A comparative study of laser induced breakdown spectroscopy analysis for element concentrations in aluminum alloy using artificial neural networks and calibration methods

A comparative study of analysis methods (traditional calibration method and artificial neural networks (ANN) prediction method) for laser induced breakdown spectroscopy (LIBS) data of different Al alloy samples was performed. In the calibration method, the intensity of the analyte lines obtained from different samples are plotted against their concentration to form calibration curves for different elements from which the concentrations of unknown elements were deduced by comparing its LIBS signal with the calibration curves. Using ANN, an artificial neural network model is trained with a set of input data of known composition samples. The trained neural network is then used to predict the elemental concentration from the test spectra. The present results reveal that artificial neural networks are capable of predicting values better than traditional method in most cases.     

Einsatz von rechenanlagen in der emissionsspektrochemie für aufstellung,bewertung und linearisierung der analytischen eichgeradenThe use of computers in emission spectrometry for the establishment,evaluation and linearization of analytical calibration curves

(The use of computers in emission spectrometry for the establishment, evaluation and linearization of analytical calibration curves)The problems of establishing optimum linear calibration lines for atomic emission spectrometry are discussed, with emphasis on use of photographic recording techniques. The calculation procedure, which is based on the least-squares method, generates additional statistical values which permit the linearity to be checked. As the desired linearity is not always achieved at the first attempt, the process is repeated after unreliable input data have been removed.     

Non-linear and non-constant variance calibration curves in analysis of volatile organic compounds for testing of water by the purge-and-trap method coupled with gas chromatography/mass spectrometry

Currently used operating conditions for analysing volatile organic compounds (VOCs) by purge-and-trap gas chromatography/mass spectrometry (GC/MS) produced non-linear calibration curves with non-uniform variance. Second-order polynomial models therefore had to be used in weighted regression analysis of measurements of replicates spiked at various concentrations. A transparent procedure based on a reported method of very low computational complexity allowed calculation of the parameters of second-order models, confidence bands of regression lines, prediction bands, and confidence intervals of discriminated analyte concentrations. Tolerance intervals were introduced for this last purpose. Critical, detection and quantification levels drawn from the calibration curves were compared with those calculated by the EPA method.     

An expression of uncertainty in calibration using stepwise or separate dilution of a stock solution.

The traditional method for linear calibration can estimate the confidence intervals of calibration lines from a set of experimental data for a single calibration line. However, the following situations, often encountered in laboratories, are out of reach of the method, since the concentrations of the standard solutions are not independent of each other: (A) a standard solution is diluted from a more concentrated one in a stepwise way (stepwise dilution); (B) every standard solution for a calibration experiment is prepared from a stock solution, but the stock solution is newly prepared for each calibration (separate dilution with the variable concentration of the stock solution). This paper puts forward a theory to calculate the confidence intervals of calibration lines in the above situations. Analyses made up of sample weighing, dilution, HPLC measurement and calibration with the linear least-squares fitting are taken as examples. The proposed theory is numerically compared to the traditional method.     

Selection of a Representative Matrix for Calibration in Multianalyte Determination of Pesticides in Vegetables by Liquid Chromatography-Electrospray Tandem Mass Spectrometry

An analytical method for determining residues of twenty pesticides by liquid chromatography (LC) coupled to electrospray ionisation (ESI) tandem mass spectrometry (MS-MS) in eight commodities, cucumber, tomato, pepper, green bean, eggplant, zucchini, melon and watermelon, has been developed and validated. On one hand, calibration curves prepared in solvent were compared with calibration curves prepared in a blank matrix extract of each target matrix. On the other hand, calibration curves and recoveries for each commodity were compared. Cucumber was selected as potential reference matrix for the target vegetables.     

