Spectrophotometric bioanalytical flow-injection system for control of hemodialysis treatment

A spectrophotometric flow-injection analysis (FIA) system for monitoring clinical hemodialysis is demonstrated. The role of a dialysate urea detector incorporated in this bioanalytical system is played by an optical flow-through biosensor based on Prussian Blue film with chemically linked urease forming a monomolecular layer of the enzyme. This pH-enzyme optode-FIA system is useful for the selective determination of post-dialysate urea in the range of concentration corresponding to its level in real clinical samples (2-16 mmol l(-1)). This bioanalytical system allows the analysis of about 15 samples of spent dialysate per hour. The operational and storage stabilities of the applied biosensor are longer than 2 weeks and 2 months, respectively. Clinical evaluation of the bioanalytical system was performed.     

Spectrophotometric determination of uranium in process streams of a uranium extraction plant

This paper deals with the development and standardization of procedures for the determination of uranium on a routine basis in various process streams of a uranium extraction plant, covering a wide range of concentrations from 350 g 1(-1) down to 5 mg 1(-1) using only a spectrophotometric technique. The self-absorption of uranyl ion in dilute phosphoric acid and the violet-blue colour of the UO(2)(2+)-Arsenazo III complex in 4 M HC1 were exploited for high and low concentrations of uranium, respectively. The methods described were applied to samples of varying nature such as aqueous, organics and solids, involve minimal sample preparation and do not require prior separation of uranium from impurities. The interfering impurities in different process streams were also studied. Large quantities of silica as undissolved material poses a serious interference in the case of UNS and UNF. Considerable quantities of iron in UNS, UNF, UNR and UNRC cause interference. Possible remedies in these cases are suggested. Problems with the direct spectrophotometric measurement of organic samples is discussed. The effect of the presence of large quantities of ammonium nitrate and sodium nitrate in WD samples on the determination of uranium is also discussed. The results are compared with those obtained by volumetry and X-ray fluorescence spectrometry for higher concentrations of uranium and by extraction-spectrophotometry (ethyl acetate-thiocyanate method) for lower concentrations. Relative standard deviation of 1% and 5% for high and low concentrations, respectively, were obtained, which are adequate as far as process stream samples are concerned. The compared results are in fair agreement. The problems associated with the determination of uranium in these process streams are discussed. Experimental results for 10 different process streams normally encountered in a uranium extraction plant are tabulated.     

Spectrophotometric determination of dissolved tri n-butyl phosphate in aqueous streams of Purex process

A spectrophotometric method is developed for the determination of dissolved tri-n butyl phosphate (TBP) in aqueous streams of Purex process used in nuclear fuel reprocessing. The method is based on the formation of phosphomolybdate with added ammonium molybdate followed by reduction with hydrazine sulphate in acid medium. Orthophosphate and molybdate ions combine in acidic solution to give molybdophosphoric (phosphomolybdic) acid, which upon selective reduction (with hydrazinium sulphate) produces a blue colour, due to molybdenum blue. The intensity of blue colour is proportional to the amount of phosphate. If the acidity at the time of reduction is 0.5?M in sulphuric acid and hydrazinium sulphate is the reductant, the resulting blue complex exhibits maximum absorption at 810?C840?nm. The system obeys Lambert?CBeer??s law at 830?nm in the concentration range of 0.1?C1.0???g/ml of phosphate. Molar Absorptivity was determined to be 3.1?×?10^4?L?mol^?1?cm^?1 at 830?nm. The results obtained are reproducible with standard deviation of 1?% and relative error less than 2?% and are in good agreement with those obtained by ion chromatographic technique.     

Spectrophotometric flow-injection determination of nickel in biological materials

A flow injection method has been developed for the direct determination of free available Pb(II) and total Pb content in wine samples. The method is based on the chemical sorption of Pb(II), from pH 7 buffered solutions, on a packed polyurethane foam column, modified by addition of 2-(2-benzothiazolylazo)-p-cresol (BTAC). After this step, lead was directly eluted with a stream of 0.1 mol l(-1) HCl into an air C(2)H(2) flame in which lead was determined by atomic absorption spectrometry. Total lead was analyzed after sample digestion with nitric acid and hydrogen peroxide, being free available lead determined by direct sample on-line preconcentration and elution. The method provides a limit of detection (3sigma) of 1 mug l(-1) lead and relative standard deviation, which varies from 6 to 0.7% for lead concentration of 10 and 500 mug l(-1). Total content of lead in wine samples analyzed varied from 8 to 42 mug l(-1) being obtained free available values of Pb(II) under the limit of detection of the method. Recovery studies on natural wine samples, spicked with inorganic lead, evidenced the remaining capability of ligands, present in the wine, to avoid lead retention on the polyurethane foam loaded with BTAC.     

