Drop Count Kits

Liquid drops or tablets are added to the sample and counted until a colour change occurs in the sample.  When this happens the number of tablets or drops used is multiplied by a factor to give a concentration.

If you imagine colour change taking place after 6 drops, you would multiply by 40 to give 240 mg/L.  However, 5 drops would have been equivalent to 200 mg/L.  So, the ‘true’ level is anywhere between 200 and 240.  By subtracting 20 from the higher figure you get a result of 220 which will be within 20 mg/L of wherever the ‘true’ figure is.

The reasons for carrying out a test, the situation and the application all effect the choice of what test method is best for you.

For example, whilst accuracy and repeatability might be the most important factors in a modern laboratory.  Weight, speed of test, and the lack of requirement for electricity might be more important in a field expedition.