Flow injection analysis of fluoride in electroplating baths with potentiometric detection

A high dispersion FIA system with a fluoride selective and a double junction reference electrode in cascade arrangement was developed for the determination of the fluoride content in chromium electroplating baths. The analyses of seven synthetic baths prepared in the laboratory and two samples provided by the industry gave results with a mean recovery value of 100.5%, and a mean variation coefficient of 1.6%. These data were better than those obtained by the EDTA complexometric titration, the reference technique, with a mean recovery of 94.0% and a mean variation coefficient of 7.5%. The sampling rate for the FIA manifold was 20 samples per hour.     

Determination of total nitrogen in food by flow injection analysis (FIA) with a potentiometric differential detection system

A flow injection set-up based on potentiometric detection and gas diffusion device for the determination of total nitrogen in food is described. The detection system consisted of two ammonium-sensitive electrodes placed sequentially and each alternately operating as reference electrode. Tubular electrodes without an inner reference solution were prepared with a PVC membrane composed of nonactin in Tris (2-ethylhexyl) phosphate and potassium tetrakis (4-chlorophenyl) borate to reduce the membrane resistance. The food sample digests were inserted into the system, and the ammonium present was converted into ammonia gas. The gas diffused through a gas-permeable membrane to a buffer acceptor stream with a pH that ensured transformation to the ammonium cation, which was potentiometrically detected. Good agreement between FIA results and those provided by the reference procedure was obtained, with relative deviation errors below 5%. Using the proposed system, low reagent consumption is possible, a sampling rate of about 30 samples/h was achieved, as well as a good reproducibility for consecutive injections of the same sample (variation coefficient < 2%). Received: 8 October 1998 / Revised: 7 January 1999 / Accepted: 12 January 1999     

Fluorimetric determination of fluoride in a flow assembly integrated on-line to an open/closed FIA system to remove interference by solid phase extraction

A simple flow injection fluorimetric method for fluoride determination is proposed. The method is based on the enhanced fluorescence of quercitin-Zr(IV) complex when fluoride ion is present in the sample. An open/closed FIA manifold with a mini-column of Dowex 50W X8 resin was used to remove the most important interference (aluminum). The two FIA assemblies were integrated on-line to automate the pretreatment of the water sample and fluoride determination. The calibration graph was linear over the range 0.1-3.0 mug ml(-1) of fluoride with a correlation coefficient of 0.999 and LOD 0.06 mug ml(-1). The relative standard deviation was 2.5% and the sample throughput was 52 h(-1) without pretreatment and 10 h(-1) with pretreatment of the sample. The method was applied to the determination of fluoride in water samples.     

Determination of cyanide by a flow injection analysis-atomic absorption spectrometric method

A new flow injection analysis (FIA) procedure is proposed for the indirect atomic absorption spectrometric determination of cyanide. The FIA manifold is based on the insertion of the sample into a distilled water carrier, then the sample flows through a solid-phase reactor filled with silver iodide entrapped in polymeric resin beads. The calibration graph is linear over the range 0.2-6.0 mg l-1 of cyanide (correlation coefficient 0.9974), the detection limit is 0.1 mg l-1, the sample throughput is 193 h-1 and the RSD is 0.8%. The method is simple, quick and more selective than other published FIA procedures. The reproducibility obtained by using different solid-phase reactors and solutions is in the range 2.2-3.1% (RSD). The method was applied to the determination of cyanide in commercial samples such as pharmaceutical formulations and industrial electrolytic baths.     

