Spectrophotometric Flow Injection Analysis Research Articles

Spectrophotometric Analysis of Nitrite in Gunshot Recentness Examinations from Non Toxic Ammunitions: Expanding the Frontiers of Forensic Chemistry

Nitrite ions consist on an important chemical clue related to gunshot examination, concerning to estimation of the time since discharge. Current forensic laboratory methods for nitrite analysis in gunshot residues are well established for investigating conventional ammunition residues. However, the use of these methods to analyze the so-called ecological or “non-toxic” ammunition has been less studied. Here, we have developed a spectrophotometric flow injection analysis method to test nitrite in samples of “non-toxic” ammunition residues. The ammunition used in these experiments was the NTA (non-toxic ammunition) model, .38 caliber, We also investigated the kinetics of nitrite decomposition for this type of ammunition over time. Sulfanilic acid and 1-naphthylethylenediamine in acetic acid were used as colorimetric reagents. The linear dependence of the spectrophotometric signal on the nitrite concentration was as follows: A = 2.07 x 104 µmol-1 L [NO2-] + 6.78 x 10-3 with a correlation coefficient (r) of 0.9994. The standard deviation (SD) of the analytical curve was 3.17 x 10-3 resulting in a limit of detection (LOD) = 0.46 µmol L-1 and a limit of quantification (LOQ) = 1.56 µmol L-1. The proposed instrumental method was more sensitive than conventional colorimetric tests and permitted the detection window to be extended to 32 days while ensuring the safety and reliability required for forensic analysis, in comparison to 7-10 days usually proposed for conventional ammunition. Therefore, the proposed method can be safely employed in forensic laboratories for routine analysis of nitrite ions in GSR samples from ecological or “non-toxic” ammunition.

New Spectrophotometric Methods for Estimation of Diosmin in Pharmaceutical Formulations Using Batch and FIA Systems

A new attempt is made to determine diosmin (DIO) in its pure form and in dietary supplements by using spectrophotometric flow injection analysis (FIA) assay method conjugated with batch method. The analysis was achieved depending on the oxidative coupling reaction with N, N-dimethyl-p-phenylenediamine (DMPD) to form a green dye which is measured at wavelength of 677 nm. The tested methods were found to be economical, delicate, precise and sturdy. The validation variables of the batch and FIA methods gave linearity in the determination range of DIO (1-35) μg/mL and (5-120) μg/mL demonstrated calibration graphs with linearity coefficient values of r2 =0.9989 and r2 =0.9991, respectively. Limits of quantitation (LOQ) values were found to be (0.8463 and 1.022) μg/mL, while limits of detection (LOD) were (0.2539 and 0.3067) µg/mL for the two methods, respectively. The precision for the developed methods denoted by relative standard deviation (RSD %), were 0.386 and 0.55 %, while the accuracy based on recovery values (Rec %) were 100.273 and 100.24, respectively. The relative error (RE %) was less than 1% for the batch method and (1.1%) for the FIA method. The values of these parameters were observed to fall within the specified accepted limits; therefore, the tested methods seem to be adequate for the analysis of DIO in pharmaceutical preparations.

On-line spectrophotometric determination of ferrous and total iron in monominerals by flow injection combined with a Schlenk line-based digestion apparatus to exclude oxygen

An on-line photochemical method for measuring the ferrous iron [Fe(II)] and total iron [Fe(T)] contents in monominerals is described herein. A special digestion apparatus connected with a Schlenk line was designed to exclude oxygen during sample digestion. Subsequently, a spectrophotometric flow injection analysis (FIA) system was employed to automate the determination. As a result, a facile, reliable, and accurate analytical procedure was obtained, and both the sample and reagent consumption were reduced compared with traditional spectrophotometric procedures. In addition, the concentrations of the reductant and the chromogenic agent were optimized along with the sample leaching conditions (e.g., the amounts of H2SO4 and HF). Furthermore, the method precision was assessed by comparing the obtained results with those of four geological reference materials (relative standard deviation (RSD) for Fe(II) <2.30%, RSD for Fe(T) <1.75%). Finally, the accuracy of the method was assessed for four monomineral samples using the standard addition method, with recovery percentages of 95.74–104.69% and 95.07–104.56% being obtained for Fe(II) and Fe(T), respectively.

