Alfonso Guiraúm

Flow-injection chemiluminescence determination of cobalt(II) and manganese(II)

Abstract Flow-injection analysis (FIA) was applied to the determination of Co(II) and Mn(II). The method is based on the measurement of metal-catalysed light emission from luminol oxidation by potassium periodate. The apparatus consists of a flow-injection analysis system with a flow cell formed by a spiral of transparent tubing suitable for chemiluminescence measurement. Potassium periodate, unlike hydrogen peroxide, which is the oxidant normally used in luminol chemiluminescence systems, is very stable, gives a low baseline and does not generate bubbles in the tubes of the FIA system. The typical signal is a narrow peak, in which the height is proportional to the light emitted and hence to the concentration of metal ions. The detection limit of Co(II) is 0.01 ng ml−1 and the linear range extends up to 12 ng ml−1; for Mn(II) these limits are 0.02 and 9 ng ml−1, respectively. The optimum concentrations for the reagents are 10−3 M luminol in Na2CO3-KOH buffer (pH 12.9) and 10−4 M KIO4 in water. The optimum flow-rates are water 11.1 ml min−1, luminol 2.5 ml min−1 and KIO4 solution 2.1 ml min−1. Interferences by several metal ions were examined.

Flow injection chemiluminescence method for the selective determination of chromium(III)

Flow injection (FI) has been applied to the determination of CrIII in water and food samples. The method is based on measurement of the light emitted from the CrIII-catalysed oxidation of luminol by H2O2. The apparatus consists of an FI system with a flow cell suitable for chemiluminescence detection. The flow cell, situated near the photodetector, is a coiled tube made from transparent polytetrafluoroethylene. The typical signal is a narrow peak, the height of which is proportional to the light emitted and, therefore, to the concentration of CrIII. The detection limit is 0.01 ppb and the linear range extends up to 6 ppb. The concentrations of the reagents, the pH and the flow rates were optimized. Interferences by several metal ions were examined, and the system was shown to possess a high selectivity. The method was successfully applied to the determination of CrIII in water and food samples.

Metal toxicity in Chlamydomonas reinhardtii. Effect on sulfate and nitrate assimilation

Cadmium (Cd(2+)) or copper (Cu(2+)) ions are toxic for Chlamydomonas reinhardtii growth, at 300 microM, and the alga may accumulate about 0.90+/-0.02 and 0.64+/-0.02% of its dry weight, respectively. Metal contamination changes the elemental composition of dried alga biomass, which indicates the possibility to use C. reinhardtii as biosensor and bioremediator of the aquatic contamination by heavy metals. Either, Cd(2+) or Cu(2+), inhibits about 20% of the nitrate consumption rate by the cells, while only Cd(2+) increases about 40% the sulfate consumption rate. The presence of 1 mM calcium (Ca(2+)) in the culture medium increases the C. reinhardtii productivity (about 50%), the nitrate uptake rate (about 20%) and the sulfate uptake rate (about 30%). In addition, Ca(2+) overcomes the Cd(2+) (300 microM) toxicity by decreasing (about 35%) the intracellular accumulation of metal. Sulfur-starvation induces in C. reinhardtii the expression of serine acetyltransferase and O-acetylserine(thiol)lyase activities, but decreases 50% the consumption rate of nitrate by the cells. Sulfate is also required for the full expression of the nitrate reductase (NR), nitrite reductase (NiR) and glutamate synthase activities.

Determination of Trivalent and Hexavalent Chromium in Waste Water by Flow Injection Chemiluminescence Analysis

Abstract Flow injection analysis (FIA) has been applied to the determination of both Cr(III) and Cr(VI) in waste water. The method is based on the measurement of Cr(III)-catalyzed light emission from luminol oxidation by hydrogen peroxide and the apparatus consists of a FIA system with a flow cell suitable for chemiluminescence detection. Cr(III) is determined directly by the chemiluminescence, meanwhile Cr(VI) is reduced previously to Cr(III) by H2O2 in acidic medium and then the total amount of chromium is determined. The concentration of Cr(VI) is obtained by the difference between the Cr(III) and Cr(VI) determinations. We have analyzed synthetic mixtures of both species, Cr(VI) and Cr(III), using this method and its application to waste water has been shown to be very efficient. The method is simple, inexpensive, sensitive (subnanomolar concentrations), selective and rapid. Tens of samples per hour can be performed with tolerance to potential interferants.

