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 nitrogen in small quantities of biological materials

Summary A new spot test for ammonium, by its reaction with ruthenium trichloride-triphenylphosphine, having a Ig limit of identification is reported. On the basis of this spot reaction a spectrophotometric method is described for the determination of minute quantities of NH₄-N from biological materials.

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Zusammenfassung Eine neue Tüpfelreaktion auf Ammonium wurde beschrieben, die auf der Umsetzung mit Rutheniumtrichlorid-Triphenylphosphin beruht. Die Erfassungsgrenze beträgt 1g. Mit Hilfe dieser Reaktion lassen sich kleinste Mengen Ammoniumstickstoff spektrophotometrisch in biologischem Material bestimmen.

     

Spectrophotometric determination of vanadium in biological materials with N-benzylbenzohydroxamic acid

A spectrophotometric method for the determination of vanadium in biological materials with N-benzylbenzohydroxamic acid is proposed. The method is highly selective for vanadium and is free from rigid control of reaction conditions. No separation of iron prior to the determination of vanadium is necessary. Cu(II), Co(II), Ni, Mn(II), Cr(III), Ce(IV), Zr, Mo(VI), Ca, Sr, Ba, UO(2)(II) and many others metal ions do not interfere. Fairly large quantities of Ti(IV) and W(VI) are tolerated.     

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 phosphorus as phosphate in organic compounds and materials of biological origin using a flow-injection manifold with a mixing chamber

Summary A flow-injection manifold with mixing chamber has been developed for the determination of phosphate by reaction with molybdate and crystal violet. The insoluble blue dye salt is kept in colloidal solution with poly(vinyl alcohol) and measured at 560 nm. The injection rate is 100 h^–1. The detection limit is 0.01 g PO ₄ ^3– /ml based on 250 l injection volumes. The system has been applied to the determination of phosphate in serum samples and after appropriate mineralisation to organic compounds and to plant materials.     

Spectrophotometric flow-injection determination of copper and nickel in plant digests exploiting differential kinetic analysis and multi-site detection

A novel strategy for implementing differential reaction-rate methods in flow-injection analysis is proposed and applied to the determination of copper and nickel in plant digests using 2-(5-brom-2-pyridylazo)-5-(diethylamino)-phenol (Br-PADAP) as the color-forming reagent. Multi-site detection is involved, therefore the flow cell is displaced between two monitoring sites, and the analytical signals refer to different conditions of sample dispersion, reaction development and timing.The system handles 20 samples h⁻¹ and requires 0.32 mg Br-PADAP per determination. Signal additivity was evaluated within 98 and 102%, and linear responses (r > 0.999; n = 6) were verified for both copper and nickel up to 0.80 mg l⁻¹. Detection limits of 0.01 and 0.04 mg l⁻¹ Cu and Ni were estimated by considering the highest concentration of the counter analyte. Results are precise (R.S.D. < 2%) and in agreement with ICP-OES (95% confidence level). Potentialities and limitations of the approach are discussed.     

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 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 aluminium and nickel

A simple spectrophotometric method, based on the complexes with xylenol orange (XO) and EDTA, is presented for the rapid determination of aluminium and nickel, respectively, in synthetic samples of hydrotalcite. The method only requires the solubilization in sulphuric acid of the inorganic material before the ligand addition. Under optimum conditions, the complexes Al-XO and Ni-EDTA showed maximum absorption at 554 nm and 380 nm, respectively. The method obeyed Beer's law in the concentration range 0.14-1.8 microg mL(-1) of aluminium, and 30-2730 microg mL(-1) of nickel. Molar absorptivities were 2.45 x 10(4) and 14.85 L mol(-1) cm(-1) while Sandell's sensitivities were 1.1 x 10(-3) and 3.9 microg cm(-2) for aluminium and nickel, respectively. The standard addition technique was used and the recoveries obtained revealed that the proposed procedure shows good accuracy.     

Spectrophotometric determination of nickel with p-acetylarsenazo

A spectrophotometric method for the determination of trace amounts of nickel is described. At pH 6, nickel reacts with p-acetylarsenazo to form a 1:2 coloured complex with an absorption maximum at 630 nm. The apparent molar absorptivity is 6.5 x 10(4) l.mol(-1) . cm(-1) . Beer's law is obeyed over the concentration range of 0-0.8 microg/ml. The proposed method is selective, sensitive and can be applied to the determination of nickel in aluminum alloy.     

