Single Calibration Graph Research Articles

Facile formation of surface functionalised α-Fe2O3 nanoparticles and their role in developing dual sensors towards cysteamine quantification

The innovative one step method employed here for the synthesis and surface modification of α-Fe2O3 is equally efficient and viable. The role of surface modification in maximising the output is obvious as terephthalic acid (TPA) crowned Fe2O3 (T-Fe2O3) nanoparticles exhibited better electrochemical properties than bare Fe2O3 when employed as an electrode modifier. It is first time, cysteamine sensors based on T-Fe2O3 nanoparticles were developed and displayed great response in terms of widest linear range, improved selectivity and sensitivity. When combined with glassy carbon electrode (GCE), the sensor achieved broad linear range from 8 µM to 3732 µM which is superior than reported till now. The sensor illustrated with disposable Screen printed electrode (SPE) exhibited widest linear range from 25 to 3900 µM with great linearity in a single calibration graph attributed by the high sensitivity of SPE. The results obtained with SPE lead pathway for designing of portable sensors.

A single calibration graph for the direct determination of ascorbic and dehydroascorbic acids by electrogenerated luminescence based on Ru(bpy)(3)2+ in aqueous solution

Ascorbic (H2A) and dehydroascorbic (DA) acids were for the first time directly determined in a single chromatographic run by means of the tris(2,2'-bipyridine)ruthenium(II) (Ru(bpy)(3)2+) based electrogenerated chemiluminescence (ECL) detection. For the first time, it was demonstrated that DA, a nonelectroactive compound, is ECL active and is responsible for the ECL behavior of H2A. This fact, together with the lack of a DA standard, suggested the use of a calibration graph obtained for H2A, for determining both analytes. The proven ECL activity of DA, together with literature data relative to the standard redox potentials of the different species coming from H2A, led to a reconsideration of the proposed ECL reaction mechanism for H2A. The role of the OH- ion in the reaction mechanism of the two analytes appeared to be crucial. H2A and DA could be separated by a suitable C18-reversed-phase HPLC column using an aqueous 30 mM H3PO4 solution as the mobile phase. The optimal ECL response was achieved by polarizing the working electrode at 1.150 Vvs SCE (standard calomel electrode) (oxidation diffusion limiting potential for both H2A and Ru(bpy)(3)2+). The Ru(bpy)(3)2+ solution, at pH 10 for carbonate buffer, was mixed to the eluent solution in a postcolumn system, obtaining, still at pH 10, the final 0.25 mM Ru(bpy)(3)2+ concentration. The detection limit found for the two analytes was 1 x 10(-7) M. The method was successfully applied to the determination of the analytes in a commercially available orange fruit juice.

Use of a single calibration graph for the determination of major elements in geological materials by laser ablation inductively coupled plasma atomic emission spectrometry with added internal standards

The possibility of internal standardisation in laser ablation inductively coupled plasma atomic emission spectrometry (LA-ICP-AES) of geological materials by added Sc2O3 and Y2O3 has been examined to cover the wide range of concentrations of major and minor constituents both in silicate rocks and limestones. A Nd:YAG laser (355 nm, 10 Hz, 10 mJ per shot) was used for the ablation of discs obtained by fusion of the mixture of samples and oxides of Sc and Y with lithium tetraborate. The flux/sample ratio was in the range from 6 to 10. The contents of analytes were within the concentration range from hundredths to tens of percentage. The trace elements copper and nickel were studied, too. An ICP emission spectrometer OPTIMA 3000 DV was used for the measurement of Si, Al, Ca, Mg, Sr, Ba. Fe, Ti, Mn, Ni, Cu. Na and K analyte lines and Y and Sc reference lines in the axial observation mode. The long-term and the short-term repeatability of measurement were improved by employing scandium or yttrium internal references lines for the above analytes from 6% to 1.5% of RSD and from 2.4% to 1.0% of RSD, respectively. The correlation of signals with concentrations was improved in terms of the correlation coefficient r from 0.90-0.97 to 0.98-0.998 and the relative uncertainty on the centroid of concentrations was improved 2-3 times. A single calibration graph covering the concentration range both in silicates and carbonates is possible for each of elements. as the matrix effects are compensated for by internal standards and the excess of Li2B4O7.

Quantitative Determination of Swertiamarin and Gentiopicroside in Centaurium erythrea andC. turcicum by Densitometry

Swertiamarin and gentiopicroside were quantified simultaneously using thin layer chromatography (silica gel) with densitometry (240 nm). The single calibration graph was linear in the interval 1.0–16.0 μg in the presence of an external standard. The standard deviation did not exceed 5% and the relative error varied in the range 0.5–6%. The procedure was applied to determine these iridoids in ten samples of Centaurium erythrea and C. turcicum from various regions in Bulgaria.

Approach to the Solution of Carbon Content Influence in the X-Ray Fluorescence Analysis of Ferromanganese

This work aimed to evaluate the influence of carbon on CrKα intensity measurements from ferromanganese test samples. Sample preparation was carried out by melting the ferroalloy, diluted with iron in proportions from 13 + 27 to 17 + 23, in an open induction furnace. Two chemically standardized ferromanganeses, one with a low carbon content (<0.5%) and the other with a high carbon content (<6%), were used to prepare the test samples. Samples for calibration were obtained from different iron dilution proportions of both materials, with two calibration graphs resulting. The influence of carbon was evaluated by measuring samples prepared with a constant manganese content and with variable carbon contents, with suitable mixing of the two aforementioned ferromanganeses. The correlation C% → IMnKα was established and the correction factor was calculated. On application of the carbon correction factor, a single calibration graph is obtained, and the calculated Mn concentrations for all the samples prepared with the same Mn content present an RSD value of 0.34%. The F-test was applied in order to evaluate the effects due to sample preparation, and to the variability throughout the analysis, on the total variance. Accuracy was tested by analyzing four ferromanganese Reference Materials: CRM 583-1; BCS 208/2; BCS 280/2, and IRSID 502-1.

