A Novel Catalytic Procedure for the Determination of Ultratrace Zirconium

 A novel catalytic procedure for zirconium was proposed based on Zr(IV) catalyzed oxidation of gallocyanine by hydrogen peroxide in hexamethylene tetramine-hydrochloric acid buffer medium. The calibration graph is linear for 0–110 ngċml⁻¹, and the detection limit is 0.4 ngċml⁻¹ Zr(IV). Most foreign ions do not interfere with the determination, except for Cu²⁺, Fe³⁺ and Cr(VI). The interferences of Cu²⁺ and Fe³⁺ could be eliminated by masking with EDTA and mannitol, and that of Cr(VI) by reducing to Cr(III) with ascorbic acid. The typical features of this procedure are that it is sensitive for zirconium, and the determination could be carried out at room temperature. It had been used to the determination of zirconium in zirconium bronze, simulated samples and a certified reference material. The recoveries were 98.6 ∼ 102%, and relative standard deviations (R.S.D.) were 0.9 ∼ 1.5%, respectively. Received September 12, 1999. Revision April 10, 2000.     

Application of an in situ plated lead film electrode to the analysis of testosterone by adsorptive stripping voltammetry

Adsorptive stripping voltammetry is a very sensitive and selective method for determination of drugs and organic substances in biological fluids. We have shown that determination of testosterone by adsorptive stripping voltammetry is possible using a lead film electrode. The lead film plating process and accumulation of testosterone were performed simultaneously from an acetate buffer solution of pH = 5.2 at a potential of −1.1 V. The measurements were carried out in undeaerated solutions. The detection limit was 9 × 10⁻⁹ mol L⁻¹ for an accumulation time of 120 s; the relative standard deviation for 1 × 10⁻⁷ mol L⁻¹ testosterone was 3.8%. The proposed voltammetric procedure for determination of testosterone could be applied to its determination in a pharmaceutical preparation and human urine samples directly without any separation steps.     

Flow injection analysis with in-line solid phase extraction for the spectrophotometric determination of sulfonated and unsulfonated Quinoline Yellow in Cologne

An integrated solid-phase spectrophotometry/ FIA  method is  proposed for the determination of the synthetic colorant matter Quinoline Yellow (QYWS) in the presence of its unsulfonated derivative QYSS. The procedure is based on the retention and preconcentration of the low level QYSS on a C-18 silica gel minicolumn, followed by sequential measurement of its absorbance at λ = 410 nm after its elution with methanol. The applicable concentration range, the detection limit and the relative standard deviation were the following: for QYWS, from 0.10 to 30.0 mg L^–1; 0.013 mg L^–1; and 0.6%; and for QYSS, between 10 and 1,000 μg L^–1; 2 μg L^–1; and 1.3%, respectively. The method was applied to the determination of small amounts of QYSS present in QYWS in Colognes. Percentages of recovery between 98% and 99% were obtained in all instances. The method was also satisfactorily applied to the determination of these compounds in samples of commercial Colognes comparing the results for QYWS with those offered by an HPLC reference method and also validating the results chemometrically. Received: 21 January 2000 / Revised: 17 March 2000 / Accepted: 22 March 2000     

A green flow-based procedure for fluorimetric determination of acid-dissociable cyanide in natural waters exploiting multicommutation

A flow system designed with solenoid valves is proposed for determination of weak acid dissociable cyanide, based on the reaction with o-phthalaldehyde (OPA) and glycine yielding a highly fluorescent isoindole derivative. The proposed procedure minimizes the main drawbacks related to the reference batch procedure, based on reaction with barbituric acid and pyridine followed by spectrophotometric detection, i.e., use of toxic reagents, high reagent consumption and waste generation, low sampling rate, and poor sensitivity. Retention of the sample zone was exploited to increase the conversion rate of the analyte with minimized sample dispersion. Linear response (r = 0.999) was observed for cyanide concentrations in the range 1–200 μg L⁻¹, with a detection limit (99.7% confidence level) of 0.5 μg L⁻¹ (19 nmol L⁻¹). The sampling rate and coefficient of variation (n = 10) were estimated as 22 measurements per hour and 1.4%, respectively. The results of determination of weak acid dissociable cyanide in natural water samples were in agreement with those achieved by the batch reference procedure at the 95% confidence level. Additionally to the improvement in the analytical features in comparison with those of the flow system with continuous reagent addition (sensitivity and sampling rate 90 and 83% higher, respectively), the consumption of OPA was 230-fold lower.     