Application of artificial neural networks to predictions in flow-injection spectrophotometry

It is demonstrated that predictions can be obtained in spectrophotometric flow-injection analysis (FIA) based on an experimental parameter, that is, the degree of reaction, which takes into account the hydrodynamic and chemical characteristics of the spectrophotometric reaction used. The search algorithm is based on constructing a model of a chemical-analytical process using a learning artificial neural network that enables the prediction of the degree of reaction for some reagents not studied yet. The trained neural network is used for the a priori evaluation and comparison of a number of reagents for the determination of aluminum by FIA.

Sensitive flow-injection spectrophotometric analysis of bromopride

A flow injection spectrophotometric procedure employing merging zones is proposed for direct bromopride determination in pharmaceutical formulations and biological fluids. The proposed method is based on the reaction between bromopride and p-dimethylaminocinnamaldehyde (p-DAC) in acid medium, in the presence of sodium dodecyl sulfate (SDS), resulting in formation of a violet product (λmax=565nm). Experimental design methodologies were used to optimize the experimental conditions. The Beer–Lambert law was obeyed in a bromopride concentration range of 3.63×10−7 to 2.90×10−5molL−1, with a correlation coefficient (r) of 0.9999. The limits of detection and quantification were 1.07×10−7 and 3.57×10−7molL−1, respectively. The proposed method was successfully applied to the determination of bromopride in pharmaceuticals and human urine, and recoveries of the drug from these media were in the ranges 99.6–101.2% and 98.6–102.1%, respectively. This new flow injection procedure does not require any sample pretreatment steps.

A spectrophotometric flow injection system for streptomycin determination in veterinary samples

In this work a spectrophotometric flow injection analysis system for streptomycin determination in veterinary samples, is being proposed. The method is based on streptomycin alkaline hydrolysis that forms guanidine, followed by the reaction with Fe(II). The colored product has absorption peak at 520nm. To evaluate and optimize the system parameters, chemometrics tools, such as factorial design, Pareto chart and Doelhert design, were used. The veterinary samples are diluted in water and introduced in the FIA system, therefore no sample preparation is required. The optimized system presented: linear range of 60 up to 1000mgL−1, limit of detection of 18mgL−1 and sampling rate of 36 readings per hour. The precision was checked and the CV for veterinary sample readings were always less than 6.5%. The accuracy was studied by comparison with chromatographic method, thus, five samples of pharmaceutical veterinary were determined by HPLC and by the proposed method, and the results are in agreement (t-test, p=0.05).

New Application of Produced Pigment from Bacteria to Detect of Ammonia in Combination with Flow Injection for Ammonia Analysis

A novel detection method for ammonium ions based on a spectrophotometric FIA (Flow Injection Analysis) with use of pyocyanine as a coloring reagent in combination with micro fluidic gas diffusion device was developed in this study. A blue pigment produced by microorganisms was isolated, characterized and then, applied to an FIA (Flow Injection Analysis) as a coloring reagent followed by investigation of the properties. The pigment was separated by a silica-gel column chromatography, and the molecular weight was determined by EI-MS. The structure was analyzed by 1H-NMR. The isolated compound was found to be identical to pyocyanine. The pigment-producing microorganism was identified as Pseudomonas sp. from 16S DNA analysis. Noting that the property of the pyocyanine of which absorbance depended on the pH shift, the compound as a coloring reagent was applied to an FIA for determinaiton of ammonium ions.

