Cyclic Flow Injection Analysis Research Articles

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

Cyclic Flow Injection Analysis for Heavy Metal Ions Using Xylenol Orange

Spectrophotometric determinations of heavy metal ions with xylenol orange (XO) have been carried out using cyclic flow injection analysis. A cation-exchanger mini-column (Amberlite IR124) was incorporated after a flow-through cell for the on-line regeneration of the used reagents and the accumulation of heavy metal ions. A solution of 1.0×10−5 M XO in 0.01 M acetate buffer (pH 5.0) in a single reservoir (100 mL) was continuously circulated, and sample solutions were injected into the stream. Cadmium(II), copper(II), iron(III), lead(II), zinc(II) and lanthanum(III) were sensitively monitored and determined. The regeneration and recycling of the XO reagent allowed as many as 50 repetitive determinations of heavy metal ions with the same 100 mL circulating reagent solution.

Repetitive Determination of Chemical Oxygen Demand by Cyclic Flow Injection Analysis Using On-line Regeneration of Consumed Permanganate

A cyclic flow injection analysis (cyclic FIA) for the repetitive determination of chemical oxygen demand (COD) was developed. The acidic KMnO4 method was carried out by adopting a single-line circulating flow system. The oxidant (KMnO4) consumed by the oxidation of organic substances was regenerated and reused repeatedly, resulting in an extreme reduction of hazardous wastes. Only 50 ml of the reagent carrier solution containing 0.2 mM KMnO4 and 1 mM HIO4 in 0.8 M H2SO4 solution was continuously circulated through the system. The KMnO4 could play two roles: acting as an oxidant of the organic substances and/or a spectrophotometric reagent. The co-existing HIO4 acted as a regenerator of KMnO4, which made it possible to recycle the system repeatedly. Under two different digestions (70 and 130 degrees C), 50 repetitive determinations of standard sodium oxalate (6.5 mg COD L(-1)) and D-glucose (7.2 mg COD L(-1)) were skillfully carried out with a slightly decreased baseline. The analytical frequency was 30 samples per hour for COD determination. The proposed method saved consumption of the used reagents, KMnO4 and H2SO4, and thus these wastes were extremely reduced. The obtained COD values with the proposed method were co-related with those provided by the manual standard method, but were fairly low owing to the insufficient digestion step.

Clean analytical methodology for the determination of lead with Arsenazo III by cyclic flow-injection analysis

A clean analytical methodology, where the sample determined and the reagent used are both toxic, has been proposed. A cation exchange mini-column was incorporated after the flow-through cell for on-line regeneration of the main reagent and the accumulation of heavy metal ions. The method involves the spectrophotometric determination of lead with Arsenazo III, the accumulation of lead onto the cationic exchanger, and subsequent regeneration of the chromogenic reagent, which makes the system reversible and the reagents reusable. The developed method provides a satisfactory way to cut down on the toxic reagent consumption and the produced volume of waste, an important step towards the zero emissions research initiative concept. The excellent repeatability and reproducibility, and the simplicity of this method are well suited for continuous measurements. The method was successively applied to the assay of lead in high-octane gasoline.

Reagents regeneration flow injection analysis (RRFIA) for spectrophotometric determination of methamphetamine coupled with solvent extraction

Methamphetamine (MPA), being a stimulant drug, reacts with tetrabromophenolphthalein ethyl ester (TBPEH) to form a red-violet ion associate, TBPEHMPA, in 1,2-dichloroethane (DCE) at pH 9. The maximum absorption wavelength was at 570 nm. After measuring, yellow TBPEH with DCE could be regenerated by mixing with the buffer solution at pH 3. The regenerated TBPEH/DCE could be reused as an ion association reagent and extracting solvent. In addition, the reagent regeneration could be performed by the on-line flow injection system and the cyclic flow injection analysis system was demonstrated for the determination of MPA without consumption of ion association reagent and organic solvent. The calibration curve was linear in the range of 0.5–3.5 × 10 −5 M with good repeatability. The sample throughput was 20 h −1.

