Showing papers on "Calibration curve published in 1981"

A rapid electrothermal atomic absorption spectrophotometric method for cadmium and lead in human whole blood.

Abstract: A rapid graphite-furnace atomic absorption spectrophotometric procedure is described for determining cadmium and lead in heparinized human whole blood. A known aliquot of the blood sample is diluted fivefold with an aqueous solution composed of 5 g each of diammonium hydrogen phosphate and Triton X-100 per liter, the solution is vigorously agitated, and a 10-microL aliquot is injected into a pyrocoated graphite tube under optimized instrumental conditions. Values for Cd and Pb in the sample are obtained by direct comparison to linear working curves prepared from aqueous standards of the metals in the diammonium hydrogen phosphate-Triton medium; there is no need to use the method of standard addition or matrix-matched calibration curves. Also, the method is free of matrix effects. At least 30 samples can be analyzed per hour. The rapidity, simplicity, and sensitivity of the method make it attractive as a screening technique for routine environmental surveillance involving large throughput of samples.

Water Activity Determination with the Proximity Equilibration Cell

Abstract: The objective was to develop a new method for water activity (aw) determination. A reference material (circle of filter paper) of known sorption isotherm was equilibrated to the sample. Sorption isotherm data for this paper were obtained by equilibrating for 24 hr to each of six salt slushes; these data were described well by a linear equation relating moisture content to log (1 − aw). This equation served as the calibration curve. Results showed that this new method (1) does not require a vacuum, (2) gives a linear calibration equation, (3) is applicable over the aw range from 0.40–0.98, and (4) with minor replication can bring the standard deviation of the mean to less than ± 0.01.

Automatic calibration system for ultrasonic inspection

Abstract: A method and apparatus is disclosed for calibrating an ultrasonic inspection system having a plurality of transducers (12a, 12b, 12c) coupled by a common amplifier (16) to a distance-amplitude correction (D-AC) circuit comprised of a multiplying digital-to-analog converter (26') which receives, as a function of the transit time of an ultrasonic signal measured by a clock counter (34), a D-AC correction stored in a look-up table in a random access memory (24'). The D-AC correction function stored in the look-up table for each transducer is the inverse of a return signal response curve determined by measuring the peak amplitude of return signals from calibration holes at known depths in a test block (10) while in a calibrate mode, i.e., with a switch (SW) in a state to bypass the MDAC. An equation of a curve that best fits the peak measurements is then found by a digital computer (20) and used to determine the values of points along a curve superimposed on the response curve, except at near field where the calibration system is provided with truncation for near-field effects. Inverse values of these points are then stored in the look-up table for use as correction factors applied to the amplitudes of return signals during an inspection mode of operation. In that way, all return signals from flaws of the same size are caused to have the same amplitude regardless of depth, without the need for utilizing tedious and time-consuming manual calibration methods.

Calibration and Long-Term Stability of a PIXE Set-Up

Abstract: A general mass calibration procedure of a PIXE set-up is described. As an example, the results of the calibration of the PIXE set-up in Lund are given. For the calibration commercially available standards were used. The parameters of a physical model were adjusted to fit a calibration curve. To decrease errors due to inhomogeneities of the standard foils, the average from four different pieces of each foil was taken. The accuracy of the calibrated system in Lund is estimated to be better than 5% for individual elements and still less for ratios of adjacent elements. For long-term quality control of the results, a special sample has been designed. This consists of a thick silver plate with a small copper spot in the centre. It is very sensitive to small changes in a PIXE set-up. By analysing this sample periodically, mistakes in the arrangement are promptly detected-a feature which is much appreciated in a mixed research, development and routine analysis laboratory. Also a measure of the long-term stability is obtained. For the Lund system, the long-term stability is 2.5% for a homogeneous sample and 4% for a small (inhomogeneous) sample.

Size Exclusion Chromatography (SEC) of Complex Polymers - Generalized Analytical Corrections for Imperfect Resolution

Abstract: Herein is reported generalized analytical solutions which permit correction for imperfect resolution when the molecular weight calibration curve is nonlinear and the variance of single-species chromatograms changes significantly with molecular size of the polymer solute. Two kinds of generalized analytical solutions have been obtained. One is a solution of Tung's integral equation for the corrected chromatogram or the molecular weight distribution and the other is a solution for the corrected molecular weight averages of the whole polymer. Also discussed is the use of local corrections for imperfect resolution across the chromatogram with detectors such as the low angle laser light scattering spectrophotometer (LALLS) when used with micro and macropackings.