Analytical techniques used for monitoring the biodegradation of fluorinated compounds in waste streams from pharmaceutical production

During the assessment of the environmental impact of new pharmaceutical processes the selection and testing of suitable environmental treatment technologies is carried out. A large component of process waste stream treatment practice is aerobic biotreatment in wastewater treatment plants, as it is cost effective and generally more environmentally friendly than harsher chemical/physical treatments. Pharmaceutical syntheses use a range of halogenated compounds (either as reagents, solvents or intermediates) which pose particular challenges to microbial degradation. This is especially so for some fluorinated compounds due to the resilience to enzymatic cleavage of the C-F bond in some cases. The data presented here were obtained from a case study involving the monitoring of the biodegradation of 4-fluorocinnamic acid by means of a range of chromatographic techniques. These methods were used to monitor not only the disappearance of the compound but also the formation of degradation products in order to confirm mineralisation. In addition mass spectrometry was used to elucidate the metabolic pathway.     

Spectrophotometric flow-injection determination of sulphate in soil solutions

A flow-injection procedure for spectrophotometric determination of sulphate in soil solutions is proposed. Samples are directly soaked from the soils under field conditions, in-line filtered through ceramic plates, and preserved with thymol. The method involves reaction with barium dimethylsulphonazo(III) (DMSA) in the presence of dimethylsulphoxide (DMSO) with further measuring the decrease in absorbance at 668 nm. A linear response is observed up to about 5 mgl ⁻¹ SO₄, and detection limit (3σ criterion) is 0.1 mg l⁻¹ SO₄. Only 4.5 μg DMSA is consumed per determination. The system is rugged and baseline drift is not observed during extended operation periods. About 60 samples are injected per hour, and the results are precise (r.s.d. <2%) and in agreement with ion chromatography.     

Spectrophotometric determination of iron with ferrozine by flow-injection analysis

Two methods for the determination of iron by normal FIA and reversed FIA were developed using sodium 3-(2-pyridyl)-5,6-diphenyl-1,2,4-triazine-4',4'-disulphonate (ferrozine). The reagent formed a chelate with Fe(II) in hexamethylentetramine buffered medium at pH 5.5. In one previous reaction coil Fe(III) was reduced to Fe(II) by ascorbic acid and in the other reaction coil the complexation reaction was developed. The linear range of the determination was 0.5-6 and 0.1-5 mug ml(-1) of iron for normal FIA and reversed FIA respectively. The proposed method was sensitive (detection limit 0.012 and 0.010 mug ml(-1)), rapid and reproducible (RSD 0.3 and 0.28%). The method was satisfactorily applied to the determination of iron in waste water, toadstool tissue, potato leaves, human hair and bauxites at a sampling rate of 90 and 50 samples h(-1) for normal FIA and reversed FIA respectively.     

Spectrophotometric determination of silicon in silicates by flow-injection analysis

A flow-injection spectrophotometric method has been developed for the accurate, continuous determination of silicon in silicate rocks. A rock sample solution is prepared by fusion with a 1:1 mixture of lithium carbonate and boric acid and subsequent dissolution of the cake in 1 M hydrochloric acid. The preparation technique is the same as that used for the determination of total iron, aluminium, calcium, titanium, and phosphorus in silicate rocks by flow-injection spectrophotometry. Because of the marked polymerization of silicic acid in acid solution, silicic acid is depolymerized in alkaline medium after a simple cation-exchange column filtration of the rock sample solution and then determined by a static or an FIA spectrophotometric method. The FIA system consists of two channels which carry the carrier solution and molybdate reagent, and allows the colour reaction to proceed under controlled conditions. The FIA system permits high throughput of 70 samples per hour. The procedure has been applied to a variety of standard silicate rocks of the U.S. Geological Survey and the Geological Survey of Japan, and gave satisfactory agreement with the recommended values.     

