Reverse flow injection spectrophotometric determination of iodate and iodide in table salt

A very simple and sensitive reverse flow injection method is described for the determination of iodate and iodide. The iodate reacts with excess iodide in acidic medium to form tri-iodide, which can be spectrophotometrically monitored at 351 nm, and the absorbance is directly related to the concentration of iodate in the sample. The determination of iodide is based on oxidizing iodide to iodate. The calibration curve is linear in the range of 0.02-3.0 μg ml⁻¹ I with r²=0.9998, and the limit of detection is 0.008 μg ml⁻¹ I. The chemical and flow injection variables were studied and optimized to make the procedure suitable for quantitating iodate and iodide in table salts. It is shown that the reverse flow injection analysis could greatly improve the sensitivity and precision for determination of iodate with a relative standard deviation of 0.9%. A complete analysis, including sampling and washing, could be performed in 35 s. The procedure was applied successfully to the determination of iodate and iodide in table salts, and the results were statistically compared with results determined by standard iodometry method.     

Spectrophotometric determination of iodate,iodide and acids by flow injection analysis

The production of iodine by reaction of iodate and iodide in acidic solution is used for the spectrophotometric determination of 1–6 × 10^?5 M iodate, 2–8 × 10^?3 M iodide, and ca. 10^?3 M acids. The sample is injected into a carrier stream containing the other two ions. The injection rate is ca. 100 h^?1.     

Downscaling a multicommuted flow injection analysis system for the photometric determination of iodate in table salt

In this work a downscaled multicommuted flow injection analysis setup for photometric determination is described. The setup consists of a flow system module and a LED based photometer, with a total internal volume of about 170 μL. The system was tested by developing an analytical procedure for the photometric determination of iodate in table salt using N,N-diethyl-henylenediamine (DPD) as the chromogenic reagent. Accuracy was accessed by applying the paired t-test between results obtained using the proposed procedure and a reference method, and no significant difference at the 95% confidence level was observed. Other profitable features, such as a low reagent consumption of 7.3 μg DPD per determination; a linear response ranging from 0.1 up to 3.0 m IO₃⁻, a relative standard deviation of 0.9% (n = 11) for samples containing 0.5 m IO₃⁻, a detection limit of 17 μg L⁻¹ IO₃⁻, a sampling throughput of 117 determination per hour, and a waste generation 600 μL per determination, were also achieved.     

Spectrophotometric determination of periodate, iodate and bromate mixtures based on their reaction with iodide.

A rapid, simple, precise and accurate method is proposed for the determination of ternary mixtures of periodate-iodate-bromate based on their reaction with iodide ion at different pH values. The absorbance was measured at 352 nm. Three sets of reaction conditions were developed. In the first set of conditions, only periodate reacted with iodide, but in the second set the periodate and iodate reacted with iodide and in the third set the three ions reacted with iodide during the first 3 min after initiation of the reaction. The method could be used for individual determinations of periodate, iodate and bromate in the concentration range of 0.05-8.0 microg/ml, 0.05-5.0 microg/ml and 0.2-12 microg/ml, respectively. The data were evaluated by simultaneous equations.     

Simple flow injection system for colorimetric determination of iodate in iodized salt

This work presents a flow injection (FI) system that was developed for determination of iodate. The system utilizes the oxidation of iodide by the analyte to iodine, which subsequently forms tri-iodide. In the presence of starch, the blue I₃⁻–starch complex is developed within the sample zone and can be colorimetrically detected at 590 nm. Optimization was carried out to make the system suitable for quantitating iodate added to table salts. To prevent accumulation of the blue complex residue on walls of tubing and the flow cell, a port was placed in the system for injection of 10⁻³ M thiosulfate plug (100 μl). An injection of this cleaning solution after each sample injection is recommended to avoid positive baseline shift. By means of the paired t-test, the amounts of iodine (mg I kg⁻¹) were statistically compared with the results determined by titration and by iodide ion selective electrode. No significant disagreement at 95% confidence was observed. The proposed system is very simple, uses common chemicals and provides rapid analysis (65 injections per h) with high precision (R.S.D.=0.66%, n=10). A detection limit of 2 mg I kg⁻¹ salt can be achieved.     

