No abstract

A rapid sequential injection spectrophotometric method for the selective determination of 2,4,6-trinitrotoluene (TNT) in soil samples is presented. The method is based on a derivatization reaction of TNT with sodium sulfite in a basic acetone medium. The reaction conditions, namely the percentage of acetone used in the reaction, the sample and reagent volumes, the mixing coil volume, and the reaction time, were optimized. The reaction was found to be particularly sensitive to the concentration of acetone; an acetone/water medium of 88% (v/v) acetone was found to be optimal. A study of the response of the method to other explosives demonstrated that the method is selective for TNT. In particular, it was shown that the method had little (<2%) or no response to other secondary explosives such as 2,4- or 2,6-dinitrotoluene (DNT). An average precision of 6.1% RSD was established for five soil samples (n = 4). The limit of detection was 0.5 μg mL-1 for aqueous standards and 80 μg g-1 for ∼300 mg soil samples. Analysis time was approximately three minutes per sample. Quantitative results from the determination of TNT in authentic contaminated soil samples compared favorably to those obtained using a standard method. The extension of the method to water samples and the means by which samples can be preconcentrated on-line using solid-phase extraction (SPE) techniques are discussed.

The application of flow injection methodology to the determination of trace concentrations of primary explosives is presented. The approach is demonstrated with a sequential injection amperometric method for the determination of the azide ion (N 3 2 ). The proposed method can be applied to the determination of sodium azide or lead azide, a primary explosive, without regard to other sources of lead in environmental samples. The sequential injection system used for the analysis forms the basis for a proposed field-portable instrument for the analysis of primary explosives. A microporous gas permeable membrane in a gas diffusion unit (GDU) is used to separate the analyte from other anions that can also be oxidized at the amperometric cell. The behaviour of the GDU was optimized with respect to the pH of the donor stream and the timing of the preconcentration step. A study of anions that are commonly found in environmental samples showed that the species that will interfere with the analytical signal can be removed by the GDU. Results from three water samples that were spiked with 0.40 ppm of azide are presented. RSDs in the range 3-5% were typically obtained using the method. The useful working range of the method was linear up to 0.5 ppm and non-linear up to 20 ppm (second-order model). The limit of detection was 24.6 ppb.

A sequential injection (SI) method for the determination of mercury via cold vapor atomic absorption spectrophotometry is presented. The method differs from flow injection (FI) cold vapor methods for the determination of mercury because of the simplicity of the system required for the method: one pump, one valve, a gas-liquid separator, and an atomic absorption spectrophotometer equipped with a quartz cell. Under optimal conditions, the method has the following figures of merit: a linear calibration range of 1.0 to 20 microg L(-1); a detection limit of 0.46 microg L(-1); and a precision of 0.90% RSD (8 microg L(-1)). The procedure allows for a sampling rate of one injection per 80 s (excluding sample pretreatment). Results from the determination of mercury in water and fish specimens are also presented. The figures of merit of the method are compared to two other SI methods for the determination of mercury.