Scientometric Picture of the Evolution of the Literature of Automation in Spectroscopy and Its Current State

The current study focuses on the status of automation and mechanization in spectroscopy for analytical chemistry publications compiled during the period 1980–2006, in Analytical Abstracts. Flow injection analysis (FIA), sequential injection analysis (SIA), multicommutation, and monosegmented and segmented flow strategies were considered. For assessing the evolution of scientific productivity, the total number of publications concerned with the different methodologies was evaluated. In order to provide a picture of the state of the art of this field, the most important journals, the most active authors, and the most productive countries in the field of automation were evaluated in the period of the first years of this century.     

An improved flow-based procedure for microdetermination of total tannins in beverages with minimized reagent consumption

A flow system designed with solenoid micro-pumps is introduced for spectrophotometric determination of total tannins based on the Folin– Denis reaction. The procedure minimizes the main drawbacks related to the AOAC batch procedure, i.e. interferences from reducing species in the samples, high reagent consumption and waste generation, and low sampling rate. Linear response was observed for tannic acid concentrations in the range 2–100 mg L⁻¹, with a detection limit (99.7% confidence level) of 0.3 mg L⁻¹. The sampling rate and coefficient of variation (n = 10) were estimated as 75 measurements per hour and 1.1%, respectively. Results of determination of total tannin in tea, beer and wine samples were in agreement with those achieved by the batch reference procedure at the 95% confidence level. In comparison to the batch procedure, the reagent consumption and effluent generation were 83 and 60-fold lower, respectively. Correspondence: Fábio R. P. Rocha, Instituto de Química, Universidade de S?o Paulo, PO Box 26077, S?o Paulo, 05513-970 SP, Brazil     

Spectrophotometric Multicommutated Flow System for the Determination of Hypochlorite in Bleaching Products

Abstract

A multicommutation flow system for the spectrophotometric determination of hypochlorite in bleaching products is proposed. In this system, N,N-diethyl-p-phenylenediamine (DPD) reacts with hypochlorite, and the product was monitored at 515 nm. The analytical curve for hypochlorite was linear in the concentration range from 2.68 × 10^?5 to 1.88 × 10^?4 mol L^?1 (2–14 mg L^?1) with a detection limit of 6.84 × 10^?6 mol L^?1 (0.51 mg L^?1). The sampling rate was 45 h^?1, and a relative standard deviation of 1.4% (n = 10) was obtained. The recovery of this analyte ranged from 97.2% to 102.5%, and the results found using the proposed spectrophotometric multicommutated flow system agreed with the data obtained using a reference method (iodometric titration) at the 95% confidence level.     

Automatic Stepwise Potentiometric Titration in a Monosegmented Flow System

 An automatic stepwise potentiometric titration carried out in a monosegmented flow system is proposed. A tubular hydrogen ion-selective electrode without inner reference solution was employed as sensor. The titration procedure was implemented by exploiting continuous variations in volumetric fractions achieved by inserting different sample and titrant aliquots into the analytical path and maintaining the sample zone volume. Every sample plug was separated from the carrier solution by air bubbles to minimize dispersion and to distinguish each sample plug signal. The flow set-up comprised a set of computer-controlled three-way solenoid valves, and the software was written in Quick BASIC 4.5 allowing end-point determination while the titration was in progress. The feasibility of the system was ascertained by analyzing soft drinks, isotonic beverages, alcohol free beers and industrial fruit juices. Results were in agreement with those obtained by a conventional titration, and no significant difference at 95% confidence level was observed. Other profitable features such as a 1% standard deviation (n = 10), and an analytical throughput of 22 samples per hour were also achieved. Received January 24, 2000. Revision June 16, 2000.     

Green chemistry and the evolution of flow analysis. A review

Flow analysis has achieved its majority as a well-established tool to solve analytical problems. Evolution of flow-based approaches has been analyzed by diverse points of view, including historical aspects, the commutation concept and the impact on analytical methodologies. In this overview, the evolution of flow analysis towards green analytical chemistry is demonstrated by comparing classical procedures implemented with different flow approaches. The potential to minimize reagent consumption and waste generation and the ability to implement processes unreliable in batch to replace toxic chemicals are also emphasized. Successful applications of greener approaches in flow analysis are also discussed, focusing on the last 10 years.     