Peculiarities of polyacrylamide analysis by aqueous GPC

Abstract: Various commercially available stationary phases of gel permeation chromatography (GPC) were tested to determine their effectiveness in aqueous exclusion chromatography. It was found that controlled pore glass (GPG) is the most suitable material for the separation of polyacrylamides and poly(acry1amide-co-sodium acrylate), dextrans, and poly(sodium styrene–sulfonates) in 0.1M aqueous Na2S04 solutions of ionic strength 0.3. A calibration curve was established by using broad molecular weight distribution polyacrylamide standards in a trial and error procedure. To avoid artificial oscillations on the evaluated distribution curves a cubic B-spline representation of the calibration curve was used instead of the conventional polynomials. By applying this system the solution instability of polyacrylamides was observed by GPC and is discussed because of its general importance to the applicability of indirect molecular weight determination methods for polyacrylamides. The effectiveness of aqueous GPC was demonstrated in an evaluation of thermal degradation measurements of polyacrylamides. Finally, the feasibility of universal calibration of aqueous GPC by means of poly(sodium styrene–sulfonates) was investigated. It is apparent that in spite of some problems concerning adsorption of the polymer universal calibration is a successful tool for calibrating aqueous GPC.

Effect of experimental design on assay calibration

Abstract: Criteria are developed for the maximisation of the amount of information available from an analytical calibration graph. For linear calibration graphs, the methods involve replicate determinations of standards at two points, which are chosen so that they occur at the extremes of the calibration range. The increase in precision that can be obtained by using an optimised design can be considerable, particularly when the variance in the assay errors is not constant. The methods described can be extended readily to non-linear calibration graphs.

Formulation of analytical procedures involving flame atomic-absorption spectrometry

Abstract: Different atomic-absorption spectrometers may vary significantly in sensitivity, precision and shape of the analytical calibration graph, even when the instrument is properly adjusted. Proposals are made for the formulation of analytical procedures that take account of existing differences between instruments and criteria are given for the optimum adjustment of the instruments. The use of only the linear part of the calibration graph is discouraged in favour of the formulation of a useful concentration range that is derived from the acceptable precision. Suggestions are given for the stepwise dilution of the samples.

Automated Aluminum Analysis with the Aluminon Method1

Abstract: An automated method of aluminum analysis by the aluminon (ammonium salt of aurin tricarboxylic acid) procedure is described. The method employs ascorbic acid for removal of Fe(III) interference and eliminates, with proper sample pretreatment, the need for a protective colloid. The calibration curve has a correlation coefficient > 0.99 and a standard deviation around the regression line of ± 0.07 absorbance units up to 1.2-ppm Al in solution. Standard autoanalyzer components are utilized in the system and computer interfacing is possible.

An Improved Ion-exchanger Colorimetry for the Determination of a Trace Amount of Phosphate

Abstract: A highly sensitive and selective method has been developed for the determination of a trace amount of phosphate. It is based on the concentration of phosphate as the familiar molybdenum blue complex on the coagulated material prepared from finely divided anion and cation exchangers, collection of the mixed resin on a filter paper, and the subsequent measurement of the absorbance of the complex on the resulting thin layer of resin phase. The calibration curve shows a good proportionality in the concentration range of 1 to 6 μg P1−1. The absorbance corresponding to 1 μg P1−1 is 0.095. The method is successfully applied to the determination of phosphate in a tap water and a river water.

Optimization of Peak Separation and Broadening in Aqueous Gel Permeation Chromatography (GPC). Dextrans

Abstract: Herein is reported an experimental optimization of the aqueous size-exclusion chromatography of dextrans on untreated CPG-10 glass packings. The molecular weight calibration curve was independent of ionic strength and there was no evidence of polymer adsorption on the glass packings. However, in the absence of salt in the mobile phase, chromatograms did show a high molecular weight shoulder which is attributed to small negative charges on the dextran molecules resulting in ion exclusion from the pores of the negatively charged glass. These high molecular weight shoulders were completely eliminated with the addition of a small amount of salt (e.g. 0.05 M NaSO4). A proper choice of pore sizes was essential to obtain good separation with minimal peak broadening giving a linear molecular weight calibration curve with a wide separation range and a small correction for imprefect resolution. Corrections to MN and MW were generally less than 5%. To establish an optimal column combination, it is recommend...