Coupled column liquid chromatography for the rapid determination of N-methylcarbamates and some of their main metabolites in water

Summary A sensitive and selective coupled-column liquid chromatography (LC-LC) method was developed for the trace level determination of some N-methylcarbamates and some of their main metabolites as aldicarb, aldicarb-sulphoxide, aldicarb-sulphone, carbofuran and 3-hydroxicarbofuran in drinking and ground waters. The limit of determination can be reduced to 0.1 μg.L⁻¹ by solid phase extraction with a subsequent evaporation step. Environmental samples spiked at 0.1 μg.L⁻¹ were preconcentrated off-line with graphite carbon and then analyzed by LC-LC with UV detection yielding average recoveries between 81–109% (n=5) with RSD between 5–9%. The overall procedure allowed a sample throughput of up to 30 samples per day.     

Redox-potentiometric determination of polyethylene glycol-20 000 by its reaction with iodine

A simple and rapid procedure for the potentiometric determination of polyethylene glycol with a molecular mass of 20000 (PEG-20000) was proposed. The procedure is based on the empirically found stoichiometry of the reaction of PEG-20000 precipitation with iodine. Titration was performed to a constant potential of the I ₃ ⁻ /3I⁻¹ redox couple measured with a platinum electrode. The relative standard deviation for PEG-20000 concentrations from 6.0 to 19.9 g/L was ≤5%.     

Solid Phase Spectrophotometry for the Determination of Cobalt in Pharmaceutical Preparations

 A new sensitive method exploiting solid-phase spectrophotometry is proposed for the determination of cobalt in pharmaceutical preparations. The chromogenic reagent 1-(2-thiazolylazo)-2-naphthol (TAN) was immobilized on C18 bonded silica loaded into a home-made cell with 1.5 mm of optical path for cobalt determination. Cobalt(II) reacts with TAN on C18 material, at pH 6.0–7.5, to give a coloured complex which has maximum absorption at 572 nm. In this way, the sample was passed through the cell and Co(II) ions were quantitatively retained on the solid-phase. After the direct measurement of light-absorption in the solid phase, only the cobalt was eluted with 0.1 mol L⁻¹ hydrochloric acid. The cell was washed with water and then another sample solution could be passed through the cell. The procedure allowed the determination of cobalt in the range of 10–160 μg L⁻¹ with coefficient of variation of 4.7% (n=10) and apparent molar absorptivity of 2.62 × 10⁶ L mol⁻¹ cm⁻¹ using sample volume of 3-mL. Received May 15, 2000. Revision August 28, 2000.     

Separation and determination of selenium in water samples by the combination of APDC coprecipitation: X-ray fluorescence spectrometry

A sensitive and non chromatographic analytical procedure for the separation of inorganic selenium species in natural water has been performed. A combination of APDC coprecipitation and determination by an absolute thin layer Energy dispersive X-ray fluorescence spectrometry method was used. The influence of various analytical parameters such as element concentration, oxidation states and pH on the recoveries of Se (IV) was examined. The presence of organic matter and bicarbonate anions, typical components in Cuban groundwater samples, was also tested. Negligible matrix effects were observed. At pH 4 a 100% recovery was found for Se (IV). The coprecipitation recovery of the oxidized selenium species (Se (VI)) was null for the selected concentration range (5–100 μg L⁻¹). When the Se (VI) was reduced by heating the solution with 4 mol L⁻¹ HCl, quantitative recovery was also obtained. The determination of total selenium was conducted by the application of the oxidation–reduction process and the analytical procedure for Se (IV). Se (VI) content was calculated as the difference between total selenium and Se (IV). The detection limit was 0.13 μg L⁻¹. The relative standard deviation was lower than 3.5% for 5 μg L⁻¹ of Se (IV). The trueness of the method was verified by using standardized hydride generation-atomic absorption spectrometry technique. The results obtained using the EDXRF technique were in good agreement with the ones determined by HG-AAS. The proposed method was applied to the determination of Se (IV) in surface water and groundwater samples.     

