) is added to a known sample of water. The intensity of colour is then measured to determine the concentration of a particular chemical present in the water (eg. Chlorine). The concentration of the parameter can be determined with a colorimeter, either a Comparator & Disc, (visual system) or a photometer (electronic / digital) system.
Different chemical substances absorb different and varying visual light frequencies. Since the absorption of a substance is proportional to its concentration, ie a more concentrated solution gives a higher absorbance reading, therefore the concentration of a known solute can be measured using a colorimeter.
Since about 1865, the Lovibond® Comparator system has been used around the world for chemical analysis of water, dairy, beer, fruit juices, medical, etc. The discs are fitted with guaranteed colour stable, non-fading glass filters.
- Visual (manual) or digital?
The visual systems (Checkit Comparator or Comparator 2000+) are based on visual comparison with coloured filters, which are calibrated to allow direct measurement of concentration levels. (The visual systems are user-friendly and robust, for both field and laboratory use.)
The micro-processor digital systems are easier to use, are more accurate and have highly reproducible results as they are not dependent on the human eye.
- Glass or plastic discs? The plastic discs (used with the Checkit Comparator) are lower cost, however slightly less accurate and durable than the glass discs (used with the Comparator 2000+). The plastic discs have an expiry date due to UV fading, whereas the glass discs are guaranteed colour stable. Glass discs are more precise and have a larger selection of test discs for more parameters.
- Level of expertise of personnel? When using the usual Comparator and Disc system, the operator needs to have a good eye for colour and it is best to have the same person doing tests in the same environment for good repeatability. The digital systems require no expertise.
- What level of accuracy do you require? Comparator & Disc accuracy depends on the human eye and environmental / lighting conditions that the measurements are done in – thus a very subjective means of analysis.With Photometer / digital units, the inaccuracy is ± 0.5 – 1% of the full scale. Digital units are more accurate than visual colorimeters.
- Cost per test once you have purchased the initial equipment? As you are aware, there are many chemical analysis systems on the market. It is imperative that you point out to your customer that they need to compare the cost per test when considering various options. After the initial purchase, the cost per test for both the Lovibond® Comparators and photometers is lower than many other products.The cost per test for a visual vs a digital system is the same, as the same reagents are required.
- What is the Guarantee? The guarantee for both Lovibond®visual and digital systems is two years. The German quality is renowned and Selectech has customers that are still using the same visual Comparator 2000+ system for 20+ years!
- When do you need a lighting unit? This is recommended in buildings where there is no natural lighting or changing light conditions, eg chicken coups, processing / production plants, laboratories, etc.
- When do you need a nessleriser? A nessleriser is used when very low concentrations need to be analysed. If you refer to the handbook,”Lovibond® Simple Methods of Water Analysis”, it indicates whether the analysis is based on either a Nessleriser or Comparator method, when you select the required parameter.
Questions to ask Yourself:
- Do you want a visual or electronic / digital measuring instrument?
- What parameters do you wish to test for? There are more than 400 different discs for measuring various parameters, ie Ammonia, Chlorine, pH, Fluoride, etc – please inform us of the parameters in your quote request. You can always add discs later.
- What concentration range do you wish to measure? For a parameter like Chlorine, there are 24 different ranges ( discs) available. If you are uncertain about the range. please give us some information about what you are measuring, eg if you are measuring effluent water, drinking or process water and we will be able to assist you.We have extensive experience on the standards required in different industries, so feel free to call Selectech and discuss your testing requirements.
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