Overcoming the challenges associated with Proficiency Testing (PT) schemes for online chlorine analysis

摘要

Proficiency Testing (PT) and Inter Laboratory Comparison (ILC) schemes are Quality Assurance (QA) tools used by laboratories to demonstrate that they are competent to execute analytical methods. Establishment of Rand Water's online testing capacity required the development of suitable PT/ILC schemes to ensure the accuracy of the data. Over the past four years Rand Water has implemented and managed a PT scheme for online pH and conductivity analyses. The scheme has now been extended to online chlorine analyses. Establishment of the PT/ILC schemes for online analyses presented a number of challenges. These included: 1) difficulties associated with the introduction of external control samples into online systems; 2) the absence of on-site analysts to receive and process control samples; 3) the distribution of analysers over an extensive reticulation system and 4) the need to measure volatile parameters such as disinfectant residuals. These challenges were addressed by using portable instruments, rather than reference samples to compare the performance of online analysers. The principle was that a highly trained analyst would travel from site to site and compare measurements made with a single portable instrument against data recorded by online analysers. This presentation will consider the challenges encountered in the establishment of this system and present examples of typical data sets generated by the scheme. It will also attempt to highlight and discuss deviations from more conventional PT schemes.