Simultaneous determination of arsenic, antimony and selenium by gas-phase diode array molecular absorption spectrometry, after preconcentration in a cryogenic trap

This paper describes a method for the simultaneous determination of As(III), Sb(III) and Se(IV) by combining hydride generation and gas phase molecular absorption spectrometry. A system for continuous hydride generation has been designed and developed, based on the use of a double process of gas-liquid separation, and optimal compromise operation conditions for the three compounds have been found. After generation, the hydrides are collected in a liquid nitrogen cryogenic trap, and then evaporated and driven to the flow cell of a diode array spectrophotometer, in which the transient signals over the 190–250 nm wavelength interval are measured. Under the recommended conditions (sample flow: 35 ml min⁻¹, 0.5 M HCl; reductor flow: 4 ml min⁻¹ of 4% NaBH₄, solution) linear response ranges above 50 μg 1⁻¹ for As(III), 30 μg 1⁻¹ for Sb(III) and 200 μg 1⁻¹ for Se(IV) are obtained with detection limits of 22 μg 1⁻¹, 15 μg 1⁻¹ and 65 μg 1⁻¹, respectively. Multiwavelength linear regression equations were used for the simultaneous determination of the three elements in different synthetic samples, with good precision and accuracy and to study simultaneously the interference from different chemical species for the three compounds. Results were similar to those obtained by other techniques using hydride generation.     

Investigation of on-line coupling electrothermal atomic absorption spectrometry with flow injection sorption preconcentration using a knotted reactor for totally automatic determination of lead in water samples

A flow injection on-line sorption preconcentration electrothermal atomic absorption spectrometric system for fully automatic determination of lead in water was investigated. The discrete non-flow-through nature of ETAAS, the limited capacity of the graphite tube and the relatively large volume of the knotted reactor (KR) are obstacles to overcome for the on-line coupling of the KR sorption preconcentration system with ETAAS. A new FI manifold has been developed with the aim of reducing the eluate volume and minimizing dispersion. The lead diethyldithiocarbamate complex was adsorbed on the inner walls of a knotted reactor made of PTFE tubing (100 cm long, 0.5 mm i.d.). After that, an air flow was introduced to remove the residual solution from the KR and the eluate delivery tube, then the adsorbed analyte chelate was quantitatively eluted into a delivery tube with 50 μl of ethanol. An air flow was used to propel the eluent from the eluent loop through the reactor and to introduce all the ethanolic eluate onto the platform of the transversely heated graphite tube atomizer, which was preheated to 80°C. With the use of the new FI manifold, the consumption of eluent was greatly reduced and dispersion was minimized. The adsorption efficiency was 58%, and the enhancement factor was 142 in the concentration range 0.01–0.05 μg l⁻¹ Pb at a sample loading rate of 6.8 ml min⁻¹ with 60 s preconcentration time. For the range 0.1–2.0 μg l⁻¹ of Pb a loading rate of 3.0 ml min⁻¹ and 30 s preconcentration time were chosen, resulting in an adsorption efficiency of 42% and an enhancement factor of 21, respectively. A detection limit (3σ) of 2.2 ng l⁻¹ of lead was obtained using a sample loading rate of 6.8 ml min⁻¹ and 60 s preconcentration. The relative standard deviation of the entire procedure was 4.9% at the 0.01 μg l⁻¹ Pb level with a loading rate of 6.8 ml min⁻¹ and 60 s preconcentration, and 2.9% at the 0.5 μg l⁻¹ Pb level with a 3.0 ml min⁻¹ loading rate and 30 s preconcentration. Efficient washing of the matrix from the reactor was critical, requiring the use of the standard addition method for seawater samples. The analytical results obtained for seawater and river water standard reference materials were in good agreement with the certified values.     

Flow-injection in-line complexation for ion-pair reversed phase high performance liquid chromatography of some metal-4-(2-pyridylazo) resorcinol chelates

Flow injection (FI) was coupled to ion-pair reversed phase high performance liquid chromatography (IP-RPHPLC) for the simultaneous analysis of some metal-4-(2-pyridylazo) resorcinol (PAR) chelates. A simple reverse flow injection (rFI) set-up was used for in-line complexation of metal-PAR chelates prior to their separation by IP-RPHPLC. The rFI conditions were: injection volume of PAR 85 μL, flow rate of metal stream 4.5 mL min⁻¹, concentration of PAR 1.8 × 10⁻⁴ mol L⁻¹ and the mixing coil length of 150 cm. IP-RPHPLC was carried out using a C₁₈ μBondapak column with the mobile phase containing 37% acetonitrile, 3.0 mmol L⁻¹ acetate buffer pH 6.0 and 6.2 mmol L⁻¹ tetrabutylammonium bromide (TBABr) at a flow rate of 1.0 mL min⁻¹ and visible detection at 530 and 440 nm. The analysis cycle including in-line complexation and separation by IP-RPHPLC was 16 min, which able to separate Cr(VI) and the PAR chelates of Co(II), Ni(II) and Cu(II).     

