Flow analysis-hydride generation-Fourier transform infrared spectrometric determination of antimony in pharmaceuticals

In this work, a flow analysis system with hydride generation and Fourier transform infrared (FTIR) spectrometric detection has been developed for the determination of antimony in pharmaceuticals. The method is based on the on-line mineralization/oxidation of the organic antimonials present in the sample and pre-reduction of Sb(V) to Sb(III) with K₂S₂O₈ and KI, respectively; prior to the stibine generation. The gaseous SbH₃ is separated from the solution in a gas phase separator, and transported by means of a nitrogen carrier into a short pathway (10 cm) IR gas cell, where the corresponding FTIR spectrum is acquired by accumulating 3 scans in a continuous mode. The 1893 cm⁻¹ band was used for the quantification of the antimony. The procedure is carried out in a closed system, which reduces sample handling and makes possible the complete automation of the antimony determination. The figures of merit of the proposed method (linear range: 0-600 mg l⁻¹, limit of detection (3σ)=0.9 mg l⁻¹, limit of quantification (10σ)=3 mg Sb l⁻¹, precision (R.S.D.) less than 1% and sample frequency=28 h⁻¹), are appropriate for the designed application. Furthermore, precise and accurate results were found for the analysis of different antimonial pharmaceutical samples, indicating that the methodology developed represents a valid alternative for the determination of antimony in pharmaceuticals, which could be suitable for the routine control analysis.     

Fourier transform infrared spectrometric determination of Ziram

A procedure has been developed for vapour-phase Fourier transform infrared determination of Ziram, a dithiocarbamate pesticide. The method is based on the evolution of CS₂, after decomposition of the dithiocarbamate with diluted H₂SO₄ at 50°C. The CS₂ evolved was swept by a carrier flow of nitrogen to a laboratory-made infrared gas cell of 39 mm pathlength and 490 μl volume. The signals were registered as a function of time. The area of peaks obtained from absorbance measurement in the wavenumber range between 1600 and 1450 cm⁻¹ were interpolated in a calibration line established from Ziram standards treated in the same way as samples. The method provided an absolute limit of detection of 0.055 mg, a variation coefficient of the order of 6% for an analyte mass of 50 mg, and an analysis time of 3.5 min.     

Flow injection determination of nitrite by fluorescence quenching

A simple, sensitive and selective fluorimetric method for the determination of nitrite ion in waters using a merging zones flow injection system is described. The fluorimetric determination is based on the measurement of the quenching effect produced by nitrite on proflavine (3,6-diaminoacridine) fluorescence (λ_ex/λ_em=290/519 nm).

The optimum experimental conditions were investigated by merging 0.5 ml of the sample and 0.5 ml of a solution of 5 mg l⁻¹ of proflavine (in 0.1 M HCl) in a flow injection system, on-line connected to a flow-cell placed in the conventional sample compartment of a spectrofluorimeter. The selected carrier solution and final flow rate were 0.1 M HCl and 0.5 ml min⁻¹, respectively. A reaction coil of 2 ml was used. As a result of the simplicity of this system, a sample throughput of about 50 samples h⁻¹ can be achieved with the proposed methodology.

The detection limit was 1.1 ng ml⁻¹ (3σ criterion) of nitrite. The repeatability for five sample injections containing 100 ng ml⁻¹ of nitrite was ±0.3% and the observed linear range extended up to 400 ng ml⁻¹. Also, the effect of interferences from various metals and anions commonly present in waters was also studied.

The method was successfully applied to the determination of low levels of nitrite in different water samples (river, fountain, tap and commercial drinking waters).     

Flow injection catalytic spectrophotometric simultaneous determination of nitrite and nitrate

A new flow injection catalytic spectrophotometric method is proposed for the simultaneous determination of nitrite and nitrate based on the catalytic effect of nitrite on the redox reaction between crystal violet and potassium bromate in phosphoric acid medium and nitrate being on-line reduced to nitrite with a cadmium-coated zinc reduction column. The redox reaction is monitored spectrophotometrically by measuring the decrease in the absorbance of crystal violet at the maximum absorption wavelength of 610 nm. A technique of inserting a reduction column into sampling loop is adopted and the flow injection system produces a signal with a shoulder. The height of shoulder in the ascending part of the peak corresponds to the nitrite concentration and the maximum of the peak corresponds to nitrate plus nitrite. The detection limits are 0.3 ng ml⁻¹ for nitrite and 1.0 ng ml⁻¹ for the nitrate. Up to 32 samples can be analyzed per hour with a relative standard deviation of less than 2%. The method has been successfully applied for the simultaneous determination of nitrite and nitrate in natural waters.     