Spectrophotometric flow injection determination of trace amounts of thiocyanate based on its reaction with 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol and dichromate: assay of the thiocyanate level in saliva from smokers and non-smokers

A simple and very sensitive spectrophotometric flow injection (FI) procedure for the determination of trace amounts of thiocyanate is described. The proposed method is based on the reaction between thiocyanate and 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol, which, in 2 mol dm-3 acidic media in the presence of a strong oxidizing agent, produces an intensely coloured product. Several oxidants are potentially applicable, but it is shown that dichromate is preferable. As the reaction product formed is unstable and the signal inherently is recorded on a high background level, it is demonstrated that FI constitutes an ideal method in order to monitor reproducibly and repeatedly the kinetically transient signal that is obtained. Based on optimization by a factorial experimental design, the detection limit of the procedure was found to be 3.5 mumol dm-3, and the standard deviation between samples was 0.16 mumol dm-3. No significant interferences were observed; a 1000-fold excess of cyanide could readily be tolerated within the experimental error. With a sample volume of 50 microliters being injected, the sampling frequency was 60 samples h-1. The system was tested with saliva samples from non-smokers and smokers, and the results show that it is possible to distinguish between these two categories of individuals. As an added benefit, the detection limit of the analytical procedure allows the samples to be diluted 100-fold, so that centrifugation for 5 min is the only preliminary sample preparation that is necessary.     

双硫腙褪色光度法测定痕量铈

研究了Ce(Ⅳ)在H2SO4介质中和溴化十六烷基吡啶存在下催化H2O2氧化双硫腙的褪色反应及其动力学条件,测定了反应级数和表观活化能,建立了测定痕量铈的新方法。双硫腙的最大吸收波长为450nm,该方法的检出限为1 9×10-9g/mLCe(Ⅳ),线性范围为0～150ng/mLCe(Ⅳ),方法可用于人发中痕量铈的测定。     

Spectrophotometric flow injection determination of formetanate and m-aminophenol in water after reaction with p-aminophenol

An automated procedure has been developed for the determination of formetanate and its metabolite m-aminophenol (MAP) in water samples. MAP can be selectively determined in the presence of formetanate by direct on-line reaction with p-aminophenol and spectrophotometric measurement of the absorbance at 576 nm in the presence of KIO(4), as oxidizing agent. The method has a limit of detection of 5 x 10(-7)M, it provides a recovery percentage from 95 to 104% and permits one to carry out 120 measurements/hr. The spectrophotometric determination of formetanate must be carried out after a previous hydrolysis to MAP. To determine formetanate in the presence of MAP, two steps are necessary. Firstly, the MAP content is selectively determined as has been mentioned above. After that, the sample is treated with 0.05M NaOH at 90' degrees C, to hydrolyze the formetanate to MAP, and then the sum of both is determined spectrophotometrically. The difference between the results obtained in each step gives the formetanate concentration. The developed procedure for the determination of formetanate provides a sensitivity of 1070 absorbance units mol(-1) l and a limit of detection of 1.9 x 10(-7)M, which corresponds to 50 mug/l of formetanate hydrochloride. The method has been applied to the analysis of natural water samples fortified with formetanate and MAP, and formetanate has also been quantitatively recovered in irrigation waters at a concentration level of 1.9 x 10(-6)M which corresponds to 500 mug/l. On the other hand, working in the stopped-flow mode, for a reaction time of 100 sec, the sensitivity of the formetanate determination can be increased to 4642 absorbance units mol(-1) l but the limit of detection remains of the order of 44 mug/l.     

Sequential flow injection determination of iodate and periodate with spectrophotometric detection

A flow injection (FI) system is described for the sequential determination of periodate and iodate based on their reaction with iodide at pH 3.5. Two sample plugs were injected into the same carrier stream sequentially. One injection is for the iodate determination and the other for the sum of iodate and periodate determination. For iodate determination, molybdate solution buffered at pH of 3.5 was used for selective masking of periodate. The influences of reagent concentrations were studied by a univariable method and the influence of FI manifolds was studied using univariable and simplex method. Periodate and iodate can be determined in the range of 0.050-5.0 and 0.050-10 microg/ml, respectively. The 3 sigma limit of detection was 0.030 and 0.050 microg/ml for periodate and iodate, respectively. The proposed method has been applied for the sequential determinations of periodate and iodate in water samples.     

Spectrophotometric determination of iodine species in table salt and pharmaceutical preparations

A sensitive spectrophotometric method for the determination of iodine species like iodide, iodine, iodate and periodate is described. The method involves the oxidation of iodide to ICl(2)(-) in the presence of iodate and chloride in acidic medium. The formed ICl(2)(-) bleaches the dye methyl red. The decrease in the intensity of the colour of the dye is measured at 520 nm. Beer's law is obeyed in the concentration range 0-3.5 microg of iodide in an overall volume of 10 ml. The molar absorptivity of the colour system is 1.73 x 10(5) l mol(-1) cm(-1) with a correlation coefficient of -0.9997. The relative standard deviation is 3.6% (n=10) at 2 microg of iodide. The developed method can be applied to samples containing iodine, iodate and periodate by prereduction to iodide using Zn/H(+) or NH(2)NH(2)/H(+). The effect of interfering ions on the determination is described. The proposed method has been successfully applied for the determination of iodide and iodate in salt samples and iodine in pharmaceutical preparations.     

