Automatic flow system for simultaneous determination of iron and chromium in steel alloys employing photometers based on LEDs as radiation source

Abstract

A multicommutated flow system for simultaneous determination of iron and chromium in steel alloys by photometry is described. The flow network consisted of an automatic injector and four solenoid valves assembled to form two independent analytical pathways, each one comprising reaction coils and a flow cell. The light source (LED) and detector (photodiode) were attached to the flow cells to form a compact unit. The flow system was microcomputer controlled by Quick BASIC 4.5 software, which carried out all steps of the analytical procedure. The feasibility of the system was proved by the determination of iron and chromium in steel alloys and its accuracy was accessed by comparing results with those obtained by plasma atomic emission spectrometry (ICP-AES). No significant difference at the 95% confidence level was observed.Other profitable features such as low reagent consumption (0.33 mg 1,10-phenantroline and 0.03 mg 1,5-diphenylcarbazide per determination); relative standard deviations (n ¼ 5) of 0.4% for iron and 1.2% for chromium; and an analytical throughput of 160 determinations per h were also achieved. IntroductionThe simultaneous determination of two or more analytes at a time by flow-injection analysis became very attractive after the work proposed by Stewart and Ruzicka (1976) [1]. Afterwards, a large number of flow procedures for multiparameter determination per sample using different detection techniques have been described [2][3][4][5][6].When a multidetermination flow system is implemented using UV-Vis spectrophotometry as the detection technique, the reagents' incompatibility is one difficulty that may appear. This drawback has been surmounted by designing flow systems based on merging zones [2,3] or on sandwich-technique approaches [4]. When analytes compound absorb radiation at the same wavelengths, the flow networks have been designed to determine each analyte at a different time [5]. On the other hand, if chemical species absorb at a different wavelength, simultaneous determination had been carried out, nevertheless equipment with the ability to sweep automatically the wavelengths have been employed [6,7].A light-emitting diode (LED) has been employed as a radiation source in some photometric procedures, its advantages being robustness and low current consumption [8,9]. Nevertheless, depending on the LED type, the width of the emission band can range from 30 to 100 nm [10][11][12][13]. However, by carefully selecting the methods, LEDs can became a good option as a radiation source in flow system when multidetermination is performed with photometric detection employing non-expensive instrumentation [14][15][16][17].The flow network for multicomponent determination can became complex, mainly when the selected spectrophotometric methods required two reagent solutions per analyte [3,18]. This difficulty can be minimized by employing the multicommutation approach that allowed facilities to handle several reagent solutions using a single pumping channel [19,20].In the present work, the intention ...

Instrumentation and Automated Photometric Titration Procedure for Total Acidity Determination in Red Wine Employing a Multicommuted Flow System

“…The volume of the titrant solution injected into the titration chamber was controlled by the time interval elapsed while valve V 3 (Figure 3) was maintained switched ON. It is known that the pumping pulsation pattern could unfavorably affect the precision of the solution volume delivered [20][21][22][23][24]. Consequently, in order to overcome this effect, synchronization steps (St 4 , St 9 ) were carried out prior to switching valve (V 3 ) ON, which was used to deliver the titrant solution.…”

“…The strategies adopted allowed titration endpoint detection; nevertheless, acidity quantification was dependent on an analytical curve, which was derived from measurements obtained by processing a set of standard solutions. This condition was not required when using the multicommuted process in the flow system [20][21][22], thus allowing true titration to be implemented for the first time [23,24], which was done by exploiting a binary search strategy. Using the means provided by binary search strategy, a procedure was developed to determine acidity in silage material, with the ability to compensate the effect caused by sample color [25].…”

Evaluation of a Multicommuted Flow System for PhotometricEnvironmental Measurements

“…They are available in a large variety of wavelengths in the visible and near UV spectrum with a long lifetime, providing simple and inexpensive devices for photometric measurements. In the last decades, LEDs [1] have been used mainly for absorbance [2][3][4][5][6][7][8][9] and fluorescence [10,11] measurements. LEDs have been also employed in polarimetry [12], liquid-chromatography, and capillary electrophoresis [13].…”