流动注射催化光度法测定NO2-的研究

以流动注射分光光度法,基于NO-2在酸性条件中对溴酸钾氧化胭脂红酸有催化作用这一原理测定NO-2。对实验条件进行了优化。实验结果表明,室温下,当cKBrO3=0.14mol L,c胭脂红酸=3.5×10-4mol L,cH2SO4=1.2mol L时,方法的线性范围为0.005～0.3μg mL,检出限为0.002μg mL。利用该方法对几种河水水样进行了测定。     

Flow injection kinetic spectrophotometric method for the determination of trace amounts of nitrite

In this work, a new, simple and sensitive flow injection catalytic kinetic spectrophotometric determination of nitrite is reported based on catalytic effect of nitrite on the redox reaction between sulfonazo III and potassium bromate in acidic media. The reaction was monitored by measuring the decrease in the absorbance of sulfunazo III at 570 nm. Various chemical (such as the effect of acidity, reagents concentrations) and instrumental parameters (flow rate, reaction coil length, injection volume and temperature) were studied and were optimized. Under the optimum conditions calibration graph was linear in the nitrite concentration ranges of 8.00 × 10⁻³-3.00 × 10⁻¹ μg/ml (with slope of 2.40) and 3.50 × 10⁻¹-1.80 μg/ml (with slope of 0.42). The detection limit was 6.00 × 10⁻³ μg/ml of nitrite, the relative standard deviation (n = 10) was 1.25% and 0.88% for 5.00 × 10⁻² and 2.00 × 10⁻¹ μg/ml of nitrite respectively. About 60 samples in 1 h can be analyzed. The interfering effects of various chemical species were studied. The method was successfully applied in the determination of nitrite in food and environmental samples.     

Vapour phase Fourier transform infrared spectrometric determination of thiourea

A novel and precise procedure for the determination of thiourea based on vapour-generation Fourier transform infrared spectrometry is described. A 4 ml volume of 1.4% m/v iodine solution was injected into a glass vessel containing 5 ml of thiourea and 0.2 ml of 1 M sodium hydrogencarbonate solution. The CO2 evolved under these conditions was swept by a stream of nitrogen to an infrared gas cell. At 200 s after injection of the iodine solution, the vapour phase FTIR spectra were continously recorded, as a function of time, between 2500 and 2200 cm(-1), which includes the CO2 absorption band at 2350 cm(-1). From the absorbance data in the 2399-2284 cm(-1) range, integrated absorbance measurements were obtained providing transient recordings which correspond to the absorbance of CO2 in the selected wavenumber range. The method provided a limit of detection of 10 ppm of thiourea, a throughput of 14 samples h(-1) and an RSD of 1.1% for three independent analyses of a 500 ppm thiourea solution. Results obtained for a series of real samples compared well with those obtained using potentiometric titration as a reference method.     

Fourier transform infrared spectrometric strategies for the determination of Buprofezin in pesticide formulations

Two different strategies for Buprofezin determination, an off-line extraction and stopped-flow determination and an automated procedure, based on the on-line extraction of Buprofezin samples with chloroform and flowing action analysis-fourier transform infrared (FIA-FT-IR) spectrometric measurement of the extracts, have been developed. For the treatment of the off-line extraction mode, data a three-factor partial least squares (PLSs) calibration was developed, using the region from 1465.7 to 1342.3 cm⁻¹ with a single point baseline defined at 2051.9 cm⁻¹ and based on the use of chloroform solutions of Buprofezin. The method provides a R.S.D. <0.1%, recoveries of the order of 100% and generates 25 ml of CHCl₃ waste for each sample.On the other hand, the recommended FIA method provided a 3 s limit of detection of 20 μg ml⁻¹, which corresponds to 0.12% (w/w) in the solid sample, a repeatability of 0.8% as R.S.D., and a maximum sampling frequency for the whole procedure of 6 h⁻¹.The waste generation, being lower than the off-line strategy, is only 3 ml of CHCl₃ per sample.     

