Multicommuted Flow Analysis Research Articles

Development of a high sensitivity photometric procedure for the determination of vanadium in mineral and fresh waters employing a downsized multicommuted flow analysis approach

This article focuses on the development of an analytical procedure for the photometric determination of vanadium in fresh and mineral waters, implemented employing a downsized multicommuted flow analysis approach.

Multicommuted Flow Analysis Procedure for Total Polyphenols Determination in Wines Employing Chemiluminescence Detection

A flow procedure based on a multicommuted flow analysis process for the determination of polyphenolic compounds in wine employing chemiluminescence as detection technique is described. The method was based on the reaction of hypochlorite with gallic acid, the remaining hypochlorite reacted with luminol in an alkaline medium generating electromagnetic radiation with maximum emission at 425 nm. The luminescence intensity presented an inverse relationship to the concentration of polyphenol compounds, which was monitored employing a homemade luminometer. The flow system manifold was designed to use solenoid mini-pumps for propelling fluids in order to obtain a setup of downsized dimension. After setting the variables control of the flow system and the concentrations of the reagent, the following features were achieved: a linear response ranging from 10 to 100 mg L−1 gallic acid (R2 = 0.997), a relative standard deviation of 3.4 (n = 11) for a 50 mg L−1 gallic acid solution, a detection limit of 6.6 mg L−1, a sampling throughput of 180 determination h−1, and a waste generation of 1.1 mL per determination.

Development of a Multicommuted Flow Analysis Procedure for Photometric Determination of TotalN-ureide in Soybean Tissues

In the current work, an automated procedure for photometric determination of N-ureide in soybean tissues is described. The photometric procedure was based on the reaction of N-ureide with hypochlorite, followed by its reaction with phenol in an alkaline medium, forming the indophenol blue compound, monitored at 660 nm. The flow system manifold based on the multicommuted process was tailored to allow its integration with a LED-based photometer in order to form a compact unit. After setting the appropriated operational conditions related with instrument setup and analytical procedure, the overall effectiveness was ascertained by the determination of N-ureide in soybean tissues. Accuracy assessed by applying the paired t-test between results obtained using a reference method showed that there is no significant difference at 95% confidence level. Other useful features were also achieved, such as a linear response ranging from 30 up to 260 µmol L-1 N-ureide (r = 0.9995); a detection limit of 1.0 µmol L-1 N-ureide, a relative standard deviation of 3% (n = 15), consumption of 0.55 and 6.8 mg hypochlorite and phenol per determination, respectively; waste generation of 3.3 mL per determination and sampling throughout 36 determinations per hour.

An environmentally friendly photometric procedure for ammonium determination in rainwater employing a multicommutation approach

In the present work, an automated procedure for photometric ammonium determination in rainwater using a multicommuted flow analysis approach is proposed. A homemade LED based photometer was designed to couple a flow cell with a path length of 100 mm in order to improve sensitivity. After establishing the adequate operational conditions, the proposed procedure was applied for the determination of ammonium in rainwater samples. The assessment of accuracy, by applying the paired t-test between these results and the results obtained using a reference method, showed that there is no significant difference at a 95% confidence level. Other useful features such as a linear response ranging from 0.05 to 1.20 mg L−1 NH4+; a detection limit of 19 μg L−1 NH4+; a blank relative standard deviation (n = 15) of 2.9%; a reagent consumption of 1.5 mg sodium salicylate and 0.15 mg sodium nitroprusside; a waste generation of 3.1 mL per determination; and a sampling throughput of 38 determinations per hour were also achieved.

