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.
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
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
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
December
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 report covering the results of a study is then sent by e-mail to the participants within according to the schedule.
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.
