April J. Carman

Stable Carbon and Nitrogen Isotope Ratios of Sodium and Potassium Cyanide as a Forensic Signature

Abstract:  Sodium and potassium cyanide are highly toxic, produced in large amounts by the chemical industry, and linked to numerous high‐profile crimes. The U.S. Centers for Disease Control and Prevention has identified cyanide as one of the most probable agents to be used in a chemical terrorism event. We investigated whether stable C and N isotopic content of sodium and potassium cyanide could serve as a forensic signature for sample matching, using a collection of 65 cyanide samples. Upon analysis, a few of the cyanide samples displayed nonhomogeneous isotopic content associated with degradation to a carbonate salt and loss of hydrogen cyanide. Most samples had highly reproducible isotope content. Of the 65 cyanide samples, >95% could be properly matched based on C and N isotope ratios, with a false match rate <3%. These results suggest that stable C and N isotope ratios are a useful forensic signature for matching cyanide samples.

Anionic Forensic Signatures for Sample Matching of Potassium Cyanide Using High Performance Ion Chromatography and Chemometrics

Potassium cyanide was used as a model toxicant to determine the feasibility of using anionic impurities as a forensic signature for matching cyanide salts back to their source. In this study, portions of eight KCN stocks originating from four countries were separately dissolved in water and analyzed by high performance ion chromatography (HPIC) using an anion exchange column and conductivity detection. Sixty KCN aqueous samples were produced from the eight stocks and analyzed for 11 anionic impurities. Hierarchal cluster analysis and principal component analysis were used to demonstrate that KCN samples cluster according to source based on the concentrations of their anionic impurities. The Fisher-ratio method and degree-of-class separation (DCS) were used for feature selection on a training set of KCN samples in order to optimize sample clustering. The optimal subset of anions needed for sample classification was determined to be sulfate, oxalate, phosphate, and an unknown anion named unk5. Using K-nearest neighbors (KNN) and the optimal subset of anions, KCN test samples from different KCN stocks were correctly determined to be manufactured in the United States. In addition, KCN samples from stocks manufactured in Belgium, Germany, and the Czech Republic were all correctly matched back to their original stocks because each stock had a unique anionic impurity profile. The application of the Fisher-ratio method and DCS for feature selection improved the accuracy and confidence of sample classification by KNN.

Source Attribution of Cyanides Using Anionic Impurity Profiling, Stable Isotope Ratios, Trace Elemental Analysis and Chemometrics

Chemical attribution signatures (CAS) for chemical threat agents (CTAs), such as cyanides, are being investigated to provide an evidentiary link between CTAs and specific sources to support criminal investigations and prosecutions. Herein, stocks of KCN and NaCN were analyzed for trace anions by high performance ion chromatography (HPIC), carbon stable isotope ratio (δ(13)C) by isotope ratio mass spectrometry (IRMS), and trace elements by inductively coupled plasma optical emission spectroscopy (ICP-OES). The collected analytical data were evaluated using hierarchical cluster analysis (HCA), Fisher-ratio (F-ratio), interval partial least-squares (iPLS), genetic algorithm-based partial least-squares (GAPLS), partial least-squares discriminant analysis (PLSDA), K nearest neighbors (KNN), and support vector machines discriminant analysis (SVMDA). HCA of anion impurity profiles from multiple cyanide stocks from six reported countries of origin resulted in cyanide samples clustering into three groups, independent of the associated alkali metal (K or Na). The three groups were independently corroborated by HCA of cyanide elemental profiles and corresponded to countries each having one known solid cyanide factory: Czech Republic, Germany, and United States. Carbon stable isotope measurements resulted in two clusters: Germany and United States (the single Czech stock grouped with United States stocks). Classification errors for two validation studies using anion impurity profiles collected over five years on different instruments were as low as zero for KNN and SVMDA, demonstrating the excellent reliability associated with using anion impurities for matching a cyanide sample to its factory using our current cyanide stocks. Variable selection methods reduced errors for those classification methods having errors greater than zero; iPLS-forward selection and F-ratio typically provided the lowest errors. Finally, using anion profiles to classify cyanides to a specific stock or stock group for a subset of United States stocks resulted in cross-validation errors ranging from 0 to 5.3%.

Multiple Stable Isotope Characterization as a Forensic Tool to Distinguish Acid Scavenger Samples

Abstract:  Acid scavengers are frequently used as stabilizer compounds in a variety of applications. When used to stabilize volatile compounds such as nerve agents, the lower volatility and higher stability of acid scavengers make them more persistent in a post‐event forensic setting. Compound‐specific isotope analysis of carbon, nitrogen, and hydrogen in three acid‐scavenging compounds (N,N‐diethylaniline, tributylamine, and triethylamine) were used as a tool for distinguishing between different samples. Combined analysis of multiple isotopes improved sample resolution, for instance differentiation between triethylamine samples improved from 80% based on carbon alone to 96% when combining with additional isotope data. The compound‐specific methods developed here can be applied to instances where these compounds are not pure, such as when mixed with an agent or when found as a residue. Effective sample matching can be crucial for linking compounds at multiple event sites or linking a supply inventory to an event.

The preparation of non-radioactive glassy surrogate nuclear explosion debris (SNED) loaded with isotopically altered Xe

The measurement of Kr and Xe isotope ratios in nuclear explosion debris can be performed requiring little sample preparation. Fragments of debris are simply crushed or heated to release trapped gases Kr and Xe arising from fission product decay. As a suitable test material for this measurement, we have been investigating a method to incorporate isotopically enriched 129Xe in glassy materials that mimic nuclear explosion debris. The approach used to prepare these materials will be described along with some of the example results obtained.

Simulating the effects of underground nuclear explosions with an exploding wire

Exploding wires can deposit significant amounts of energy on nS–µS timescales into a confined space. Most exploding wire studies have been performed in air but we have started to investigate enclosing the wire element in solid matrices like concrete to mimic the effects of an underground nuclear explosion. Temperatures and pressures achieved are quite sufficient to induce structural cracking and localized flash melting. As a result exploding wires would appear to form the perfect trigger for releasing chemical species in geological media to study migration behavior. Details of the apparatus and some illustrations of its potential will be given.

ICP-MS Workshop

This is a short document that explains the materials that will be transmitted to LLNL and DNN HQ regarding the ICP-MS Workshop held at PNNL June 17-19th. The goal of the information is to pass on to LLNL information regarding the planning and preparations for the Workshop at PNNL in preparation of the SIMS workshop at LLNL.

Computational Analysis of Coriant and PNNL Radioxenon Data Viewers

The analysis by Coriant of the beta-gamma coincidence data coming from the ARSA systems show a systematic basis towards lower concentrations for all isotopes and a systematic increase in the minimum detectable concentrations. These variations can be directly traced to the method of analysis that is used by the Coriant software compared to the methods that have been developed by the International Noble Gas Experiment collaboration. This report details the differences and suggests solutions where appropriate. The report writers recommend that the algorithm changes be made to the Coriant software to bring up to the international standards.