Thermal stability of an explosive detonator

Mercuric 5-nitrotetrazole is a possible replacement for lead azide. The thermal decomposition peak maximum ranged from 185 to 270°C as the heating rate increased from 0.1 to 100°C min⁻¹. The activation energy and frequency factor for thermal decomposition were determined from dynamic and isothermal DSC and isothermal TG data; the average values were 38.8 kcal mol⁻¹ and 3.56×10¹⁴ s⁻¹. A half-life experiment confirmed the kinetic constants and indicated that the decomposition reaction was first order. The heat of explosion was determined by a pressure DSC test and found to be 2587 J g⁻¹. The linear coefficient of expansion was 37±2×10⁻⁶°C⁻¹ from −60 to 160°C and indicated secondary transitions near −10 and 90°C. The specific heat was 0.0003154T+0.1339 in the region −40–90°C. The critical temperature for a slab with a half-thickness of 0.035 cm was calculated to be 232 °C.     

The rovibrational analysis of the high-resolution IR spectrum of CD2HF below 1200 cm: an interacting tetrad of vibrational levels

The spectrum of CD₂HF was measured by high-resolution interferometric Fourier-transform IR (FTIR) spectroscopy (apodised instrumental band with:0.004 cm⁻¹ fwhm) between 800 and 1200 cm⁻¹ covering the four lowest fundamentals. A complete rotational analysis using a semi-automatic assignment procedure yields accurate band centres (ν₉: 912.2028 cm⁻¹, ν₆:964.4994 cm⁻¹, ν₅: 1050.5104 cm⁻¹, ν₄: 1093.8632 cm⁻¹) and a complete set of first-order Coriolis coupling constants. The most important couplings occur between ν₉ and ν₆ (ξ_a= 1.069 cm⁻¹, ξ_c= −0.3535 cm⁻¹) and between ν₅ and ν₄ (ξ_b= −0.80606 cm⁻¹). The analysis was guided by and compared with results from our ab initio calculations for Coriolis constants and transition moments using CADPAC at TZP/MP2 level.     

Ion chromatographic determination of traces of some oxoanions with direct spectrophotometric detection

Investigation of the use of a single analytical procedure using the non-suppressed ion chromatographic method with direct spectrophotometric detection capable of determining eight oxoanions simultaneously is presented in this paper. Potassium phosphate was found to be the most suitable eluent for UV absorbance detection at 205 nm. Oxoanions AsO³⁻₃, SeO²⁻₃, AsO³⁻₄, VO⁻₃, SeO²⁻₄, WO²⁻₄, MoO²⁻₄ and CrO²⁻₄ were detected at ng ml⁻¹ levels with well separated peaks at retention time < 25 min. The working range is in the range ng ml⁻¹ to 50 μg ml⁻¹. The method is sufficiently sensitive to determine As (V), V(V), Mo(VI) and Cr(VI) anions (and NO⁻₃) directly in a river water sample. The accuracy of these results was established by comparison with conventional atomic absorption methods.     

Studies on elution conditions for the determination of anions by supressed ion-interaction chromatography using a graphitized carbon column

A new method has been developed for ion-interaction chromatography with suppressed conductivity detection and a new graphitized carbon packing, which is sintered from carbonic material at a high temperature. Combinations of various eluting agents, tetrabutylammonium hydroxide (TBA) and acetonitrile have been investigated to optimize the separation of eight common anions (F⁻, Cl⁻, NO₂⁻, Br⁻, NO₃⁻, SO₄²⁻, HPO₄²⁻ and I⁻). Calibration curves were linear from 0.5 to 10 μg/ml for F⁻, from 1.0 to 20 μg/ml for Cl⁻, NO₂⁻ and NO₃⁻, from 2.5 to 50 μg/ml for Br⁻ and SO₄²⁻ and from 5.0 to 100 μg/ml for HPO₄²⁻ and I⁻ with a correlation coefficient (r) of 0.999 or better. The relative standard deviations (R.S.D.s) of peak areas were between 0.2 and 0.9% for 10 repeated measurements. The application of this newly developed method was demonstrated by the determination of chloride, bromide and sulfate in pharmaceutical compounds using the direct injection method. The analytical results were within ±2% (relative) of the theoretical value, and thus in good agreement with the theoretical value for each sample.     

