Investigation of isotopic linkages between precursor materials and the improvised high explosive product hexamethylene triperoxide diamine.

The results of isotope ratio mass spectrometry (IRMS) on hexamethylene triperoxide diamine (HMTD) and its precursor hexamethylenetetramine (hexamine) is presented. HMTD was prepared from hexamine using several different sources of hexamine under both controlled laboratory conditions and in field experiments that represent the less controlled conditions that are likely to be observed in forensic casework scenarios. Precursor and product carbon isotope δ values consistently fit a linear relationship regardless of precursor or conditions. The magnitude of the isotope fractionation observed is affected by the efficiency of the reaction, with greater yielding reactions giving rise to HMTD with δ values more similar to the precursor material than lower yielding reactions. Nitrogen isotope δ values comparing precursor with product show some linearity when the reaction conditions are carefully controlled; however, results indicate a poor fit with linearity when synthesis conditions are more variable. Despite the greater variation, the HMTD product consistently has a more positive δ value compared with the hexamine precursor. The results observed from these experiments suggest hexamine reacts to form HMTD in a 1:1 ratio. Having prepared multiple HMTD samples from various precursors using a range of experimental conditions, we have observed results that may be useful in forensic investigations of improvised explosive materials.

N(2): a potential pitfall for bulk (2)H isotope analysis of explosives and other nitrogen-rich compounds by continuous-flow isotope-ratio mass spectrometry.

Observations made during the (13)C isotope analysis of gaseous CO(2) in the simultaneous presence of argon in the ion source of the isotope ratio mass spectrometer prompted us to investigate what influence the simultaneous presence of nitrogen would have on both accuracy and precision of bulk (2)H isotope analysis of nitrogen-rich organic compounds. Initially an international reference material, IAEA-CH7, was mixed with silver nitrate in various ratios to assess the impact that N(2) evolved from the pyrolysis of nitrogen-rich organic compounds would have on measured delta(2)H-values of IAEA-CH7. In a subsequent experiment, benzoic acid was mixed with silver nitrate to mimic the N:H ratio of organic-rich nitrogen compounds such as cellulose nitrate and RDX. The results of both experiments showed a significant deterioration of both accuracy and precision for the expected delta(2)H values for IAEA-CH7 and benzoic acid when model mixtures were converted into hydrogen and nitrogen, and subsequently separated by gas chromatography using standard experimental conditions, namely a 60 cm packed column with molecular sieve 5 A as stationary phase held at a temperature of 85 degrees C. It was found that bulk (2)H stable isotope analysis of nitrogen-rich organic compounds employing published standard conditions can result in a loss of accuracy and precision yielding delta(2)H values that are 5 to 25 per thousand too negative, thus suggesting, for example, that tree-ring (2)H isotope data based on cellulose nitrate may have to be revised.

Investigation of isotopic linkage between precursor and product in the synthesis of a high explosive.

In criminal proceedings involving illegally manufactured substances, evidence demonstrating the manufacture is required for successful prosecution. In many circumstances the presence of manufacturing equipment and 'recipes' are clear indicators. However establishing chemical links between starting materials and products would be beneficial additional evidence in such circumstances. Isotope analysis is becoming more commonly employed in disputes over authenticity and provenance of materials such as food stuffs or pharmaceuticals [S. Benson, C. Lennard, P. Maynard, C. Roux, Forensic applications of isotope ratio mass spectrometry--a review, Forensic Sci. Int., 157 (2006) 1-22]. We report here the results of an isotope study investigating a link between hexamine used as a starting material and the product explosive RDX, manufactured using the Woolwich process. Isotopic composition of hexamine and RDX was analysed by stable isotope ratio mass spectrometry. Five different hexamine samples were selected from a group of eleven for use in this study. One of the five hexamine samples was used twice, providing data on the reproducibility of the synthesis. Carbon and nitrogen isotope analysis of the hexamine starting material and RDX products reveals a reproducible relationship between reactant and product.