流动注射化学发光法测定痕量NO_2~-的研究与应用

Based on the principle of the reaction of NO2-with I-and formation of I2 in HCl solution,and the chemiluminescence(CL) reaction between luminol and I2 in an alkaline medium.A fairly sensitive,simple and rapid flow-injection analysis-chemiluminescence method for the determina-tion of trace nitrite with the luminal-I——NO2-coupling luminescence system has been developed.Experiment conditions of flow-injection analysis are optimized.When satisfying the condition that Luminol as 4.0×10-4 mol/L,0.7 % KI,0.04 mol/...     

Vapour phase Fourier transform infrared spectrometric determination of L-cysteine and L-cystine

A novel and selective procedure for the determination of l-cysteine and l-cystine based on vapour-generation Fourier transform infrared spectrometry is described. Potassium iodate solution was injected into a glass vessel containing l-cysteine and/or l-cystine. The evolved CO was swept by a stream of nitrogen to an infrared gas cell. The vapour phase FTIR spectra were continuously recorded, as a function of time, between 2240 and 2000cm(-1), which includes the CO absorption band. The maximum absorbance at 2170cm(-1) was selected as a measurement criterion. The calibration curve was linear over the range 6-300mgL(-1). The method provided a limit of detection of 2mgL(-1) of l-cysteine, a throughput of 12samples h(-1) and an R.S.D. of 1.76% for five independent analyses of a 75mgL(-1)l-cysteine solution. For the measurement of l-cysteine and l-cystine separately, after measuring total concentration of l-cysteine and l-cystine, l-cysteine was masked with p-benzoquinone at a pH of 3 and individual l-cystine was determined. The amount of l-cysteine was obtained by difference. The method was applied to the determination of l-cysteine and l-cystine in pharmaceutical and urine samples. Results obtained for real samples compared well with those obtained by a reference spectrometric method.     

Polymeric optical sensors for selective and sensitive nitrite detection using cobalt(III) corrole and rhodium(III) porphyrin as ionophores

Cobalt(III) 5,10,15-tris(4-tert-butylphenyl) corrole with a triphenylphosphine axial ligand and rhodium(III) 5,10,15,20-tetra(p-tert-butylphenyl) porphyrin are incorporated into plasticized poly(vinyl chloride) films to fabricate nitrite-selective bulk optodes via absorbance measurements. The resulting films yield sensitive, fast and fully reversible response toward nitrite with significantly enhanced nitrite selectivity over other anions including lipophilic anions such as thiocyanate and perchlorate. The selectivity patterns differ greatly from the Hofmeister series based on anion lipophilicity and are consistent with selectivity obtained with potentiometric sensors based on the same ionophores. The optical nitrite sensors are shown to be useful for detecting rates of emission of nitric oxide (NO) from NO releasing polymers containing S-nitroso-N-acetyl-DL-penicillamine.     

Determination of nitrite and nitrate in human serum

A simple and effective assay for nitrite and nitrate in human serum has been developed using ion chromatography. Initial experiments using isocratic carbonate-bicarbonate elution with conductivity detection on a Dionex QIC system with an AS4A-SC column showed promise but were unsatisfactory because of co-elution problems with nitrite. Carbonate and chloride were investigated as eluents using a gradient system, and direct UV detection at 214 nm was used in place of conductivity detection. Dionex AS4A, AS9A, AS12, Nucleopac PA-100 and Carbopac PA-100 columns were compared for selectivity and resistance to overload. The final method, using a chloride concentration gradient, pH buffering and direct UV detection with a Carbopac PA-100 column, shows good resolution, does not suffer from chloride overload and is simple to use. The method is being used in an investigation of the role of nitric oxide in pre-eclampsia, a hypertensive disorder during pregnancy.     