Spectrophotometric determination of catecholamines with metaperiodate by flow-injection analysis

A flow-injection Spectrophotometric method for the determination of adrenaline and isoprenaline, based on the reaction with metaperiodate, is described. The calibration graphs are linear up to 2 × 10⁻⁴ M. Flow injection allows the measurement of 120 samples per hour. The method was successfully applied to the determination of both catecholamines in pharmaceuticals.     

Spectrophotometric flow-injection determination of ascorbic acid by generation of triiodide

A method is proposed for the flow-injection determination of ascorbic acid (0.1–40 μg ml^?1). Iodine is generated in the flow system as triiodide ion or the triiodide/starch complex giving a steady spectrophotometric signal at 350 or 580 nm, respectively; inverse peaks caused by ascorbic acid samples are measured. The method is applied to the determination of ascorbic acid in a fruit juice, jam and vitamin C preparation.     

Spectrophotometric determination of silicate with Rhodamine B by flow-injection analysis

A spectrophotometric flow-injection method for the determination of silicate based on the formation of an ion pair between molybdosilicic acid and Rhodamine B is proposed. It allows silicate to be determined over the concentration range 0.17–2.0 mg 1^?1 at a sampling rate of 40 h^?1, is reasonably precise and is highly tolerant to ions that commonly occur in waters. It has been applied with satisfactory results to the determination of silicate in various types of water.     

Field-portable flow-injection analysers for monitoring of air and water pollution

There has been a rapid growth in the development of field-portable analytical instrumentation capable of in-situ and real-time feedback of data from remote sites. Advances have been made in applications for many technologies aided by developments in electronics, computing and telecommunications systems. This report presents a brief review of these developments and particularly of portable flow-injection systems applied in both the liquid and gas phase modes of operation with potentiometric sensors and gas sensors of the tin-oxide semiconductor types.     

Spectrophotometric determination of sulphate in sodium hydroxide solutions by flow-injection analysis

A spectrophotometric flow-injection procedure is described for the determination of sulphate in sodium hydroxide solutions. Sulphate catalyses the reaction between zirconium and methylthymol blue to form a complex measured at 586 nm. Optimal reaction conditions are discussed. The calibration graph is linear over the range 0.05–0.5 g l^?1 sulphate with a relative standard deviation of 0.02. The sample throughput is 20 h^?1. Sulphate is easily determined in 1 M sodium hydroxide; the results agree with those obtained by the conventional gravimetric method and by ion chromatography.     

Trace and ultratrace analysis methods for the determination of phosphorus by flow-injection techniques

Trace (≤1 mg/l or 30 μM) and ultratrace (≤1 μg/l or 30 nM) analysis methods for phosphorus determination by flow-injection analysis are reviewed. Most of the methods cited in this review are fundamentally based on the reaction of orthophosphate with molybdate to form heteropoly acids, such as molybdenum yellow and molybdenum blue, and some of the methods are based on the formation of such secondary reactions as ion associates and their aggregates with bulky cations, such as cationic dyes and quaternary ammonium ions. The heteropoly acids themselves can be measured by spectrophotometry, and the ion associate formed with a cationic dye, Malachite Green (MG), can be measured based on the coloration of MG. Light scattering detection methods can be used for measuring the aggregates of ion associates formed with bulky cations. Highly sensitive detection of phosphorus can be accomplished by fluorophotometry; Rhodamine B (RB) and its analogues react with molybdophosphate to form ion associates, which shows fluorescence quenching of RB: LOD is about 5 nM. The detection method based on the chemiluminescence of luminal oxidized with molybdophosphoric acids is probably the most sensitive of all the detection methods reported so far: LOD of the method is as low as 1 nM. The LOD of the molybdenum blue method can be improved by using a liquid core waveguide: LOD is 0.5 nM.     

Multidetection flow-injection techniques for manipulation of sensitivity : Amplification and dilution methods

Different multidetection flow-injection techniques are considered for the manipulation of analytical sensitivity and for broadening the determination range of an analyte with maximum accuracy. Conventional spectrophotometric detection in linear or cyclic flow systems and a diode-array detector for monitoring several wavelengths simultaneously are used. The formaldehyde/pararosaniline/sulfite system is used for studying these techniques.     