Flow injection determination of selenium by successive retention of Se(IV) and tetrahydroborate(III) on an anion-exchange resin and hydride generation electrothermal atomization atomic absorption spectrometry with in-atomizer trapping: Part 1. Method development and investigation of interferences

A sample solution was passed at 20 ml min⁻¹ through a column (150×4 mm²) of Amberlite IRA-410Stron anion-exchange resin for 60 s. After washing, a solution of 0.1% sodium borohydride was passed through the column for 60 s at 5.1 ml min⁻¹. Following a second wash, a solution of 8 mol l⁻¹ hydrochloric acid was passed at 5.1 ml min⁻¹ for 45 s. The hydrogen selenide was stripped from the eluent solution by the addition of an argon flow at 150 ml min⁻¹ and the bulk phases were separated by a glass gas–liquid separator containing glass beads. The gas stream was dried by passing through a Nafion® dryer and fed, via a quartz capillary tube, into the dosing hole of a transversely heated graphite cuvette containing an integrated L’vov platform which had been pretreated with 120 μg of iridium as trapping agent. The furnace was held at a temperature of 250°C during this trapping stage and then stepped to 2000°C for atomization. The calibration was performed with aqueous standards solution of selenium (selenite, SeO₃²⁻) with quantification by peak area. A number of experimental parameters, including reagent flow rates and composition., nature of the gas–liquid separator, nature of the anion-exchange resin, column dimensions, argon flow rate and sample pH, were optimized. The effects of a number of possible interferents, both anionic and cationic were studies for a solution of 500 ng 1⁻¹ of selenium. The most severe depressions were caused by iron (III) and mercury (II) for which concentrations of 20 and 10 mg  1⁻¹ caused a 5% depression on the selenium signal. For the other cations (cadmium, cobalt, copper, lead,. magnesium, and nickel) concentrations of 50–70 mg 1⁻¹ could be tolerated. Arsenate interfered at a concentration of 3 mg⁻¹, whereas concentrations of chloride, bromide, iodide, perchlorate, and sulfate of 500–900 mg l⁻¹ could be tolerated. A linear response was obtained between the detection limit of 4 ng 1⁻¹, with a characteristic mass of 130 pg. The RSDs for solutions containing 100 and 200 ng 1⁻¹ selenium were 2.3% and 1.5%, respectively.     

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.     

Reverse flow injection spectrophotometric determination of iron(III) using chlortetracycline reagent

A simple reversed flow injection colourimetric procedure for determining iron(III) was proposed. It is based on the reaction between iron(III) with chlortetracycline, resulting in an intense yellow complex with a suitable absorption at 435 nm. A 200 μl chlortetracycline reagent solution was injected into the phosphate buffer stream (flow rate 2.0 ml min⁻¹) which was then merged with iron(III) standard or sample in dilute nitric acid stream (flow rate 1.5 ml min⁻¹). Optimum conditions for determining iron(III) were investigated by univariate method. Under the optimum conditions, a linear calibration graph was obtained over the range 0.5–20.0 μg ml⁻¹. The detection limit (3σ) and the quantification limit (10σ) were 0.10 and 0.82 μg ml⁻¹, respectively. The relatives standard deviation of the proposed method calculated from 12 replicate injections of 2.0 and 10.0 μg ml⁻¹ iron(III) were 0.43 and 0.59%, respectively. The sample throughput was 60 h⁻¹. The proposed method has been satisfactorily applied to the determination of iron(III) in natural waters.     