Two rapid and sensitive automated methods for the determination of nitrite and nitrate in soil samples

Spectrophotometric flow injection methods were developed for the individual determination of nitrite or nitrate, and for the simultaneous determination of nitrite and nitrate, in soil samples. Nitrite was determined directly using a modified version of the Griess-Ilosvay diazo-coupling reaction, measuring at 543 nm the absorbance of the azo-dye complex formed. Simultaneous nitrite and nitrate determinations were based on on-line nitrate reduction in a micro column containing copperised cadmium. A single chromogenic reagent containing all the necessary reactants was used in both methods. For determinations, the chemical and instrumental variables were optimised by univariate analysis and simplex chemometric method. The optimised conditions gave a linear calibration range between 0.05 and 1.6 µg m L^− 1 for N-NO₂⁻ and between 0.05 and 7.0 µg m L^− 1 for N-NO₃⁻. The detection limits for nitrite and nitrate were 22 µg L^− 1 and 44 µg L^− 1 respectively. The proposed methods allowed up to 35-40 samples per hour to be analysed with good precision. The simultaneous method was successfully used for the determination of nitrite and nitrate in soil samples (the results obtained were validated against those obtained by reference methods). The proposed methods are simpler and faster than conventional methods and could be routinely used in environmental monitoring laboratories.     

Spectrophotometric simultaneous determination of nitrite, nitrate and ammonium in soils by flow injection analysis

A new rapid flow injection procedure for the simultaneous determination of nitrate, nitrite and ammonium in single flow injection analysis system is proposed. The procedure combines on-line reduction of nitrate to nitrite and oxidation of ammonium to nitrite with spectrophotometric detection of nitrite by using the Griess-llosvay reaction. The formed azo dye was measured at 543 nm. The influence of reagent concentration and manifold parameters were studied. Nitrite, nitrate and ammonium can be determined within the range of 0.02–1.60 μg mL⁻¹, 0.02–1.60 μg mL⁻¹ and 0.05–1.40 μg mL⁻¹, respectively. R.S.D. values (n = 10) were 2.66; 1.41 and 3.58 for nitrate, nitrite and ammonium, respectively. This procedure allows the determination and speciation of inorganic nitrogen species in soils with a single injection in a simple way, and high sampling rate (18 h⁻¹). Detection limits of 0.013, 0.046 and 0.047 μg mL⁻¹were achieved for nitrate, nitrite and ammonium, respectively. In comparison with others methods, the proposed one is more simple, it uses as single chromogenic reagent less injection volume (250 mL in stead of 350 mL) and it has a higher sampling rate.     

Flow analysis-hydride generation-Fourier transform infrared spectrometry. A new analytical technique for the simultaneous determination of antimony,arsenic and tin

The combination of flow analysis (FA), hydride generation (HG) and Fourier transform infrared (FTIR) spectrometry is proposed as a novel and powerful analytical technique for the individual and simultaneous determination of antimony, arsenic and tin in aqueous samples. The analytes were transformed into the volatile hydride form by on-line reaction with sodium tetrahydroborate in acidic medium. The gaseous analyte hydrides [M(n)H(m), (g)] generated, were transported by means of a carrier gas stream inside the IR gas cell and the corresponding FTIR spectrum was acquired in a continuous mode. The 1893, 1904 and 2115 cm(-1) bands of the SbH3, SnH4, and AsH3 were selected for the determination of antimony, tin and arsenic, respectively. The limit of detection (3sigma) obtained by using a short-path (10 cm) IR gas cell were 0.25, 0.30 and 1.2 mg l(-1) for the determination of antimony, tin and arsenic, respectively; while the precision (relative standard deviation, RSD, n 5) found from a standard solution containing 50 mg l(-1) of each element was, in all cases, less than 0.3%. However, the use of a long-path (7.25 m) IR gas cell improved the figures of merit (sensitivity, limits of detection and quantification) nearly 60-fold. The effect of the main experimental and instrumental variables, such as acidic media, sodium tetraborohydrate concentration, nitrogen flow rate, nominal resolution and the scan accumulation on the analytical signals of the antimony, tin and arsenic hydrides, were studied. Further, the potential of the proposed technique for the simultaneous determination of these elements was tested, analyzing synthetic samples containing different amounts of Sb, Sn and As.     

The role of nitric oxide in cancer improved methods for measurement of nitrite and nitrate by high-performance ion chromatography

The short lifetime of nitric oxide (NO) in vivo impedes its quantitation directly; however, the determination of nitrite and nitrate ions as the end-products of NO oxidation has proven a more practical approach. High-performance ion chromatographic analysis of nitrite in biological fluids is hampered by the large amount of chloride ion (up to 100mmol/l) which results in insufficient peak resolution when utilizing conductimetric detection. Analysis of both anions in small sample volumes is also constrained by the need to minimise sample handling to avoid contamination by environmental nitrate. We report a means to remove Cl⁻ ions from small sample volumes using Ag⁺ resin which facilitates quantitation of either nitrite and nitrate anions in biological samples, using silica or polymer based ion-exchange resins with conductimetric or electrochemical and spectrophotometric detection. Including a reversed-phase guard column before the anion-exchange guard and analytical column also greatly extends column lifetime.     