Simultaneous determination of silicon and phosphorus in biological standard materials with on-line column flow-injection spectrophotometry

Summary A simultaneous determination of silicon and phosphorus in biological standard materials with on-line column flow-injection spectrophotometry (FIA) is described. Biological materials are ashed, fused with a lithium carbonate-boric acid mixture, and dissolved in a hydrochloric acid solution. Interfering cations are removed by a simple cation-exchange column filtration. The acid effluent is evaporated to dryness, fused with a small amount of sodium carbonate for depolymerization, taken up in dilute EDTA solution, and analyzed for silica and phosphorus by FIA. For the simultaneous determination of these elements, TSK-gel SAX was used, and the eluent was 0.085 mol/l NaCl/0.01 mol/l NH₃/0.001 mol/l EDTA. Several standard reference materials [bovine liver (NBS), chlorella and pepperbush (NIES)] were analyzed for both elements. The results of phosphorus determination for bovine liver are in satisfactory agreement with the NBS certificated value. ICP measurements were applied to analyses of chlorella and pepperbush for silica and phosphorus. The agreement of the analytical results between FIA and ICP is satisfactory. Silica in bovine liver was determined in the present study for the first time.

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Simultanbestimmung von Silicium und Phosphor in biologischen Standardmaterialien mit Hilfe von On-line Fließinjektions-Spektralphotometrie

     

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 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.     

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.     

Separation and determination of Cd in biological materials by continuous-flow fluid extraction coupled to flow-injection ICP-AES

An FI-ICP-AES method for the determination of trace levels of cadmium in biological samples is described based on the complexation of the metal ion with 1,5-bis(di-2-pyridyl)methylene thiocarbohydrazide (DPTH) and its subsequent on-line extraction into isobutyl methyl ketone (IBMK). The detection limit for cadmium is 8.7 ng/ml and the calibration is linear at least from 10 to 2000 ng/ml. The relative standard deviation for 7 replicate measurements is 3.4% for 100 ng/ml of cadmium. Results from the analysis of some certified biological reference materials are given.     

Spectrophotometric determination of proteins in biological fluids

A comparative analysis of procedures of the spectrophotometric determination of total protein with various organic dyes, Bromocresol Green, Bromophenol Blue, and Pyrogallol Red, in biological fluids is presented. It is shown that the results of determination with various dyes can differ because of the specific features of reagent interaction with the components of biological fluids. A new organic reagent, Bromopyrogallol Red, possessing equal sensitivity to different protein fractions (albumins and globulins) and ensuring a minimum error of the determination of total protein in clinical examinations using calibration solutions of various compositions is proposed. A procedure for the determination of total protein in biological fluids is developed and tested on real samples of urine and blood serum.     

Spectrophotometric flow-injection determination of zinc in plant digests based on a spot test

A spot test was implemented in a flow-injection system for the spectrophotometric determination of zinc in digests of plant materials. It is based on the influence of Zn²⁺ on the oxidation rate of 1-naphthylethylenediamine (NED) by hexacyanoferrate(III) under acidic conditions. In order to control the precipitate formation and to maintain the resulting suspension, a micellar medium was established by adding Triton X-100. The proposed system handles about 65 samples per hour, meaning 72 μg NED and 9.0 mg K₃[Fe(CN)₆] per determination. Baseline drift is usually <0.01 absorbance per hour and the analytical signals for 0.5-2.5 mg l⁻¹ Zn range within ca. 0.07-0.45 absorbance. Linearity of the analytical curve is fair (r>0.999, n=6) and detection limit was estimated as 0.2 mg l⁻¹ Zn. Results are precise (R.S.D.<1%, n=10) and in agreement with flame atomic absorption spectrometry and with certified values of standard reference materials.     

Spectrophotometric flow-injection determination of cellobiose dehydrogenase activity in fermentation samples with 2,6-dichlorophenolindophenol

Cellobiose dehydrogenase activity (0.25–1 U Ml^?1) is monitored by oxidation of cellobiose to cellobionolactone, thus reducing 2,6-dichlorophenolindophenol to a colourless compound. To prevent any β-glucosidase from reacting, gluconolactone is added as inhibitor. The sample throughput is 120 h^?1.     

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.     

Phosphorus determination in biological materials

Summary An analysis scheme for the spectrophotometric determination of phosphorus as phosphate in biological materials has been worked out. The wet digestion of the sample was carried out in Kjeldahl flasks by a mixture of perchloric and nitric acids. The relative standard deviation (RSD) of the obtained results is not more than 1% for amounts up to 30 g. The method was applied to various biological materials.