M. Beatriz Q. Garcia

Voltammetric determination of food colorants using a polyallylamine modified tubular electrode in a multicommutated flow system

This work describes the construction of a polyallylamine modified tubular glassy carbon electrode and its application in the electroreduction of food azo colorants (tartrazine, sunset yellow and allura red) by square wave voltammetry. The electrode modification prevented the surface fouling and, simultaneously, enhanced the analytical signal intensity. The developed unit was coupled to a multicommutated flow system which, given the complexity of samples, was designed to allow the implementation of the standard additions method in an automatic way, using only one standard solution. The described method presented a linear range up to about 2.0x10(-4)moll(-1) for the referred colorants, with a detection limit of 1.8x10(-6)moll(-1) for tartrazine, 3.5x10(-6)moll(-1) for sunset yellow and 1.4x10(-6)moll(-1) for allura red. The method was applied in the analysis of these colorants in several food samples, and no statistically significant difference between the results obtained by the proposed and the comparative method (HPLC) was found, at a 95% confidence level. Repeatability in the analysis of samples (expressed in R.S.D.) was about 3% (n=10).

Flow amperometric determination of pharmaceuticals with on-line electrode surface renewal

In this article, a flow system developed for the amperometric determination of a great variety of pharmaceuticals that are known to lead the rapid poisoning of the working electrode surface is described. The referred system was made up of two parallel flow channels that shared the voltammetric detector of tubular configuration, whose movement in the manifold followed the concept of multi-site location of detector. In this way, after each measurement, the conditioning of the working electrode was possible through the passage by its surface of a regeneration solution without implying the alteration of the carrier that flowed in the analytical channel of the manifold. The methodology proposed was evaluated through the determination of two drugs belonging to two distinct therapeutic groups: an antihypertensive (diltiazem) and a non-steroid anti-inflammatory (nimesulide). The results obtained after evaluation of various pharmaceutical formulations on the Portuguese market were in the case of diltiazem compared with those supplied by the reference US Pharmacopoeia XXIV method, with no statistically significant differences having been observed for a confidence interval of 95%. In the case of nimesulide, since no official reference method exists, a series of recovery experiments were proceeded with and a mean value of 101.1% with a R.S.D. of 0.7% was obtained.

On the suppression of zinc-copper interactions in square wave anodic stripping voltammetry in flowing solution by addition of gallium ions

Abstract The problems arising from the formation of copper-zinc intermetallic compounds in square wave anodic stripping voltammetry at wall-jet mercury thin-film electrodes in continuous flow systems have been investigated. These effects are reduced to zero by spiking the analyte solution with gallium ions and ensuring a sufficiently low value of pH, either by using acetate buffer or acidifying the generally-used sodium perchlorate electrolyte. Advantages of this approach are assessed, as are the benefits of stopping solution flow during the determination step of each experiment.

Square-wave anodic stripping voltammetry in stationary and flowing solution: a comparative study

A comparison has been made between square-wave anodic stripping voltammetry (SWASV) at a stationary, mercury thin-film electrode and at a wall-jet mercury thin-film electrode in flowing solution using cadmium(II) and lead(II) as test species. Mercury thin films were prepared on glassy carbon electrode substrates. The effects of square wave amplitude and frequency on the peak current and peak potential in the determination step were studied, and these parameters optimized. Deposition time was varied, and the effect of flow rate in flowing solution investigated. Practical detection limits were found to be 10–8 mol l–1 at stationary electrodes and 2 × 10–9 mol l–1 at wall-jet electrodes. It was found that SWASV gives good results in the presence and absence of dissolved oxygen for both analysis modes, which augurs well for its future application in flow systems, and particularly at wall-jet electrodes.

Relocation of a Tubular Voltammetric Detector for Standard Addition in FIA

In this work a new strategy for the automation of the standard addition method by FIA with voltammetric detection is described, based on the concept of multi-site detection. In the system developed, a single voltammetric detector with mobility in the FIA manifold, carried out sequential measurement of the sample plug before and after addition of the standard solution. The construction and evaluation of the voltammetric detector of tubular configuration and internal diameter similar to the tubing of the FIA manifold, whose incorporation in the system allowed the measurement process to be carried out without change of the hydrodynamic characteristics of the sample plug, is also mentioned. To evaluate the usefulness of the proposed multi-site voltammetric detection system, this was used in the amperometric determination of ascorbic acid in fruit juices where the standard addition method is frequently required to overcome the matrix effect. The results obtained with the FIA system were compared with those from the reference procedure proposed by AOAC. No statistical difference between methods was found at the 95% confidence level. The relative deviations between both methods were always less than or equal to 3.8%. The sampling rate was about 55 samples per hour (110 measurements).

Flow Lectin Affinity Chromatography-A Model with Sambucus nigraAgglutinin

The study of proteomes has become an important way to assess changes occurring in disease conditions. Nonetheless, the dominance of highly abundant serum proteins significantly complicates the discovery and analysis of low-abundant glycoproteins that may constitute potential disease biomarkers. Several techniques have been used to perform serum proteome partitioning such as affinity chromatography based on protein A and G, avian IgY, monoclonal antibodies and lectins. Lectins are particularly well-suited to bind and selectively isolate certain glycan structures present in complex samples like biological ones. The lectin reversibly captures glycoproteins with a particular glycostructure present in the sample in different abundance rates, yielding, after elution, an enriched pool of glycoproteins for glycoproteomic studies. However, lectin affinity chromatography (LAC) for biochemical applications is mainly carried out in batch conditions, which implies a long procedure time, expensive reagents or columns and special equipments or installations. This work proposes the development of a lab-made and easy to implement flow LAC procedure, using Sambucus nigra agglutinin (SNA) immobilized on agarose beads to isolate the STn glycan (a pan-carcinoma biomarker) present in glycoproteins of cancer patients serum. Under flow conditions, the proposed LAC procedure allows the automation of the process, especially important when several samples need to be run. Additionally, the flow system does not require expensive installations or experienced personnel, and it can be tailored to perform LAC with any lectin, according to the purpose of the glycoproteomic analysis. Significance: This work aims to demonstrate the feasibility and the benefits of performing lectin affinity chromatography under flow conditions and with a very simple flow manifold, when compared with the batch procedure usually carried out in Biochemistry and Molecular Biology laboratories. The easiness to implement this simple manifold, without requiring expensive equipments or installations, allows its use in any laboratory, even in those with financial limitations. Several advantages of the developed methodology are pointed out, versus the use of batch procedures or commercial kits or columns, especially when routine analyses need to be performed.