Validation of a high-performance chromatographic method for determination of cefotaxime in biological samples

An analytical method for detecting and quantifying cefotaxime in plasma and several tissues is described. The method was developed and validated using plasma and tissues of rats. The samples were analyzed by reversed phase liquid chromatography (HPLC) with UV detection (254 nm). Calibration graphs showed a linear correlation (r > 0.999) over the concentration ranges of 0.5–200 μg/mL and 1.25–25 μg/g for plasma and tissues, respectively. The recovery of cefotaxime from plasma standards prepared at the concentrations of 25 μg/mL and 100 μg/mL was 98.5 ± 3.5% and 101.8 ± 2.2%, respectively. The recovery of cefotaxime from tissue standards of liver, fat and muscle, prepared at the concentration of 10 μg/g was: 89.8 ± 1.2% (liver), 103.9 ± 6.5% (fat) and 97.8 ± 2.1% (muscle). The detection (LOD) and quantitation (LOQ) limits for plasma samples were established at 0.11 μg/mL and 0.49 μg/mL, respectively. The values of these limits for tissues samples were approximately 2.5 times higher: 0.3 μg/g (LOD) and 1.25 μg/g (LOQ). For plasma samples, the deviation of the observed concentration from the nominal concentration was less than 5% and the coefficient of variation for within-day and between-day assays was less than 6% and 12%, respectively. The method was used in a pharmacokinetic study of cefotaxime in the rat and the mean values of the pharmacokinetic parameters are given. Received: 25 May 1998 / Revised: 27 July 1998 / Accepted: 1 August 1998     

Analytical control of organic additives in electrolytic baths by UV spectroscopy in combination with multivariate analysis

A method for the simultaneous determination of organic additives in Zn(II) and Ni(II) electrolytic baths is proposed. Absorbance and first-derivative spectra were subjected to direct and inverse multiple linear regression (CLS and ILS, respectively) in order to choose the optimum alternative. The use of a factor design to prepare the samples enables the identification of interactions between analytes and their correction by ILS. The results provided by first-derivative spectra were slightly better than those obtained with absorbance spectra (prediction errors were always less than 2% with the former). The ILS procedure was applied to three industrial baths used to a different extent, with highly satisfactory results. Received: 15 June 1998 / Revised: 7 September 1998 / Accepted: 15 September 1998     

Flow injection near-infrared determination of ethanol in chloroform

A simple and direct flow injection (FIA) procedure has been developed for the determination of the stabilizing agent ethanol in chloroform samples. The procedure is based on the use of the absorbance band of ethanol in the near-infrared (NIR) region at 2272 nm, measured in front of a reference sample of chloroform stabilized with amylene. The method developed provides a limit of detection of 0.0045% (v/v) and a dynamic range until 10% (v/v) with a typical variation coefficient of 0.4% for six independent analysis of a real sample containing approximately 1% (v/v) of ethanol. The sample injection frequency allowed by the method is 78 h^–1.     

Determination of total nitrogen in food by flow injection analysis (FIA) with a potentiometric differential detection system

A flow injection set-up based on potentiometric detection and gas diffusion device for the determination of total nitrogen in food is described. The detection system consisted of two ammonium-sensitive electrodes placed sequentially and each alternately operating as reference electrode. Tubular electrodes without an inner reference solution were prepared with a PVC membrane composed of nonactin in Tris (2-ethylhexyl) phosphate and potassium tetrakis (4-chlorophenyl) borate to reduce the membrane resistance. The food sample digests were inserted into the system, and the ammonium present was converted into ammonia gas. The gas diffused through a gas-permeable membrane to a buffer acceptor stream with a pH that ensured transformation to the ammonium cation, which was potentiometrically detected. Good agreement between FIA results and those provided by the reference procedure was obtained, with relative deviation errors below 5%. Using the proposed system, low reagent consumption is possible, a sampling rate of about 30 samples/h was achieved, as well as a good reproducibility for consecutive injections of the same sample (variation coefficient < 2%).     

