Raluca I. Stefan

Sequential injection spectrophotometric determination of iron as Fe(II) in multi-vitamin preparations using 1,10-phenanthroline as complexing agent.

A sequential injection analysis (SIA) system is proposed for the determination of iron (II). Fe(II) was determined by SIA based on the reaction between 1,10-phenanthroline and iron (II), yielding an orange-red colour complex with absorption maximum at 512nm. The method involved aspiration of 187mul sample/standard zone followed by a zone of a reagent solution containing 140mul of 7.8 x 10(-4)moll(-1) 1,10-phenanthroline into a carrier stream to be stacked inside a holding coil and flow reversed through a reaction coil to a detector. The optimum condition was evaluated and the calibration curve is linear over a range of 0.25 to 5.0mgl(-1) of Fe(II) with detection limit of 18mugl(-1). A sample throughput of 40h(-1) was established. This technique is found to be simple, accurate, reproducible and sensitive. The proposed method was successfully applied for the determination of total iron as Fe(II) in pharmaceutical products (multi-vitamin tablets) and is especially useful for the determination of iron (II) in tablets with lower iron (II) contents. The results were found to be in good agreement with the results obtained by manual UV/Vis spectrophotometry and flame atomic absorption spectrometry (FAAS) and with claimed values by the manufacturers.

Chemical speciation by sequential injection analysis: an overview

The simplicity of the sequential injection (SIA) manifold and its low need for maintenance makes it an ideal tool in speciation. As miniaturization and reduction of reagent consumption are also ultimate goals in chemical sensing, it is useful to review the use of combined injection and programmed flow as a central issue in designing SIA systems with chemical sensors and structurally simplified chemical analysers. This overview gives an insight into the current state, analytical scope and performance characteristics of sequential injection systems as analytical tools for speciation. The suitability of SIA for speciation analysis is illustrated by the methods used in the conduits of sequential injection systems for the chemical conversion of different chemical forms into detectable chemical species. Configurations of the basic sequential injection speciation analysis systems were designed around a multi-syringe-time-based-injection system with one detector, direct and indirect speciation of different forms using a single detector including diode array detection and direct speciation of different forms using multiple detection. Examples showing the use of SIA for the simultaneous determination or speciation of metal ions, inorganic anions and organic compounds are given with some recent results from our research groups.

Speciation of Mn(II) and Mn(VII) by on-line spectrophotometric sequential injection analysis

An on-line sequential injection analysis system with spectrophotometric detection using 4-(2-pyridylazo) resorcinol as reagent is proposed for the speciation of Mn(II) and Mn(VII). The sampling frequency is 30 determinations per hour. The linear range for Mn(II) is 0.020–0.500 mg/l with a detection limit of 0.005 mg/l and for total Mn 0.025–0.550 mg/l with a detection limit of 0.008 mg/l. The % RSD is 0.27 and 0.34 for Mn(II) and Mn(VII), respectively (n = 10). Chemical masking of Fe and Al was achieved by on-line addition of a 0.1 mol/l NaF solution. The proposed system yielded results that compare very well with standard methods.

Spectrophotometric determination of bromate by sequential injection analysis

A simple and rapid on-line spectrophotometric method for the determination of bromate is proposed. The method is based on the reaction of bromate and 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (5-bromo-PADAP) with SCN(-), a red complex is formed and monitored at 550nm. The linear range found is between 0.18 and 3.00mgl(-1) with a detection limit of 0.15mgl(-1). The sampling rate was calculated to be 45 samples per hour. The proposed method has a precision of less than 0.8%.

Simultaneous flow injection determination of calcium and fluoride in natural and borehole water with conventional ion-selective electrodes in series

An on-line automated system for the simultaneous flow injection determination of calcium and fluoride in natural and borehole water with conventional calcium-selective and fluoride-selective membrane electrodes as sensors in series is described. Samples (30 mul) are injected into a TISAB II (pH=5.50) carrier solution as an ionic strength adjustment buffer. The sample-buffer zone formed is first channeled to a fluoride-selective membrane electrode and then via the calcium-selective membrane electrode to the reference electrodes. The system is suitable for the simultaneous on-site monitoring of calcium (linear range 10(-5)-10(-2) mol l(-1) detection limit 1.94x10(-6) mol l(-1) recovery 99.22%, RSD<0.5%) and fluoride (linear range 10(-5)-10(-2) mol l(-1) detection limit 4.83x10(-6) mol l(-1) recovery 98.63%, RSD=0.3%) at a sampling rate of 60 samples h(-1).

