M. Bonner Denton

Characterization of the explosive triacetone triperoxide and detection by ion mobility spectrometry

The improvised explosive triacetone triperoxide (TATP) was synthesized and characterized by 1H-nuclear magnetic resonance (NMR), 13C-NMR, Raman and infrared (IR) spectroscopy. Triacetone triperoxide was subsequently analyzed by ion mobility spectrometry (IMS) in positive ion mode, and detected as a cluster of three peaks with a drift time of the most intense peak at 13.06 ms. Triacetone triperoxide was then analyzed after dissolution in toluene, where a dramatic increase in peak intensity was observed, at a flight time of 12.56 ms (K0=2.71 cm2V(-1)s(-1)). Triacetone triperoxide was subsequently analyzed by coupling the ion mobility spectrometer to a triple quadrupole mass spectrometer, where a single peak at m/z of 223 atomic mass units identified the species present in the ion mobility spectra as being triacetone triperoxide.

Stability studies of tetracycline in methanol solution.

The stability of tetracycline in methanol solution was investigated by UV-visible spectroscopy, HPLC and TLC methods. After dissolution in methanol, tetracycline decomposed rapidly under the influence of light and atmospheric oxygen, forming more than fourteen different degradation products. None of the previously reported degradation products, such as the epi- and anhydro-compounds, were detected as the final degradation products. The molecular structures for eight of the compounds were suggested by their product-ion mass spectra. A degradation sequence was proposed for the reactions of tetracycline with methanol. A new HPLC-MS mobile phase was developed, which solved the clogging problem at the interface between the HPLC and MS chamber and enabled a high separation efficiency.

Evaluation of Inductively Coupled Plasma Optical Emission Spectrometry as a Method for the Elemental Analysis of Organic Compounds

The application of inductively coupled plasma optical emission spectrometry (ICP-OES) to the elemental analysis of organic compounds is evaluated successfully for seven nonmetallic elements. A comparison of this method with previously reported microwave techniques shows that, while both methods are sensitive (detection limits in the low nanogram region), ICP-OES has fewer complications and appears to be less prone to interferences than the analogous microwave techniques. The results of these studies suggest that ICP-OES should be applicable to the simultaneous multielement analysis of the gaseous effluents from a gas chromatograph.

Evaluation of a New Array Detector Atomic Emission Spectrometer for Inductively Coupled Plasma Atomic Emission Spectroscopy

A unique echelle spectrometer system employing charge injection device (CID) array detector technology for use in inductively coupled plasma atomic emission spectroscopy (ICP-AES) is described. Due to improvements in optical design, this system offers increased wavelength coverage and improved light throughput over those of previous systems. Low sensitivity in the far-ultraviolet has been considered a major draw-back when silicon-based detectors are used, due to absorbance in the insulating SiO2 layer. The problem has been overcome through the use of a wavelength conversion phosphor. Therefore, detection limits comparable to those available with most commercial instruments have been obtained even in the far-UV. Operating parameters including precision, resolution, and background correction are also discussed. An analysis of the National Institute of Standards and Technology (NIST) Standard Reference Material (SRM) 1643b demonstrates that the system is capable of simultaneously determining at least 15 elements using 31 emission wavelengths with a high degree of accuracy.

Evaluation of a 512-channel Faraday-strip array detector coupled to an inductively coupled plasma Mattauch-Herzog mass spectrograph.

A 512-channel Faraday-strip array detector has been developed and fitted to a Mattauch-Herzog geometry mass spectrograph for the simultaneous acquisition of multiple mass-to-charge values. Several advantages are realized by using simultaneous detection methods, including higher duty cycles, removal of correlated noise, and multianalyte transient analyses independent of spectral skew. The new 512-channel version offers narrower, more closely spaced pixels, providing improved spectral peak sampling and resolution. In addition, the electronics in the amplification stage of the new detector array incorporate a sample-and-hold feature that enables truly simultaneous interrogation of all 512 channels. While sensitivity and linear dynamic range remain impressive for this Faraday-based detector system, limits of detection and isotope ratio data have suffered slightly from leaky p-n junctions produced during the manufacture of the semiconductor-based amplification and readout stages. This paper describes the new 512-channel detector array, the current dominant noise sources, and the figures of merit for the device as pertaining to inductively coupled plasma ionization.

