Monitoring Cyanide Concentration Changes in Environmental Water Samples as a Function of Sample Preservation and Holding TimeIdentifying and Combatting Inappropriate Laboratory Practices
Poster Presentation
Prepared by T. Smith
O.I. Analytical/ Xylem, 151 Graham Road, College Station, Texas, 77840, United States
Contact Information: tim.smith@xylem.com; 979.690.5229
ABSTRACT
Most cyanide analysis sampling protocols specify preservation of samples at a pH of 12 or higher. Sample preservation is intended to minimize changes in analyte concentration to allow sample storage for up to 14 days prior to analysis. The source of a water sample, sample pre-treatment, and the presence of possible matrix interferences must also be considered in determining appropriate sampling and preservation procedures to avoid inadvertent formation or destruction of cyanide species. Matrix interferences can cause either negative or positive analytical biases depending upon the composition of a sample being tested. The species of cyanide present in a sample is directly affected by the pH, and presence of; oxidizers, sulfur or sulfur compounds, and transition metals. The U.S. EPA is aware of problems related to sampling and preservation practices and has recently taken steps to address these problems. ASTM D 7365-09a(15) Standard Practice for Sampling, Preservation, and Mitigating Interferences in Water Samples for Analysis of Cyanide) was included in the U.S. EPA Method Update Rule (MUR) of September 23, 2015 applicable to 40 CFR 136 Clean Water Act methods for testing of wastewater samples.
This poster will demonstrate the potential decreases and increases in total and available cyanide concentrations as a function of metals present, treatment chemicals added, and ph.