A LED based photometer for solid phase photometry: zinc determination in pharmaceutical preparation employing a multicommuted flow analysis approach

Neste trabalho e proposto um fotometro baseado em LED (diodo emissor de luz) para fotometria em fase solida. O fotometro foi desenvolvido para permitir o acoplamento da fonte de radiacao (LED) e do fotodetector direto na cela de fluxo, tendo um caminho optico de 4 mm. A cela de fluxo foi preenchida com material solido (C 18 ), o qual foi utilizado para imobilizar o reagente cromogenico 1-(2-tiazolilazo)-2-naftol (TAN). A exatidao foi avaliada empregando dados obtidos atraves da tecnica ICP OES (espectrometria de emissao por plasma indutivamente acoplado). Aplicando-se o teste-t pareado nao foi observada diferenca significativa em nivel de confianca de 95%. Outros parâmetros importantes encontrados foram faixa de resposta linear de 0,05 a 0,85 mg L -1 Zn, limite de deteccao de 9 µg L -1 Zn (n = 3), desvio padrao de 1,4 % (n = 10), frequencia de amostragem de 36 determinacoes por h, e uma geracao de efluente e consumo de reagente de 1,7 mL e 0,03 µg por determinacao, respectivamente. In this work, a LED (light emitting diode) based photometer for solid phase photometry is described. The photometer was designed to permit direct coupling of a light source (LED) and a photodiode to a flow cell with an optical pathlength of 4 mm. The flow cell was filled with adsorbing solid phase material (C 18 ), which was used to immobilize the chromogenic reagent 1-(2-thiazolylazo)-2-naphthol (TAN). Aiming to allow accuracy assessment, samples were also analyzed employing ICP OES (inductively coupled plasma optical emission spectrometry) methodology. Applying the paired t-test at the 95% confidence level, no significant difference was observed. Other useful features were also achieved: linear response ranging from 0.05 to 0.85 mg L -1 Zn, limit of detection of 9 µg L -1 Zn (3σ criterion), standard deviation of 1.4% (n = 10), sampling throughput of 36 determinations per h, and a waste generation and reagent consumption of 1.7 mL and of 0.03 µg per determination, respectively.

Turbidimetric determination of sulfate in rainwater employing a LED based photometer and multicommuted flow analysis system with in-line preconcentration

In the present work, an automatic procedure for turbidimetric determination of sulfate in rainwater, based on the multicommuted flow analysis approach, is proposed. The photometer set-up was developed at the laboratory, and includes: a LED (λ = 420 nm), a long pathlength flow cell (100 mm), and a photodiode. A preconcentration step is included in order to improve sensitivity. After establishing the adequate operational conditions, the proposed procedure presented the following useful features: a linear response ranging from 0.1 mg L-1 up to 2.0 mg L-1 sulfate, a detection limit (3σ criterion) of 0.04 mg L-1 sulfate, a relative standard deviation of 1.5% for 0.5 mg L-1 sulfate solution (n = 7), barium chloride consumptions of 17.0 mg per determination, and waste generation of 7.3 mL per determination. Accuracy assessment was achieved by applying the paired t-test between results obtained using the proposed procedure and ICP-OES and showed that there is no significant difference at 95% confidence level.

An Approach to an Inhibition Electronic Tongue to Detect On-Line Organophosphorus Insecticides Using a Computer Controlled Multi-Commuted Flow System

An approach to an inhibition bioelectronic tongue is presented. The work is focused on development of an automated flow system to carry out experimental assays, a custom potentiostat to measure the response from an enzymatic biosensor, and an inhibition protocol which allows on-line detections. A Multi-commuted Flow Analysis system (MCFA) was selected and developed to carry out assays with an improved inhibition method to detect the insecticides chlorpyrifos oxon (CPO), chlorfenvinfos (CFV) and azinphos methyl-oxon (AZMO). The system manifold comprised a peristaltic pump, a set of seven electronic valves controlled by a personal computer electronic interface and software based on LabView® to control the sample dilutions into the cell. The inhibition method consists in the injection of the insecticide when the enzyme activity has reached the plateau of the current; with this method the incubation time is avoided. A potentiostat was developed to measure the response from the enzymatic biosensor. Low limits of detection of 10 nM for CPO, CFV, and AZMO were achieved.