Low-molecular-mass anion screening for forensic environmental analyses by capillary zone electrophoresis with indirect UV detection

A method for low-molecular-mass anion screening is described using a buffer composed of 5-sulfosalicylate (SS) as a visualizing ion, hexadimethrine bromide as an electroosmotic flow modifier and Tris as a pH buffer component, at pH 8.6. All ions with effective mobility higher than 2610⁻⁹ m² s⁻¹ V⁻¹ can be separated within 7.5 min under −30 kV. By using the moderately mobile SS (5410⁻⁹ m² s⁻¹ V⁻¹), not only the sensitivity of the detection is improved due to its high UV absorptivity, but also a smaller overall overloading effect is achieved. Meanwhile, the resolution of the high mobility ions, which is normally critical, remains almost the same as compared to a chromate buffer. With an electrokinetic injection, the limit of detection (LOD) of the common ions is 2–13 nM and the detection range is linear up to 0.5–3 μM. With a hydrostatic injection the LOD is 0.15–1 μM and the detection range is linear up to 25–200 μM. The identification of ions is performed by comparing the mobility of the ions with that of standards, taking the apparent and effective mobility of HCO₃⁻, which is normally present in the sample solution, as a reference.     

Ion chromatography of organic-rich natural waters from peatlands: I. Cl, NO2, Br, NO3, HPO4, SO4 and oxalate

Organic-rich natural waters from peat bogs in continental (Switzerland) and maritime (Shetland Islands, Scotland) areas were analysed for Cl⁻, NO₂⁻, Br⁻, NO₃⁻, HPO₄²⁻, SO₄²⁻ and oxalate using ion chromatography. These anions can be determined simultaneously in the surface and pore water samples from the continental bogs using a 250-μl injection loop. Using this loop, the detection limits were ca. 5 ng/g for the monovalent anions and SO₄²⁻ and 10 ng/g for HPO₄²⁻ and oxalate. An organics-removal cartridge (Dionex OnGuard P) was used to remove humic materials. These cartridges did not significantly affect the measured concentrations of anions in blind standards. Analyses of deionized water treated with these cartridges are not significantly different from those for untreated deionized water. For the maritime bogs, the relatively high concentrations of Cl⁻ (more than 100μ/g in many samples) and SO₄²⁻ (up to 50 μg/g) require two separate determinations for complete analyses. A 10-μl injection loop was used to determine Cl⁻, Br⁻ and SO₄²⁻. A 250-μl injection loop was used to measure NO₂⁻, NO₃⁻, HPO ₄²⁻ and oxalate. In each instance a Dionex OnGuard P cartridge was used to remove humic materials. In addition, a chloride-removal cartridge (Dionex OnGuard AG) was used to remove Cl⁻ when the larger injection loop was used. This cartridge has no significant effect on the measurement of HPO_4-²⁻ at concentrations of 20 ng/g. In each of the bog water chromatograms there were usually a number of unknown peaks. These are probably due mainly to organic anions.     

Fingerprint patterns from laser-induced Azido photochemistry of spin-labeled photoaffinity ATP analogs in matrix-assisted laser desorption/ionization mass spectrometry

The photochemical reaction of azide derivatives induced by ultraviolet (UV) laser in matrix-assisted laser desorption/ionization mass spectrometry (MALDI) is reported. A novel synthesized class of azide aromatic derivatives, spin-labeled photoaffinity non-nucleoside adenosine triphosphate (ATP) analogs which are useful probes in study of muscle contraction mechanism, is used in this investigation. In the negative ion MALDI spectra of these ATP analogs, “fingerprint” peaks corresponding to [M − 10 − 1]⁻, [M − 12 − 1]⁻, [M − 16 − 1]⁻, [M − 26 − 1]⁻, [M − 28 − 1]⁻, [M − 41 − 1]⁻, and [M − 42 − 1]⁻ were observed with relative intensities depending on the MALDI matrix. Only the [M − 16 − 1]⁻ is present in the similar mass spectra of the analog in which the azido group is replaced by a hydrogen. A model is suggested for the photochemical reactions of azide derivatives under UV laser irradiation. The photoreaction fingerprint information is diagnostically useful in characterization of azido compounds, especially for spin-labeled photoaffinity non-nucleoside ATP analogs.     