Spectrophotometric determination of trace amounts of cadmium and lead with iodide and Rhodamine B

Summary Highly sensitive spectrophotometric methods have been developed for determination of cadmium and lead, based on the CdI₄ ^2– or PbI₄ ^–2 anionic complexes with Rhodamine B in the presence of polyvinyl alcohol to form ion-association complexes. The molar absorptivity is 4.2×10⁵l·mole^–1·cm^–1 at 600 nm for cadmium and 5.7×10⁵l·mole^–1·cm^–1 at 610 nm for lead. The complexes have the composition [CdI₄ ^2–]·[RhB⁺]₂ and [PbI₄ ^2–]·[RhB⁺]₂ as established by Job's method of continuous variations and the molarratio method. The colour reaction selectivity is fairly good and the method can be applied for direct spectrophotometric determination of cadmium or lead in some pure metals. A species [PbI₃ ^–]·[RhB⁺] can also be formed, and extracted into toluene or a toluene/diethyl ether mixture.

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Spektrophotometriscbe Bestimmung von Spuren Cadmium und Blei mit Jodid und Rhodamin B

Zusammenfassung Hochempfindliche spektrophotometrische Methoden für die Bestimmung von Cadmium und Blei wurden entwickelt; sie beruhen auf der Reaktion von CdJ₄ ^2– bzw. PbJ₄ ^2– mit Rhodamin B in Gegenwart von Polyvinylalkohol unter Bildung von Ionenassoziat-Komplexen. Die molare Absorptivität für Cadmium beträgt 4,2×10⁵l·mol^–1·cm^–1 bei 600 nm und für Blei 5,7×10⁵l·mol^–1·cm^–1 bei 610 nm. Wie nach der Methode der kontinuierlichen Variation nach Job bzw. mittels Molarverhältnis ermittelt wurde, lautet die Formel [CdJ₄] [RhB]₂ bzw. [PbJ₄] [RhB]₂. Die Selektivität der Farbreaktion ist gut. Das Verfahren kann zur direkten spektrophotometrischen Bestimmung von Cadmium bzw. Blei in verschiedenen reinen Metallen verwendet werden. Auch eine Verbindung [PbJ₃ ^–] [RhB⁺] kann hergestellt werden, die sich mit Toluol oder mit einem Gemisch aus Toluol und Diethylether extrahieren läßt.

     

Spectrophotometric determination of trace molybdenum in plants and seeds with 3,5-dibromo-4-hydroxyphenylflurone

A novel spectrophotometric method based on a new reagent, 3,5-dibromo-4-hydroxyphenylflurone, was developed for the determination of molybdenum in plants and seeds. 3,5-Dibromo-4-hydroxyphenylflurone showed outstanding analytical characteristics for spectrophotometric determination of molybdenum. The reaction conditions are simple and stable. In 0.2 mol l(-1) phosphoric acid medium (which can combine with iron and other metal ions and greatly improves the selectivity of the color system), molybdenum(VI) reacts with 3,5-dibromo-4-hydroxyphenylflurone to form a 1:2 red complex with an absorption maximum at 530 nm, the color reaction can completed in 2 min and the absorbance of the molybdenum complex remains stable for at least 72 h at room temperature. Its stability constant is 1.21 x 10(28) at 25 degrees C. Beer's law is obeyed over the range 0-0.6 microg ml(-1) Mo(VI). The reagent has very high sensitivity and selectivity; the molar absorptivity of the complex is 1.35 x 10(5) 1 mol(-1) cm(-1) and the limit of quantification, the limit of detection and relative standard deviation (n = 10) were found to be 6.7 ng ml(-1), 2.2 ng ml(-1) and 1.01%, respectively. Cu (50000-fold), Fe (20000-fold), K (20000-fold), NH4+ (20000-fold), Mg (15000-fold), Zn (10000-fold), Na (10000-fold), Al (4000-fold), Ca (25000-fold), Mn (2000-fold), Ce (500-fold), Cr (400-fold) and Bi (200-fold) do not interfere with the determination of trace levels of molybdenum up to the excesses indicated. The selectivity is much superior to that of other published methods. The proposed method was applied to the direct determination of molybdenum in plants and seeds with satisfactory results. The synthesis of the reagent and conditions of color reaction were studied in detail.     

