Medical Aspects of Chemical Warfare (2008) - The Black Vault

Medical Aspects of Chemical Warfarecollection appeared to stabilize cyanide atthe higher temperatures; (3) the addition ofthe silver sulfate immediately after collectionincreased storage time of biological samples at4°C for at least 2 weeks; and (4) the addition ofsilver sulfate also appeared to quench the reactionof cyanide and bovine serum albumin toform iminothiazolidine and cysteine residuesin blood plasma. Forming other stable cyanidecomplexes, for example, by adding sodiumnitrite to form methemoglobin or by addinghydroxocobalamin, has also been performedsuccessfully. 87,98• Cyanide may form during storage. Artifactualformation of cyanide may also occur inbiological samples depending on storage conditions.91,97,99–101 It has been suggested that oxyhemoglobin,100 thiocyanate oxidase, 91,101 andgranulocytes (white blood cells) 99 may oxidizethiocyanate to cyanide and that these reactionsare dependent on the temperature and pH ofthe sample. Lundquist’s temperature dependenceanalysis was found to be different fromearlier studies 69,96,97 and his use of silver ionsmay also improve thiocyanate stability. 82 Microorganismsare also responsible for cyanideproduction, 101 and low temperature storagehelps to eliminate their growth.These considerations, common to all the analyticalmethods, are a major source for the vast discrepanciesin cyanide and cyanide metabolite levels reported fromcasualties. Because of the detoxification processes andcyanide’s physical and nucleophilic properties, directanalysis of cyanide is not normally done with urineor saliva samples, although traces have been found inurine, saliva, and expired air. The cyanide metabolitesthiocyanate and ATCA may be determined in urine,saliva, and blood plasma. Correlation of their concentrationsto cyanide exposure have been examined. 96,102–104,150–153Advantages to measuring thiocyanate are thatappreciable concentrations may be found immediatelyafter exposure, and that it is considered to be morestable than cyanide. However, the true concentrationmay also be difficult to determine because of itsconversion back to cyanide during storage. 153 ATCAis stable in biological samples for months at freezingand ambient temperatures. 154 Based on determinationof pK avalues (carboxylic acid: 2.03; amine: 8.48) andnuclear magnetic resonance studies, 154 ATCA formsa bipolar ion in solution and is therefore not volatile.It has been suggested that ATCA has lower initialconcentrations than thiocyanate, but its stability andapplicability to sensitive analytical techniques mayprove more beneficial. Disadvantages for both ATCAand thiocyanate, as with cyanide, include naturallyoccurring background levels that are different for eachperson, making it difficult to quantify low-level cyanideexposure without establishing baseline levels foran individual prior to exposure. 96,155 In addition, cyanidedistribution and concentrations in organs differdepending on the route of administration and primatespecies type. Organ cyanide concentrations have alsobeen used for blood cyanide intoxication levels inforensic cases; however, the postmortem productionand transformation of cyanide must be considered ininterpreting the results. 85,86,92,156–159The analytical determination of cyanide is not aneasy task because of its volatility, nucleophilic properties,and lack of color. Although numerous methodshave been developed, each must be used with precautionsbecause of interferences and instrumentationcapabilities. However, all the methods have helped insome way or another to provide insight into the detectionof cyanide in biological fluids. When selecting ananalytical method, several factors in addition to thedetection limit and length of time needed (Table 11-2)must be considered:• Does the method include consideration ofpreserving cyanide and its metabolites duringstorage?• Does the method include correct storage ofstock solutions 95 or use fresh preparationsdaily?• Does the method include consideration oftypical interferences found in blood?• Does the method test for cyanide with andwithout clinically used antidotes present?• Does the method include analysis procedures(eg, pH, heating, and acidification) that couldresult in the loss of cyanide? Are rubber stoppersor septums used?• Are the chemicals used in the determinationtoxic or carcinogenic?• Is the method precise, accurate, inexpensive,and practical?The literature displays a great deal of inconsistencyin reporting on how cyanide or thiocyanate analyticalmethods faired during storage, the validation of themethod in the presence of antidotes, and timing ofsample collection. Several authors strongly emphasizethe importance of collection and storage of cyanidecontaminatedbiological samples. 82,87,105–109,158–160 Becauseno simple, fast, lightweight, sensitive, and accuratemethods are currently available for detection of cyanidein biological fluids, none are appropriate for diagnostic380