Application of off-line size-exclusion chromatographic fractionation-matrix assisted laser desorption ionization time of flight mass spectrometry for proanthocyanidin characterization

In this work, we wanted to devise a reliable method to characterize polymerized forms of tannins, their structural information and mass distribution. Size-exclusion chromatography (SEC) is a chromatographic technique used to determine molecular mass (weight) distributions of polymers. One important step in the data treatment is the modeling of the calibration curves. Polystyrenes (PS) are standards usually used because no commercial procyanidin (PC) standards are available. An off-line coupling of SEC and MALDI was carried out to measure differences between polystyrenes and procyanidins. Thus, a new calibration curve was established; from 1000 to 8000 Da, there is a good correlation between the MALDI and PS calibration curves, in this field the PS calibration is correct and enables true mass determination. For masses above 8000 Da, PS calibration overestimates the real molecular weight of PC, overestimation of 53%. And for masses below 1000 Da, PS calibration underestimates their real molecular weight (10-15%). This means that to truly characterize PC, calibration based on PC standards is required.     

Efficiency calibration curves in gamma-ray spectrometry for samples with different matrices

A new method for determination of efficiency calibration curves in -spectrometry is described. From the calibration curves for a bulky sample and a point source, the curves for sources with the same geometrical parameters as the bulky sample but different attenuation coefficients may be calculated. The method was tested at an energy of 88 keV on a set of samples with attenuation coefficients between 0.2 and 2 cm² g^–1. The conditions where the new method is useful are discussed.     

Development of a methodology for the determination of americium and thorium by ICP-AES and their inter-element effect

Due to the scarcity of good quality uranium resources, the growth of nuclear technology in India is dependent on the utilization of the vast thorium resources. Therefore, Advance Heavy Water Reactor is going to acquire significant role in the scenario of Indian nuclear technology, where (Th, Pu)O₂ will be utilized as fuel in the outermost ring of the reactor core. This will lead to a complex matrix containing thorium as well as americium, which is formed due to β- decay of plutonium. The amount of americium is dependent on the burn up and the storage time of the Pu based fuels. In the present case, attempt was made to develop a method for the determination of americium as well as thorium by ICP-AES. Two emission lines of americium were identified and calibration curves were established for determination of americium. Though the detection limit of 283.236 nm line (5 ng mL⁻¹) of americium was found to be better than that of 408.930 nm (11 ng mL⁻¹), the former line is significantly interfered by large amount of thorium. Three analytical lines (i.e. 283.242, 283.730 and 401.913 nm) of thorium were identified and calibration curves were established along with their detection limits. It was observed that 283.242 and 401.913 nm line are having similar detection limits (18 and 13 ng mL⁻¹, respectively) which are better than that of 283.730 nm (60 ng mL⁻¹). This can be attributed to the high background of 283.273 nm channel of thorium. The spectral interference study revealed that even small amount of americium has significant contribution on 283.242 nm channel of thorium while the other two channels remain practically unaffected. Considering both these facts, spectral interference and analytical performance (detection limits and sensitivity), it was concluded that 401.913 nm line is the best analytical line out of the three lines for determination of thorium in presence of americium.     

ICP—AES分析的线性回归校准曲线

本文对ICP-AES分析中2种线性回归方法的校准曲线作了比较和讨论。对大多数元素而言,用加权法得到的校准曲线的斜率比不加权校准曲线的斜率略大,减小3校准曲线在低浓度部分的弯曲,曲线明显优于不加权校准曲线。将2种方法得到的校准曲线进行比较时,应将剩余标准偏差(或剩余变差平方和)及曲线截距等加以综合考虑。用含零标的标准系列制作校准曲线可使曲线的截距更接近原点,有利于提高在低浓度部分校准分析的准确性。     

A new electrochemical method for trace water determination in methanol

A new electrochemical method for the determination of trace water in methanol has been developed. This method is based on the effect, that a minor change in the water content affects the value of conductivity measured for dissolved in the solutions electrolyte. The conductivity measurements were performed for four inorganic salts, i.e. NaCl, KCl, RbCl, and CsCl in solutions with different amounts of water traces in methanol and the calibration curves for three of them were determined. With the exception of cesium chloride the high values of correlation coefficients for the regression lines as well as low limits of detection were achieved in all cases which indicates that this method is a useful tool for the determination of the trace amounts of water in methanol.     