Flow Injection Spectrophotometric Analysis of Human Salivary α-Amylase Activity Using an Enzyme Degradation of Starch–Iodine Complexes in Flow Channel and Its Application to Human Stress Testing

Flow injection spectrophotometric analysis (FIA) of human salivary α-amylase was developed using an enzyme degradation reaction of starch-iodine complexes. In this proposed method, the salivary α-amylase, known as a human stress indicator, is directly and rapidly determined without any pretreatment. In this study, the optimum starch-iodine complexes (i.e., optimum molecular weight and amylase-amylopectin compounding ratio) were selected, and their rapid degradation in the flow channel was investigated to determine salivary amylase in the FIA system. The determination range of α-amylase was obtained from 0.25 to 5.0 kilo Novo unit per milliliter (KNU/mL), and these concentrations were equivalent to the real concentration of amylase in human saliva. The quantitative values obtained by this method were found to be highly reproducible with 1.6% (n=25) of the relative standard deviation for 1.0 KNU/mL. The detection limit (3σ) was 60 NU/mL. In addition, the method requires small volume of a sample (20 µL), and 30 samples was sequentially measured within one hour. Real human saliva collected before and after exercise was utilized to demonstrate the feasibility of human stress test and analytical performance of this approach.

Determination of Thiocyanate by Kinetic Spectrophotometric Flow Injection Analysis

A simple and rapid flow injection spectrophotometric method has been developed for the determination of amount of thiocyanate in wastewaters and well water samples. It is based on the reaction of thiocyanate in hydrochloric acid with janus green and bromate. Reaction was monitored spectrophotometrically by measuring janus green absorbance at λmax = 554 nm. The calibration graph was linear over the range 0.02–1.0 μg mL−1 and the detection limit was 0.016 μg mL−1 (s/n = 3). The throughput was 25 samples per hour.

Simultaneous determination of Cr(III) and Cr(VI) in tannery wastewater using low pressure ion chromatography combined with flow injection spectrophotometry

Trivalent and hexavalent chromium have been successfully separated and determined using low pressure ion chromatography combined with flow injection spectrophotometric analysis (LPIC–FIA). A column packed with crosslinking starch microspheres was used for on-line separation of Cr(III) from Cr(VI) in a flow-injection system because of its absorptive effect on Cr(III). To determine the concentration of Cr(III) and Cr(VI) in samples, we used 3.0mmol/L nitric acid to elute adsorbed Cr(III) from the column and then used ceric sulfate–sulfuric acid as oxidant to convert all Cr(III) into Cr(VI). Then, Cr(VI) directly came from the samples and Cr(VI) came from Cr(III) successively formed a amaranthine complex with diphenycarbazide and the complex shows a maximum absorption at 530nm. Analytical parameters including the concentration of eluent and oxidant solution, oxidizing temperature, length of oxidizing reaction coil, reaction coil and injection coil, interfering effects, etc., were optimized. The limit of detection was 1.25μg/L for Cr(VI) and 3.76μg/L for Cr(III). The linear relationship between absorption with the concentration of Cr(VI) and Cr(III) was 0.001–1.000mg/L and 0.030–1.000mg/L with correlation coefficients of 0.9995 and 0.9994, respectively. The relative standard deviation of Cr(VI) and Cr(III) was 1.21% and 1.66%, respectively (n=10). Major cations and anions did not show any interference. We validated this method through certified reference materials and through measuring the recovery in tannery wastewater.

Optimized and validated flow-injection spectrophotometric analysis of topiramate, piracetam and levetiracetam in pharmaceutical formulations

Application of a sensitive and rapid flow injection analysis (FIA) method for determination of topiramate, piracetam, and levetiracetam in pharmaceutical formulations has been investigated. The method is based on the reaction with ortho-phtalaldehyde and 2-mercaptoethanol in a basic buffer and measurement of absorbance at 295 nm under flow conditions. Variables affecting the determination such as sample injection volume, pH, ionic strength, reagent concentrations, flow rate of reagent and other FIA parameters were optimized to produce the most sensitive and reproducible results using a quarter-fraction factorial design, for five factors at two levels. Also, the method has been optimized and fully validated in terms of linearity and range, limit of detection and quantitation, precision, selectivity and accuracy. The method was successfully applied to the analysis of pharmaceutical preparations.