A catalytic adsorptive stripping voltammetric procedure for trace determination of Cr(VI) in natural samples containing high concentrations of humic substances

A simple and fast catalytic adsorptive stripping voltammetric procedure for trace determination of Cr(VI) in natural samples containing high concentrations of humic substances has been developed. The procedure for chromium determination in the presence of DTPA and nitrates was employed as the initial method. In order to enhance the selectivity vs. Cr(III) the measurements were performed at 40°C. Interference from dissolved organic matter such as humic and fulvic acids was drastically decreased by adding Amberlite XAD-7 resin to the voltammetric cell before the deaeration step. The whole procedure was applied to a single cell, which allowed monitoring of the voltammetric scan. Optimum conditions for removing humic and fulvic acids due to their adsorption on XAD-7 resin were evaluated. The use of XAD-7 resin also minimize interferences from various cationic, anionic, and nonionic surfactants. The calibration graph for Cr(VI) for an accumulation time of 30 s was linear in the range 5 × 10⁻¹⁰ to 5 × 10⁻⁸ mol L⁻¹. The relative standard deviation for determination of Cr(VI) at a concentration of 1 × 10⁻⁸ mol L⁻¹ was 3.5% (n = 5). The detection limit estimated from 3 times the standard deviation for low Cr(VI) concentrations and an accumulation time of 30 s was about 1.3 × 10⁻¹⁰ mol L⁻¹. The proposed method was successfully applied to Cr(VI) determination at trace levels in soil samples.     

Correction of the interference by mixing the reagents in the bioluminescent determination of ATP in environmental samples by an interfaced PC photometer and a robust regression procedure

 An automated procedure for correcting the interference due to mixing the reagents in the determination of ATP by a bioluminescent technique is described. The measurements were performed by an in-house interfaced PC photometer. An automated procedure based on a robust regression method and outliers detection was applied to exclude the time of the mixing of the reagents from the global time of reaction. In fact the mixing of the reagents is responsible of the poor analytical precision (RSD%>25) and low sensitivity (limit of detection≈2×10^-8 mol/l). By this procedure, the precision (RSD%<7) and sensitivity (limit of detection≈8×10^-10 mol/l) were improved. The method was applied to the determination of ATP in marine sediments and good recovery within 90–108% was obtained. For non-polluted samples the measurement can be carried out by direct comparison with standard solutions. The standard addition procedure is recommended for polluted samples. Received: 25 April 1996/Revised: 28 June 1996/Accepted: 3 July 1996     

Correction of the interference by mixing the reagents in the bioluminescent determination of ATP in environmental samples by an interfaced PC photometer and a robust regression procedure

 An automated procedure for correcting the interference due to mixing the reagents in the determination of ATP by a bioluminescent technique is described. The measurements were performed by an in-house interfaced PC photometer. An automated procedure based on a robust regression method and outliers detection was applied to exclude the time of the mixing of the reagents from the global time of reaction. In fact the mixing of the reagents is responsible of the poor analytical precision (RSD%>25) and low sensitivity (limit of detection≈2×10^-8 mol/l). By this procedure, the precision (RSD%<7) and sensitivity (limit of detection≈8×10^-10 mol/l) were improved. The method was applied to the determination of ATP in marine sediments and good recovery within 90–108% was obtained. For non-polluted samples the measurement can be carried out by direct comparison with standard solutions. The standard addition procedure is recommended for polluted samples. Received: 25 April 1996/Revised: 28 June 1996/Accepted: 3 July 1996     

Determination of phenols in waters using micro-pumped multicommutation and spectrophotometric detection: an automated alternative to the standard procedure

An automated and greener spectrophotometric procedure has been developed for the determination of phenol in water at 700 nm. The method uses the reaction between phenol, sodium nitroprusside, and hydroxylamine hydrochloride in a buffered medium at pH 12.3. The flow manifold comprises four solenoid micro-pumps employed for sample and reagent introduction into the reaction coil and to transport the colored product formed to the detector. The linear dynamic range was 50–3,500 ng mL⁻¹ (R = 0.99997; n = 6) and the method provided a limit of detection (3σ) of 13 ng mL⁻¹. The sampling throughput was estimated to be 65 measurements per hour and the coefficient of variation was 0.5% (n = 10) for a 1.0 μg mL⁻¹ phenol concentration. Recoveries of 92–105% were obtained for phenol determination in spiked water samples at concentration levels from 50 to 5,000 ng mL⁻¹. The use of multicommutation reduced the reagent consumption 25-fold, the sample consumption 225-fold, and the waste generation 30-fold compared with the batch procedure. The proposed method is an environmentally friendly alternative to the official 4-aminoantipyrine method since it avoids the use of chloroform.     