Analysis of acrylamide in coffee and dietary exposure to acrylamide from coffee

An analytical method for analysing acrylamide in coffee was validated. The analysis of prepared coffee includes a comprehensive clean-up using multimode solid-phase extraction (SPE) by automatic SPE equipment and detection by liquid chromatography tandem mass spectrometry using electrospray in the positive mode. The recoveries of acrylamide in ready-to-drink coffee spiked with 5 and 10 μg l⁻¹ were 96±14% and 100±8%, respectively. Within laboratory reproducibility for the same spiking levels were 14% and 9%, respectively. Coffee samples (n = 25) prepared twice by coffee machines and twice by a French Press Cafetière coffee maker contained 8±3 μg l⁻¹ and 9±3 μg l⁻¹ acrylamide. Five ready-to-drink instant coffee prepared twice contained 8±2 μg l⁻¹. Hence, the results do not show significant differences in the acrylamide contents in ready-to-drink coffee prepared by coffee machine, French Press or from instant coffee. Medium roasted coffee contained more acrylamide (10 μg l⁻¹) than dark roasted coffee (5 μg l⁻¹). Males aged 35–45 years, drinking on average 1.1 l coffee per day are exposed to the highest doses of acrylamide from coffee. The dietary intake of acrylamide from coffee comprises, on an average, 10 μg day⁻¹ for males and 9 μg day⁻¹ for females aged 35–45 years. Probabilistic modelling of the exposure of Danish consumers (all adults) to acrylamide from coffee shows a mean exposure of 6.5 μg day⁻¹ and a 95 percentile of 18 μg day⁻¹.     

Equilibrium and structural studies of silicon(IV) and aluminium(III) in aqueous solution—10. A potentiometric study of aluminium(III) pyrocatecholates and aluminium(III) hydroxo pyrocatecholates in 0.6 M Na(Cl)

Equilibria between aluminium(III), pyrocatechol (1,2-dihydroxybenzene, H₂L) and OH⁻ were studied in 0.6 M Na(Cl) medium at 25°C. The measurements were performed as emf titrations (glass electrode) within the limits 1.5 ≤ − log[H⁺] ≤ 9; 0.0005 ≤ B ≤ 0.015 M; 0.006 ≤ C ≤ 0.03 M and 2 ≤ C/B ≤ 30 (B and C stand for the total concentrations of aluminium(III) and pyrocatechol respectively). All data can be explained with a main series of complexes: A1L⁺, log β_−2,1,1 = − 6.337 ± 0.005; A1L₂⁻, log β_−4,1,2 = −15.44 ± 0.017 and A1L₃³⁻, log β_−6,1,3 = − 28.62 ± 0.024 together with two minor species: Al(OH)L₂²⁻, log β_−5,1,2 = − 23.45 ± 0.079 and Al₃(OH)₃L₃, log β_−9,3,3 = − 29.91 ± 0.066. Of the two, the latter probably is a type of average composition complex principally occurring at low C/B quotients. The first acidity constant for pyrocatechol as determined in separate experiments is log β_−1,0,1 = − 9.198 ± 0.001. The standard deviations given are 3σ(log β p,q,r). Data were analyzed with the least squares computer program LETAGROPVRID. In a model calculation using kaolinite as solid phase, we compared the complexation ability of this system with that of the system Al³⁺-OH⁻-salicylic acid, reported earlier in this series.     