Spectrophotometric Flow Injection Analysis of Chromium(VI) Coupled with On-line Solid-phase Extraction with Anion-exchange Resin Cartridge Column

Trace amount of CrO4 2− in water sample was collected and concentrated on a cartridge type mini-column (4 cm in length and 2 mm i.d.) packed with anion-exchange resin, Toyopearl QAE-550C. The collection and concentration were carried out automatically using a sequential injection procedure. The handling sequence was the steps of cleaning, washing and conditioning of the resin, collection of CrO4 2− on the resin, and elution of CrO4 2− from the resin to a detection system. The CrO4 2− eluate was introduced into the photometric flow injection analysis system using 1,5-diphenylcarbazide as a derivatizing reagent. When an aliquot of 5.0 mL or 20 mL sample solution was treated, the sensitivity increased by 6.4 and 23 times, respectively. By combing the automated on-line pretreatment system with the photometric flow injection system, CrO4 2− at 10 mol L level was determined without expensive detectors such as ICP-AES. On the basis of the interference study, the proposed system was applied to the analysis of a river water sample. Concentration of CrO4 2− at 2.5x10 mol L was determined, and satisfactory results were also obtained with recovery tests.

Simple Flow Injection Analysis System for the Spectrophotometric Determination of Trace Amounts of Nitrite in Water Samples

A simple and sensitive spectrophotometric flow injection analysis system has been developed for the determination of trace amounts of nitrite. The method is based on the reaction of nitrite with sulfanilamide in acidic medium to form a diazonium salt which then couples with thenoyltrifluoroacetone in alkaline medium to give an azo dye. Beer’s law is obeyed at 470 nm over a nitrite concentration range of 1-1200 µg L -1 , and a detection limit for nitrite is 0.3 µg L -1 is achieved with a relative standard deviation of 1.4% at 50 µg L -1 (n=8). An injection rate of about 40 h -1 is possible using this method, which was successfully applied to the determination of nitrite in rain water, tap water, pond water, and river water samples.

Spectrophotometric Determination of 1-(3-Dimethylaminopropyl)-3-ethylcarbodiimide Hydrochloride by Flow Injection Analysis

1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC.HCl) is a very useful agent to form amide bonds (peptide bonds) in an aqueous medium. A simple and fast detection system was developed using the reaction with pyridine and ethylenediamine in acidic aqueous solution and spectrophotometric flow injection analysis. The absorbances were measured at 400 nm and the reaction was accelerated at 40 degrees C. The calibration graph showed good linearity from 0 to 10% of EDC.HCl solutions: the regression equation was y=3.15x10(4)x (y, peak area; x, % concentration of EDC.HCl). The RSD was under 1.0%. Sample throughput was 15 h(-1). This method was applied to monitoring the EDC.HCl concentration that remained after the anhydration of phthalic acid in water, esterification of acetic acid in methanol or dehydration condensation of malonic acid and ethylenediamine in water.

Development of novel detection reagent for simple and sensitive determination of trace amounts of formaldehyde and its application to flow injection spectrophotometric analysis

In this paper, a novel detection reagent for formaldehyde determination is proposed, and is applied to a simple and highly sensitive flow injection method for the spectrophotometric determination of formaldehyde. The method is based on the reaction of formaldehyde with methyl acetoacetate in the presence of ammonia. The increase in the absorbance of the reaction product was measured at 375nm. An inexpensive light emitting diode (LED)-based UV detector (375nm) was, for the first time, used. Under the optimized experimental conditions, formaldehyde in an aqueous solution was determined over the concentration range from 0.25 to 20.0×10−6M with a liner calibration graph; the limit of detection (LOD) of 5×10−8M (1.5μgL−1) was possible. The relative standard deviation of 12 replicate measurements of 5×10−6M formaldehyde was 1.2%. Maximum sampling throughput was about 21samples/h. The effect of potential interferences such as metals, organic compounds and other aldehyde was also examined. The analytical performance for formaldehyde determination was compared with those obtained by the conventional acetylacetone method, which uses visible absorption spectrophotometry. Finally, the proposed method was successfully applied to the determination of formaldehyde in natural water samples.

