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.     

Determination of verapamil hydrochloride with 12-tungstophosphoric acid by resonance Rayleigh scattering method coupled to flow injection system

A flow injection analysis (FIA) method coupled to resonance Rayleigh scattering (RRS) detection for the determination of verapamil hydrochloride (VP) was proposed. In pH 1.0 acidic medium, 12-tungstophosphoric acid (TP) reacted with VP to form an ion-association complex, which resulted in a significant enhancement of RRS intensity. The maximum scattering peak was located at 293 nm. RRS intensity was proportional to the concentration of VP in the range of 0.017-13.0 μg mL⁻¹, and the detection limit (3σ) was 5.1 ng mL⁻¹. The proposed method exhibited satisfactory reproducibility with a relative standard derivation (R.S.D.) of 2.1% for 11 successive determinations of 5.0 μg mL⁻¹ VP. Therefore, a novel method for the determination of VP by FIA-RRS was developed. The optimum reaction conditions and the parameters of the FIA operation such as flow rate, injection volume, reactor length, and so on had been optimized in this paper. The present method had been applied to the determination of VP in serum samples and pharmaceuticals with satisfactory results. The maximal sample throughput in the optimized system was 80 h⁻¹.     

A novel planar miniaturized potentiometric sensor for flow injection analysis of nitrates in wastewaters, fertilizers and pharmaceuticals

A novel all-solid-state miniaturized nitrate sensor is developed, characterized and used for flow injection analysis (FIA) of nitrates in various samples. The sensor incorporates silver bis(bathophenanthroline) nitrate [Ag(bath)₂NO₃] as an electroactive material in a plasticized PVC membrane. The sensing membrane (3 mm × 5 mm) is immobilized on a wafer polyimide microchip (size 13.5 mm × 3.5 mm) to offer a planar miniaturized design easily used in a single channel wall-jet flow injection system. Under hydrodynamic mode of operation (FIA) the sensor displays fast response, high sensitivity, long term stability and good selectivity for NO₃⁻ in the presence of many common associated anions. The calibration slope is 55.1 ± 0.1 mV decade⁻¹ over the concentration range 1.0 × 10⁻¹ to 1.0 × 10⁻⁶ mol L⁻¹, the lower detection limit is 0.05 μg mL⁻¹, the working pH is 2-9,and the output is 70-90 samples h⁻¹. Validation of the assay method reveals good performance characteristics and suggests application for routine determination of NO₃⁻ in industrial wastewaters, fertilizers and pharmaceuticals. The results agree fairly well with data obtained by the standard spectrophotometric methods.     

Flow injection analysis of ethyl xanthate by in-line dialysis and UV spectrophotometric detection

A simple and sensitive spectrophotometric flow method for determination of low concentrations of the flotation collector O-ethyldithiocarbonate (ethyl xanthate, CH₃CH₂-O-CS₂⁻) in solutions is described. The method is based on ethyl xanthate detection at 301 nm in medium of NaOH 50 mmol L⁻¹. By injection of 200 μL of sample, the analytical method shows linear response for the ethyl xanthate concentration from 0.5 up to 500 μmol L⁻¹. Successive injections of 4 μmol L⁻¹ ethyl xanthate (n = 23) show a coefficient of variation lower than 0.6%, denoting high repeatability. The detection limit is 0.3 μmol L⁻¹. At a flow rate of 2.0 mL min⁻¹, a frequency of 120 injections/h of ethyl xanthate can be attained. By introduction of a tangential dialysis cell in the FIA system, the manual sample filtration step with 0.22 μm filter was eliminated and the residual interference of suspended material, was completely overcome even for unfiltered sludge suspension samples, an important advantage that compensates for the frequency reduction to 25 injections/h elevation and detection limit elevation to 2 μmol L⁻¹, still outreaching for many applications. Potential applications of the method embrace the at line determination of ethyl xanthate in the ore processing industry, control of the concentration at its optimal level during the flotation process, as well as monitoring of residues in the effluents.     

