Water Proficiency Testing
The SABS Water-Check Proficiency Testing scheme is a high frequency inter-laboratory inorganic chemistry water proficiency-testing programme with the objective of providing a rapid report-back service to participants for self-evaluation.
The SABS Water-Check is designed to allow flexibility in participation. No specific methods or instrumentation are prescribed. The programme is divided into three categories, each category being scheduled on a quarterly basis.
Programme Design
- Group 1: Heavy metals in water: aluminium, barium, beryllium, boron, cadmium, chromium, cobalt, copper, iron, lead, manganese, molybdenum, nickel, silicon, strontium, vanadium, zinc, mercury, arsenic and selenium. Scheduled: January, April, July and October.
- Group 2: Nutrients and oxygen demand: nitrogen, nitrate, ammonia, total phosphate, orthophosphate, oxygen absorbed, chemical oxygen demand, dissolved organic carbon and total organic carbon. Scheduled: February, May, August and November.
- Group 3: Major constituents in water: pH, conductivity, dissolved solids, calcium, magnesium, sodium, potassium, chloride, fluoride, sulphate, alkalinity, nitrate and turbidity. Scheduled: March, June, September and December.
Study Protocol
The programme structure therefore allows a laboratory to choose participation in one two or all three groups. All participants are coded for confidentiality purposes. Real, spiked and /or synthetic samples are prepared for each study. Samples are dispatched at the beginning of each calendar month with a report-back deadline near the end of the month. A preliminary report covering the results of a study is then either faxed or sent by e-mail to the participants within a week of the report-back deadline.
Study Report
The report on each study consists of a robust statistical analysis of results, with the inclusion of outliers, against the median or true value. The Z-score for each result is tabulated and then summarized for each laboratory. Correlation of analysis where applicable e.g. cation /anion balancing is performed with the evaluation of each laboratory's performance. Laboratories are not rated against each other but a graphical display of average absolute Z-scores is provided for self-evaluation.