Cyclic Flow Injection Analysis with Spectrophotometric Detection for Assay of Acidity in Fruit Juices and Soft Drinks

A single-line flow system, through which a reagent carrier stream is circulated, is proposed for the spectrophotometric determination of acidity (expressed as citric acid content) in fruit juices and soft drinks. The reagent carrier solution consists of pH indicator (Methyl Orange, MO) and sugar (sucrose) in an acetate buffer solution. The method is based on the acid-base neutralization detecting the color change of MO. The resulting solution, after passing through a flow through cell, returns to the reservoir and reused repeatedly. Sucrose is added in the reagent carrier solution to compensate both the differences in refractive index and viscosity between the reagent carrier solution and the sample solution, which make the sample injection directly without any dilution process. Several parameters were optimized, resulting in a simple, fast, and ready constructed acidity analyzer. Fruits juices and soft drinks could be analyzed without any prior chemical treatment. Among several organic acids, citric acid is the major acid in fruit juices. It is frequently added to the industrial drinking derivatives to keep quality and flavor of products constant. The acidity is determined routinely during the processing of drinking products. It is expressed usually as citric acid content. Commonly used techniques for this analysis is titration with the standard base(1). Normally all batch titrations involve quite high volume of reagents consumption and manually operations which are subjected to time consuming and personal error. Therefore, an on-line, near real time acidity analyzer is very desirable. Flow injection analysis (FIA) is widely accepted as an analytical technique capable to perform rapid analysis, and offers many advantages over batch titration (2-4). For the assay of acidity in fruit juices, several procedures (5-7) based on the flow injection method have been proposed employing mixing chamber or variation in reagent flow rate, using spectrophotometry or potentiometry as detection techniques. Imato and Ishibashi reported the spectrophotometric FIA determination of strong acids and bases using a pH indicator and buffer solution (8,9). This method is excellent because the estimation of end point is not necessary. The calibration graph can be constructed from the peak heights (absorbances) of the standard solutions of various concentrations. We developed this method into a cyclic FIA for the determination of strong acids and bases, where the reagent carrier solution was circulated and reused repeatedly (10). Recently we found this cyclic FIA was applicable to citric acid determination in a similar manner as above. In quality control, actual sample analysis without any prior chemical treatment should be desirable in order to decrease sample handling steps while also saving time of analysis. These facilities can be provided by exploiting the direct determination with the simplest manifold. This paper therefore describes the

Flow injection spectrophotometric determination of iron(III) using diphenylamine-4-sulfonic acid sodium salt

AbstractA highly sensitive and very simple spectrophotometric flow-injection analysis (FIA) method for the determination of iron(III) at low concentration levels is presented. The method is based on the measurement of absorbance intensity of the red complex at 410 nm formed by iron(III) and diphenylamine-4-sulfonic acid sodium salt (DPA-4-SA). It is a simple, highly sensitive, fast, and low cost alternative method using the color developing reagent DPA-4-SA in acetate buffer at pH 5.50 and the flow-rate of 1 mL min−1 with the sample throughput of 60 h−1. The method provided a linear determination range between 5 μg L−1 and 200 μg L−1 with the detection limit (3S) of 1 μg L−1 of iron(III) using the injection volume of 20 μL. FIA variables influencing the system performance were optimized. The amount of iron(III) and total iron in river and seawater samples was successfully determined. Repeatability of the measurements was satisfactory at the relative standard deviation of 3.5 % for 5 determinations of 10 μg L−1 iron(III). The accuracy of the method was evaluated using the standard addition method and checked by the analysis of the certified material Std Zn/Al/Cu 43 XZ3F.

