Spectrophotometric flow injection determination of total phosphorus in beer using on-line UV/thermal induced digestion

A flow injection system for the automatic determination of total phosphorus in beer is described. The developed manifold uses a two-stage photooxidation/thermal digestion procedure together with oxidizing and hydrolyzing reagents to convert all forms of phosphorus compounds to orthophosphate. Polyphosphates are hydrolyzed by acid and heat, and organo-phosphates are digested by UV-catalyzed peroxodisulfate oxidation. The orthophosphate formed is then spectrophotometrically determined by the phosphomolybdenum blue reaction, using stannous chloride as reducing agent. The results obtained for a set of 19 beer samples (with concentrations from 120 to 735 mg P/L) were in good agreement with the reference method, the maximum relative deviation found being 4.7%. Relative standard deviations for ten consecutive determinations were lower than 1.5%, and a detection limit of 1 mg P/L was achieved. Received: 18 May 1999 / Revised: 5 July 1999 / Accepted: 7 July 1999     

Flow injection spectrophotometric determination of fosfestrol, following on-line thermal induced digestion and using an orthophosphate calibration graph

A novel flow injection (FI) system for the spectrophotometric determination of diethyl stilbestrol diphosphate (fosfestrol) in pharmaceutical formulations is described. On-line thermal induced digestion of the analyte by peroxodisulfate ion was performed and the orthophosphate ion generated was determined spectrophotometrically (λ_max=690 nm) using a molybdenum blue based FI approach. As the achieved conversion of the analyte was quantitative, an orthophosphate calibration graph can be used for its determination as well. The chemical and FI variables affecting the digestion were investigated. A linear calibration graph was obtained in the range 5.0×10⁻⁷-1.0×10⁻⁴ mol l⁻¹ fosfestrol. The relative standard deviation was very good (s_r=0.8% at 5.0×10⁻⁵ mol l⁻¹ fosfestrol, n=12) and the 3σ detection limit was 2.5×10⁻⁷ mol l⁻¹. The sampling rate was 60 injections h⁻¹. The average accuracies for the determination of the analyte in a pharmaceutical formulation evaluated by comparison of the results with those obtained by the supplier (Asta Medica) and the method recommended by the US Pharmacopoeia were also very good (e_r of +0.8 and −0.3%, respectively). Average recoveries of known amounts of the analyte ranging between 97.9 and 100.8% were also obtained.     

Spectrophotometric determination of copper by flow injection analysis with an on-line reduction column

A silver reductor minicolumn is used ina flow-injection system for reduction of copper(II) to copper(I), which is detected spectrophotometrically using bathocuproine disulphonic acid. The reductor functions very well at flow rates up to 4 ml min^?1; this allows sample injection ar rates up to 120 h^?1. Linear calibration is achieved for 5 × 10^?7– 1 × 10^?4 M copper. The detection limit is 3.4 ng and the midrange precision is 1%.     

Spectrophotometric determination of total phenolics by solvent extraction and sorbent extraction optosensing using flow injection methodology

Flow injection analysis (FIA) procedures for the Spectrophotometric determination of phenol involving in-line concentration by solvent and sorbent extraction have been developed. The imine product formed in the reaction between phenol and 4-aminoantipyrine (4-AAP) is either extracted into chloroform (solvent extraction) or is temporarily retained on C₁₈-modified silica material contained in a microcolumn (sorbent extraction). In the latter case two variants of detection have been used namely the Spectrophotometric measurement of the methanolic eluent containing the concentrated dye and at-column optosensing of the retained reaction product followed by methanol elution to maintain reversibility of the process. In the solvent extraction procedure a 10-fold increase of sensitivity compared to the common FIA method without extraction is achieved but no corresponding improvement in detectability is observed. Under optimized conditions the detection limit amounts to 8 μg l⁻¹. Using sorbent extraction methodology, high concentration factors can be obtained when large sample volumes are used. The only limitation in getting correspondingly lower detection limits are an increasingly high and variable blank value with sampling volume. The detection limits obtained for measurement of the absorbance in the eluent and on-column optosensing are 11 μg l⁻¹ and 0.4 μg l⁻¹, respectively. A study of the extractability of various phenol derivates using both solvent and sorbent extraction revealed lower relative response rates compared to the FIA method without extraction. Phenolics that possess an additional acidic group are present in ionized form at the high pH of the assay and are not extractable at all.     

