Bombardier beetle based biosensor.

A biosensor constructed by combining an oxygen electrode with the liquid ejected by bombardier beetles (Pheropsophus aequinoctialis) immobolized on a collagen membrane is developed for hydrogen peroxide. The sensor presents a linear range of 2.0 x 10(-4)-2.0 x 10(-3) M and a reproductibility of approximately 2%. It shows a better lifetime than similar ones employing purified catalase. The selectivity is good since other enzymes are not present in the natural source employed.

Determination of lead(II) by argentimetry.

A titrimetric method for determination of lead(II), based on the reaction between plumbite and silver ions, is described. Sodium hydroxide solution is added to the sample until the precipitate of lead hydroxide has redissolved. The solution is then made 0.025M in sodium chloride and titrated with silver nitrate. The titration is monitored with a silver electrode. An error smaller than 0.5% has been obtained for 0.05M lead (II).

Investigation of the use of thermometric titrimetry for the determination of acidic substances in wine.

The use of thermometric titrimetry in the determination of acidic substances in red wine is described. The titration curve obtained in the thermometric titration of red wine with strong base presents two inflections. The stoichiometry corresponding to the first inflection presents good agreement with the so-called "total acidity" of wine, and is proposed for its determination. The second inflection is related to the content of phenolic substances in red wine.

Development of a voltammetric method for the determination of iron(III) in Zn-Fe alloy galvanic baths.

A square wave voltammetric method with a static mercury drop electrode (SMDE) was developed for the quantitative determination of iron (III) in Zn-Fe alloy galvanic baths. Real alloy bath samples were analyzed by the standard addition method and recovery tests were carried out. 0.50 mol L-1 sodium citrate (pH 6.0) or 0.20 mol L-1 oxalic acid (pH 4.0) were applied as supporting electrolytes resulting in both cases in a peak potential of about -0.20 V vs. AgIAgCl (saturated KCl). The iron (III) concentration in the alloy bath was 9.0 x 10(-4) mol L-1. A good correlation (r = 0.9999) was achieved between the iron (III) concentration and the peak current in the electrolytes studied, with linear response ranges from 1.0 x 10(-6) to 1.2 x 10(-4) mol L-1. Interference levels for some metals such as copper (II), lead (II), chromium (III) and manganese (II) that can hinder the Zn-Fe alloy deposition were evaluated; only copper (II) interferes seriously.

Determination of molybdenum in steel by adsorptive stripping voltammetry in a homogeneous ternary solvent system.

A new alternative approach for the determination of molybdenum in steel is proposed, using adsorptive stripping voltammetry (AdSV). The determinations are performed in a homogeneous ternary solvent system (HTSS) composed of N,N-dimethylformamide, ethanol and water, with alpha-benzoinoxime (alpha BO) as the complexing agent and a sodium acetate-acetic acid buffer as the support electrolyte. The HTSS composition was optimized by mixture design modelling. The AdSV measurements were performed in the differential pulse mode using an accumulation potential of -1050 mV. Under these optimized experimental conditions, the Mo(VI)-alpha BO reduction current peak potential is observed at potentials near -1250 mV, much lower than those usually reported, and the calibration plot follows the polynomial equation I = 0.359 + 0.265 [CMo(VI)] - 0.015 [CMo(IV)]2 (r2 = 0.997), for Mo concentrations up to 10.0 micrograms L-1. There is a linear range in this calibration plot for Mo(VI) concentrations up to 0.20 microgram L-1, defined by the equation I = 0.353 + 0.385 [CMo(VI)] (r2 = 0.980). In both cases, I is the absolute value for the current in microA and CMo(VI) is the concentration of Mo in microgram L-1. The detection limit for this linear concentration range was estimated as 20 pg L-1. A RSD of 0.43% is associated with the signals at a Mo(VI) level of 0.72 microgram L-1. From the common method-interfering species tested, only iron at Fe/Mo(VI) ratios above 500 and vanadium and tungsten at M/Mo(VI) ratios above 100 appear to affect the analytical response significantly. Phosphorous may also reduce the analytical signal at P/Mo(VI) ratios above 100, due to the formation of the competitive P-Mo complex. The suggested routine procedure was tested by analyzing four stainless steel samples and the results compared well with the ICP-AES measurements. The higher sensitivity of this method permits direct determination of Mo(VI) in steels, eliminating the need of analyte concentration or separation steps in the sample processing procedure.