Methods for separation of trace amounts of platinum and investigation of the influence of interfering elements during platinum determination in copper ores and copper concentrates by graphite furnace atomic absorption spectrometry

A THGA graphite furnace with Zeeman background correction has been used to determine platinum content in copper ore and copper concentrate at the part per billion (ppb) concentration level. Two different procedures for the separation of trace platinum have been applied: (i) use of an ion exchange resin; and (ii) a two-stage method based on platinum separation on inorganic carriers. The influence of interfering elements in the matrix (Cu, Pb, Fe, Ti, V, Au, Pd, Ir, Rh and Al) has been examined using a graphite furnace. It was found that the presence of Cu (12.5–100 mg l⁻¹), Pb (100–500 mg l⁻¹), Fe (100–2000 mg l⁻¹), Ti (25–100 mg l⁻¹), V (25–100 mg l⁻¹), Au (25–300 mg l⁻¹), Pd (20–250 mg l⁻¹), Ir (0.5–3.5 mg l⁻¹) and Rh (0.025–1 mg l⁻¹) in the samples analyzed has no effect on the platinum absorption signal when using a recommended temperature program (T_pyr=1300°C, T_at=2450°C). Spectral interference was observed, which was due to aluminum, as a result of the close neighborhood of the Pt 265.945-nm and Al 266.039-nm lines. This interference could not be eliminated by the Zeeman background correction.     

Preparation of novel ion exchange polyurethane foam and its application for separation and determination of palladium in environmental samples

The new strong anion exchanger (PUFIX) from polyurethane foam was prepared by coupling of the primary amine of the foam matrix with ethyl iodide. PUFIX was characterized using different tools (IR spectra, elemental analysis, density and thermal analysis). The sorption properties of the new anion exchanger (PUFIX) and chromatographic behaviour for separation and determination of palladium(II) ions at low concentrations from aqueous iodide or thiocyanate media were investigated by a batch and dynamic processes. The maximum sorption of Pd(II) was in the pH range of 0.3–2. The kinetics of sorption of the Pd(II) by the PUFIX was found to be fast with average values of half-life of sorption (t_1/2) of 3.32 min. The variation of the sorption of Pd(II) with temperature gives average values of ΔH, ΔS, ΔG and ΔE to be −38.3 kJ mol⁻¹, −100.7 J K⁻¹ mol⁻¹, −8.3 and 11.8 kJ mol⁻¹, respectively. The sorption capacity of PUFIX was 1.69 mmol g⁻¹ for Pd(II), preconcentration factors of values ≈250 and the recovery 99–100% were achieved (R.S.D. ≈ 1.24%). The lower detection limit, 1.28 ng mL⁻¹ was evaluated using spectrophotometric method (R.S.D. ≈ 2.46%).     

Determination of phosphate in hydroponic nutrient solutions using flow injection potentiometry and a cobalt-wire phosphate ion-selective electrode

The direct flow injection potentiometric (FIP) analysis of phosphate in hydroponic nutrient solution has been carried out using a cobalt-wire ion-selective electrode (ISE). Synthetic hydroponic nutrient solution, commercial hydroponic nutrient solution and working hydroponic farm nutrient solution were analysed for phosphate using the FIP technique. It is shown that FIP results compare favourably to standard methods of analysis such as spectrophotometry and indirect photometric ion-pair chromatography. Reproducible FIP response curves with a slope of −(47.57±0.03) mV per decade and intercept of −(169.7±0.1) mV were obtained for four separate calibrations in the concentration range 5.0×10⁻⁴–1.0×10⁻² M H₂PO₄⁻. Anion corrections for interferences by Cl⁻, NO₃⁻ and SO₄²⁻ were applied to all samples using the selectivity coefficients determined independently using a fixed interference method. Nevertheless, it was found that anion corrections were not necessary, as the deviations fell within the bounds of experimental error for the cobalt-wire ISE technique (i.e.±2–5% R.S.D.). The proposed FIP method enables the direct determination of phosphate in hydroponic nutrient solutions.     

Artificial neural networks for prediction of mycobacterial promoter sequences

A multilayered feed-forward ANN architecture trained using the error-back-propagation (EBP) algorithm has been developed for predicting whether a given nucleotide sequence is a mycobacterial promoter sequence. Owing to the high prediction capability (97%) of the developed network model, it has been further used in conjunction with the caliper randomization (CR) approach for determining the structurally/functionally important regions in the promoter sequences. The results obtained thereby indicate that: (i) upstream region of −35 box, (ii) −35 region, (iii) spacer region and, (iv) −10 box, are important for mycobacterial promoters. The CR approach also suggests that the −38 to −29 region plays a significant role in determining whether a given sequence is a mycobacterial promoter. In essence, the present study establishes ANNs as a tool for predicting mycobacterial promoter sequences and determining structurally/functionally important sub-regions therein.     

