André F. Lavorante

Interfacing flow injection with capillary electrophoresis and inductively coupled plasma mass spectrometry for Cr speciation in water samples

A hyphenated system coupling flow injection (FI), capillary electrophoresis (CE) and inductively coupled plasma mass spectrometry (ICP-MS) is proposed. Two interfaces were developed in order to couple all three systems: the first to couple FI to CE and the second to couple CE to ICP-MS. The first interface was a chamber with micro channels connecting the FI system to the electrophoresis capillary inlet. The capillary outlet was coupled to a concentric nebulizer in the ICP-MS by using the second interface with an electrolyte sheath flow and grounding electrode. Sample aliquots were sequentially introduced by the FI system with a few nanolitres being electrokinetically injected into the electrophoresis capillary in a reproducible manner. The system performed analysis of a continuous sequence of samples with no interruption of the applied voltage during sample replacement or column conditioning. The feasibility of this system was evaluated for Cr speciation. The separation time was improved by forming an anionic complex between Cr(III) and DTPA. Therefore, the analysis of both Cr species, Cr(III)-DTPA2− and CrO42−, attained compatible sample processing between CE and the interfaced techniques FI and ICP-MS. The anionic chromium species were separated in less than 2 min by applying 20 kV in a phosphate electrolyte with TTAOH (tetradecyltrimethylammonium hydroxide) as electroosmotic flow modifier adjusted to pH 8. The transient signals from both species monitored at m/z 53 were characterized by excellent resolution and precision. Peaks obtained using Cr(VI) and Cr(III) standard solutions with concentration ranging from 50 to 200 µg L−1 presented good correlation.

Multi‐commutation in Flow Analysis: A Versatile Tool for the Development of the Automatic Analytical Procedure Focused on the Reduction of Reagent Consumption

Abstract In this work, a general view of multi‐commutation in flow analysis process is presented. The manuscript comprises a comprehensive description of the basic manifolds designed to demonstrate the multi‐commutation concept including the operational modes and the inherent features. A multi‐function flow system with the ability to carry out three‐operation modes without any hardware modification is also described. Intending to demonstrate the versatility of the flow system based on multi‐commutation process, a set of experiments was designed comprising an in‐line dilution and stopped flow approach. Standard solutions of iron and of orthophosphate were selected as models to demonstrate the analytical potential of the proposed system. The results obtained are presented and discussed. The authors were invited to contribute this paper to a special issue of the journal entitled “Spectroscopy and Automation”. This special issue was organized by Miguel de la Guardia, Professor of Analytical Chemistry at Valencia University, Spain.

Micropumping multicommutation turbidimetric analysis of waters

A micropumping multicommutation manifold to perform turbidity determinations in waters is described. The procedure is based on the use of a combination of hydrazine sulfate and hexamethylenetetramine, to obtain an external standard of nephelometric turbidity units (NTU), which could compare the absorbance measurements at high wavelengths for samples with a calibration line obtained from a concentrated formazine standard diluted on-line. To minimize sample and reagent consumption and waste generation, the flow system was designed with two solenoid micro-pumps, one of them for the alternative introduction of the formazine standard and samples and the other one for the water carrier. The multicommutation approach makes possible the on-line dilution of a single standard to obtain the external calibration. The linear response was ranged up to 160NTU. The coefficient of variation was estimated as 1.6 and 3.2% for 10 and 100mm flow cell, respectively, for solutions containing 40NTU (n=10). Approximately, 60 determinations can be carried out per hour with limit of detection values of 1 and 0.1NTU, consuming only 160 or 240muL formazine solution and generating 1.8 or 2.0mL waste per determination, using measurement cells of 10 and 100mm optical pathlength, respectively. The procedure was successfully applied to 11 different water samples. Recovery studies were carried out and results obtained were between 97.5+/-0.2 and 100+/-1%. The development of a homebuilt light emitting diode (LED)-based portable flow analysis instrument was checked for in situ turbidimetric measurements, providing this equipment a LOD value of 0.09NTU working with a blue LED at 464nm and a LOD value of 0.1NTU working with an IR LED.

A spectrophotometric flow procedure for the determination of cationic surfactants in natural waters using a solenoid micro-pump for fluid propulsion

An automatic flow-analysis procedure for spectrophotometric determination of cationic surfactants in surface water using a solenoid micro-pump for propelling solutions of reagents and sample is described. The proposed method is based on a ternary formation complex between chromazurol S, the Fe(III) ion, and the cationic surfactant. The flow network comprised four solenoid micro-pumps controlled by a microcomputer, which performed the sampling step by loading a reaction coil with sample and reagent solutions and displacing the sample zone through the analytical path. The system is simple, easy to operate, and very flexible, with sufficient sensitivity to determine cationic surfactants in water without any pre-concentration or separation step. After determining the best operational conditions, favourable features such as a linear response between 0.34 and 10.2 mg L−1 of surfactant (R = 0.999), a relative standard deviation of 0.6% (n = 11) for a sample containing 3.4 mg L−1 of surfactant, a detection limit of 0.035 mg L−1 of surfactant, and a sampling throughput of 72 determinations per hour were achieved. The system was used to determine cationic surfactant in river-water samples, and recovery values between 91 and 106% were achieved.

Eletroforese capilar acoplada à espectrometria com plasma: uma ferramenta eficiente para a especiação

The most important features of the CE-ICP hyphenation, as well as its advantages and drawbacks as a tool for speciation are discussed. The fundamental principles of capillary electrophoresis and inductively coupled plasma mass spectrometry are also presented. Some applications involving different designs proposed in the literature to couple CE and ICP system for elemental speciation are reviewed.

An Alternative Sample Introduction Device for a Home‐Made Capillary Electrophoresis System

Abstract A home‐made capillary electrophoresis (CE) system with an alternative interface for hydrodynamic injection of sample solutions is described. The interface is an acrylic chamber whose efficiency of injection was evaluated by the separation of cysteine and methionine standards. Important parameters inherent to this system such as peristaltic pump rotation, system grounding, and injection time were carefully investigated. Although this is a batch‐wise system, the interface showed a good efficiency for nano‐liter injections and relative standard deviations (RSD) smaller than 3% for both signal measurement and migration time were obtained. This new interface allowed a minimal capillary handling and also guaranteed an excellent performance in terms of sample solution injection into the home‐made system.