Spectrophotometric determination of molybdenum in rocks with thiocyanate

A rapid procedure for the determination of microgram amounts of molybdenum in rocks is described. After acid decomposition, molybdenum is extracted from a hydrochloric acid solution into xylene with tributyl phosphate. After back-extraction with water, molybdenum is extracted as the α-benzoinoximate into chloroform, stripped into hydrochloric acid extracted as the thiocyanate into amyl alcohol, and determined spectrophotometrically. The molybdenum thiocyanate color produced is stable, sensitive, and reproducible. Results of analyses of several of the U.S. Geological Survey standard rocks are given.     

Spectrophotometric determination of calcium with a flow injection system

The indirect spectrophotometric determination of 0.8–7.2 ppm calcium in the presence of magnesium, phosphate and sulphate by flow injection analysis (f.i.a.) is described. The method is based on the exchange reaction between the calcium and the zinc complex of ethylene glycol-bis(2-aminoethylether)tetraacetic acid (EGTA) in the presence of 4-(2-pyridylazo)resorcinol (PAR): Ca + Zn(EGTA) + 2 PAR ? Zn(PAR)₂ + Ca(EGTA). A home-made and a commercial flow injection system with a sampling rate of 80 h^?1, are compared. Results for water samples are in good agreement with those obtained by atomic absorption spectrometry.     

Spectrophotometric determination of palladium with sulfochlorophenolazorhodanine by flow injection

Sulfochlorophenolazorhodanine (as its sodium salt) has been used in the automated development of a sensitive flow-injection procedure for the spectrophotometric determination of palladium. The resulting method has high sample throughput, good precision, and low consumption of both sample and reagents. The optimum pH for the reaction is 5.0 and the response is constant at pH between 4.7 and 5.3. The sensitivity (calibration slope) of the procedure is 4.4 x 10(3) l./mole. The linear dynamic range is 0.045-30.0 mug/ml. The sample throughput is at least 120/hr. An automated procedure for optimization of analytical variables is described and a two-variable response surface for the system is given. Interference studies on 19 metal ions show that the method has good selectivity.     

Spectrophotometric flow injection determination of chloride in ethanol

A flow injection procedure is described for the spectrophotometric determination of chloride in ethanol, based on the mercury(II) thiocyanate—iron(III) reaction. Effects of reagent composition and ethanol content of the sample are investigated in detail. The proposed system can analyse 120 samples of ethanol (94–100% v/v) per hour, with a relative standard deviation lower than 1%, when the chloride content ranges from 0.1–6.0 ppm. Recoveries of ca. 96% are found.     

A novel method for the determination of iodide in table salt by X-ray fluorescence

A novel HI generation technique was developed and evaluated for the determination of iodide in table salt. HI was generated from the samples by the addition of concentrated sulfuric acid and adsorbed onto an ion-exchange resin loaded paper disk. The disk was then measured by X-ray fluorescence. The method compared favorably to the cellulose pellet technique, being more sensitive and reproducible and requiring less time per analysis. The method was applied to six samples of table salt and one of sea salt.     

Spectrophotometric simultaneous determination of creatinine and creatine by flow injection with reagent injection

The reactions of creatinine with picric acid and of creatine with 1-naphthol and biacetyl, both in an alkaline medium, have been used to develop a flow injection method for the simultaneous determination of creatinine and creatine, respectively. The sample containing both analytes is continuously merged with a picrate stream and mixed through the reactors; the coloured stream passes through a flow cell in a spectrophotometer set at 520 nm, recording a continuous signal proportional to the creatinine concentration. The mixture of the reagents 1-naphthol and biacetyl is inserted into the stream by use of the injection valve, which results in a peak (superimposed on the continuous signal), proportional to the creatine concentration. Linear calibration graphs for both analytes were obtained up to 30 mg l^–1 with relative standard deviations <2%, and a sampling rate of 42 measurements h^–1. The method was applied to the determination of creatinine and creatine in broth cube samples.     

Spectrophotometric determination of trace uranium in geological samples by flow injection analysis with on-line levextrel resin separation and preconcentration

A flow-injection system with on-line separation and preconcentration is described for the spectrophotometric determination of trace uranium in geological samples. Uranium is selctively adsorbed from 0.7 mol l^?1 nitric acid on a microcolumn (40 mm long, 4.4 mm i.d.) containing levextrel CL-5209 resin (120–200 mesh) and separated from the sample matrix and most of the co-existing ions; 10-fold concentration is obtained. Eluted uranium is determined spectrophotometrically with arsenazo-III. The detection limit is μg l^?1 uranium and calibration is linear up to 0.3 mg l^?1 uranium With dual columns operated alternately for adsorption and elution, 30 samples can be analyzed per hour. Masking agents are added to eliminate interferences from thorium and iron. The method is sensitive and highly selective, easy to operate and suitable for routine analysis of geological samples for uranium.