Chemiluminescence Method for the Determination of Glutathione in Human Serum Using the Ru(phen)3 2+ – KMnO4 System

A simple, rapid and specific chemiluminescence (CL) method for the determination of glutathione has been developed. The method is based on the enhanced CL of the reaction between Ru(phen)₃ ²⁺ (phen = 1,10-phenanthroline) and KMnO₄ by glutathione in HCl medium. Under the optimum conditions, the response is linearly proportional to the concentration of glutathione between 1.5 × 10⁻⁷ and 1.0 × 10⁻⁵ mol L⁻¹. The dection limit for glutathione (5.8 × 10⁻⁸ mol L⁻¹) is about 10 and 200 times better than those of the spectrophotometric method using Ellman regent and the Lucigenin – CL method, respectively. The final procedure allows the determination of glutathione in human serum with recoveries of 92%–108%. A satisfactory agreement was obtained with a mean relative difference of 2.5% compared to the HPLC method.     

An improved flow-based procedure for microdetermination of total tannins in beverages with minimized reagent consumption

A flow system designed with solenoid micro-pumps is introduced for spectrophotometric determination of total tannins based on the Folin– Denis reaction. The procedure minimizes the main drawbacks related to the AOAC batch procedure, i.e. interferences from reducing species in the samples, high reagent consumption and waste generation, and low sampling rate. Linear response was observed for tannic acid concentrations in the range 2–100 mg L⁻¹, with a detection limit (99.7% confidence level) of 0.3 mg L⁻¹. The sampling rate and coefficient of variation (n = 10) were estimated as 75 measurements per hour and 1.1%, respectively. Results of determination of total tannin in tea, beer and wine samples were in agreement with those achieved by the batch reference procedure at the 95% confidence level. In comparison to the batch procedure, the reagent consumption and effluent generation were 83 and 60-fold lower, respectively. Correspondence: Fábio R. P. Rocha, Instituto de Química, Universidade de S?o Paulo, PO Box 26077, S?o Paulo, 05513-970 SP, Brazil     

Spectrophotometric Determination of Dithionite in Household Commercial Formulations Using Naphthol Yellow S

 A rapid and quantitative procedure for the determination of dithionite based on the reduction of naphthol yellow S in ammonia containing solution and measurement of the absorbance of the product formed at 502 nm is described. The mechanism of the reaction is discussed and its analytical application is shown to be possible in a concentration range of dithionite between 16.7 and 133.1 mg l⁻¹ (1.3 × 10⁻⁴ and 1.04 × 10⁻³ mol l⁻¹). The procedure was applied to the determination of dithionite in commercial formulations used in the household. In a 0.5 g sample of decolorant, dithionite was found to be present at concentrations between 25 and 35% (w/w), which can be determined without interference of its decomposition products. The results are shown to be in good agreement with those of polarographic determinations. Received April 26, 2001. Revision August 2, 2001.     

Stannum film electrode for square wave voltammetric determination of trace copper(II)

An anodic stripping voltammetric procedure for the determination of Cu(II) at an in situ-plated stannum film electrode (SnFE) was described. The results indicated that the SnFE had an attractive electroanalytical performance, with two distinct voltammetric stripping signals for copper and stannum, and showed the superior advantage for the determination of copper compared with the bismuth film electrode. Several experimental parameters were optimized. The SnFE exhibited highly linear behavior in the concentration range from 1.0 to 100.0 μg L⁻¹ of Cu(II) (r = 0.994) with the detection limit of 0.61 μg L⁻¹ (S/N = 3), and the relative standard deviation for a solution containing 40.0 μg L⁻¹ Cu(II) was 2.2% (n = 8). The procedure has been successfully applied for the determination of Cu(II) in lake water sample.     