Coupling of flow injection wetting-film extraction without segmentation and phase separation to flame atomic absorption spectrometry for the determination of trace copper in water samples

A flow injection wetting-film extraction system without segmentor and phase separator has been coupled to flame atomic absorption spectrometry for the determination of trace copper. Isobutyl methyl ketone (MIBK) was selected as coating solvent and 8-hydroxyquinoline (oxine) as the chelating reagent. By switching of a 8-channel valve and alternative initiation of two peristaltic pumps, MIBK, sample solution containing copper chelate of oxine, and air-segment sandwiched eluting solution (1.0 mol l⁻¹ nitric acid) were sequentially aspirated into an extraction coil made of PTFE tubing of 360 cm length and 0.5 mm i.d. The formation of organic film in the wall of the extraction coil, extraction of the copper chelate into the organic film and back-extraction of the analyte into the eluting solution occurred consecutively when these zones aspirated into the extraction coil were propelled down the extraction coil by a carrier solution at a flow rate of 2 ml min⁻¹. After leaving the extraction coil, the concentrated zone was transported to the nebulizer at its free uptake rate for atomization. Under the optimized conditions, an enrichment factor of 43 and a detection limit of 0.2 μg l⁻¹ copper were achieved at a sample throughput rate of 30 h⁻¹. Eleven determinations of a standard copper solution of 60 μg l⁻¹ gave a relative standard deviation of 1.5%. Foreign ions possibly present in tap water and natural water did not interfere with the copper determination. The developed method has been successfully used to the determination of copper content of tap water and river water.     

A peroxidase-tetrathiafulvalene biosensor based on self-assembled monolayer modified Au electrodes for the flow-injection determination of hydrogen peroxide

The construction and performance under flow-injection conditions of an integrated amperometric biosensor for hydrogen peroxide is reported. The design of the bioelectrode is based on a mercaptopropionic acid (MPA) self-assembled monolayer (SAM) modified gold disk electrode on which horseradish peroxidase (HRP, 24.3 U) was immobilized by cross-linking with glutaraldehyde together with the mediator tetrathiafulvalene (TTF, 1 μmol), which was entrapped in the three-dimensional aggregate formed.

The amperometric biosensor allows the obtention of reproducible flow injection amperometric responses at an applied potential of 0.00 V in 0.05 mol L⁻¹ phosphate buffer, pH 7.0 (flow rate: 1.40 mL min⁻¹, injection volume: 150 μL), with a range of linearity for hydrogen peroxide within the 2.0 × 10⁻⁷–1.0 × 10⁻⁴ mol L⁻¹ concentration range (slope: (2.33 ± 0.02) × 10⁻² A mol⁻¹ L, r = 0.999). A detection limit of 6.9 × 10⁻⁸ mol L⁻¹ was obtained together with a R.S.D. (n = 50) of 2.7% for a hydrogen peroxide concentration level of 5.0 × 10⁻⁵ mol L⁻¹. The immobilization method showed a good reproducibility with a R.S.D. of 5.3% for five different electrodes. Moreover, the useful lifetime of one single biosensor was estimated in 13 days.

The SAM-based biosensor was applied for the determination of hydrogen peroxide in rainwater and in a hair dye. The results obtained were validated by comparison with those obtained with a spectrophotometric reference method. In addition, the recovery of hydrogen peroxide in sterilised milk was tested.     

Determination of As(III) and total inorganic arsenic by flow injection hydride generation atomic absorption spectrometry

A simple procedure was developed for the direct determination of As(III) and As(V) in water samples by flow injection hydride generation atomic absorption spectrometry (FI–HG–AAS), without pre-reduction of As(V). The flow injection system was operated in the merging zones configuration, where sample and NaBH₄ are simultaneously injected into two carrier streams, HCl and H₂O, respectively. Sample and reagent injected volumes were of 250 μl and flow rate of 3.6 ml min⁻¹ for hydrochloric acid and de-ionised water. The NaBH₄ concentration was maintained at 0.1% (w/v), it would be possible to perform arsine selective generation from As(III) and on-line arsine generation with 3.0% (w/v) NaBH₄ to obtain total arsenic concentration. As(V) was calculated as the difference between total As and As(III). Both procedures were tolerant to potential interference. So, interference such as Fe(III), Cu(II), Ni(II), Sb(III), Sn(II) and Se(IV) could, at an As(III) level of 0.1 mg l⁻¹, be tolerated at a weight excess of 5000, 5000, 500, 100, 10 and 5 times, respectively. With the proposed procedure, detection limits of 0.3 ng ml⁻¹ for As(III) and 0.5 ng ml⁻¹ for As(V) were achieved. The relative standard deviations were of 2.3% for 0.1 mg l⁻¹ As(III) and 2.0% for 0.1 mg l⁻¹ As(V). A sampling rate of about 120 determinations per hour was achieved, requiring 30 ml of NaBH₄ and waste generation in order of 450 ml. The method was shown to be satisfactory for determination of traces arsenic in water samples. The assay of a certified drinking water sample was 81.7±1.7 μg l⁻¹ (certified value 80.0±0.5 μg l⁻¹).     

