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.     

Amberlite XAD resin solid-phase extraction coupled on-line to a flow injection approach for the rapid enrichment and determination of phenols in water and waste waters

A novel and expeditious approach for direct determination of phenols in water and waste waters based on solid-phase extraction coupled on-line to a flow injection analysis (FIA) manifold is described. The method employs on-line preconcentration of the phenols in an acidified sample (pH=2.0) onto a 3 cmx3 mm column packed with Amberlite XAD-4 resin. The phenols are subsequently eluted from the resin into a flowing system with an alkaline solution (pH=13) by actuating a switching valve; the eluted analytes were then quantified spectrophotometrically as the products of reaction with 4-aminoantipyrine (4-AAP) and potassium ferricyanide on passing through the flow-cell of a detector. The proposed method has a linear calibration range 0.01-1 mug ml(-1) of phenol, with a detection limit of 0.004 mug ml(-1) (S/N=3) and a sample throughput of 12 h(-1), investigated with a 4.4 ml sample volume. The relative standard deviation is 2.4% for 0.2 mug ml(-1) of the analyte. The sensitivity offered by the procedure was higher by a factor of 13 than that provided by a conventional flow injection analysis method. The analytical scheme of the proposed system is much simpler than its conventional manual counterpart due to the fact that it combines trace enrichment, sample clean-up, derivation and detection in one analytical set-up. The high speed, ease of use and automation, selectivity, and relative freedom from random contamination by sample handling make this method ideal for the phenols monitoring in water and waste waters.     

Determination of fluoride in natural waters by ion-selective electrode potentiometry after co-precipitation with aluminium phosphate

The most effective conditions for masking aluminium in the determination of mug/1. levels of fluoride in water by ion-selective electrode potentiometry after co-precipitation with aluminium phosphate have been re-examined. The effectiveness of citrate for masking aluminium increases with pH, and up to 1.5 x 10(-2)M aluminium can be masked quantitatively at pH 8.5. Fluoride (5-100 mug in 500 ml of sample solution) is quantitatively co-precipitated at pH 4.7 with approximately 90 mg of aluminium phosphate. After dissolution of the precipitate and adjustment of the solution to pH 8.5 with TISAB, the fluoride content can be measured with a fluoride ISE. The method is simple and rapid, and is suitable for the determination of trace amounts of fluoride in various water samples.     

Flow injection chemiluminescence determination of thiamine based on its enhancing effect on the luminol-hydrogen peroxide system

A new flow injection chemiluminescence (CL) method is proposed for the determination of thiamine, based upon its enhancing effect on the CL reaction of luminol with hydrogen peroxide in alkaline solution. The method allows the determination of thiamine within 0.05-8 mug ml(-1) range with a detection limit (3sigma) of 0.01 mug ml(-1). The relative standard deviation is 1.4% (n=11, 0.5 mug ml(-1) thiamine) and the sample throughput is about 90 samples h(-1). The method was successfully applied to the determination of thiamine in pharmaceutical preparations.     

Determination of hydrogen peroxide in reactor moderator solutions by flow injection analysis

A flow injection analysis (FIA) method for the determination of hydrogen peroxide in reactor moderator water has been developed and installed at the Savannah River Site (SRS) Water Quality Laboratory. The mode of detection is amperometric and the technique has an analytical range of 0.10-2.50 mug/ml with a sampling rate of 40 samples/hour. The calibration curve is linear with a correlation coefficient of 0.999 and the relative standard deviation is at the 0.50% level for both 0.10- and 2.50-mug/ml standards. When the FIA procedure is compared to the manual method previously used at the SRS Water Quality Laboratory for hydrogen peroxide analysis, it demonstrates a minimum twenty minute reduction in analysis time per sample and the total liquid waste generated per sample analyzed is reduced by 95%.     