A multicommuted flow analysis method for the photometric determination of amoxicillin in pharmaceutical formulations using a diazo coupling reaction

A multicommuted flow analysis method for the spectrophotometric determination of amoxicillin in pharmaceutical formulations is reported. The proposed method is based on the reaction of diazotised o-nitroaniline with amoxicillin in an alkaline medium, producing a yellow compound that was monitored at 435 nm. The main features of the method were: a linear relationship with amoxicillin concentration ranging from 25 to 400 mg L-1; a detection limit of 5.1 mg L-1; an analytical throughput of 50 determinations per hour; and a relative standard deviation lower than 3.9% for a typical amoxicillin sample with concentration of 100 mg L-1 (n = 10). To verify the accuracy of the method, samples were also analyzed employing an independent method, and applying the paired t-test to the results no significant difference at the 95% confidence level was observed.

An Environmental Friendly Procedure for Photometric Determination of Hypochlorite in Tap Water Employing a Miniaturized Multicommuted Flow Analysis Setup

A photometric procedure for the determination of ClO− in tap water employing a miniaturized multicommuted flow analysis setup and an LED-based photometer is described. The analytical procedure was implemented using leucocrystal violet (LCV; 4,4′,4′′-methylidynetris (N,N-dimethylaniline), C25H31N3) as a chromogenic reagent. Solenoid micropumps employed for solutions propelling were assembled together with the photometer in order to compose a compact unit of small dimensions. After control variables optimization, the system was applied for the determination of ClO− in samples of tap water, and aiming accuracy assessment samples were also analyzed using an independent method. Applying the paired t-test between results obtained using both methods, no significant difference at the 95% confidence level was observed. Other useful features include low reagent consumption, 2.4 μg of LCV per determination, a linear response ranging from 0.02 up to 2.0 mg L−1 ClO−, a relative standard deviation of 1.0% (n = 11) for samples containing 0.2 mg L−1 ClO−, a detection limit of 6.0 μg L−1 ClO−, a sampling throughput of 84 determinations per hour, and a waste generation of 432 μL per determination.

Monitoring of Sulfonamides by a Multicommutation Flow-Analysis Assembly: Use of Quenching Effect on Terbium Luminescence

Sulfonamide drugs are an important class of antimicrobial agents employed in both medicine and veterinary practice. Although there have been a variety of proposed analytical methods for their determination, many of them are not suitable for routine quality control, due to time-consuming procedures or expensive instrumentation. In this paper, we propose a simple methodology, based on the direct quenching effect produced by several sulfonamide compounds (sulfasalazine, sulfanilamide, and sulfamethoxazole) on the terbium (III) luminescence. The flow assembly was designed making use of the automatic methodology multicommutation, and the proposed method allowed the determination of up to 50 samples per hour.

Contribution of multi-commuted flow analysis combined with monolithic columns to low-pressure, high-performance chromatography

The advent of monolithic columns has facilitated the combination of chromatographic techniques with non-separation flow techniques [particularly sequential injection analysis (SIA) and multi-syringe flow-injection analysis (MSFIA)] by virtue of the low overpressure introduced by monolithic columns. So far, these combinations have provided excellent results derived from the high selectivity of liquid chromatography and ease of sample handling in non-separation flow techniques. The joint use of SIA and monolithic columns has provided SI chromatography (SIC), which could enormously facilitate sample treatments (e.g., derivatization, photooxidation or preconcentration). However, the combination of MSFIA and monolithic columns has led to multi-syringe chromatography (MSC), which extends the advantages of SIC (e.g., by implementing post-column reactions in order to derivatize eluates). We discuss the advantages and the disadvantages of SIC and MSC, and the problems to be solved in order to optimize their performances.