New rapid methods for determination of total LAS in sewage sludge by high performance liquid chromatography (HPLC) and capillary electrophoresis (CE)

Linear alkylbenzene sulfonates (LAS) are the most common synthetic anionic surfactant used in domestic and industrial detergents, with a global production of 2.4x10(6) t year(-1). After use and disposal, LAS may enter the environment by one of the several routes, including by direct discharge to surface water or discharge to water from sewage treatment plants. Sewage treatment plants break down LAS only partly: some of them remain in effluent and other fraction is adsorbed in sewage solid. New and rapid methods for determination of total LAS from sewage sludge based on microwave assisted extraction and HPLC-FL and CE-DAD determination are proposed. The extraction of total LAS is carried out by using microwaves energy, an extraction time of 10 min and 5 mL of methanol. For HPLC-FL determination, mobile phase acetonitrile-water was used, comprising 60% (v/v) from 0 to 1 min and a flow rate of 1 mL min(-1) programmed to 100% acetonitrile between 1 and 2 min and a flow rate of 2 mL min(-1). The final composition was maintained for a further 5 min. The determination of total LAS by CE-DAD was performed in a phosphate buffer (10 mM, pH 9). The separation voltage was 25 kV and the temperature of the capillary was 30 degrees C. Injections were performed in the pressure mode and the injection time was set at 12 s. The determination of total LAS is carried out in less than 5 min. The methods did not require clean-up or preconcentration steps. Detection limit for total LAS in the sludge was 3.03 mg kg(-1) using HPLC-FL and 21.0 mg kg(-1) using CE-DAD, and recoveries were >85% using both determination methods. Concentrations of total LAS obtained using both methods were compared with the sum of concentrations of homologues LAS C-10, LAS C-11, LAS C-12 and LAS C-13 obtained using microwaves assisted extraction and HPLC-FL and CE-DAD determination.

Electrochemical reduction of cefminox at the mercury electrode and its voltammetric determination in urine

The electrochemical behaviour of cefminox in phosphate buffers solutions over pH range 2.0-9.0 using differential-pulse polarography, DC-tast polarography, cyclic voltammetry and linear sweep voltammetry (staircase) has been studied. In acidic media, a non reversible diffusion-controlled reduction involving two electrons occurs and the mechanism for the reduction was suggested. A differential-pulse polarographic method for the determination of cefminox in the concentration range 5.8x10(-6)-6.0x10(-5) M with a detection limit of 1.76x10(-6) M was proposed. Also, a method based on controlled adsorptive pre-concentration of cefminox on the hanging mercury drop electrode followed by linear sweep voltammetry, allows its determination in the concentration range 8.3x10(-8)-1.5x10(-6) M with a detection limit of 2.47x10(-8) M. These methods have been used for the direct determination of cefminox in human urine with recoveries between 98 and 103%, and precision around +/-2%.

Electrochemical oxidation at carbon paste electrode of tacrine and 1-hydroxytacrine and differential pulse voltammetric determination of tacrine in pharmaceuticals and human urine

The electrochemical oxidation of tacrine and its 1-OH-metabolite, has been studied by cyclic voltammetry and differential pulse voltammetry by using carbon paste electrodes. The peak current-concentration relationship was found to be linear up to 20 micrograms ml-1 with detection limits of 0.06 microgram ml-1 for tacrine and 0.18 microgram ml-1 for 1-OH-tacrine and quantitation limits of 0.20 microgram ml-1 for tacrine and 0.37 microgram ml-1 for 1-OH-tacrine. A method for determining tacrine by differential pulse voltammetry in pharmaceuticals and human urine, in the presence of 1-OH-tacrine, has been developed.

Ion-pair extraction and spectrophotometric determination of potassium using dibenzo-18-crown-6 and bromothymol blue

A sensitive extractive-spect533rophotometric method for the determination of potassium using dibenzo-18-crown-6 and bromothymol blue as the counter ion is described. The absorbance was measured at 410 nm and the value of the molar absorptivity was 18 000 l mol–1 cm–1. A linear working range from 0.1 to 3.0 µg ml–1 of potassium was obtained and the relative standard deviation was 2.3%. Rubidium and ammonium ions gave the highest interference. The method was applied to the determination of potassium in fruits and beverages.

Spectrofluorimetric determination of cisatracurium and mivacurium in spiked human serum and pharmaceuticals

Spectrofluorimetric methods to determine cisatracurium and mivacurium are proposed and applied to the determination of both substances in human serum and to the determination of mivacurium in pharmaceuticals. The fluorimetric methods allow the determination of 5-500 ng ml(-1) of mivacurium in aqueous solutions and 5-500 ng ml(-1) of cisatracurium in water-acetonitrile solutions, both containing acetic acid-sodium acetate buffer (pH 5.5) with lambda(exc)=230 nm and lambda(em)=324 nm.

Spectrofluorimetric determination of tacrine in pharmaceuticals and spiked human serum

A spectrofluorimetric method to determine tacrine is proposed and applied to the determination of tacrine in human serum and pharmaceuticals. The fluorimetric method allows the determination of 1-70 ng ml-1 of tacrine in aqueous solutions containing acetic acid-sodium acetate buffer (pH 5.6) with lambda exc = 242 nm and lambda em = 362 nm.