Determination of dissolved copper, nickel and cadmium in natural waters by high-performance liquid chromatography

A novel technique has been developed to determine dissolved copper, nickel and cadmium in natural waters, and in particular estuarine and sea-waters, by using high-performance liquid chromatography (HPLC). The main performance criteria were that the method was sensitive, reproducible and interference free. This has been achieved by developing a system whereby the trace metals were initially preconcentrated on a bonded-silica (C2) guard column coated with an ammonium pyrrolidin-1-yldithioformate (ammonium pyrrolidine dithiocarbamate)–cetyltrimethylammonium bromide ion pair. This selectively removed the trace metals from the sample matrix, thereby excluding potential interferents. After preconcentration the metal–dithiocarbamate complexes were flushed with a modified organic mobile phase from the pre-column onto a C18 reversed-phase analytical column for separation. The complexes were detected by means of a variable-wavelength ultraviolet detector. Performance data were obtained, yielding limits of detecton of better than 0.5 µg l–1 for copper, cadmium and nickel, for 10 ml sample volumes. The precision was better than 5% relative standard deviation for concentrations in the range 0.5–10 µg l–1. Once optimized the technique was evaluated by analysing estuarine samples with a variety of salinities and comparing the data with those obtained by an accepted reliable method: chelation–solvent extraction–atomic absorption spectrometry. Results showed that there was no significant difference in the data obtained by the two methods. A single calibration graph could be used for samples of all salinities by using the HPLC method.

Determination of sulphur- and chlorine-containing compounds using capillary gas chromatography and atomic emission detection

The potential of universal calibration using capillary gas chromatography combined with atomic emission detection was evaluated for several chlorine- and sulphur-containing compounds of environmental interest. The elemental responses obtained for C, H, Cl and S were found to be affected by the molecular structure. Rapid determination of several analytes was accomplished using a single calibration graph based on one randomly selected reference compound, but 10–30% errors relative to the actual concentrations were observed in several instances. The results were significantly improved by using reference compounds with structures similar to those of the analytes of interest. the practical utility of universal calibration is illustrated by the determination of pesticides in stomach oil deposits from birds living in Antarctica.

Column liquid chromatographic determination of saccharides with a single calibration graph using post-column enzyme reactors and coulometric detection

Immobilized enzymes were used as column reactors in a column liquid chromatographic system for the specific detection of the saccharides stachyose, raffinose and sucrose. Invertase and fructose dehydrogenase (FDH) were immobilized onto poly(vinyl alcohol) beads and porous glass beads, respectively. The oligosaccharides were separated on a cation-exchange resin column with water as the mobile phase. Invertase was capable of quantitatively hydrolysing the oligosaccharides to fructose, which reacts with the hexacyanoferrate(III) ion in the presence of FDH. The hexacyanoferrate(II) ion produced was monitored coulometrically. A single calibration graph for fructose based on the peak area was used to determine each oligosaccharide. The limits of detection for stachyose, raffinose and sucrose were 27, 5 and 2 ng (in a 50 μl sample), respectively.

Direct determination of lead in soils and sediments by atomic absorption spectrometry employing a graphite capsule in flame atomiser

The construction of a graphite capsule in flame atomiser is described for the direct atomic absorption spectrometric determination of lead in soils, sediments and bone ash. A single calibration graph can be used for different materials, prepared by atomisation of different masses of various standard reference materials. The absolute limit of detection of lead at the 283.3-nm line was 2 × 10–3µg and the reproducibility was 8–20%(RSD). The effects of the physical properties of the graphite and the effect of the heating power upon the lead absorbance-time profiles were investigated. These parameters were found to have a direct influence on the sensitivity, accuracy and precision of the measurements.

A quotient method of evaluation for the catalytic-kinetic difference method

A new variant of the catalytic-kinetic difference method is presented.The course of a catalyzed reaction, which proceeds simultaneously in two mixtures containing different catalyst concentrations, is followed by photometry. The maximum of the difference in transmittance being measured is a function of the quotient of the catalyst concentrations in the two mixtures and is independent of the rate constant. With this method of evaluation, a single calibration graph suffices for the determination of two different catalysts activating the same reaction. The maximum of the difference in transmittance is independent of temperature. The reaction between cerium(IV) and arsenic(III) catalyzed by iodide or osmium serves as an example. Two further examples are mentioned.

Rapid determination of molybdenum in alloy steels by atomic-absorption spectroscopy in a nitrous oxide-acetylene flame

Atomic-absorption spectroscopy at 3132 A in a nitrous oxide-acetylene flame provides a rapid and precise determination of molybdenum in low and high alloy steels. The steel sample (1 g) is dissolved in hydrochloric and nitric acids which are then diluted to volume and sprayed directly into the flame. The observed absorbance is compared with that obtained from a calibration graph prepared from solutions containing known amounts of molybdenum and about the same amount of iron as the steel sample. The method proposed here operates in the range down to 0·2 per cent. of molybdenum and is free from interference from other alloying elements, including tungsten, in steel. The proposed method can be applied to any type of steel by using a single calibration graph.