Automatic spectrophotometric procedure for the determination of tartaric acid in wine employing multicommutation flow analysis process

In the present work, an automatic flow procedure for the determination of tartaric acid in red wine without previous sample treatment is described. The flow system comprising three-way solenoid valves designed to implement the multicommutation flow analysis process. Under microcomputer control, the analytic procedure could be accomplished automatically without any intervention of the operator. The spectrophotomer method was based on the tartaric acid reaction with sodium vanadate. Intending to prove the effectiveness of the propose procedure, a set of red wine samples was analyzed. To permit accuracy assessment, wine samples were also analyzed using the OIV reference method. Applying the paired t-test between results obtained, no significant difference at 90% confidence level was observed. Other profitable features, such as a linear relationship between 0.50 and 10.0 g l −1 tartaric acid ( r = 0.9998), a 2.1% coefficient of variation ( n = 8), a sampling frequency of 28 determinations per hour, and a reagent consumption of 0.15 mg sodium vanadate per determination were also achieved.

Interfacing in-line gas-diffusion separation with optrode sorptive preconcentration exploiting multisyringe flow injection analysis

An automatic multisyringe flow injection analysis (MSFIA) system coupling a flow-through optical fiber diffuse reflectance sensor with in-line gas-diffusion (GD) separation is proposed for the isolation, preconcentration and determination of traces of volatile and gas-evolving compounds in samples containing suspended solids, with no need for any preliminary batch sample treatment. The flowing methodology overcomes the lost of sensitivity of the in-line separation technique, when performed in a uni-directional continuous-flow mode, through the implementation of disk-based solid-phase extraction schemes. The high selectivity and sensitivity, the low reagent consumption and the miniaturization of the whole assembly are the outstanding features of the automated set-up. The proposed combination of techniques for separation, flow analysis, preconcentration and detection was applied satisfactorily to sulfide determination in environmental complex matrixes. The method based on multicommutation flow analysis involves the stripping of the analyte as hydrogen sulfide from the donor channel of the GD-module into an alkaline receiver segment, whereupon the enriched plug merges with well-defined zones of the chormogenic reagents (viz., N, N-dimethyl- p-phenylenediamine (DMPD) and Fe(III)). The in-line generated methylene blue dye is subsequently delivered downstream to the dedicated optrode cell furnished with a C 18 disk, while recording continuously the diffuse reflectance spectrum of the pre-concentrated compound. This procedure provides a linear working range of 20–500 μg l −1 sulfide with a relative standard deviation of 2.2% ( n = 10) at the 200 μg l −1 level, and a detection limit of 1.3 μg l −1.

A multicommuted flow system for the determination of dextrose in parenteral and hemodialysis concentrate solutions

A new method is presented for the automation of the determination of dextrose in parenteral and hemodialysis solutions. The method is based on multicommutation flow analysis (MCFA) and exploits enzymatic reactions providing a colored derivative that is detected spectrophotometrically (Trinder's method). The reagent, comprising glucose oxidase, peroxidase, 4-hydroxybenzoate and a buffer was obtained from a commercial kit for the determination of glycemia. The flow system used three 3-way solenoid valves operating under computer control. The necessary software was developed for the purpose and compiled in QuickBASIC 4.0 The influence of some operating variables (segment size, number of segments and reactor length) was studied. Calibration curves in the range 0–1 g/L presented a slight curvature and were fitted with a second-degree polynomial ( h = −0.0632 C 2 + 0.6039 C + 0.166, r 2 = 0.9973, h being the peak-height (absorbance) and C the concentration in g/L). The method was validated by analyzing artificial samples presenting accurately known concentrations of dextrose, and comparing the results with the known value and with value obtained by polarimetry. Recoveries were in the range 96.6–100.2%, and the difference with the polarimetric analysis was in the range 0.1–3.3%. Precision (R.S.D.,%) was better than 2.4%. Sampling frequency of the system was 90 samples/h, with a reagent consumption of 0.14 mL per sample.