Navy Cyanide Test Kit (NACTEK)

Gap Identified: Naval vessels take on supplies and water when in port. Fleet potable water sources may be in areas where there is no secure water supply. Potable water is screened for a variety of contaminants, but a gap in the testing was identified. There was no field test for cyanide in potable water. This gap is of concern to at least one command of the Naval Operational Forces and resulted in an emergency request for a system to measure the presence of cyanide in potable drinking water.

Solution: A quick and convenient field test-kit based on a colorimetric reaction on paper strips is used to measure the concentration of free cyanide. This is combined with a portable meter with a cyanide specific-ion electrode to confirm negative readings and collect additional evidence when high cyanide concentrations are detected.

To meet the extremely tight time constraints on this project, commercial off-the-shelf (COTS) items were used when available. The final kit must be reliable, portable, and simple for Navy corpsman to use. A test kit must reliably detect cyanide concentrations of 2.0 parts per million (ppm).

Background: Water quality standards and testing methods are provided in the Tri-Service Technical Bulletin, "Sanitary Control and Surveillance of Field Water Supplies." This document defines a concentration of 2.0 ppm as the acceptable level of free cyanide in potable water. This concentration is higher than the acceptable level (0.2 ppm) specified in the "National Primary Drinking Water Regulations" (NPDWR). The difference between these two standards is related to their application. The NPDWR standard limits lifetime exposures, while the Tri-Service standard is limited to consumption of 15 liters of water a day for one year or less.

Technical Issues: A chemical (colorimetric) technique can be used to provide a convenient and rapid means of measuring the free cyanide concentration in water samples. A portable meter and specific-ion electrode can be used to confirm these measurements. Cyanide specific-ion electrodes have a reported working range of 0.2 to 260 ppm.

Oxidizing agents, sulfides, and fatty acids are known to interfere with some chemical tests for cyanide. The effect of these compounds on a specific ion electrode is not known. Sensitivity to related, less toxic, species (i.e., SCN^- and Fe(CN)₆^-) is also poorly defined. Chloride, bromide, and iodide are reported to interfere with cyanide specific-ion electrodes. The magnitude of this interference needs to be evaluated and limits defined for noninterference.

Results: All of the methods tested are sensitive only to free cyanide. The effect of solutions of cyanide complexes and related ions were evaluated as part of the testing "EM Quant" test strips were selected for rapid assessment of water samples. A positive test results in production of a purple color in the sensitive area of a test strip and can be used to determine free cyanide concentrations between 1 and 30 ppm. Cyanide concentrations greater than 10 ppm turn the test solution pale yellow (Fig. 1). The presence of chloride ions at concentrations up to 300 mM had no effect. Although weakly buffered solutions in the range of pH 4 to 10 had no apparent effect on the color produced well buffered samples where pH's greater than 8 caused a noticeable reduction in the production of purple color. Tests conducted with tap water, SCN^- and Fe(CN)₆^- produced no discernable purple color on the test strip.

FIGURE 1
The colorimetrick test for the presence of cyanide results in a bright purple colir in the sensitive area of the test strip. A pale yellow color also develops in the test solution of highter syanide concentrations. Insert shows color scale used to estimate cyanide concentration.

The response of the ion-selective electrode was log linear between mV and concentration. Since the ion-selective electrode requires the addition of a concentrated alkaline reagent, pH has little effect on this test. Although chloride, bromide, and iodide are reported to interfere with the cyanide ion-selecive electrode, concentrations up to 30 mM had only a moderate effect (i.e., 3.5% error or less). The highest concentration of chloride ion tested was 272 mM, which resulted in a measured concentration of cyanide that was 16% less than the expected value.

Summary: A prototype kit was assembled and tested by a Navy corpsman (Fig. 2) within three weeks of the initial request to NRL. The Naval Cyanide Test Kit (NACTEK) can reliably detect cyanide in water at concentrations of 0.2 ppm or higher, and the initial screening can be completed in less than 1 minute. The use of two different detection technologies minimizes the chance of an inaccurate test that could result in the use cyanide-containing water. Before NACTEK, no field test was available to the Fleet to test potable water supplies for the presence of unacceptable levels of cyanide.

FIGURE 2
HM2 (SW) Clifton Butler (Naval Readiness Command, Mid-Atlantic) assists in testing the NACTEK protocols. The results from the colorimetric test are confirmed using a selective-ion electrode and test meter.

Acknowledgments: Dr. Keith B. Ward (ONR) assisted in producing the technical manuals, and HM2 (SW) Clifton Butler (Naval Readiness Command, Mid-Atlantic) assisted in testing the prototype kit.

[Sponsored by ONR]