Rapid analysis of L-dopa in urine samples using gold nanoelectrode ensembles

This work describes the application of a three-dimensional gold nanoelectrode ensembles (GNEE) for monitoring l-dopa in standards and human urine samples using flow injection analysis (FIA) with amperometric detection. Analytical results reveal that the GNEE exhibited better electrocatalytic activity than a gold disk or glassy carbon electrode. Under optimal conditions of l-dopa analysis at GNEE, the calibration plot has a linear range of 5-300 ng/mL with a coefficient of variation (CV) of 3.1% in pH 7.0 phosphate buffer saline (PBS, pH 7.0). The detection limit was 3.0 ng/mL for FIA. The high precision and sensitivity of GNEE provides a feasible means of directly determining l-dopa in urine samples.     

Pungency evaluation of onion cultivars from the Venezuelan West-Center region by flow injection analysis-UV-visible spectroscopy pyruvate determination

A flow injection analysis (FIA) method was developed for the determination of pyruvate in onion cultivars (Allium cepa L.) from the West-Center region of Venezuela. The reference Schwimmer and Weston (1961) (J. Agric. Food Chem. 9 (1961) 301) Batch method was modified and adapted to FIA conditions. The formation kinetic of the 2,4-dinitrophenylhydrazine (DNPH)–pyruvate complex was evaluated at room temperature and at 37 °C. It was demonstrated the suitability of the chromopher formation at room temperature. The optimal values for the FIA parameters were: sample injection volume 3 mL, flow rate 6 mL min⁻¹, reactor length 1.5 m, sodium hydroxide concentration 1.0 mol L⁻¹ and hydrochloric acid concentration 0.5 mol L⁻¹. The working calibration range was extended from 80 mg L⁻¹ (Batch method) to 700 mg L⁻¹ with the FIA set up. The sample dilution step is thus avoided, simplifying the whole analysis process. The pungency in representative samples of the cultivars Yellow granex 438, Ultra Hybrid and Red onion “Sangre de Toro” was evaluated by the flow injection analysis (FIA)–pyruvate method and the results were compared to the reference Batch pyruvate method and to the taste panel test. Non-significant differences were found at the 95% of confidence level between the FIA method and the Batch reference method. Correlation coefficient when comparing the FIA results to the taste panel test was r² = 0.8353. Significant differences (P < 0.05) were found in the pungency of the cultivars, the Ultra Hybrid having the highest pungency. The pungency order from minor to major was: Red onion, Texas Grano 438 and Ultra Hybrid.     

Flow injection analysis of fluoride: optimization of experimental conditions and non-linear calibration using artificial neural networks

This paper deals with the application of artificial neural networks (ANNs) to two common problems in spectroscopy: optimization of experimental conditions and non-linear calibration of the result, with particular reference to the determination of fluoride by flow injection analysis (FIA). The FIA system was based on the formation of a blue ternary complex between zirconium(IV), p-methyldibromoarsenazo and F- with the maximum absorption wavelength at 635 nm. First, optimization in terms of sensitivity and sampling rate was carried out by using jointly a central composite design and ANNs, and a neural network with a 3-7-1 structure was confirmed to be able to provide the maximum performance. Second, the relationship between the concentration of fluoride and its absorbance was modeled by ANNs. In this process, cross-validation and leave-k-out were used. The results showed that good prediction was attained in the 1-4-1 neural net. The trained networks proved to be very powerful in both applications. The proposed method was successfully applied to the determination of free fluoride in tea and toothpaste with recoveries between 96 and 101%.     

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.     

Quantification of mitoxantrone in bone marrow by high-performance liquid chromatography with electrochemical detection

An analytical method for the determination of mitoxantrone in bone marrow was developed using high-performance liquid chromatography with electrochemical detection. The extraction procedure was optimized by investigating several factors which potentially could influence the recovery of mitoxantrone from bone marrow cells. The mean recovery of mitoxantrone from rat bone marrow was found to be 81.7% with a coefficient of variation 3.8%. High-performance liquid chromatography was carried out to quantitate mitoxantrone using ametantrone as internal standard. The detection limit of our analytical method amounts to 100 pg on-column, corresponding to 1 ng/ml of cell suspension containing 2 x 10(7) cells and a day-to-day variation of maximally 8%. Storage of bone marrow samples, containing mitoxantrone, for one to fourteen days resulted in a mean recovery of 94%, as compared to freshly analysed samples. Subsequently we studied the pharmacokinetics of mitoxantrone in rat bone marrow. It appeared that after an intravenous bolus injection of mitoxantrone (2.5 mg/kg) in rats, the drug accumulated in the femoral bone marrow for about four days, and thereafter gradually declined.     