Synthesis of sulfur analogues of methyl and allyl kojibiosides and methyl isomaltoside and conformational analysis of the kojibiosides

The synthesis of methyl and allyl 5′-thio--D-kojibiosides and methyl 5′-thio--D-isomaltoside is described. The phenylselenoglycoside and trichloroacetimidate of 2,3,4,6-tetra-O-acetyl-5-thioglucose have been employed as glycosyl donors to glycosylate glucopyranosyl acceptors with 2-OH and 6-OH positions free. The disaccharides thus obtained are potential glucosidase inhibitors. The conformational preferences of allyl 5′-thiokojibioside (34) were studied by comparison of experimental NOE curves with the theoretical counterparts for the corresponding methyl glycoside 25, derived from a Boltzmann-averaged grid search using the program PIMM91. Very good agreement of experimental NOE curves derived from selective NOE measurments with the theoretical curves is found. The data are consistent with the population of a global minimum structure (Φ=−43, Ψ=−39 degrees) to the extent of 90%, and a second local minimum (Φ=−36, Ψ=−173 degrees) to the extent of 6%. An X-ray crystal structure of 34 at 190 K (R=4.2%) indicates a conformation (Φ=−46, Ψ=−23 degrees) that is similar to that of the global minimum.     

Determination of aluminium and manganese in human scalp hair by electrothermal atomic absorption spectrometry using slurry sampling

Methods for the determination of aluminium and manganese in human scalp hair samples by electrothermal atomic absorption spectrometry using the slurry sampling technique were developed. Palladium and magnesium nitrate were used as chemical modifiers. Hair samples were pulverized using a zirconia vibrational mill ball, and were prepared as aqueous slurries. Determinations can be performed in the linear ranges of 1.9–150 μg l⁻¹ Al³⁺ and 0.03–10.0 μg l⁻¹ Mn²⁺. Limits of detection of 0.9 mg kg⁻¹ and 27.6 μg kg⁻¹ were obtained for aluminium and manganese, respectively. The analytical recoveries were between 99.6 and 101.8% for aluminium and in the 98.3–101.3% range for manganese. The repeatability of the methods (n=11), slurry preparation procedure and ETAAS measurement, was 16.0 and 7.9% for aluminium and manganese, respectively. The methods were finally applied to the aluminium and manganese determination in 25 scalp hair samples from healthy adults. The levels for aluminium were between 8.21 and 74.08 mg kg⁻¹, while concentrations between 0.03 and 1.20 mg kg⁻¹ were found for manganese.     

A label-free electrochemical immunosensor based on gold nanoparticles for detection of paraoxon

An electrochemical immunosensor for the direct determination of paraoxon has been developed based on the biocomposites of gold nanoparticles loaded with paraoxon antibodies. The biocomposites are immobilized on the glassy carbon electrode (GCE) using Nafion membrane. On the immunosensor prepared paraoxon shows well-shaped CV with reduction and oxidation peaks located −0.08 and −0.03 mV versus SCE, respectively. The detection of paraoxon performed at −0.03 mV is beneficial for guaranteeing sufficient selectivity. The amount of the biocomposite consisting gold nanoparticles loaded with antibodies and the volume of Nafion solution used for fabricating the immunosensor have been studied to ensure sensitivity and conductivity of the immunosensor. The immunosensor has been employed for monitoring the concentrations of paraoxon in aqueous samples up to 1920 μg l⁻¹ with a detection limit of 12 μg l⁻¹.     