A New Construction for Potentiometric, Enantioselective Membrane Electrodes, and Use for L-Proline Assay.

Abstract A novel potentiometric, enantioselective membrane electrode based on graphite paste (graphite powder and paraffin oil) has been constructed. The graphite paste is impregnated with 2-hydroxy-3-trimethylamoniopropyl-β-cyclodextrin (as chloride salt) solution, 10−3 mol/L. The potentiometric, enantioselective membrane electrode can be used reliably for L- proline assay with the chronopotentiometry (zero current) technique, in the 5.0 x 10−5 - 1.5 x 10−1 mol/L concentration range (detection limit 1.0 x 10−5 mol/L), with an average recovery of 99.90% (RSD = 0.12%). The response characteristics of the enantioselective, potentiometric membrane electrode were also determined for D-proline. The surface of the electrode can be regenerated by simple polishing, obtaining a fresh surface ready to be used in a new assay.

Determination of the total acidity in soft drinks using potentiometric sequential injection titration

A potentiometric SI titration system for the determination of total acidity in soft drinks is proposed. The concept is based on the aspiration of the acid soft drink sample between two base zones into a holding coil with the volume of the first base zone twice to that of the second one and channelled by flow reversal through a reaction coil to a potentiometric sensor. A solution of 0.1 mol l(-1) sodium chloride is used as ionic strength adjustment buffer in the carrier stream. The system has been applied to the analysis of some South African soft drinks having a total acidity level of about 0.2-0.3% (w/v). The method has a sample frequency of 45 samples per h with a linear range of 0.1 and 0.6% (w/v). It is easy to use, fully computerised, and gives the results that are comparable to both automated batch titration and manual titration.

Design and Use of Electrochemical Sensors in Enantioselective High Throughput Screening of Drugs. A Minireview

The importance of reliable detection systems for enantiomeric assays increases with the necessity of high throughput screening analysis of raw materials for the pharmaceutical industry. The utilization of electrochemical sensors in enantioselective analysis is an accurate and precise alternative to chromatographic techniques. The reliability of the response characteristics as well as of the analytical information obtained by using electrochemical sensors is strictly correlated with the design of the sensors. The designs evaluated for sensors have been based on PVC, imprinting polymers and carbon paste matrices. Among these, carbon paste sensors have been the most reliable and have been utilized for the construction of potentiometric, enantioselective membrane electrodes as well as for amperometric biosensors, and immunosensors. There are two ways to use the electrochemical sensors in enantioselective screening analysis: selective binding and catalyst selectivity. A molecule with a special chemical architecture is required for selective binding: a lock for a key. The high reliability of analytical information obtained using these sensors has made possible the automation of potentiometric and amperometric techniques by integration of enantioselective sensors as detectors in flow injection analysis and sequential injection analysis techniques.

Information essential for characterizing a flow-based analytical system (IUPAC Technical Report)

Essential aspects for characterization of a flow-based analytical procedure or system are discussed in order to permit the composition of a checklist that will lead to a protocol for reporting results and systems in flow analysis. Aspects more related to chromatographic procedures are not considered. The intent is to present normalized proposals in the field of flow analysis for practitioners and developers.

Spectrophotometric determination of magnesium in pharmaceutical preparations by cost-effective sequential injection analysis

A simple and rapid, inexpensive spectrophotometric method was proposed for magnesium assay in pharmaceutical preparations by sequential injection analysis (SIA). The method is based on the reaction between o-cresolphthalein complexone (CPC) and Mg(II) in alkaline media, yielding a pink colored complex with absorption maximum at 570nm. Since the formation constant between Ca-CPC and Mg-CPC is similar, initially a sample/standard solution was aspirated into the holding coil followed by a mixture of masking-buffer solutions. This was done because masking of calcium should be accomplished before Mg-CPC complexation. Then the reagent was introduced into the reaction coil to produce a colored complex, which is measured spectrophotometrically at 570nm. In this way the interference of calcium was reduced. Furthermore, all the parameters that affect the reaction were evaluated. The calibration curve is linear over a range of 0-20mgl(-1) of Mg(II) with a detection limit of 0.24mgl(-1). A sample throughput of 80 samples per hour and relative standard deviation <2.0% were achieved. The proposed method was successfully applied for the assay of magnesium in three different compositions of pharmaceutical preparations (tablets). The results were found to be in good agreement with the manual flame atomic absorption spectrophotometry (FAAS) and UV-Vis spectrophotometry methods and with the claimed values by the manufactures. The t-test shows no significant difference at 95% confidence level.