Development of a sequential injection system for trace mercury determination by cold vapour atomic absorption spectrometry utilizing an integrated gas-liquid separator/reactor

A simple and robust time-based on-line sequential injection system for trace mercury determination via cold vapour atomic absorption spectrometry (CVAAS), employing a new integrated gas-liquid separator (GLS), which in parallel operates as reactor, was developed. Sample and reductant are sequentially loaded into the GLS while an argon flow delivers the released mercury vapour through the atomic absorption cell. The proposed method is characterized by the ability of successfully managing variable sample volume up to 30 ml in order to achieve high sensitivity. For 20 ml sample volume, the sampling frequency is 25 h⁻¹. The calibration curve is linear over the concentration range 0.05-5.0 μg l⁻¹ of Hg(II), the detection limit is c_L = 0.02 μg l⁻¹, and the relative standard deviation is s_r = 2.6% at 1.0 μg l⁻¹ Hg(II) level. The performance of the proposed method was evaluated by analyzing certified reference material and applied to the analysis of natural waters and biological samples.     

Micro determination of ascorbic acid using methyl viologen

A new simple and sensitive analytical spectrophotometric method is developed for the determination of ascorbic acid reduces methyl viologen to form a stable blue coloured free radical ion. This method has a sensitivity and lower limit detection of 0.1 μg ml⁻¹ of ascorbic acid (0.1 ppm) which is comparable to the flow injection analysis reported earlier. Beer's law is obeyed over the concentration range of 1.0-10 μg ml⁻¹ of ascorbic acid per 10 ml of the final solution (0.1-1.0 μg ml⁻¹) at 600 nm. The molar absorptivity and Sandell's sensitivity were found to be 1.5 × 10⁵ ± 100 l mol⁻¹ cm⁻¹ and 0.001 μg cm⁻², respectively. The method has been applied to the determination of ascorbic acid in food, pharmaceuticals and biological samples.     

Determination of picloram in natural waters employing sequential injection square wave voltammetry using the hanging mercury drop electrode

This paper describes the development of a sequential injection analysis method to automate the determination of picloram by square wave voltammetry exploiting the concept of monosegmented flow analysis to perform in-line sample conditioning and standard addition. To perform these tasks, an 800 μL monosegment is formed, composed by 400 μL of sample and 400 μL of conditioning/standard solution, in medium of 0.10 mol L⁻¹ H₂SO₄. Homogenization of the monosegment is achieved by three flow reversals. After homogenization the mixture zone is injected toward the flow cell, which is adapted to the capillary of a hanging drop mercury electrode, at a flow rate of 50 μL s⁻¹. After a suitable delay time, the potential is scanned from −0.5 to −1.0 V versus Ag/AgCl at frequency of 300 Hz and pulse height of 25 mV. The linear dynamic range is observed for picloram concentrations between 0.10 and 2.50 mg L⁻¹ fitting to the linear equation I_p = (−2.19 ± 0.03)C_picloram + (0.096 ± 0.039), with R² = 0.9996, for which the slope is given in μA L mg⁻¹. The detection and quantification limits are 0.036 and 0.12 mg L⁻¹, respectively. The sampling frequency is 37 h⁻¹ when the standard addition protocol is followed, but can be increased to 41 h⁻¹ if the protocol to obtain in-line external calibration curve is used for quantification. The method was applied for determination of picloram in spiked water samples and the accuracy was evaluated by comparison with high performance liquid chromatography using molecular absorption at 220 nm for detection. No evidences of statistically significant differences between the two methods were observed.     

A validated and fast procedure for FTIR determination of Cypermethrin and Chlorpyrifos

A FTIR methodology has been developed for the simultaneous determination of Cypermethrin and Chlorpyrifos in pesticide commercially available formulations. The method involves the extraction of both active principles with CHCl₃ and direct measurement of the peak area values between 1747 and 1737 cm⁻¹ corrected with a baseline defined at 2000 cm⁻¹ for Cypermethrin and peak height values established at 1549 cm⁻¹ corrected using a baseline situated at 1650 cm⁻¹ for Chlorpyrifos.The limits of detection achieved were of the order of 0.7 and 0.4% (w/w), and the relative standard deviation 0.4 and 0.2% for Cypermethrin and Chlorpyrifos, respectively. The developed procedure provided statistically comparable results with those obtained by HPLC, for a series of commercial samples, which validated the FTIR method. The procedure developed reduces organic solvent consumption, per sample preparation, from 51 ml CH₃CN required for HPLC to 2.5 ml CHCl₃, and reduces waste generation also increasing the sample measurement frequency, from 3 to 30 samples/h, as compared with the HPLC-UV reference method.     