Permanganate-based chemiluminescence analysis of cefadroxil monohydrate in pharmaceutical samples and biological fluids using flow injection

A chemiluminescent method using flow injection is described for the determination of cefadroxil monohydrate. The method is based on the chemiluminescence reaction of cefadroxil with potassium permanganate in sulphuric acid, sensitized by quinine. The proposed procedure allows the determination of cefadroxil over the concentration range 0.1-30 mug ml(-1) with a detection limit of 0.05 mug ml(-1) and a sample measurement frequency of 150 samples h(-1). The method was successfully applied to the determination of cefadroxil in pharmaceutical preparations and biological fluids.     

Indirect spectrophotometric determination of ascorbic acid with ferrozine by flow-injection analysis

A FIA indirect spectrophotometric determination of ascorbic acid was developed using its reducing action on Fe(III) in acidic medium and following the spectrophotometric determination of the reduced iron by using sodium 3-(2-pyridyl)-5,6-diphenyl-1,2,4-triazine-4',4'-disulphonate (ferrozine) as chromogenic reagent in buffered medium (pH 5.5) and monitoring the absorbance signal at 562 nm. A three-line manifold with two reaction coils was used: in the first reaction coil, ascorbic acid reduces Fe(III) to Fe(II); and in the second one, the complexation reaction is developed. The linear range of the method was 0.5-10 mug ml(-1) of ascorbic acid, the detection limit being 0.028 mug ml(-1). The proposed method was sensitive, rapid (sampling rate of 90 samples h(-1)) and reproducible (RSD 0.19%, n=10). Satisfactory results were obtained in the determination of ascorbic acid in pharmaceutical preparations, fruit juices and urine testifying the applicability of the method to real samples.     

Non-extraction batchwise and FIA determination of cationic and nonionic surfactants using Cu(II)-chromazurol S-surfactant complexes

Batchwise and FIA determinations have been developed for cationic and nonionic surfactants, based on the formation of ternary Cu(II)-chromazurol S-surfactant compounds. Optimum reaction conditions have been found (pH 8.0, lambda=590 and 630 nm, respectively). For the batchwise measurement, the molar absorption coefficient values epsilon(590)=5.1-5.7x10(4) l mol(-1) cm(-1) for cationic surfactants, epsilon(630)=0.7-1.5x10(4) l mol(-1) cm(-1) for nonionic surfactants. A factorial design has been carried out to determine the optimum flow conditions. Calibration curves were constructed and statistically evaluated for both the batchwise and FIA determination. For example, the linear concentration ranges for batch determination of the cationic surfactant cetyltrimethylammonium bromide and nonionic surfactant Marlophen NP 10 are 0-15 mug ml(-1) (R=0.9996, R.S.D.=6.62-0.64%) and 13-53 mug ml(-1) (R=0.9993, R.S.D.=4.48-1.40%), respectively; the respective detection limits are 0.02 and 4.0 mug ml(-1). For FIA determination of the same surfactants, the linear concentration ranges are 0-13 mug ml(-1) (R=0.9995, R.S.D.=4.44-0.49%) and 66-397 mug ml(-1) (R=0.9994, R.S.D.=8.92-1.12%), respectively, detection limits are 0.08 and 38 mug ml(-1), respectively.     

FIA-spectrophotometric determination of N-substituted phenothiazine derivatives by oxidation with a solid-phase reactor of manganese dioxide incorporated in polyester resin beads

The determination of several N-substituted phenothiazine derivatives was carried out by the reaction of the drug with managanese dioxide entrapped in a polymeric material in a packed-bed reactor; the oxidized drug was monitored at lambda(max). The calibration graph is linear over the range 5-50 mug/ml of phenothiazine derivatives with a relative standard deviation of 0.5-1% (at 10 mug/ml) and sample throughput of 40-48 h(-1). The influence of foreign compounds was studied and the method was applied to the determination of six different phenothiazine derivatives in pharmaceutical formulations.     