Spectrophotometric Flow Injection Analysis for the Determination of Trace Amount of Ammonium Ion in Seawater Coupled with On-Line Gas Diffusion/Ion Exchange Concentration Technique

外洋海水や汚染の少ない新鮮海水中のアンモニウムイオンの濃度はシングルppbからsub-ppbレベルであり，これを直接定量することはマトリックスの影響により困難である．そこで，海水塩成分からの妨害除去にガス拡散分離技術を，更に陽イオン交換樹脂カラムを用いる濃縮技術をフローインジェクション分析法にオンライン前処理法として組み入れることで，高選択な微量アンモニウムイオンの定量法を確立することができた．試料水を10分間ガス拡散装置に通し，その後イオン交換濃縮を行った後，0.5 M塩酸で溶離し，検出系に導き吸光光度検出を行うことで，検出限界はN-NH4＋として0.5 ppb，30分間拡散/濃縮では0.2 ppbという結果を得た．1 ppb標準溶液を10分間拡散/濃縮した後，定量したときの相対標準偏差は0.68%（n = 5）と良好で，実際に海水中のシングルppbレベルのアンモニウムイオンの定量に応用することができた．本システムのバルブ及びポンプの一部は，自作のタッチパネル形式の制御装置で自動制御することができ，半自動分析システムが構築された．

Spectrophotometric Flow Injection Analysis of Protein in Urine Using Tetrabromophenolphthalein Ethyl Ester and Triton X-100

A sensitive, rapid and accurate determination of protein in patient urine was carried out by flow injection analysis (FIA) using tetrabromophenolphthalein ethyl ester (TBPE·H) and Triton X-100 at pH 3.0. The detection system was based on the ion association formation between human serum albumin (HSA) and TBPE·H in the micelle formed by Triton X-100. The calibration graph was linear in the range of 0.15 – 12 mg/dL HSA with R 2 = 0.998. The 3σ limit of detection of the proposed FIA method was 0.05 mg/dL at 610 nm. The relative standard deviation (n = 10) of 3.0 mg/dL HSA was 1.2% and the sample throughput was 30 h –1 .

Application of hydrocyanic acid vapor generation via focused microwave radiation to the preparation of industrial effluent samples prior to free and total cyanide determinations by spectrophotometric flow injection analysis

A sample preparation procedure for the quantitative determination of free and total cyanides in industrial effluents has been developed that involves hydrocyanic acid vapor generation via focused microwave radiation. Hydrocyanic acid vapor was generated from free cyanides using only 5 min of irradiation time (90 W power) and a purge time of 5 min. The HCN generated was absorbed into an accepting NaOH solution using very simple glassware apparatus that was appropriate for the microwave oven cavity. After that, the cyanide concentration was determined within 90 s using a well-known spectrophotometric flow injection analysis system. Total cyanide analysis required 15 min irradiation time (90 W power), as well as chemical conditions such as the presence of EDTA-acetate buffer solution or ascorbic acid, depending on the effluent to be analyzed (petroleum refinery or electroplating effluents, respectively). The detection limit was 0.018 mg CN l(-1) (quantification limit of 0.05 mg CN l(-1)), and the measured RSD was better than 8% for ten independent analyses of effluent samples (1.4 mg l(-1) cyanide). The accuracy of the procedure was assessed via analyte spiking (with free and complex cyanides) and by performing an independent sample analysis based on the standard methodology recommended by the APHA for comparison. The sample preparation procedure takes only 10 min for free and 20 min for total cyanide, making this procedure much faster than traditional methodologies (conventional heating and distillation), which are time-consuming (they require at least 1 h). Samples from oil (sour and stripping tower bottom waters) and electroplating effluents were analyzed successfully.