Sequential spectrofluorimetric determination of free and total glycerol in biodiesel in a multicommuted flow system

A new procedure for spectrofluorimetric determination of free and total glycerol in biodiesel samples is presented. It is based on the oxidation of glycerol by periodate, forming formaldehyde, which reacts with acetylacetone, producing the luminescent 3,5-diacetyl-1,4-dihydrolutidine. A flow system with solenoid micro-pumps is proposed for solution handling. Free glycerol was extracted off-line from biodiesel samples with water, and total glycerol was converted to free glycerol by saponification with sodium ethylate under sonication. For free glycerol, a linear response was observed from 5 to 70 mg L⁻¹ with a detection limit of 0.5 mg L⁻¹, which corresponds to 2 mg kg⁻¹ in biodiesel. The coefficient of variation was 0.9% (20 mg L⁻¹, n = 10). For total glycerol, samples were diluted on-line, and the linear response range was 25 to 300 mg L⁻¹. The detection limit was 1.4 mg L⁻¹ (2.8 mg kg⁻¹ in biodiesel) with a coefficient of variation of 1.4% (200 mg L⁻¹, n = 10). The sampling rate was ca. 35 samples h⁻¹ and the procedure was applied to determination of free and total glycerol in biodiesel samples from soybean, cottonseed, and castor beans.     

In vitro monitoring of clindamycin in human urine using flow injection chemiluminescence

A sensitive chemiluminescence method for the determination of clindamycin is presented. The method is based on the inhibitory effect of clindamycin on the chemiluminescence reaction between luminol and myoglobin in a flow-injection system. The decrement in chemiluminescence intensity is linear with the logarithm of the clindamycin concentration over the range of 0.1–70.0 ng mL⁻¹ (r ² = 0.9995), with a detection limit of 0.03 ng mL⁻¹ (3σ). At a flow rate of 2.0 mL min⁻¹, the complete analytical process could be performed within 0.5 min, including sampling and washing, with a relative standard deviation of less than 3.0% (n = 5). The procedure was applied to the determination of clindamycin in human serum and in monitoring the excretion of clindamycin in human urine samples without any pretreatment process. It was found that the excretive clindamycin concentration reached its maximum 3 hours after oral administration. The clindamycin excretive ratio in 9 hours was 10.84% in the body of the volunteer.     

Fast ultrasound-assisted extraction of copper,iron, manganese and zinc from human hair samples prior to flow injection flame atomic absorption spectrometric detection

A dynamic ultrasound-assisted extraction procedure utilizing diluted nitric acid was developed for the determination of copper, iron, manganese and zinc in human hair taken from workers in permanent contact with a polluted environment. The extraction unit of the dynamic ultrasound-assisted extraction system contains a minicolumn into which a specified amount of hair (5–50 mg) is placed. Once inserted into the continuous manifold, trace metals were extracted at 3 mL min⁻¹ with 3 mol L⁻¹ nitric acid under the action of ultrasound for 2 min for zinc and 3 min for copper, iron and manganese determination, and using an ultrasonic water-bath temperature of 70 °C for zinc and 80 °C for copper, iron and manganese determination. The system permits the direct analysis of hair and yields concentrations with relative standard deviations of <3% (n = 11). The applicability of the procedure was verified by analysing human hair samples from workers exposed to welding fumes, and its accuracy was assessed through comparison with a conventional sample dissolution procedure and the use of a certified reference material (BCR 397, human hair).     

Application of factorial designs and simplex optimisation in the development of flow injection-hydride generation-graphite furnace atomic absorption spectrometry (FI-HG-GFAAS) procedures as demonstrated for the determination of trace levels of germanium

The optimisation of a volume-based FI-HG-GFAAS procedure is described for the trace determination of Ge, comprising in situ collection of the generated germane in the graphite furnace. The response function is the peak area readout (A × s). Based on a preliminary study, where factorial designs were used to identify significant factors and interactions, the procedure was optimised using both simplex and OVAT (one variable at a time) methods. The characteristics and merits of these methods are discussed. Under optimal experimental conditions, using a sample volume of 100 μL, Ge was determined at a sampling frequency of 22 h^–1. The sensitivity, in terms of the characteristic mass, m₀, was 26 pg/0.0044 A × s, with a detection limit of 0.21 μgL^–1 (3σ). The precision (relative standard deviation) was 2.0% (n = 10) at the 1 μgL^–1 level. Received: 12 September 1996 / Revised: 6 December 1996 / Accepted: 16 December 1996