Selective and sensitive detection of nitrite based on NO sensing on a polymer-coated rotating disc electrode

A new effective way of nitrite detection in complex samples is presented. It is based on chemical conversion of nitrite to nitric monoxide (NO) in acidic aqueous solution containing hexacyanoferrate(II) as a reductor. NO is then detected on a poly-eugenol coated platinum electrode. When the electrode is rotating and the reduction medium is continuously purged with nitrogen, the addition of a nitrite-containing sample produces narrowed current spikes. The peak current is proportional to nitrite content in the sample over the range of 5.0–100 μM and detection limit is 0.6 μM. The method is simple and highly reproducible. Relative standard deviation of 10 repetitions is less than 4%. Practical utility of the proposed approach is demonstrated by nitrite determination in human saliva.     

Fourier transform infrared spectrometric determination of Malathion in pesticide formulations

An environmentally friendly methodology has been developed for quality control analysis of emulsifiable concentrate pesticide formulations containing Malathion as active ingredient, using flow injection analysis (FIA)-Fourier transform infrared (FTIR) spectrometry. Five microlitres samples were directly injected into a 3 ml closed FIA manifold, in which 2 ml of CHCl₃ was re-circulated at 1.96 ml min⁻¹. After homogenisation and sample measurement, 2 μl volumes of a Malathion standard were injected, taking absorbance measurements after each injection. Peak height of the chemigrams, established from peak area values between 1027 and 1017 cm⁻¹, corrected with a baseline fixed from 1087 to 993 cm⁻¹ were employed for Malathion quantification using the standard addition approach, after reaching the steady state for every injection. A limit of detection of 12 μg ml⁻¹ was achieved. Results found by standard addition-FTIR in commercially available samples showed a good correlation with those obtained by the reference gas chromatography-flame ionisation detection procedure.     

Recent advances in nanomaterial-based electrochemical sensing of nitric oxide and nitrite for biomedical and food research

Nitric oxide (NO) and nitrite are of significant importance in clinical/biomedical research and in quality control applications for the food industry. Electrochemical sensing of NO and nitrite has been extensively pursued over the last two years. Efficient interfaces based on functional nanomaterials and bioactive molecules (e.g. metals, metal oxides, carbon-based nanomaterials, conducting polymers, and heme proteins) have been widely explored toward sensor development. Herein, we review the most recent advances in the electrochemical sensing of NO and nitrite, while the critical roles of nanomaterials in the design of advanced electrochemical sensors are highlighted.     

A simple strategy for determining ethanol in all types of alcoholic beverages based on its on-line liquid-liquid extraction with chloroform, using a flow injection system and Fourier transform infrared spectrometric detection in the mid-IR

In this work, a simple strategy for the determination of ethanol in all types of alcoholic beverages using Fourier transform infrared spectrometric detection has been developed. The methodological proposal includes the quantitative on-line liquid-liquid extraction of ethanol with chloroform, through a sandwich type cell equipped with a PTFE membrane, using a two-channel manifold; and direct measurement of the analyte in the organic phase, by means of Fourier transform infrared spectrometry. The quantification was carried out measuring the ethanol absorbance at 877 cm⁻¹_, corrected by means of a baseline established between 844 and 929 cm⁻¹. The procedure, which does not require any sample pretreatment (except for the simple degassing of beer and gassy wine samples, and a simple dilution of spirits with water), was applied to determine ethanol in different alcoholic beverages such as beers, wines and spirits. The results obtained highly agree with those obtained by a derivative FTIR spectrometric procedure, and by head space-gas chromatography with FID detection. The proposed method is simple, fast, precise and accurate. Moreover, it can be easily adapted to any infrared spectrometer equipped with a standard transmission IR cell, and provides attractive analytical features, which are comparable to, or better than those offered by other published methods. In consequence, it represents a valid alternative for the determination of ethanol in alcoholic beverages, and could be suitable for the routine control analysis.