Determination of carbon dioxide in gaseous samples by gas diffusion-flow injection

A gas diffusion-flow injection system was developed for the determination of carbon dioxide in gaseous samples. The calibration was based on the use of either gaseous carbon dioxide or aqueous sodium carbonate standards. Gaseous carbon dioxide samples and gaseous or aqueous standards were injected directly into a donor stream of 1.0×10⁻⁴ M H₂SO₄. In the gas diffusion unit, carbon dioxide diffused through a PTFE membrane into an acceptor stream containing a mixed acid/base indicator. The absorbance of the acceptor stream was monitored spectrophotometrically at 554 nm. The calibration plot was linear over the range of 5.00×10² to 1.27×10⁴ μl l⁻¹ with a sample throughput of 28 h⁻¹ and 3.2% R.S.D. ([CO₂]=2.37×10³ μl l⁻¹, n=12). The detection limit was determined as 2.50×10² μl l⁻¹. The flow system was successfully applied to the analysis of several natural gaseous samples and the headspace of milk containers during storage. The flow injection results were found to be statistically indistinguishable at the 95% confidence level from those obtained by gas chromatography using thermal conductivity detection.     

Multisyringe flow injection system for total inorganic selenium determination by hydride generation-atomic fluorescence spectrometry

A new multisyringe flow injection system for total inorganic selenium determination by hydride generation-atomic fluorescence spectrometry (HGAFS) has been proposed. The flow methodology is based on the simultaneous injection of sample in the acid media (50% HCl), a reducing sodium tetrahydroborate solution (0.18%) and a solution of hydrochloric acid (50%) which are dispensed into a gas-liquid separation cell by using a multisyringe burette coupled with one multiport selection valve. The usage of the time-based injection increases the sample throughput and provides precise known volumes of sample. The hydride of selenium is delivered into the flame of an atomic fluorescence spectrometer by means of an argon flow. A hydrogen flow has been used to support the flame.The technique can be applied over a wide range of concentrations of selenium between 0.1 and 3.5 μg l⁻¹ with good repeatability (relative standard deviation (R.S.D.) values 4.6-7% for 1 μg l⁻¹ of Se). The detection limit of the developed technique (3σ_b/S) was 0.01 μg l⁻¹. A sample throughput was 28 samples per hour (84 injections). The multisyringe technique has been validated by means of reference solid (sea lettuce) and water (hard drinking water) materials with good agreement with certified values. The analytical features were compared with those obtained by using of the commercial flow injection analysis (FIA) system. The proposed method provides a higher sampling frequency and a significant reduction of reagent and sample consumption in front the flow injection application.     

A sensitive spectrophotometric method for lead determination by flow injection analysis with on-line preconcentration

A new flow injection (FI) system for the determination of Pb(II) at trace level with a preconcentration step and spectrophotometric detection is proposed. It is based on preconcentration of lead ions on chitosan and dithizone-lead complex formation in aqueous medium (pH 9). The chemicals and FIA variables influencing the performance of the system were optimized and applied to the determination of lead in natural, well, and drinking water samples. It is a simple, highly sensitive, and low cost alternative methodology. The method provided a linear rage between 25 and 250 μg l⁻¹, a detection limit of 5.0 ng ml⁻¹ and a sample throughput of 15 h⁻¹. The obtained results of spiked samples are in good agreement between the proposed method and ICP-AES.     

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.     

Determination of chromium by GFAAS in slurries of fish feces to estimate the apparent digestibility of nutrients in feed used in pisciculture

This paper presents a simple, fast and sensitive method to determine chromic oxide (used as a biological marker of fish feed) in samples of fish feces by GFAAS through the direct introduction of slurries of the samples into the spectrometer's graphite tube. The standard samples of feces and of fish feed containing 0.10-1.00 mg kg⁻¹ of Cr₂O₃ were pre-frozen for 1 min in liquid nitrogen and then ground a cryogenic mill for 2 min, which reduced the samples’ grain size to less than 60 μm. The standard slurries were prepared by mixing 20 mg of standard samples of fish feed or feces with 1 mL of a solution containing 0.05% (v/v) of Triton X-100 and 0.50% (v/v) of suprapure HNO₃ directly in the spectrometer's automatic sampling glass. The final concentrations of Cr₂O₃ present in the standard slurries were 2, 4, 8, 16 and 20 μg L⁻¹. After sonicating the mixture for 20 s, 10 μL of standard slurries were injected into the graphite tube, whose internal wall was lined with a metallic palladium film that acted as a permanent chemical modifier. The limits of detection (LOD) and quantification (LOQ) calculated for 20 readings of the blank of the standard slurries (2%, m/v of feces or feed devoid of minerals) were 0.81 and 2.70 μg L⁻¹ of Cr₂O₃ for the standard feces slurries, 0.84 and 2.83 μg L⁻¹ of Cr₂O₃ for the standard feed slurries. The proposed method was applied in studies of nutrient digestibility of different fish feeds and its results proved compatible with the results obtained from samples pre-mineralized by acid digestion.     

