Restricted access carbon nanotubes for direct extraction of cadmium from human serum samples followed by atomic absorption spectrometry analysis.

In this paper, we propose a new sorbent that is able to extract metal ions directly from untreated biological fluids, simultaneously excluding all proteins from these samples. The sorbent was obtained through the modification of carbon nanotubes (CNTs) with an external bovine serum albumin (BSA) layer, resulting in restricted access carbon nanotubes (RACNTs). The BSA layer was fixed through the interconnection between the amine groups of the BSA using glutaraldehyde as cross-linker. When a protein sample is percolated through a cartridge containing RACNTs and the sample pH is higher than the isoelectric point of the proteins, both proteins from the sample and the BSA layer are negatively ionized. Thus, an electrostatic repulsion prevents the interaction between the proteins from the sample on the RACNTs surface. At the same time, metal ions are adsorbed in the CNTs (core) after their passage through the chains of proteins. The Cd(2+) ion was selected for a proof-of-principle case to test the suitability of the RACNTs due to its toxicological relevance. RACNTs were able to extract Cd(2+) and exclude almost 100% of the proteins from the human serum samples in an online solid-phase extraction system coupled with thermospray flame furnace atomic absorption spectrometry. The limits of detection and quantification were 0.24 and 0.80 µg L(-1), respectively. The sampling frequency was 8.6h(-1), and the intra- and inter-day precisions at the 0.80, 15.0, and 30.0 µg L(-1) Cd(2+) levels were all lower than 10.1% (RSD). The recoveries obtained for human blood serum samples fortified with Cd(2+) ranged from 85.0% to 112.0%. The method was successfully applied to analyze Cd(2+) directly from six human blood serum samples without any pretreatment, and the observed concentrations ranged from

A single FIA system coupled with reduction and distillation processes for the determination of sulfate ion by spectrophotometry.

In the present work, all steps of the sulfate reduction procedures, such as reduction, distillation and sulfate determination were joined in only one FIA system. The formed sulfide was on-line determined by employ the Fisher reaction. The proposed method presented a LOD of 1.00 µg L(-1) and a LOQ of 3.33 µg L(-1), well lower than the most commonly used turbidimetric determination, with no significant interferences. Additionally, we reached an analytical frequency of 6 measurements per hour, including all steps, beginning with the introduction of the sample up to the signal reading. Therefore, it revealed very fast, low reagent/sample consumption, agreeing with green-chemistry statements. This method has also a wide linear range (3.33 up to 1000 µg L(-1)), being useful for both low and high sulfate concentrations.

Direct introduction of water sample in multisegmented flow-injection analysis for sulfide determination.

The present paper describes an inline flow-injection analysis system for the determination of sulfide in water samples, exploiting the Fischer reaction. Water samples were collected and introduced into a reactor of the FIA system. The sulfide released, after sample acidification, was carried out with a nitrogen gas flow and mixed with N,N diethyl-p-phenylenediamine (DEPD) solution in the presence of Fe(III). The blue dye formed was measured in the wavelength range between 672-679 nm. An evaluation of the effects of chemical and flow factors was performed using the factorial design of two levels, while optimization was accomplished by a Doehlert matrix. The system presented two linear-response ranges: the first of 0.433 to 400 µg L(-1) and the second of 400 to 3500 µg L(-1). The detection and quantification limit were found to be 0.130 and 0.433 µg L(-1), respectively, while the sample throughput was 12 h(-1). The precision was evaluated as the relative standard deviation (n = 10); for 50 and 100 µg L(-1) sulfide it was found to be 1.9 and 2.3%, respectively. The method showed satisfactory selectivity regarding the main interference present in environmental samples. The accuracy of the method was successfully evaluated in environmental water samples after a comparison with a literature reference method.