Quantitative analysis using Raman spectroscopy without spectral standardization

Compared with other spectroscopic techniques, Raman spectroscopy has not generally been applied to problems of quantitative analysis, primarily because it is assumed that spectral irreproducibility due to source, sample or optical parameters requires standardization of the Raman signal. However, a custom-built Raman spectrometer with a 785 nm excitation source has yielded a spectral peak height reproducibility of 0.5% relative standard deviation. Quantitative studies of glucose in water, ethanol in water and p-xylene in m-xylene, described here, illustrate the linearity and precision of the Raman system. In order to estimate the linear dynamic range of the instrument, detection limits were determined for benzene in water and in CCl4, demonstrating a range from sub-ppm to 100% concentration. Specific factors affecting spectral reproducibility, and therefore quantitative results, are discussed. The quality of the results presented indicates that Raman spectroscopy should be a more common quantitative spectroscopic technique. Copyright

The transmission properties of an RF-only quadrupole mass filter

Abstract The performance of a quadrupole mass filter operated in the RF-only mode was investigated. Data are presented which demonstrate that the transmission properties of such devices deviate markedly from that which would be predicted from the Mathieu stability diagram. Discussion of the factors influencing the transmission efficiency of ions through an RF-only quadrupole is presented. The transmission efficiency of ionic species through an RF-only quadrupole is primarily influenced by three factors. The first of these is the formal stability of the ion trajectory as summarized by the coordinates of the particle in a, q space. The second factor is the acceptance aperture of the quadrupole in combination with the emittance of the ion source. The final factor is shown to be spatial focusing conditions which arise due to the nature of the frequency components that are contained within the trajectory of an ion as it traverses the quadrupole electrode structure. The theory of such spatial focusing conditions is reported. The measurement of naturally occurring isotope abundance ratios is used to demonstrate the magnitude of errors which may result due to the non-ideal transmission properties of the RF-only quadrupole. Suggestions are provided to minimize such mass discrimination effects.

Evaluation of a fourth-generation focal plane camera for use in plasma-source mass spectrometry

A fourth-generation focal plane camera containing 1696 Faraday-strip detectors was fitted to a Mattauch-Herzog mass spectrograph and characterized for its performance with inductively coupled plasma ionization. The camera provides limits of detection in the single to tens of ng L−1 range for most elements and has a linear dynamic range of at least nine orders of magnitude. Isotope-ratio precision better than 0.02% has also been achieved with this device, and this fourth-generation system features the broadest simultaneous mass range obtainable to date with this family of focal plane camera detectors.

The separation of dimethylarsinic acid, methylarsonous acid, methylarsonic acid, arsenate and dimethylarsinous acid on the Hamilton PRP-X100 anion-exchange column

In order to separate the potential arsenite metabolites methylarsonous acid and dimethylarsinous acid from arsenite, arsenate, methylarsonic acid and dimethylarsinic acid, the pH-dependent retention behaviour of all six arsenic compounds was studied on a Hamilton PRP-X100 anion-exchange column with 30 mM phosphate buffers (pH 5, 6, 7, 8 and 9) containing 20% (v/v) methanol as mobile phase and employing an inductively coupled plasma atomic emission spectrometer (ICP–AES) as the arsenic-specific detector. Baseline separation of dimethylarsinic acid, methylarsonous acid, methylarsonic acid, arsenate and dimethylarsinous acid was achieved with a 30 mmol dm−3 phosphate buffer (pH 5)–methanol mixture (80:20, v/v) in 25 min. Arsenite is not baseline-separated from dimethylarsinic acid under these conditions. Copyright

QUANTITATIVE DETECTION OF ENVIRONMENTALLY IMPORTANT DYES USING DIODE LASER/FIBER-OPTIC RAMAN SPECTROSCOPY

A compact diode laser/fiber-optic Raman spectrometer is used for quantitative detection of environmentally important dyes. This system is based on diode laser excitation at 782 nm, fiber-optic probe technology, an imaging spectrometer, and a state-of-the-art scientific CCD camera. The dyes studied include trypan blue, acid black 1, acid blue 40, and basic blue 7. Detection sensitivities (at rms S/N = 2) ranged from 0.2 ppm (3.24 × 10−7 M) for acid black 1, to 25 ppm (4.86 × 10−5 M) for basic blue 7.