Manual and fia methods for the determination of cadmium with malachite green and iodide

A sensitive and rapid spectrophotometric method for the determination of cadmium is described, based on the formation of a blue complex at pH 4 between the anionic iodide complex of cadmium(II) and Malachite Green; the colour is stabilized with poly(vinyl alcohol). The calibration graph for measurement at 685 nm is linear over the range 1-50 mug of cadmium per 25 ml of final solution, with a relative standard deviation of +/-1.7% for 1 mug/ml cadmium. The molar absorptivity is 6.1 x 10(4) 1.mole(-1).cm(-1). The method can be successfully adapted for FIA, the peak height being proportional to the cadmium concentration over the range 0.1-3 mug/ml; a two-channel manifold is used and an improvement in selectivity is obtained. The use of a gradient tube is demonstrated to give a good calibration for Cd(II) over the range 2 x 10(-2) -2 x 10(-6)M.     

A simple simultaneous flow injection method based on phosphomolybdenum chemistry for nitrate and nitrite determinations in water and fish samples

A direct spectrophotometric flow injection method for the simultaneous determination of nitrite and nitrate has been developed. The method is based on the oxidation of a phosphomolybdenum blue complex by the addition of nitrite and the decrease in absorbance of the blue complex is monitored at 820 nm. The injected sample is split into two segments. One of the streams was directly reacted with the above reagent and detected as nitrite. The other stream was passed through a copperised cadmium reductor column where reduction of nitrate to nitrite occurs, and the sample was then mixed with the reagent and passed through the cell of the spectrophotometer to be detected as nitrite plus nitrate. The conditions for the flow injection manifold parameters were optimised by experimental design and the concentration of nitrite and nitrate was determined in the linear range from 0.05 to 1.15 mug ml(-1) nitrite and 0.06 to 1.6 mug ml(-1) nitrate with a detection limit of 0.01 mug ml(-1) for nitrite and 0.025 mug ml(-1) for nitrate. The method is suitable for the simultaneous determination of nitrite and nitrate in fish and water samples with a sampling rate of 25+/-2 sample per hour.     

Application of a microbial sensor to the quality control of meat freshness

Isosorbide dinitrate (ISDN) is reduced voltammetrically at gold working electrode surface in aqueous sodium sulfite solution and produces a voltammogram with its peak current proportional to the concentration of ISDN in the range of 1.3-2340 mug ml(-1). Sodium sulfite is used as supporting electrolyte and oxygen removing agent and, therefore, no nitrogen gas purging for elimination of soluble oxygen in, the sample solution is required. The limit of detection (LOD) of the method is 0.0838 mug ml(-1) and the relative standard deviation (R.S.D.) of 24 replicate determination of 52 mug ml(-1) of ISDN is 3.60%. The method is used for quantitative analysis of ISDN in arterial plasma, synthetic serum and pharmaceutical dosage form. The results are compared with those obtained from GC determination method. The method is sensitive and requires little sample preparation in a wide concentration range.     

Determination of anion-exchange resin performance based on facile chloride-ion monitoring by FIA-spectrophotometry with applications to water treatment operation.

Based on a flow-injection spectrophotometry, an automatic analytical method for determination of ppb-level chloride-ion has been established. By use of this method, a novel FIA method for the determination of SBAER performance has also been developed. In this paper, the effects of concentration, dosage, and flow rate of the regenerant on BEC of SBAER were first investigated dynamically by the FIA method. In addition, the flow rate of the sample water and the temperature of the ion exchange resin were also examined. The optimum conditions were obtained: the volume of the regenerant (sodium hydroxide) was 50 mL (0.15 g resin), and its concentration was 3% (w/v); the volumetric flow rates of the regenerant and the sample water were 0.5 ml/min (4.3 m/h) and 1.5 ml/min (13 m/h), respectively. The exchanging temperature was 25 +/- 5 degrees C. The method is characterized by the use of a micro resin-column, shorter testing cycle, easy operation, and high reproducibility. The proposed method is approximately 30 times more efficient than the manual method, and it can be used for the exchange performance comparison of various SBAER.     