An improved procedure for flow-based turbidimetric sulphate determination based on a liquid core waveguide and pulsed flows

An improved flow-based procedure is proposed for turbidimetric sulphate determination in waters. The flow system was designed with solenoid micro-pumps in order to improve mixing conditions and minimize reagent consumption as well as waste generation. Stable baselines were observed in view of the pulsed flow characteristic of the systems designed with solenoid micro-pumps, thus making the use of washing solutions unnecessary. The nucleation process was improved by stopping the flow prior to the measurement, thus avoiding the need of sulphate addition. When a 1-cm optical path flow cell was employed, linear response was achieved within 20–200 mg L⁻¹, described by the equation S = −0.0767 + 0.00438C (mg L⁻¹), r = 0.999. The detection limit was estimated as 3 mg L⁻¹ at the 99.7% confidence level and the coefficient of variation was 2.4% (n = 20). The sampling rate was estimated as 33 determinations per hour. A long pathlength (100-cm) flow cell based on a liquid core waveguide was exploited to increase sensitivity in turbidimetry. Baseline drifts were avoided by a periodical washing step with EDTA in alkaline medium. Linear response was observed within 7–16 mg L⁻¹, described by the equation S = −0.865 + 0.132C (mg L⁻¹), r = 0.999. The detection limit was estimated as 150 μg L⁻¹ at the 99.7% confidence level and the coefficient of variation was 3.0% (n = 20). The sampling rate was estimated as 25 determinations per hour. The results obtained for freshwater and rain water samples were in agreement with those achieved by batch turbidimetry at the 95% confidence level.     

Simultaneous flow injection determination of calcium and fluoride in natural and borehole water with conventional ion-selective electrodes in series

An on-line automated system for the simultaneous flow injection determination of calcium and fluoride in natural and borehole water with conventional calcium-selective and fluoride-selective membrane electrodes as sensors in series is described. Samples (30 μl) are injected into a TISAB II (pH=5.50) carrier solution as an ionic strength adjustment buffer. The sample-buffer zone formed is first channeled to a fluoride-selective membrane electrode and then via the calcium-selective membrane electrode to the reference electrodes. The system is suitable for the simultaneous on-site monitoring of calcium (linear range 10⁻⁵–10⁻² mol l⁻¹ detection limit 1.94×10⁻⁶ mol l⁻¹ recovery 99.22%, RSD<0.5%) and fluoride (linear range 10⁻⁵–10⁻² mol l⁻¹ detection limit 4.83×10⁻⁶ mol l⁻¹ recovery 98.63%, RSD=0.3%) at a sampling rate of 60 samples h⁻¹.     

Tuning the parameters for fast respirometry

The aerobic bacterial respiration rate is an indicator of microbial growth and metabolism, essential for monitoring the oxidation process and organic load content of samples in a diverse field of application from influent streams in wastewater treatment facilities to industrial fermentations. This paper looks at the influence of parameters, such as culture concentration and volume, sample surface area/volume ratio and headspace volume to achieve optimisation of respirometry measurement and thus design a bench-top respirometric device, based on the monitoring of the pressure changes in a closed chamber where a bacterial culture is allowed to respire in contact with a sample. Contrary to traditional respirometry, the goal is detection of bacterial respiration within 5 min in a minimal sample volume. Both qualitative and quantitative data could be derived using a simple equation and fine-tuning of the micro-manometric parameters of the device, with a most important finding being that minimal headspace volume in combination with elevated bacterial populations maximised absolute pressure change response and favoured high sensitivity at short response time, even though the conditions indicated oxygen-limitation. Furthermore, in comparison with a commercially available respirometer the typical respiration rate of stationary phase P. putida M10 gave oxygen uptake rate (OUR) and specific oxygen uptake rate (SOUR) of 38 μmol l⁻¹ min⁻¹ and 5 μmol g⁻¹ min⁻¹, respectively with the ‘classical’ system, while the μ-Warburg device designed here showed a typical response, for the culture with the same dry cell concentration, of 66 μmol l⁻¹ min⁻¹ for the OUR and 9 μmol g⁻¹ min⁻¹ for the SOUR. The remarkable outcome from this data, therefore, is that it appears that the high surface area/volume geometry of the μ-Warburg device design has achieved less respiration limitation, even though the sample is unstirred. This presents important insight regarding future respirometer design.     

