Standard additions in flow injection analysis with atomic absorption spectrometry

In this study, we prepared a poly(3,4-ethylenedioxythiophene) (PEDOT) modified electrode by the electropolymerization of 0.01 M 3,4-ethylenedioxythiophene at a screen-printed electrode (SPE) in the presence of 0.1 M LiClO4 and 5 mM hydroxypropyl-β-cyclodexdrine. Many bio-interests were selected as test analytes. Electrochemical oxidation of cysteine in various pH buffer solutions (pH 2.0 ~12.0) was conducted at the SPE/PEDOT modified electrodes. Cyclic voltammetric studies showed that the SPE/PEDOT modified electrodes possessed great catalytic activity toward cysteine oxidation, and the best catalytic responses occurred in pH 6.0 buffer solution. Flow injection analysis (FIA) coupled amperometric detection was used in order to decrease detection limit. The FIA conditions were examined and the FIA signals were optimized. A linear calibration plot was obtained for 0.05-200 μM cysteine with a slope of 0.0527 μA/μM. The detection limit (S/N = 3) was 0.03 μM. The relative standard deviation was 1.44, 1.77, 2.88% for 3 continuous injection of 0.5, 20, 200 μM cysteine standards, respectively. Determination of cysteine in real sample was conducted using the same approach. We prepared three real samples, root beer syrup, human urine, and aspirin, as back ground solutions. The recovery of cysteine from real sample was determined using the standard addition method and the mean recovery was 93.5% and 105.0% for root beer syrup and aspirin, respectively. In the human urine real sample, the cysteine oxidation current were decreased. Moreover, we discovered that the PEDOT thin film may adsorb benzoquinone (BQ) and catechol (CA) in solution. The prepared SPE/PEDOT/BQ and SPE/PEDOT/CA modified electrodes can used for electrochemical detections of AA and NADH.

On-line elimination of spectral interference of iron matrix in the flame atomic absorption determination of zinc by anion-exchange separation

A method for the determination of trace amounts of arsenic in food samples using flow injection analysis and atomic absorption spectrometry with hydride generation (FI-HG AAS) was developed. The parameters of the flow injection system and the hydride generation were optimized with respect to reagent concentrations, atomization temperature, injection volume, reaction coil length and carrier flow rate. The limits of detection and quantification were 0.34 µg L−1 and 1.2 µg L−:1, respectively, and the analytical curve is linear up to 30.0 µg L−1 arsenic. The relative standard deviation for 12 replicates varies between 5% for 4.0 µg L−1 As and 1.8% for 30.0 µg L−1 As, with an injection frequency of up to 135 h−1. Interferences from Ni(II), Cu(II), Fe(III), Cr(III), Mo(II), Bi(III), Se(IV), Se(VI), Sb(III) and Sb(V) could be masked with a mixture of ascorbic acid-KI in a 5.0 mol L−1 HCl solution. The accuracy of the proposed method was evaluated by using certified reference materials of biological samples, and the method was used to determine the content of arsenic in fish and coffee beans.

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 μl 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 μl 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.

Calibration by the gradient ratio-standard addition method in flow injection flame atomic absorption spectrometry

A fast and reliable procedure for the determination of total and free calcium in milk is described. The method is based on the flow injection (Fl) technique. Total calcium is determined by atomic absorption spectrometry (AAS) (422.7 nm) and free calcium by spectrophotometry (580 nm). Interference in the determination of free calcium is eliminated by using a dialyser, which also separates the total and free calcium. Interference from phosphates in milk in the determination of total calcium by AAS is overcome by using a dinitrogen oxide-acetylene flame with the necessary suppression with K+. With 30-microliters samples the Fl system covers a standard working range of 100-1500 mg dm-3 of Ca2+. The system is suitable for the simultaneous determination of total calcium (relative standard deviation less than 1.30% for 1300-1500 mg dm-3 of total calcium) and free calcium (relative standard deviation less than 0.85% for 120-170 mg dm-3 of free calcium) in milk at a sampling frequency of about 60 samples h-1. The results obtained agree reasonably well with results from the AAS method.

A method was developed for determination of arsenic by Atomic Absorption Spectrometry - Hydride Generation in Flow Injection Analysis (FIA). The flow injection system was operated in the merging zones configuration, where sample and reagent are simultaneously injected into two carrier streams, HC1 and H2O, respectively. For separation of arsine a continuous gas-liquid separator was designed. The liquid phase flows to a free-running drain while the gaseous phase is purged by nitrogen into the atomization cell. The optimum conditions for the generation of arsine were established as: reaction coil of 50 cm, sample and reagent injected volume of 250 p.L, 1.0% (m/v) solution of sodium tetrahydroborate and 1.0 mol L’1 hydrochloric acid, cell temperature of 900°C, flow rates of 3.6 mL min’1 for hydrochloric acid and tetrahydroborate Solutions and a flow rate of 130 mL min-1 for the carrier gas (N2). Many elements cause interferences in this technique in gaseous and condensed phases. It was found that Mn(II), Pb(Il), Fe(IIl), Cu(II), Ni (II), Zn (II), Al (III) and Cd (II) caused signal reductions for arsenic of at least 10%. The interferences were reduced by using an on-line mini-column with 50 mg of the cation exchange resin Amberlite IRA-120. The interferences in the gaseous phase were caused by Se(IV), Sn(II), Sb(III), Bi(III) and Te (IV). To overcome these efíects, thioureia was used as masking agent. Under the optimum experimental conditions, the detection limit. defined as three times the standard deviation of the blank measurement, was found to be 0,35 ng mL’1 for As(lII) and 0,52 ng mL’1 for As(V). The relative standard deviation of 2,3% for 0,1 mg L’1 As(IIl) and 1,7% for 0,1 mg L’1 As(V) and a sampling rate of about 120 determinations per hour. The method was shown to be satisfactory for determination of traces arsenic in water samples (natural and certificate).

