Description_x000D_ General description_x000D_ This proficiency testing sample is produced in accordance with ISO/IEC 17043:2010. All information regarding the use of this material can be found in the reporting packet supplied for each sample._x000D_ Preparation Note_x000D_ This PT sample is as a 2 mL concentrate._x000D_ The solvent for this sample is water._x000D_ The PT sample has been autoclaved for preservation._x000D_ Sample preparation_x000D_ To prepare solution, partially fill a 1000-mL volumetric flask with ammonia-free, reagent-grade water (near 20 degrees C)._x000D_ Open ampule PE1575-2ML (be careful to avoid cuts on glass) and transfer 1.0 mL of concentrate to the volumetric flask._x000D_ Fill the volumetric flask to volume with reagent-grade water and mix well._x000D_ The sample is now ready for immediate analysis._x000D_ If a solution is not to be analyzed within two days after preparation, preserve a sample aliquot with 0.2 mL of concentrated sulfuric acid per 100 mL of sample (pH<2) and store at 4 degrees C until just before analysis. Analyze the preserved sample as soon as possible within the maximum 28-day holding time._x000D_ Other Notes_x000D_ Proficiency testing samples are presented as single blind. No values for the samples are released until the testing period concludes. Values of analytes vary lot to lot._x000D_ Proficiency Testing Schedule (2020-2021)_x000D_ Drinking Water_x000D_ WS20-1 January 15 - February 28, 2020_x000D_ WS20-2 March 25 - May 8, 2020_x000D_ WS20-3 July 8 - August 21, 2020_x000D_ WS20-4 September 23 - November 6, 2020_x000D_ WS21-1 January 13 - February 26, 2021_x000D_ WS21-3 July 7 - August 20, 2021_x000D_ Quick-Turn Study - (non-scheduled proficiency test that is available at any time)