Pre-column derivatization of sisomicin with o-phthalaldehyde-beta-mercaptopropionic acid and its application to sensitive high-performance liquid chromatographic determination with fluorimetric detection

The stability of the o-phthalaldehyde (OPA) derivatives of sisomicin obtained using beta-mercaptopropionic acid was investigated by reversed-phase high-performance liquid chromatography. One of the fluorescent derivatives of sisomicin was stable at least for 6 h in 50% methanol under the optimal conditions used (OPA concentration, pH and temperature). When plasma samples spiked with sisomicin were analysed, the response was linear in the calibration range 136-900 pg of sisomicin per injected volume (40 microliters). As little as 0.06 micrograms of sisomicin per 1 ml of plasma could be detected with signal-to-noise ratio greater than or equal to 2. For plasma samples spiked with 0.2 micrograms/ml sisomicin, the recovery was 97.1 +/- 6.6% (mean +/- S.D., n = 5) with a within-run coefficient of variation of 6.8% and a day-to-day coefficient of variation of 7.2%. The method was also applied to plasma samples from rabbit after a subcutaneous injection of 1 mg/kg sisomicin.     

直接竞争荧光免疫法测定中药材中的黄曲霉毒素B1

本文采用Mannich反应合成黄曲霉毒素B1(AFB1)人工抗原,免疫小鼠制备AFB1单克隆抗体。采用直接搅拌法将异硫氰酸荧光素(FITC)标记AFB1抗体,经Sephadex-50凝胶柱纯化,制得FITC-AFB1荧光标记抗体,分析其免疫学特性,从而建立了一种快速灵敏的直接竞争荧光免疫分析方法(FIA)以用于检测中药材中的AFB1含量。结果表明,AFB1-FITC标记抗体的结合比率为4.19。通过对检测体系多项影响因素的筛选优化,FIA检测方法的标准曲线方程为I=33.45 log C+25.55,R=0.9913,线性检测范围1~100 ng/m L,检测限0.69ng/m L,回收率90.4%~106.6%。该方法具有操作简单、快速灵敏、特异性高等特点,可用于中药材中AFB1的分析测定。     

Optimisation of a flow injection system with electrochemical detection using the desirability function: Application to the determination of hydroquinone in cosmetics

A procedure is proposed in which the determination of hydroquinone using a flow injection system with electrochemical detection is described. Size and coefficient of variation of the signal are optimised by a desirability function and a central composite design. The robustness of the optimum reached in the optimisation step is evaluated by means a Plackett-Burman design. The optimised FIA system is able to determine hydroquinone with a minimum detectable net concentration of 10 μg l⁻¹ with a false positive probability of 0.05 and a false negative probability less than 0.05. In samples of bleaching cream, the proposed procedure has a recovery of 102.2% with standard deviation of 4.4% and a relative error of 6.2%.     

Determination of fluoride in drinking water and in urine of adolescents living in three counties in Northern Chihuahua Mexico using a fluoride ion selective electrode

