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 20 mL concentrate._x000D_ The solvent for this sample is water._x000D_ The PT sample is not preserved._x000D_ Sample preparation_x000D_ Partially fill a 1000-mL volumetric flask with reagent-grade water (near 20 °C) and add 1 mL of trace-metal-grade nitric acid._x000D_ Open bottle PE1350-20ML and transfer 10.0 mL of concentrate to the volumetric flask._x000D_ Fill the volumetric flask to volume with reagent-grade water and mix well. the sample is now ready for immediate analysis._x000D_ Silica (SiO2) should be reported in mg/L._x000D_ NOTES: Samples, standards and reagent water blanks should all have the same acid matrix. The solution resulting from the above dilution will contain 0.15% v/v nitric acid; additional or different acids may be used as appropriate for analytical procedures or to match standards._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_ WS21-2 March 24 - May 7, 2021_x000D_ WS21-3 July 7 - August 20, 2021_x000D_ WS21-4 September 22 - November 5, 2021_x000D_ Quick-Turn Study - (non-scheduled proficiency test that is available at any time)