Repetitive determination of ascorbic acid using iron(III)-1.10-phenanthroline-peroxodisulfate system in a circulatory flow injection method

Ascorbic acid (AA) could be determined in large quantities of a co-existing oxidant. The incorporation of an on-line reagent regeneration step based on redox reaction eliminates the baseline drift in the procedure. This makes it possible to adopt a circulatory flow injection method (cyclic FIA) and to determine AA repetitively. The method is based on the reduction of iron(III) to iron(II) by the analyte, the reaction of the produced iron(II) with 1,10-phenanthroline (phen) in a weak acidic medium to form a colored complex, and the subsequent oxidation reaction of iron(II) to iron(III) by the co-existing peroxodisulfate. A solution (50 ml) of 3.0×10⁻⁴ mol l⁻¹ ferric chloride, 9.0×10⁻⁴ mol l⁻¹ phen and 5.0×10⁻² mol l⁻¹ ammonium peroxodisulfate in acetate buffer (0.2 mol l⁻¹, pH 4.5) is continuously circulated at a constant flow rate of 1.0 ml min⁻¹. Into this stream, an aliquot (20 μl) of the sample solution containing AA is quickly injected by means of a six-way valve. The complex formed is monitored spectrophotometrically (at 510 nm) in the flow system. The stream then returns to the reservoir after passing through a time-delay coil (50 m). The iron(II)–(phen)₃ complex is oxidized to iron(III)–(phen)₃ complex by peroxodisulfate which exists excessively in the circulating reagent solution. The proposed method allows as many as 300 repetitive determinations of 15 mg l⁻¹ AA with only 50 ml reservoir solution. The contents of AA in commercial pharmaceutical products were analyzed to demonstrate the capability of the developed system.     

Development of a positive pressure driven micro-fabricated liquid chromatographic analyzer through rapid-prototyping with poly(dimethylsiloxane) Optimizing chromatographic efficiency with sub-nanoliter injections

A rapid and low-cost means of developing a working prototype for a positive-displacement driven open tubular liquid chromatography (OTLC) analyzer is demonstrated. A novel flow programming and injection strategy was developed and implemented using soft lithography, and evaluated in terms of chromatographic band broadening and efficiency. A separation of two food dyes served as the model sample system. Sample and mobile phase flowed continuously by positive displacement through the OTLC analyzer. Rectangular channels, of dimensions 10 μm deep by 100 μm wide, were micro-fabricated in poly-dimethylsiloxane (PDMS), with the separation portion 6.6 cm long. Using a novel flow programming method, in contrast to electroosmotic flow, sample injection volumes from 0.5 to 10 nl were made in real-time. Band broadening increased substantially for injection volumes over 1 nl. Although underivatized PDMS proved to be a sub-optimal stationary phase, plate heights, H, of 12 μm were experimentally achieved for an unretained analyte with the rectangular channel resulting in a reduced plate height, h, of 1.2. Chromatographic efficiency of the unretained analyte followed the model of an OTLC system limited by mass-transfer in the mobile phase. Flow rates from 6 nl min⁻¹ up to 200 nl min⁻¹ were tested, and van Deemter plots confirmed plate heights were optimum at 6 nl min⁻¹ over the tested flow rate range. Thus, the best separation efficiency, N of 5500 for the 6.6 cm length separation channel, was achieved at the minimum flow rate through the column of 6 nl min⁻¹, or 3 ml year⁻¹. This analyzer is a low-cost sampling and chemical analysis tool that is intended to complement micro-fabricated electrophoretic and related separation devices.     

Silicon determination by inductively coupled plasma atomic emission spectrometry after generation of volatile silicon tetrafluoride

A method for the determination of silicon by inductively coupled plasma atomic emission spectrometry (ICP-AES) is described. The procedure is based on a discontinuous generation of volatile silicon tetrafluoride in concentrated sulphuric acid medium after injecting 125 μl of 0.1%, w/v sodium fluoride solution into 100 μl of the sample. The gaseous silicon tetrafluoride is fed directly into the ICP torch by a flow of 250 ml min⁻¹ Ar carrier gas. The calibration curve was linear up to at least 100 μg ml⁻¹ of Si(IV) and the absolute detection limit was 9.8 ng working with a solution volume of 100 μl. The relative standard deviation for six measurements of 10 μg ml⁻¹ of Si(IV) was 2.32%. The method was applied to the determination of silicon in water and iron ores.     