A novel method for measuring intracellular pH: effect of neutron irradiation on pHi of transformed cells.

A new flow cytometric method was developed for measuring the intracellular pH (pHi) of mammalian cells using a fluorescent pH indicator dye 2',7-bis-(2-carboxyethyl)-5(and-6)-carboxyfluorescein (BCECF). Emission intensities (or their ratios) measured from BCECF-loaded cells can be converted into absolute pHi values using appropriate calibration curves. By comparison of several possible measuring and data evaluation procedures a double-ratio method was suggested as the most advantageous protocol to yield reliable intracellular pH data. This method allows pHi to be determined on a cell-by-cell basis corrected for cell volume and change in geometry of input-output optics of the flow cytometer. Our method applies a standard calibration curve and does not necessitate its reconstruction for each new set of measurements. Cells of the OKT-4 and OKT-8 hybridoma lines were exposed to neutron irradiation of different doses. Irradiated cells underwent a biphasic alkalinization; an instantaneous effect detected within 1.5 h was found to be intensified over 24 h. For the interpretation of data we suggest that the increase in cytoplasmic pH following neutron treatment is evoked by two mechanisms.     

Spectrophotometric determination of trace water in organic solvents with a near infrared absorbing dye

A spectrophotometric method for the determination of trace water in organic solvents using a near infrared absorbing dye has been developed. This method is based on the effect that a minor change in polarity of the solvent caused by trace water content determines the extent of aggregation of a near-infrared dye monomer. This change can be detected spectrophotometrically. The calibration curves for methanol, ethanol, and isopropanol were determined. This method has the highest sensitivity (em = 16.73 unit) for water in isopropanol and the lowest sensitivity (em = 2.806 unit) for water in methanol. The correlation coefficient (R)(2) values for the regression lines ranges from 0.990-0.998. The linear range of the method for ethanol is 0.001-0.5%, for isopropanol is 0.001-0.1%, and for methanol is 0.001-1.0%. The limit of detection for ethanol, isopropanol, and methanol are 0.0001, 0.0001, and 0.005% water, respectively. The developed method is sensitive, simple and easy to operate, and the cost of analysis is low.     

Optimization of analytical methods based on non-linear asymptotic calibration graphs: Effect of the Time of Hydrolysis on the Enzymatic Determination of Pyridostigmine

A method for enzymatic determination of pyridostigmine is considered. The nonlinear calibration graphs obtained are functions of nine independent variables. The optimization of the curves is discussed, with the relative error as the criterion of optimization. A graphical method is suggested, which allows easy determination of the relative error, of the best concentration for sampling, and of the limit of response. A shortcut method of optimization for asymptotic calibration curves is suggested, and illustrated by optimizing the time of hydrolysis of acetylcholine by cholinesterase. Some determinations of pyridostigmine in water, urine and bovine serum are presented, employing the suggested method.     

Prozentuales und logarithmisches Verfahren zur Berechnung von Eichkurven

Two methods, one on the basis of percent and another on the basis of logarithm, for the calculation of calibration curves are reported. By these procedures the lower values of the calibration curves are represented more strongly than by the normal method of the least sum of error squares. Instead of the coefficient of correlation a coefficient of quality is defined, to characterize the quality of the calibration curves. The coefficient of quality is calculated from the percentage deviations of the calculated x-values in the way of the standard deviation.     

Use of tandem calibration for analyzing steels and alloys by inductively coupled plasma atomic emission spectrometry

A method is proposed for plotting calibration graphs by reference analyte solutions (tandem calibration) for the analysis of steels and alloys by inductively coupled plasma atomic emission spectrometry (ICP-AES) with spark ablation. The use of spectral lines of analytes and an internal standard with similar values of sums of ionization and excitation energy ensures an excellent repeatability and accuracy of the results of analysis using tandem calibration. A nebulizer chamber for the simultaneous introduction of solutions and solid sample aerosols into inductively coupled plasma (ICP) is designed. The optimal parameters of the introduction of sample aerosols and a method of plasma observation are chosen; the requirements for the choice of the analytical lines of analytes are proposed.     