Multi-syringe flow injection system with in-line microwave digestion for the determination of phosphorus

A multi-syringe system for spectrophotometric determination of total phosphorus involving in-line digestion is proposed. Sample and digestion solution were dispensed and directed towards a digestion vessel located inside a domestic microwave oven (MWO) where sample digestion took place. Afterwards, the digested sample was merged with the necessary reagents for the colorimetric determination based on the molybdenum blue method. Several digestion conditions were studied regarding composition of digestion solution, digestion time and power set on the MWO. The system was applied to waste water samples and results shown a good agreement with the reference method. Repeatable results (R.S.D.<2.41%) and determination frequency of 12 h⁻¹ were obtained.     

Spectrophotometric determination of pH by flow injection

Flow injection is used for the determination of pH over a wide range. Using an appropriate combination of pH-indicating dyes, plots of absorbance vs. pH are linear in the range pH < 1–8 for static measurements and pH 3.6–6.8 in the flow-injection experiment. In the current configuration, the flow-injection method has the capability of measuring approximately 100 samples h^?1 with a precision and accuracy of ±0.2 pH. The reasons for the linear calibration graphs, effects of ionic strength and day to day reproducibility are presented together with results for lake-water samples.     

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.     

Spectrophotometric determination of chloride in waters using a multisyringe flow injection system

A multisyringe flow injection system (MSFIA) with spectrophotometric detection is proposed as a fast, robust and low-reagent consumption system for the determination of chloride (Cl⁻) in waters. The system is based in the classic reaction of Cl⁻ with Fe³⁺ and Hg(SCN)₂, but due to the hazardous properties of this last reagent, the proposed methodology has been developed with the aim to minimize the consumption of this one, consuming less than 0.05 mg of Hg for a Cl⁻ determination, being the system of this type with the lowest Hg consumption. The linear working range was between 1 and 40 mg L⁻¹ Cl⁻ and the detection limit was 0.2 mg L⁻¹ Cl⁻. The repeatability (RSD) was 0.8% for a 10 mg L⁻¹ Cl⁻ solution, and the injection throughput was 130 h⁻¹. The proposed system is compared with other chloride monitoring flow systems, this comparison is realized with a point of view of the equilibrium between the obtained analytical features and produced residues toxicity. The proposed system was applied to the determination of Cl⁻ in mineral, tap and well water.     

Three component flow injection analysis with on-line dialysis. Simultaneous determination of free calcium, total calcium and total chloride in milk by flow injection analysis and on-line dialysis

Summary A fast and reliable fully automated three-component flow injection procedure for the simultaneous determination of free calcium, total calcium and total chloride in milk is described where the three components from a single sample injection (30 l milk samples) are determined at a sampling rate of 60 samples per hour. The samples are directed to three different channels by using two dialysers in series. Interferences in the determination of free calcium are eliminated by using a dialyser (first in the series) which also separates the total and free calcium. Free calcium is determined by UV/VIS spectrophotometry at 580 nm and total calcium by atomic absorption spectrometry (AAS) at 422.7 nm. Interferences from phosphates in milk in the determination of total calcium by AAS are overcome by using a nitrous oxide-acetylene flame with the necessary suppression with potassium ions. A second dialyser in series is used to eliminate interferences, especially the interference of casein, before the dialysed chloride is measured with a coated tubular chloride-selective electrode. The results obtained for the free calcium, total calcium and total chloride in milk at a sampling rate of 60 samples per hour compared well with data obtained by standard methods. With 30 l samples the relative standard deviation for milk samples having different concentrations of free calcium (110–170 mg/l free calcium), total calcium (1000–1500 mg/l total calcium) and total chloride (1000–1800 mg/l total chloride) were better than 0.37, 1.01 and 0.25, respectively.     

