Myth: “There are good and bad online analysers for heavy metals”.
Many of the vendors claim in their brochures that there online analysers are cheap and work affordable and of course are very precise and accurate.
In most cases the quality of online analysers is quite good and the differentiation between vendors can only be made in services, ease of operation and non hazardous consumables. The Seibold model of TCM1 (total cost of measurement) includes all of these differentiation factors.
Facts about quality of online analysers:
The much more precise question is: “What technology is suitable to my application, expectations and needs?”
Each technology has it’s advantages and disadvantages. You can start by declaration of the sample: complex matrix (interference’s, loaded), changing matrix, turbidity, temperature of the sample. Declaration of measurement needs: concentration range, limit of detection (LOD), measurement frequency, detection of a limit value or acurate results over a greater concentration range.
At this point in time there are manly two online technologies for choice2,3:
- Colourimetric: Absorption of coloured complex after adding a reagent
- Potentiometric: ISE Electrodes4
- Technology to watch: light sensors, sounds very promising, have not delivered yet
Potentiometric measurements are less expensive than colourimetric measurements. Vice versa is the quality and the stability. Colorimetric errors are in the range of 1-3%, while electrodes have an error in the range of 10%-20%. In online measurements electrodes have to be calibrated every day, while colorimetric measurements will deliver accurate results for month.
In making choice for a vendor for online analysis you first consider the measurement technology and than the TCM.
(1) See more about the Seibold TCM.
(2) Guidelines for drinking-water quality
(3) If you consider voltammetry a online technology, no it’s not. First it is a qualitative method and second you need a well trained technician and third multiple sample treatment steps before meaningful results are on display.
(4) Advatages of ISE technology measurements.