Vergleich von Röntgen- und optischer Emissionsspektralanalyse mit der Glimmlampe bei Anwendung auf AgCu-Binärlegierungen

For the binary eutectic system AgCu, calibration curves are established over a large concentration range (0.3–99.7%). These calibration curves are bent in X-ray spectrochemical analysis as well as in optical emission spectral analysis with a glow discharge lamp as a result of matrix effects. Linearization is achieved by the “method of binary ratios.” By making use of this simple calibration method, it is possible to obtain results with high precision and accuracy: the relative S. D. depends on concentration and is approximately 0.05(1?c). Both methods of spectrochemical analysis are therefore suitable (at least for binary systems) for the determination of major and minor constituents.     

A review of the work of the German Society for Thermal Analysis (GEFTA) on standardization

Working groups of the German Society for Thermal Analysis (GEFTA) are active in the fields of calibration of dynamic calorimeters (DSC), calibration of dilatometers, evaluation of DSC curves and standard samples for dynamic mechanical analysis (DMA). Two papers on the temperature calibration of DSC instruments have been published, which recommend a calibration procedure and calibration materials. Another recommendation on caloric calibration is in preparation. Certified calibration samples for dilatometers are available for the temperature range ?190° to 700°C.     

Development of a method for the determination of ibafloxacin in plasma by HPLC with flourescence detection and its application to a pharmacokinetic study

A simple, rapid, and sensitive high-performance liquid chromatographic method is developed for the determination of ibafloxacin in rabbit plasma. Plasma proteins are precipitated with acetonitrile, and after extraction with methylene chloride followed by desecation, ibafloxacin is determined by reversed-phase chromatography with fluorescence detection exciting at 330 nm and emission at 368 nm. Peaks corresponding to ibafloxacin and the internal standard (salycilic acid) are obtained at 9.8 and 5.2 min, respectively. The method is validated for a limit of quantitation of 10 ng/mL. The intraday relative standard deviation ranges from 4.78-7.15%, and the interday precision ranges from 1.32-4.03%. The method shows linearity for the two calibration curves used (10-100 ng/mL and 100-2000 ng/mL). The procedure described is applied successfully to a pharmacokinetics study of ibafloxacin in rabbits.     

An initial-rate potentiometric method for the determination of uric acid using a fluoride ion-selective electrode

The principle of a general potentiometric method based on Emerson-Trinder reaction for the assay of various hydrogen peroxide generating systems is reported. Emerson-Trinder reaction, habitually employed as a spectrophotometric indicator reaction, is exploited in this method as a potentiometric indicator reaction. This method is based on the detection of F⁻ ions, liberated from the oxidation of a fluorophenol compound used as hydrogen-donor in Emerson-Trinder reaction, by a fluoride ion-selective electrode. The ability and usefulness of this method are illustrated by an initial-rate potentiometric determination of uric acid in aqueous and human serum samples, for which, initial-rate reaction progress curves, linear calibration curve, within-day precisions, upper and lower detection limits, and also its analytical recovery were reported.     

Calibration and curve fitting for extended range AAS

Several curve fitting methods, including linear, quadratic, and rational least squares fits and linear, cubic spline, and Stineman interpolations, are evaluated for their ability to fit highly nonlinear atomic absorption analytical calibration curves. In addition, the number of standards required to effectively calibrate a dynamic range covering 3 orders of magnitude of concentration is determined. Finally, the concentration ranges providing minimum relative concentration precision (RCP) are identified and the slopes of the calibration curves in these ranges are noted. Concentration ranges of minimum RCP also provide minimum curve fitting errors and generally have log-log slopes of approximately 0.5 indicating that linearity alone is not a sufficient criterion for choosing suitable calibration and curve fitting concentration ranges.