Gas diffusion-flow injection determination of total inorganic carbon in water using tungsten oxide electrode

A novel gas diffusion-flow injection method has been developed for the rapid and sensitive determination of total inorganic carbon (TIC) in water. The method is based on the diffusion of CO₂ across gas permeable membrane from a donor stream containing 0.1 M HCl to an acceptor stream of sodium acetate (10⁻⁵ mol l⁻¹ and pH 10). The CO₂ trapped in the acceptor stream passes through an electrochemical flow cell contains a tungsten oxide wire and a silver/silver chloride electrode, where it was sensitively detected. The parameters affecting the sensitivity of the electrode such as buffer concentration, pH, flow rate and injected volume were studied in detail. The electrode response was linear in the concentration range from 5 to 100 μg ml⁻¹ CO₃²⁻ with a correlation coefficient (R²) of 0.998. Precision (R.S.D.) was 1.42% for 20 μg ml⁻¹ standard solution of CO₃²⁻ (n=10). The detection limit was 0.20 μg ml⁻¹ CO₃²⁻. The method was evaluated by the injection of real natural water samples and an average recovery of 100.1% was obtained. The sampling rate was 30 samples h⁻¹. The method is simple, feasible with satisfactory accuracy and precision and thus could be used for monitoring TIC in water.     

A renewable copper electrode as an amperometric flow detector for nitrate determination in mineral water and soft drink samples

A novel approach was developed for nitrate analysis in a FIA configuration with amperometric detection (E = −0.48 V). Sensitive and reproducible current measurements were achieved by using a copper electrode activated with a controlled potential protocol. The response of the FIA amperometric method was linear over the range from 0.1 to 2.5 mmol L⁻¹ nitrate with a detection limit of 4.2 μmol L⁻¹ (S/N = 3). The repeatability of measurements was determined as 4.7% (n = 9) at the best conditions (flow rate: 3.0 mL min⁻¹, sample volume: 150 μL and nitrate concentration: 0.5 mmol L⁻¹) with a sampling rate of 60 samples h⁻¹. The method was employed for the determination of nitrate in mineral water and soft drink samples and the results were in agreement with those obtained by using a recommended procedure. Studies towards a selective monitoring of nitrite were also performed in samples containing nitrate by carrying out measurements at a less negative potential (−0.20 V).     

Comparison of soluble manganese(IV) and acidic potassium permanganate chemiluminescence detection using flow injection and sequential injection analysis for the determination of ascorbic acid in Vitamin C tablets

The limits of detection (3s) for ascorbic acid were 5×10⁻⁸ M with acidic potassium permanganate using both flow injection analysis (FIA) and sequential injection analysis (SIA) whereas the soluble manganese(IV) afforded 1×10⁻⁸ M and 5×10⁻⁹ M for FIA and SIA, respectively. Determinations of ascorbic acid in Vitamin C tablets were achieved with minimal sample pretreatment using a standard additions calibration and gave good agreement with those of iodimetric titration.     

FT-Raman spectrometry determination of Malathion in pesticide formulations

A fast and environmentally friendly method has been developed for Fourier transform-Raman (FT-Raman) spectrometry determination of Malathion in pesticide emulsifiable concentrate formulations. The method is based on the measurement of intensity peak height values at 1737 cm⁻¹ Raman shift corrected using a baseline defined at 1900 cm⁻¹. Samples were diluted with CHCl₃ and the FT-Raman spectra collected in back-scattering mode over 3.3 min at a nominal resolution of 4 cm⁻¹ accumulating 50 scans per spectra and using a laser power of 1250 mW. The developed procedure provided a limit of detection of 1.8% w/w in the original sample. Results found by FT-Raman spectrometry were statistically comparable with those obtained by flow injection Fourier transform infrared spectrometry, FIA-FTIR, and gas chromatography (GC) and were in good agreement with those reported by the manufacturer. The FT-Raman developed procedure reduces drastically the chlorinated solvent waste generation and avoids the contact of the operator with toxic products, being a fast alternative to the CIPAC recommended GC procedure.     