Flow injection analysis of nitrite by gas phase molecular absorption UV spectrophotometry

A flow injection method on the basis of gas phase molecular absorption is described for the determination of nitrite in the aqueous solution. 200 mul of nitrite solution is introduced into a carrier stream of distilled water. The carrier stream containing nitrite zone is reacted with a stream of hydrochloric acid (2 M). The stream is then segmented by O(2) gas. The produced gaseous products are purged into the O(2) segments, react with O(2) and are carried toward the gas-liquid separator. The gaseous phase is separated from the liquid stream by the use of home-made gas-liquid separator and then is swept into a home-made flow cell. The absorbance of gaseous phase is measured at 205 nm using a UV/VIS spectrophotometer. Under selected conditions, two linear ranges, up to 1000 mug ml(-1) and 1000-2000 mug ml(-1) of nitrite were obtained. The limit of detection was 7.5 mug ml(-1) NO(2)(-). The relative standard deviations of repeated measurements of 100 and 500 mug ml(-1) NO(2)(-) were 3.7 and 1.0%, respectively. Up to 30 samples h(-1) can be analyzed. Interferences in the proposed method were few and were readily overcome. The proposed method was successfully applied to the determination of nitrite in the spiked water samples, a number of meat products and urine.     

Study on the solid phase extraction of Co(II)-QADEAB chelate with C(18) disk and its application to the determination of trace cobalt

A sensitive, selective and rapid method has been developed for the determination mug l(-1) level of cobalt based on the rapid reaction of cobalt(II) with 2-(2-quinolylazo)-5-diethylaminobenzoic acid (QADEAB) and the solid phase extraction (SPE) of the colored chelate with Waters Porapak(R) Sep-Park C(18) disk. The QADEAB can react with Co(II) in the presence of pH 3.8 acetic acid-sodium acetate buffer solution and cetyl trimethylammonium bromide (CTMAB) medium to form a violet chelate of a molar ratio 1:2 (cobalt to QADEAB). This chelate can retained on Waters Porapak(R) Sep-Park C(18) disk quantitatively when they passed the disk as aqueous solution. After the enrichment finished, the retained chelate can be eluted from disk by 2.5 ml of ethanol (contain 5% acetic acid). In the measured solution, the molar absorptivity of the chelate is 1.58x10(5) l mol(-1) cm(-1)at 635 nm, and Beer's law is obeyed in the range of 0.01-0.4 mug ml(-1). The relative standard deviation for 11 replicate sample of 0.01 mug ml(-1) level is 2.23%. The detection limit is 0.01 mug l(-1) (in original samples). This method can be applied to the determination of mug l(-1) level of cobalt in drinking water with satisfactory results.     

Spectrophotometric and complexometric methods for the determination of thorium and fluoride using bromocresol orange reagent

The ternary purple coloured complex formed between Th(4+), bromocresol orange (BCO) and cetylpyridinium bromide (CPB) in acidic medium was investigated spectrophotometrically. Results obtained revealed the formation of 1:1:1, Th:BCO:CPB complex in aqueous solution at pH approximately 0.5 with a logarithmic conditional stability constant of 12.04+/-0.1, I=0.1 at 25 degrees C. The colour of the ternary complex was used for the determination of thorium(IV) in the range of 0.02-2.6 mug ml(-1) Th(4+), =9.2x10(4) l mol(-1) cm(-1) at 560 nm. Beside its high sensitivity, the reaction was also proved to be highly selective for Th(4+). Thorium(IV) was determined in presence of great number of transition metal ions, rare earths and different anions. Th(4+) was also determined with high accuracy and precision by its titration with disodium ethylenediaminetetraacetate (Na(2)EDTA) using BCO as an indicator at pH approximately 0.5. The endpoint was detected either visually or spectrophotometrically (lambda=550 nm). The proposed procedures were successfully applied for the determination of Th(4+) in standard Th-U ores and in a series of naturally occurring ores or minerals containing thorium. A spectrophotometric method was also described for the determination of fluoride ion, which was based upon the decrease in colour intensity of the Th-BCO complex on mixing it with F(-) ion. The proposed method was convenient, rapid and sensitive for fluoride. It could be used for the determination of fluoride ion in the 0.02-3.00 mug ml(-1) range (S.D.+/-0.9%). The proposed method was successfully applied for direct determination of F(-) ion in water obtained from different origins and the results were satisfactory.     