This study was carried out to determine fluoride in drinking water and in urine of adolescents, ages 15-20 years, living in Northern Chihuahua Mexico. Participants are from a cross-sectional study on health effects of chronic fluoride exposure from drinking water. A total of 201 participants (106 female and 95 male) in the study were recruited from three counties. Samples of drinking water of each county were collected and analyzed using the U.S. EPA Fluoride Ion-Selective Method. Statistically significant difference of fluoride content in water was found among the three counties of recruitment (Cd. Juarez; 0.3 mg/L, Samalayuca, 1.0 mg/L, and Villa Ahumada, 5.3 mg/L). Fluoride content in wells and tap water samples of Villa Ahumada ranged from 5.0 to 5.7 mg/L. Fluoride content of these samples was above the level permitted by Mexican regulations. The fluoride content in bottled water obtained from local stores in Villa Ahumada ranged from 0.3 to 3.7 mg/l.Fluoride in urine samples of each participant was also analyzed using the U.S. EPA Ion-Selective Method. The mean fluoride urine concentration (reported in mg/g creatinine) in adolescents living in these counties was 0.792±0.39, 1.33±0.67 and 2.22±1.16 (Cd. Juarez, Samalayuca and Villa Ahumada), respectively. The high fluoride urinary levels found in participants from Villa Ahumada may be associated to the high fluoride level (5.3 mg/L) in dinking water.The accuracy of measurements was assessed with reference materials in water and in urine. Mean fluoride recovery was 99.0% and 99.6% in water and in urine, respectively. The levels obtained were within the assayed 5% confidence levels.     

Determination of citric acid in soft drinks using flow injection with potentiometric detection

A flow injection analysis (FIA) system with potentiometric detection has been developed for the determination of citric acid in commercial fruit juices using a copper-selective tubular electrode. It consists of the complexation of citrate ion with copper (II) ion, monitoring the free copper (II) concentration. Linear relationships between the potential and log concentrations of citric acid in the range of 1 × 10^–3 mol/L – 1 × 10^–2 mol/L were attained with samples injected in the system without prior treatment. Repeatability was determined by assessing the relative standard deviation for ten replicate injections of different juice samples which varied from 1.2% to 3.0%. The results provided by the automated system were compared with those of an enzymatic conventional method used for the analysis of citric acid in food and a relative deviation of less than 4.0% was found. Recovery trials resulted in values from 97.0% to 101.0%. The system allows a sampling frequency of 60 samples/h. Received: 22 October 1998 / Revised: 14 December 1998 / Accepted: 16 December 1998     

Construction and evaluation of tetrafluoroborate selective electrodes

Summary The construction and evaluation of three types of tetrafluoroborate electrodes without internal reference solution is described. Sensors for electrodes of Type A and Type B use tetraoctylammonium tetrafluoroborate as carrier and 2-nitrophenyloctylether and dibutylphthalate, respectively, as solvent mediators. Electrodes of Type C use the 92-05-02 Orion commercial sensor based on a complex of tris(1,10-phenanthroline)-Ni(II) dissolved in p-nitrocymene. Membranes were applied on a conductive support consisting of a mixture of graphite with a non-conductive epoxy resin. The three types of electrodes showed a similar behaviour with linear responses within the concentration range 10^–5–10^–1 mol/l in tetrafluoroborate, with slopes of 58 mV per decade when the pH of the solutions was between 3 and 11.5. Electrodes of Type A showed the lowest short term hysteresis after treatment with interfering species and offered the best reproducibility and lifetime. Therefore, they were used in the determination of tetrafluoroborate ion in plating baths by means of the sample addition method, giving results with an average spike recovery of 100.5% and a mean coefficient of variation of 1.0%.     

In-situ concentration and determination of mercury by graphite furnace atomic absorption spectrometry with Pd-Rh as the chemical modifier

A method has been proposed for the determination of mercury by cold vapor generation graphite furnace atomic absorption spectrometry (CV-GFAAS) with Pd-Rh as coating and chemical modifier. The trapping efficiency for mercury with Pd-Rh was higher than with Pd alone. The characteristic mass of the method, which gives an integrated absorbance of 0.0044 s, was found to be 55 pg and the absolute detection limit (3 σ) of 37 pg was obtained with the proposed modifier. The method was successfully applied to the determination of mercury in standard reference water samples, wastewater samples and cosmetics with a recovery range of 95–104%. Received: 10 April 1998 / Revised: 20 August 1998 / Accepted: 23 September 1998