Development of a novel flow injection liquid-liquid microextraction method for the on-line separation and preconcentration for determination of zinc(II) using 5-(8-hydroxy-2-quinolinylmethyl)-2,8-dithia-5-aza-2,6-pyridinophane as a sensitive and selective fluorescent chemosensor

A novel flow injection analysis (FIA) system based on liquid-liquid microextraction and fluorimetric determination was developed for the determination of traces of the Zn²⁺ ion using 5-(8-hydroxy-2-quinolinylmethyl)-2,8-dithia-5-aza-2,6-pyridinophane (L) as a sensitive and selective fluorimetric sensor, with λ_ex = 373 nm and λ_em = 530 nm, and hexanol as the extracting organic solvent. In the designed FIA system, the phase separation takes place via gravitation forces in the absence of any segmenter. The influence of pH and ionic strength of the solution, amount of ligand, nature of counter ion, volume of organic solvent, extraction time and coil length was investigated. Under optimized experimental conditions, the calibration curve found to be liner over a concentration range of 0.025-4.53 μg mL⁻¹ (R² = 0.9951) with a limit of detection of 2.3 ng mL⁻¹. The enrichment factor was 45 and relative standard deviation for 7 replicate determinations was 2.43%. The method is very fast and uses low levels of organic solvents. The proposed method was applied successfully to the determination of zinc(II) in human hair, human serum and two inorganic sludge samples.     

Amperometric determination of bonded glucose with an MnO(2) and glucose oxidase bulk-modified screen-printed electrode using flow-injection analysis

A screen-printed amperometric biosensor based on carbon ink double bulk-modified with MnO₂ as a mediator and glucose oxidase as a biocomponent was investigated for its ability to serve as a detector for bonded glucose in different compounds, such as cellobiose, saccharose, (-)-4-nitrophenyl-β-d-glucopyranoside, as well as in beer samples by flow-injection analysis (FIA). The biosensor could be operated under physiological conditions (0.1 M phosphate buffer, pH 7.5) and exhibited good reproducibility and stability. Bonded glucose was released with glucosidase in solution, and the free glucose was detected with the modified screen-printed electrode (SPE). The release of glucose by the aid of glucosidase from cellobiose, saccharose and (-)-4-nitrophenyl-β-d-glucopyranoside in solution showed that stoichiometric quantities of free glucose could be monitored in all three cases.The linear range of the amperometric response of the biosensor in the FIA-mode flow rate 0.2 mL min⁻¹, injection volume 0.25 mL, operation potential 0.48 V versus Ag/AgCl) extends from 11 to 13,900 μmol L⁻¹ glucose in free form. The limit of detection (3σ) is 1 μmol L⁻¹ glucose. A concentration of 100 μmol L⁻¹ yields a relative standard deviation of approximately 7% with five injections. These values correspond to the same concentrations of bonded glucose supposed that it is liberated quantitatively (incubation for 2 h with glucosidase).Bonded glucose could be determined in beer samples using the same assay. The results corresponded very well with the reference procedure.     

Flow injection spectrophotometric determination of andrographolide from Andrographis paniculata

A simple flow injection colourimetric procedure for determining andrographolide was proposed. It is based on the reaction between andrographolide with 3,5-dinitrobenzoic acid, resulting in an intense purplish red complex with a suitable absorption at 536 nm. A standard or sample solution was injected into the 3,5-dinitrobenzoic acid stream (flow rate of 1.0 ml min⁻¹) which was then merged with potassium hydroxide stream with the same flow rate. Optimum conditions for determining andrographolide were investigated by univariate method. Under the optimum conditions, a linear calibration graph was obtained over the range 5.0-150.0 μg ml⁻¹ and the detection limit was 1.50 μg ml⁻¹ (3σ). The relatives standard deviation of the proposed method calculated from 10 replicate injections of 10.0 and 80.0 μg ml⁻¹ andrographolide were 0.66% and 1.64%, respectively. The sample throughput was 50 h⁻¹. The proposed method has been satisfactorily applied to the determination of andrographolide in herb plant samples.