Determination of trace phosphate ion in water by visual method after preconcentration on a membrane filter for field work

A sensitive visual method based on comparing the color intensity of precipitate as phosphomolybdenum blue on a membrane filter, has been developed for the determination of trace phosphate ion in water for field work. A sample solution containing 0.05-5.0 mug of phosphate was treated in a 25-ml polypropylene syringe, and the resulting precipitate was filtered through a membrane filter attached to the syringe. The color intensity of the precipitate on the membrane filter was measured visually following the standard series method. The coefficient of variation for five measurements at 0.5 mug of phosphate is 11%. The detection limit is 0.02 mug of phosphate ion in 22.5 ml (0.9 mug PO(3-)(4)/l) of water sample when the effective filtration area is 0.78 cm(2). The interference of various ions was studied and optimum conditions were developed for the determination of phosphate ion in natural water.     

Spectrophotometric determination of micro amounts of cadmium in waste water with cadion and triton X-100

A spectrophotometric method for determination of micro amounts of cadmium in waste water with Cadion and Triton X-100 is described. The interference of foreign ions can be eliminated by masking with an ascorbic acid-Rochelle salt-potassium cyanide-potassium fluoride mixture. After demasking with formalin, cadmium is determined directly in aqueous solution without separation. Beer's law is obeyed for 0-8 mug of Cd in 25 ml of solution. The method is more sensitive than the dithizone method, its apparent molar absorptivity at 480 nm being 1.19 x 10(5) 1. mole(-1). cm(-1). Results obtained by using the proposed method on waste water samples agree well with those obtained by atomic-absorption spectrophotometry.     

Adaptation of a commercial ion selective fluoride electrode to a tubular configuration for analysis by flow methodologies

The determination of fluoride ions in water samples is accomplished by using a tubular flow through detector constructed by drilling a channel through a commercially available LaF(3) crystal electrode in such a way that the original contacts of the non-modified unit are maintained. Its performance when incorporated in both FIA and SIA systems was evaluated and the results show that the tubular unit retains the characteristics of the non-modified electrode. In SIA conditions an extended linear range of response and lower detection limit were achieved when compared with the electrode performance in FIA conditions. These aspects together with the additional advantage of low sample and reagent consumptions in SIA when compared to FIA, makes the incorporation of the proposed tubular ISE in a SIA system the preferred approach for on line determination and monitoring of fluoride content in natural water samples.     

Flow injection spectrophotometric determination of lactic acid in skimmed milk based on a photochemical reaction

A spectrophotometric method for the determination of lactic acid in milk samples based on the use of a photochemical reaction carried out in a Flow Injection System is proposed. Determination is based on the reaction between lactic acid and Fe(III), which is reduced to Fe(II) in the presence of UV light, being the latter made to react with o-phenanthroline. The complex formed between Fe(II) and o-phenanthroline, Fe(o-phen)(3)(2+) (ferroin) is a coloured compound and it can be spectrophotometrically monitored at 512 nm. The method shows a linear range between 0.5 and 50 mug ml(-1) with a limit of detection of 0.16 mug ml(-1). The precision was +/-2.15 expressed as relative standard deviation (n=11) and the sample throughput of 30 samples h(-1). Also non-linear adjustments have been made and validated by ANOVA. The proposed method has been applied to the determination of lactic acid in both synthetic and milk samples.