Analysis of a Suspect Explosive Component: Hydrogen Peroxide in Hair Coloring Developer

Article excerpt

Introduction

The objective of this article is to demonstrate the approach used for the analysis of a suspect explosive component submitted as case evidence. Samples of evidence taken from the home of a suspect who was under suspicion for producing bombs were submitted to the FBI Laboratory. The evidence included two five-ounce cans labeled citric acid, five tubes labeled hexamine, an empty one-pint bottle labeled Welloxide[R] liquid stabilizer developer, and a small vial containing a portion of the liquid originally in the Welloxide[R] bottle. Welloxide[R] is a hair coloring developer that contains hydrogen peroxide ([H.sub.2][O.sub.2]) to oxidize hair in the coloring process. The extremely unstable explosive material, hexamethylenetriperoxidediamine (HMTD), can be produced by combining 45 g of 30% hydrogen peroxide, 14 g of hexamine, and 21 g of powdered citric acid (Urbanski 1985). To demonstrate, in this case, that all the required components to prepare HMTD were present, it was necessary to verify the contents of the containers as labeled. This article specifically concerns the analysis of the Welloxide[R] liquid developer to determine if there was sufficient [H.sub.2][O.sub.2] to produce HMTD. Analysis schemes to identify HMTD explosive have been reported (Reutter et al.1983; Zitrin et al. 1983), but in this case it was necessary to identify each precursor. Because peroxides are highly corrosive, care was taken to use a method that would not damage instruments during the chemical analysis. Infrared (IR) and Raman spectrometry techniques were chosen for the analysis because both offer safe sampling methods.

Forensic IR analysis is a well-established method (Bartick and Tungol 1993; Suzuki 1993), and Raman spectroscopy is an emerging method in forensic analysis. Using an attenuated total reflectance (ATR) accessory with a horizontal internal reflection element (IRE) is a convenient IR analysis technique for liquid and solid samples (Harrick et al. 1992). Liquid samples can be deposited on the IRE for direct analysis with no sample preparation. Raman spectroscopy, however, has the advantage over IR in that samples can be analyzed directly through glass vials and in water without interference from water absorption. Raman spectral bands result from scattered energy caused by an electron dipole moment (polarization) that produces a shift from an excitation laser frequency (Colthup et al. 1990). Raman peaks are usually plotted as intensity versus wavenumber shift ([cm.sup.-1]). IR peaks result from an absorption of energy caused by molecular dipole moment vibrations and are plotted as intensity versus frequency in wavenumbers ([cm.sup.-1]). Raman and IR are considered complimentary methods but are frequently used independently. By using both of these methods, more chemical structural information can be obtained.

In 1928 C. V. Raman of India discovered the Raman effect, and in 1930 he was awarded the Nobel Prize for his discovery. Until recently, Raman spectroscopy has not been used widely outside of research laboratories. It was difficult to perform Raman analysis because the instrumentation was very complex, poor response was obtained, and samples fluoresced when subjected to the excitation source. When samples fluoresce, the spectral features are often washed out. Fluorescence often masked the Raman signal and yielded poor or no spectral information. Recent developments in Raman instrumentation, including dispersive and Fourier transform (FT) instruments, have reduced these problems. Advances include improved excitation lasers, holographic notch filters, monochromators, fiber-optic sampling probes, and charge-coupled-device (CCD) detectors (Chase 1994). Current Raman spectrographs have become fast and easy to use with far fewer difficulties than earlier instruments, and as a result, Raman spectrometry has gained new interest in research, industry, and forensic science for routine analysis. Particular interest has developed with forensic and law enforcement personnel because of the potential to analyze unopened containers of possibly hazardous samples both in the laboratory and with portable instruments in the field. …