A simple on‐line flow injection analysis pre‐concentration technique has been developed. The flow injection system consisted of a 4‐channel peristaltic pump, two 6‐way rotary injection valves containing a microcolumn of Chelex‐100 resin, and a flame atomic absorption spectrometer, allowing the determination of lead at a concentration as low as ppb. The degree of pre‐concentration depended on the injected sample volume. Lead contained in NBS 1634b and other heavy oil samples was determined using the system. Samples were ashed directly in a furnace at 550°C for two hours, dissolved with perchloric acid and then injected into the system. The sampling frequency also depended on the injected sample volume.

Several authors have investigated so-called cool flames as atom reservoirs in atomic absorption spectrometry; these flames are usually entrained air-hydrogen flames in which the combustible gas (hydrogen) is diluted with the argon or nitrogen of a nebulizing gas. Such low temperature flames are well known to be very prone to chemical interferences. These chemical interferences could be eliminated by using the addition technique and the solvent extraction method. The present authors have also demonstrated that the premixed inert gas(entrained air)-hydrogen flames produced with the specially designed multi-flame burner can be used as suitable atom reservoirs for the determinations of zinc, tin, bismuth, arsenic and selenium, and gallium by atomic absorption spectrometry and that the chemical interferences encountered in their determinations can be removed by the addition of a large amount of lanthanum chloride, ferric chloride, magnesium chloride, and stannous chloride as interference-releasing agents.

An novel analytical method consisting of flow-injection sampling and chemiluminescence (CL) detection for determination of anticancer drug hydroxycamptothecinum (HCPT) is described. It is based on the CL reaction of potassium permanganate-formaldehyde-HCPT system. The formaldehyde-sensitized CL emission mechanism was proposed for HCPT-potassium permanganate (KMnO(4))-HCOH systems by comparing the fluorescence emission with CL spectra. Illuminant was the single-state bimolecular oxygen, (1)O(2) (1)O(2)((1)Delta(g) (1)Delta(g)), which was from (1)O(2)((1)Delta(g)) produced in the reaction system, and emits CL spectra at 639 nm. The presence of formaldehyde can sensitized CL emission, because it may be to accelerate the generation of (1)O(2) ((1)Delta(g)). The optimum conditions for CL emission were investigated and optimized. The CL intensity was correlated linearly with concentration of HCPT in the range of 0.010-60.0 mg L(-1). The determination limit is 0.006 mg L(-1). The relative standard deviation is 1.6% for 11 parallel measurements of 0.20 mg L(-1) HCPT standard solution. The proposed method has been applied for the determination of HCPT in pharmaceutical preparations, serum, and urine. The results of the quantitative analysis for HCPT studied using the developed method showed a good agreement with provided by using an official method.

A rapid flow injection (FI) spectrophotometric procedure for tetracycline determination is described. It is based on the injection of a 100 microl sample solution containing tetracycline into merged streams of aluminium(III) chloride (0.01 mol 1(-1)) and Tris-buffer in the presence of KCl (0.06 mol l(-1)), pH 7.0, with the same optimum flow rate of 3.2 ml min(-1). A yellow Al(III)-tetracycline complex was monitored at 376 nm. The flow injection system and the experimental conditions were optimized by means of the univariate method. The procedure was applied to the determination of tetracycline in pharmaceutical preparations with a high sampling rate of at least 165 h(-1). A high precision with a relative standard deviation was obtained less than 0.72 and 0.30% of 5.0 and 10 microg ml(-1) (n=11), respectively. The detection limit (3sigma) and the quantification limit (10sigma) were 0.07 and 0.72 mg l(-1), respectively. There were no interference effects from traditional excipients in the dosage forms when the method was applied to pharmaceutical preparations. The matrix effect could be reduced by the standard addition method.

A novel simple sensitive and effective on-line flow injection column preconcentration platform using poly-tetrafluoroethylene turnings as sorbent was developed prior to flame atomic absorption spectrometric (FAAS) determination of palladium in vehicle exhaust catalysts, hydrogenation catalysts and environmental water samples. The method is based on the sorption of palladium(II)-diethyldithiophosphate, which was found to be more effective than dithiocarbamate ones. Methyl isobutyl ketone (MIBK) was used as eluent prior atomisation and quantification. All parameters like pH, DDPA concentration, flow rates, preconcentration time that affect the sensitivity of the method as well as interferences of other metals were investigated in detail. The enhancement factor calculated as 114 for 60 s preconcentration time while the sampling frequency as 40 h−1. The detection limit was 0.9 μg L−1 and the relative standard deviation (RSD) was 2.8% at 20.0 μg L−1 concentration level. The accuracy of the proposed method was estimated by analysing certified reference material and spiked environmental samples. The analytical features of the method were compared with other on-line column preconcentration methods reported in the literature.

Standard additions in flow injection analysis based on merging zones and gradient exploitation: application to copper determination in spirits

Chemiluminescence determination of potassium bromate in flour based on flow injection analysis

Determination of some estrogens by flow injection analysis with acidic potassium permanganate–formaldehyde chemiluminescence detection