Cloud-point extraction/preconcentration on-line flow injection method for mercury determination

A cloud-point extraction/preconcentration (CPE/P) step is incorporated on-line into a flow injection system which is used to determine low levels of Hg(II) added to natural water samples. The analyte is complexed with dithizone. A solid reagent column (SRC) is used to prepare the reagent on-line by using 5% (v/v) Triton X-100 solution as solvent. The CPE/P is carried out by using the non-ionic surfactant Triton X-100. After obtaining the cloud-point on-line, the surfactant-rich phase containing the complex is collected in a mini column packed with cotton wool. Then, a hot water stream is passed through the column to elute the complex and the absorbance is measured at 500 nm.All the flow and chemical variables are optimized and the enhancement factor for the system is estimated. The calibration is linear over the range 0.05-0.5 μg ml⁻¹, the R.S.D. is 4.8%, the limit of detection (signal:noise = 3) is 0.014 μg ml⁻¹ and the sample throughput is 30 h⁻¹. An open/closed system is used to eliminate the interference of iron(III).     

啤酒中单宁的分光光度分析

单宁(鞣酸)具有涩味,啤酒中单宁含量直接影响饮用的口感[1,2]。测定鞣酸常用高锰酸钾滴定法[1]和钨酸钠一磷钼酸比色法[4],前者终点误差较大,后者消耗试剂多,灵敏度不高。本文以铁(Ⅲ)和1·0-邻二氮菲作试剂,探讨了测定啤酒中鞣酸的分光光度法,并将所测结果与钨酸钠-磷钼酸比色     

Spectrophotometric determination of uranium by flow injection analysis using U/TEVA.SpecTM chromatographic resin

A flow injection analysis (FIA) system is described for the determination of uranium. The system consists of a microcolumn packed with. U/TEVA.Spec^TM, chromatographic resin for on-line sample separation. The eluate is mixed with 4-(2-pyridylazo) resorcinol (PAR). The colored product is continuously monitored spectrophotometrically.     

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 determination of nitrite in foodstuffs by flow injection analysis

A simple method for the determination of nitrite in foodstuffs by flow injection analysis is described. Nitrite samples are prepared in a microwave oven, treated with a 1 mol/lNH₄Cl solution at a pH of 9 (all under nitrogen atmosphere) and are immediately analysed. Nitrite is diazotised in the FIA system with N-(1-naphthyl) ethylenediammonium dichloride to form the highly coloured azo dye, which is measured at 540 nm. The detection limit is 0.036 mg/kg for sample injections of 400 l. The sampling rate is about 50 samples per hour and the relative standard deviation is 0.67%.     

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 phosphorus in steel using phosphoantimonyl molybdate complex

An improved method for the spectrophotometric determination of phosphorus in steel has been described. Reduction of the phosphomolybdate complex with ascorbic acid and antimony has been found to be advantageous over other methods. No heating is necessary for the formation of the complex and it is stable for more than 24 hr. The “molybdenum blue” formed shows maximum absorption at 882 nm and the molar extinction coefficient is 25,670. The method has been found useful for the determination of microquantities of phosphorus in steel.     

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.     

Comparison of digestion methods for determination of total phosphorus in river sediments

In this study, four digestion methods used to determine total phosphorus in river sediments, including Na₂CO₃ fusion, the H₂SO₄ and H₂SO₄ + H₂O₂ methods and the SMT protocol were investigated. Interference effects of iron, calcium and organic matter in river sediments, and the substances contained in the digestion agents on the photometric determination of the phosphates were analysed. The digestion methods were tested on ten river sediment samples. Statistical analysis of the results showed significant differences between sample treatments relating to the mean total phosphorus concentration.     

Spectrophotometric determination of fluoride with lanthanum/alizarin complexone by flow injection analysis

Lanthanum/alizarin complexone (1:1) in 70% acetone is used in conjunction with a 500-cm reaction coil at 60°C to determine 0.03–1.2 mg l^?1 fluoride at 24 samples per h. The method is applied to tap-water samples.