Cyclic Flow-Injection Analysis for the Repetitive Determination of Zinc with 2-(5-Bromo-2-pyridylazo)-5-[N-n-propyl-N-(3-sulfopropyl)amino]phenol and EDTA

A circulatory flow-injection method (cyclic FIA) for the repetitive determination of zinc has been proposed. The procedure involves the use of 2-(5-bromo-2-pyridylazo)-5-[N-n-propyl-N-(3-sulfopropyl)amino]phenol (5-Br-PAPS) together with EDTA as a reagent carrier solution, which is recycled in a single-line flow system via a reservoir. The formed 5-Br-PAPS-Zn(II) complex was measured spectrophotometrically at 552 nm, and the signal intensity corresponded to the zinc concentration. After passing through a flow-through cell, the carrier stream then returned to the reservoir, and the main reagent, 5-Br-PAPS, was successfully regenerated by a ligand-exchange reaction with EDTA, allowing the repetitive determination of zinc. The calibration curve for zinc was linear in the concentration range from 0.4 to 10.0 mg dm(-3) with a correlation coefficient of 0.9995 (n = 6). The detection limit of this method was 0.02 mg dm(-3) (S/N= 3). This method allowed as many as 300 repetitive determinations of 2.0 mg dm(-3) zinc solution with only 100 cm3 of the circulating carrier solution, providing a reduction in the consumption of reagents and an elimination of waste, an important approach towards clean chemistry.

Cyclic flow-injection analysis for Fe(II)-1,10-phenanthroline using polyurethane foam

The spectrophotometric determination of Fe(II) with 1,10-phenanthroline (phen) was carried out by a cyclic flow-injection analysis. Tandem glass columns (4 mm i.d., 8 cm long, each) packed with polyurethane foam (PUF, weight; 0.16 g×2) for the removal of Fe(II)-(phen)3 complex were incorporated in the system, allowing a repetitive determination of Fe(II). A solution of 2.0×10−3 M phen and 5.0×10−4 M sodium dodecyl sulfate (SDS) in a 0.1 M acetate buffer (pH 4.7) in a single reservoir (50 ml) was continuously circulated at a constant flow rate of 1.5 ml min−1. Into the stream, an aliquot (5 μl) of a sample containing Fe(II) was injected by means of a 6-way valve. The formed complex was monitored spectophotometrically at 510 nm. The stream was passed through glass columns, which were introduced after the flow-through cell, and then returned to the reservoir. The colored Fe(II)-(phen)3-SDS ion associates were adsorbed onto PUF, which allowed a baseline constant, and made it possible to adopt a cyclic FIA. This method allowed as many as 100 repetitive determinations of 6 ppm Fe(II) solutions with the same 50 ml of the circulating solution.

Cyclic flow-injection analysis for repetitive determination and monitoring

一流路系のフローシステムを構築して，フローセルを通過した試薬溶液を廃棄することなく，繰り返し試薬溶液として利用する，サイクリックフローインジェクション法について述べた．試薬溶液中において，主反応に対して逆向きに作用する阻害剤（inhibitor）の共存下で検出・定量を行うという，新しいコンセプトを導入して，試薬溶液の繰り返し利用を可能にした．また，イオン交換，あるいはキレート樹脂を充填したカラムを系内に導入して，試料と反応後の試薬再生にも成功した． 緩衝液の緩衝能を利用した強酸・強塩基の定量，塩化銀沈殿がアンモニア溶液に溶解することを利用した塩化物イオンの定量，エチレンジアミン四酢酸存在下4-（2-ピリジルアゾ）レゾルシノールによる銅（II）イオンの定量，多量の酸化剤存在下，鉄-フェナントロリン錯体の酸化・還元系を利用したアスコルビン酸の定量，イオン交換，キレート樹脂カラムを組み込んだカルシウム，銅（II）イオンの定量について述べた． サイクリックフローインジェクション法は，試薬溶液量を最小限に調製できるので，ゼロエミッションの理念に沿った分析法となる．また，単純化されたシステムにより，再現性，精度，耐久性に極めて優れた分析法で，品質・工程管理におけるモニタリングやルーチン分析に適している．

Repeated use of a reagent solution as a model of Fe(II)-1,10-phenanthroline in cyclic-flow injection analysis.

Repeated use of a reagent solution as a model of Fe(II)-1,10-phenanthroline in cyclic-flow injection analysis.