Multicommutated Flow Analysis System for Determination of Horseradish Peroxidase and Its Inhibitors

A fully mechanized multicommutated flow analysis (MCFA) system dedicated to determining horseradish peroxidase (HRP) activity was developed. Detection was conducted using a flow-through optoelectronic detector-constructed of paired LEDs operating according to the paired emitter-detector diode (PEDD) principle. The PEDD-MCFA system is dedicated to monitoring the enzyme-catalyzed oxidation of p-phenylenediamine (pPD) by a hydrogen peroxide. Under optimized conditions, the presented bioanalytical system was characterized by a linear response range (33.47–200 U/L) with a detection limit at 10.54 U/L HRP activity and 1.66 mV·L/U sensitivity, relatively high throughput (12 signals recordings per hour), and acceptable precision (RSD below 6%). Additionally, the utility of the developed PEDD-MCFA system for the determination of HRP inhibitors allowing the detection of selected thiols at micromolar levels, is demonstrated. The practical utility of the flow system was illustrated by the analysis of some dietary supplements containing L-cysteine, N-acetylcysteine, and L-glutathione.     

Determination of Phenols In Natural Waters with A Flow-Analysis Method and Chemiluminescence Detection

ABSTRACT

A simple flow-manifold with time based sample introduction system was elaborated and used to determine phenols in natural waters. Use of computer controlled solenoid valves and direct chemiluminescence detection enables very low reagent consumption. A quantity of less than 1.5 μmol of potassium permanganate and 600μmol of sulphuric acid per determination is used. The use of on-line preconcentration column filled with XAD-4 resin enables determination with the detection limit of 5 ng-ml^?. The sample throughput is 12-h^? when the column is used and 60-h^? without a column.     

A Multicommuted Flow‐based System for Hydrogen Peroxide Determination by Chemiluminescence Detection Using a Photodiode

Abstract

A simple, rapid, and automated assay for hydrogen peroxide in pharmaceutical samples was developed by combining the multicommutation system with a chemiluminescence (CL) detector. The detection was performed using a spiral flow‐cell reactor made from polyethylene tubing that was positioned in front of a photodiode. It allows the rapid mixing of CL reagent and analyte and simultaneous detection of the emitted light. The chemiluminescence was based on the reaction of luminol with hydrogen peroxide catalyzed by hexacyanoferrate(III).

The feasibility of the flow system was ascertained by analyzing a set of pharmaceutical samples. A linear response within the range of 2.2–210 µmol l^?1 H₂O₂ with a LD of 1.8 µmol l^?1 H₂O₂ and coefficient of variations smaller than 0.8% for 1.0×10^?5 mol l^?1 and 6.8×10^?5 mol l^?1 hydrogen peroxide solutions (n=10) were obtained. Reagents consumption of 90 µg of luminol and 0.7 mg of hexacyanoferrate(III) per determination and sampling rate of 200 samples per hour were also achieved.     

Automatic Fluorimetric Procedure for the Determination of Aluminium in Plant Nutrient Solution and Natural Water Employing a Multicommutated Flow System

A fluorimetric flow procedure for the determination of aluminium in plant nutrient solutions and natural waters using morin (3,5,7,2,4-(pentahydroxyflavone) as a fluorimetric reagent is described. The flow system comprised a set of three-way solenoid valves that were assembled to implement the multicommutation and monosegmented flow approaches. The calibration graph was linear in the range between 0.1 to 1.0mgL^–1 Al³⁺. A relative standard deviation of 1.7% (n=7) for a typical sample containing 0.5mgL^–1 Al was achieved. Comparing the results with those obtained by atomic emission spectrometry (ICP-AES), no significant difference at the 95% confidence level was observed. Other profitable features such as an analytical throughput of 60 determinations per hour; a reagent consumption of 1.6µg of morin per determination and a detection limit of 0.04mgL^–1 were also achieved.