Spectrophotometric determination of nitrate and nitrite in soil and water samples with a diazotizable aromatic amine and coupling agent using column preconcentration on naphthalene supported with ion-pair of tetradecyldimethylbenzylammonium and iodide

Composite diazotization-coupling reagents containing sulfanilamide (SAM), sulfapyridine (SP) or sulfathiazole (ST) as the diazotizable aromatic amines and sodium 1-naphthol-4-sulfonate (NS) as the coupling agent using column preconcentration on naphthalene-tetradecyldimethylbenzylammonium(TDBA)-iodide adsorbent have been used for the spectrometric determination of trace nitrate and nitrite in soil and water samples. Nitrite ion reacts with SAM in the pH range 2.0–5.0, SP in the pH range 2.0–2.5 and ST in the pH range 2.0–3.3 in HCl medium to form water-soluble colourless diazonium cations. These cations were coupled with NS in the pH range 9.0–12.0 for the SAM system, 9.6–12.0 for the SP system and 8.5–12.0 for the ST system to be retained on naphthalene-TDBA-I material packed in a column. The solid mass is dissolved from the column with 5 ml of dimethylformamide and the absorbance is measured spectrometerically at 543 nm for SAM-NS, 533 nm for SP-NS and 535 nm for ST-NS. Nitrate is reduced to nitrite by a copper-coated cadmium reductor column and the nitrite is then treated with the diazotization-coupling reagent by column preconcentration. The absorbance due to the sum of nitrate and nitrite is measured and nitrate is determined by difference. The calibration graph was linear over the range 2–40 ng NO₂⁻-N ml⁻¹ and 1.5–30 ng NO₃⁻-N ml⁻¹ in aqueous samples for the SAM and ST systems and 2–48 ng NO₂⁻-N ml⁻¹ and 1.5–36 ng NO₃⁻-N ml⁻¹ in aqueous samples for the SP system, respectively. The sensitivity, accuracy and precision of the systems decreased in the order STSAMSP. The detection limits were 1.4 ng NO₂⁻-N ml⁻¹ and 1.1 ng NO₃⁻-N ml⁻¹ for SAM, 1.6 ng NO₂⁻-N ml⁻¹ and 1.2 ng NO₃⁻-N ml⁻¹ for SP, and 1.0 ng NO₂⁻-N ml⁻¹ and 0.75 ng NO₃⁻-N ml⁻¹ for ST, respectively. The preconcentration factors are 8, 5 and 6 for SAM-NS, SP-NS and ST-NS, respectively. Interferences from various foreign ions have been studied and the methods have been applied to the determination of ng ml⁻¹ levels of nitrite and nitrate in soil and water samples. The mean recovery was 95–102% for all three systems.     

Simultaneous derivative spectrophotometric determination of thorium and uranium in a micellar medium

Derivative photometric methods for trace analysis of Th(IV) and UO₂(II), and their simultaneous determination in mixtures using 5,8-dihydroxy-1,4-naphthoquinone in a micellar medium are reported. Molar absorptivity and Sandell's sensitivity of 1:2 Th(IV) and 1:1 UO₂(II) complexes at their λ_max, 614.5 nm and 637.0 nm are, 1.19 × 10⁴ 1/mol/cm and 1.12 × 10⁴ 1/mol/cm and 1.95 × 10⁻² μg/cm² and 2.13 × 10⁻² μg/cm² μg/cm², respectively. Calibration graph is linear over the range 9.28 × 10⁻²−18.56 μg/ml of Th(IV) and 9.52 × 10⁻²−19.04 μg/ml of UO₂(II). Though presence of Th(IV) and UO₂(II) causes interference in each others determination, 9.28 × 10⁻¹−9.28 μg/ml Th(IV) and 9.52 × 10⁻¹−9.52 μg/ml UO₂(II) when present together, can be simultaneously determined using derivative spectra.     

Ideal gas thermodynamic properties of benzenediols: Pyrocatechol, resorcinol and hydroquinone

The vibrational fundamentals have been selected using the available literature data. −271.96, −274.89 and −261.71 kJ mole⁻¹ are selected for the enthalpies of formation (g, 298.15 K) for pyrocatechol, resorcinol and hydroquinone, respectively. The ideal gas thermodynamic properties are obtained assuming one, three and two rotational isomers for 1,2-, 1,3-, and 1,4-benzenediol, respectively.