Flow-injection potentiometric determination of triiodide by plasticized poly(vinyl chloride) membrane electrodes and its application to the determination of chlorine-containing disinfectants

Plasticized poly(vinyl chloride) (PVC) membranes of different compositions were tested for use in the construction of potentiometric flow detectors for triiodide. A membrane with a 2:1 (w/w) 2-nitrophenyl octyl ether to PVC ratio was selected. The influence of thiosulphate in the carrier solution composition and of the flow-injection variables on the determination of triiodide was studied. In the selected conditions, a linear relationship between peak height and log[I₃⁻] was obtained between 5 × 10⁻⁶ and 1 × 10⁻⁴ mol l⁻¹ triiodide. Peak height relative standard deviations for 2 × 10⁻⁵ and 1 × 10⁻⁴ mol l⁻¹ triiodide were ±0.4 and ±1.8%, respectively, and sampling frequency was 80 samples per hour. The method proposed was applied satisfactorily to the iodometric determination of different chlorine-containing disinfectants, among them trichloroisocyanuric acid and dichloroisocyanurate in several types of commercial sample.     

Study of the performance of an optochemical sensor for ammonia

An optical sensor for ammonia based on ion pairing has been investigated. A pH-sensitive dye (bromophenol blue) was immobilized as an ion pair with cetyltrimethylammonium in a silicone matrix. The colour of the dye changes reversibly from yellow to blue with increasing concentration of ammonia in the sample. The concentration of ammonia can be determined by measuring the transmittance at a given wavelength. All measurements were performed with a dual-beam, solid state photometer. The measurement range is from 6 × 10⁻⁷ to 1 × 10⁻³ M (0.01 to 17 μg ml⁻¹) in 0.1 M sodium phosphate buffer, pH 8. The 90% and 100% response times at a flow rate of 2.5 ml min⁻¹ are 4 min and 10 min, respectively, for a change from 41.9 to 82.5 μM ammonia, or 12 min and 48 min, respectively, for change from 160 to 0 μM ammonia. A continuous drift in signal baseline and ammonia sensitivity limited the measurement stability. The sensor was useful over a period of a few days. The storage stability is more than 10 months (dry). No interference due to pH was observed in the range from pH 5 to pH 9. Sensor performance is seriously affected by amines and cationic detergents. The sensor could be sterilized with 3% hydrogen peroxide or dry heat (90 °C).     

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.     

Column technology for capillary electrochromatography

Column technologies for capillary electrochromatography (CEC) are reviewed. To achieve high efficiency, the inner diameters of open-tubular and packed columns should be less than 25 and 200 μm, respectively. To obtain acceptable separation speed under typical CEC conditions (e.g. 30 kV, 1 mm s⁻¹ electroosmotic flow velocity, and 2–4×10⁻⁸ m² V⁻¹ s⁻¹ electroosmotic mobility) the column lengths for open-tubular and packed columns should be less than 120 and 60 cm, respectively. Capillary CEC columns are generally classified into three types: packed, open-tubular, and continuous-bed or monolithic. The various column preparation procedures and the advantages and disadvantages of each column type are discussed in detail.     

Simple flow-injection system for the simultaneous determination of nitrite and nitrate in water samples

A novel spectrophotometric reaction system was developed for the determination of nitrite as well as nitrate in water samples, and was applied to a flow-injection analysis (FIA). The spectrophotometric flow-injection system coupled with a copperised cadmium reductor column was proposed. The detection was based on the nitrosation reaction between nitrite ion and phloroglucinol (1,3,5-trihydroxybenzene), a commercially available phenolic compound. Sample injected into a carrier stream was split into two streams at the Y-shaped connector. One of the streams merged directly and reacted with the reagent stream: nitrite ion in the samples was detected. The other stream was passed through the copperised cadmium reductor column, where the reduction of nitrate to nitrite occurred, and the sample zone was then mixed with the reagent stream and passed through the detector: the sum of nitrate and nitrite was detected. The optimised conditions allow a linear calibration range of 0.03–0.30 μg NO₂⁻-N ml⁻¹ and 0.10–1.00 μg NO₃⁻-N ml⁻¹. The detection limits for nitrite and nitrate, defined as three times the standard deviation of measured blanks are 2.9 ng NO₂⁻-N ml⁻¹ and 2.3 ng NO₃⁻-N ml⁻¹, respectively. Up to 20 samples can be analyzed per hour with a relative standard deviation of less than 1.5%. The proposed method could be applied successfully to the simultaneous determination of nitrite and nitrate in water samples.