Mathematical modelling of sequential determinations by flow-injection sandwich techniques

Preliminary results obtained in the evaluation of a mathematical model for flow-injection systems, including chemical kinetics, with an eight-way injection valve are presented. The use of this kind of injection valve permits the insertion of the sample bolus between two different reagent solutions (sandwich techniques). The model considers the system as a tubular reactor with axially dispersed plug flow. As an example for systems with chemical reaction, the enzymatic determination of glucose was chosen. The parameters of the model (dispersion coefficients and reaction rate constants) were experimentally evaluated by using a tracer or by unidirectional optimization, respectively. The effect of different parameters of the flow system on the analytical signal for one analyte and one reagent was simulated, and the model results are compared with experimental data obtained under the same conditions.     

Spectrophotometric detection of arsenic using flow-injection hydride generation following sorbent extraction preconcentration

An automated system with a C(18) bonded silica gel packed minicolumn is proposed for spectrophotometric detection of arsenic using flow-injection hydride generation following sorbent extraction preconcentration. Complexes formed between arsenic(III) and ammonium diethyl dithiophosphate (ADDP) are retained on a C(18) sorbent. The eluted As-DDP complexes are merged with a 1.5% (w/v) NaBH(4) and the resulting solution is thereafter injected into the hydride generator/gas-liquid separator. The arsine generated is carried out by a stream of N(2) and trapped in an alkaline iodine solution in which the analyte is determined by the arsenomolybdenum blue method. With preconcentration time of 120 s, calibration in the 5.00-50.0 mug As l(-1) range and sampling rate of about 20 samples h(-1) are achieved, corresponding to 36 mg ADDP plus 36 mg ammonium heptamolybdate plus 7 mg hydrazine sulfate plus 0.7 mg stannous chloride and about 7 ml sample consumed per determination. The detection limit is 0.06 mug l(-1) and the relative standard deviation (n=12) for a typical 17.0 mug As l(-1) sample is ca. 6%. The accuracy was checked for arsenic determination in plant materials from the NIST (1572 citrus leaves; 1573 tomato leaves) and the results were in agreement with the certified values at 95% confidence level. Good recoveries (94-104%) of spiked tap waters, sugars and synthetic mixtures of trivalent and pentavalent arsenic were also found.     

Spectrophotometric determination of chlorhexidine with bromocresol green by flow-injection and manual methods

A spectrophotometric study of the chlorhexidine/bromocresol green/Triton X-100 system is reported; at pH 5.3, both 2:1 and 1:1 bromocresol green/chlorhexidine complexes are formed. In the manual spectrophotometric method, Beer's law is obeyed for chlorhexidine concentrations of 2.9–32.2 μg ml^?1 (r.s.d. 0.4–1.3%); the molar absorptivity is 12 500 l mol^?1 cm^?1. In the flow-injection method, the calibration graph is linear for the chlorhexidine range 23.0–83.9 μg ml^?1 (r.s.d. 0.8%); the injection is ca. 60 h^?1. Benzocaine, acetylsalicylic acid, ascorbic acid and sucrose are tolerated at 10^?2?10^?3 M levels. Hibitane 5% was analyzed successfully.     

Enzymatic flow-injection determination of l-phenylalanine using the stopped-flow and merging-zones techniques

A flow injection enzymatic method for the spectrophotometric determination of l-phenylalanine has been developed. l-phenylalanine is deaminated in the presence of l-amino acid oxidase and the keto acid formed is made to react with borate to give a coloured enol-borate complex that can be detected at 282 nm. Catalase is added to the catalyzed reaction to prevent the keto acid being destroyed by the hydrogen peroxide generated. Kinetic determinations are performed by measuring the change in absorbance between 2 and 4 min. The proposed procedure, involving both merging-zones and stopped-flow techniques, can be applied to the quantitation of l-phenylalanine between 10 and 260 mg l(-1). Detection limit and R.S.D. are 1.1 mg l(-1) and 3.0%, respectively.     

Hot-wire amperometric monitoring of flowing streams

This paper describes the design of a hot-wire electrochemical flow detector, and the advantages accrued from the effects of locally increased temperature, mainly thermally induced convection, upon the amperometric monitoring of flowing streams. A new hydrodynamic modulation voltammetric approach is presented, in which the solution flow rate remains constant while the temperature of the working electrode is modulated. Factors influencing the response, including the flow rate, temperature pulse, or applied potential, have been investigated. The hot-wire operation results also in a significant enhancement of the flow injection amperometric response. The minimal flow rate dependence observed with the heated electrode should benefit the on-line monitoring of streams with fluctuated natural convection, as well as various in-situ remote sensing applications.