Comparison of the Japanese industrial standard and α‐correction methods for X‐ray fluorescence analysis of steels

Abstract: In the X-ray fluorescence analysis of steels, a correction method is usually used to eliminate absorption-enhancement effects. It is a desirable that the correction factors should be common to all experimental conditions and therefore the fluorescent X-ray intensity should be specified in a common unit. For this purpose, the JIS method converts the fluorescent X-ray intensity into a tentative analytical value from the calibration curve of binary alloys, while the α-correction methods employs the ratio of the intensity of an analytical sample to that of a pure substance for the fluorescent X-ray intensity. In this report a detailed comparison of these methods is made, and the good and bad points of the JIS method discussed.

Air sampling and analysis of trimellitic anhydride

Abstract: Trimellitic anhydride (TMA) is collected from air on a DM-800 (PVC-copolymer) membrane filter. The filter is extracted with methanol and the volume of the extract is reduced by evaporation; BF3/methanol is then added to the extract to form the TMA trimethyl ester. The BF3 adduct is precipitated with a combination of reagents and the supernatant solution is injected into a gas chromatograph equipped with an FID. The unknown concentration of samples is determined from a calibration curve. The range of the method is 19 to 96 µ/sample with a pooled relative standard deviation of 8%. The recovery of TMA from DM-800 filters was quantitative. This new method uses a one-step derivatization procedure and has a detection limit of 2 µg; the ester derivative is stable for at least two days and has a retention time of less than 8 minutes. This method may also be applicable to other organic anhydrides and carboxylic acids.

Electron probe analysis of microdroplets: Factors affecting the proportionality between measured X‐ray intensity and concentration

Abstract: SUMMARY Factors liable to limit the validity of liquid sample analysis by electron microprobe are investigated. For lyophilized samples composed of large 2–6 μm crystals, linear calibration curves may still be obtained for Na, Mg, P, Cl, K and Ca by raising the accelerating voltage to 18 kV, provided the X-ray take-off angle of the electron microprobe is 40°. Routinely prepared lyophilized samples are composed of discrete crystals. Their size is reproducible, depending on the composition of the dried deposit, and ranges from 0.1 to 0.5 μm for deposits mainly composed of NaCl. Within this range, the proportionality of X-ray intensity to concentration is not affected by particle size. The concentration range for which X-ray intensities remain proportional to concentrations is experimentally determined for the six elements above as a function of sample mass thickness and accelerating voltage. For certain elements, the proportionality constant is shown to vary with the composition of the solution. As regards chlorine concentration determinations, analysis of plasma ultrafiltrate and recovery experiments suggest that the proportionality constant is definitely 10% higher for this ultrafiltrate than for standard solutions.

Magnitude image diameter calibration of the ukstu j-survey films

Abstract: A calibration curve and table are presented for deriving approximate magnitudes from the UKSTU J-survey.

A theoretical procedure to determine coefficients from the Rasberry–Heinrich calibration curve in XRF spectroscopy

Abstract: Relative X-ray fluorescent intensity data have been generated numerically for binary samples under mono-chromatic excitation in those cases of absorption plus enhancement that are dealt with in this work. These data were fitted to the empirical Rasberry–Heinrich equation, keeping both coefficients different from zero, since from our numerical calculations it is shown that in most cases the best fit is achieved when A ≠ 0. Furthermore, this approach shows that a third coefficient introduced into the empirical equation improves the fitting. The aforementioned results suggest that the empirical equation could be deduced from the theoretical equation of fundamental parameters under suitable approximation. The result is an equation similar to that of Rasberry and Heinrich, from which analytical approximated coefficients are obtained. It is then possible to calculate a calibration curve using fundamental parameters values.

Method of determining the proportion of solid and/or liquid and/or gaseous substances in a mixture or stratum of these substances

Abstract: The method is used, in particular, for the determination of soil moisture. An electrical resistance wire embedded in the substances or the mixture is heated in each case for a short time with a predetermined quantity of electrical energy. Calibration measurements are carried out for the individual substances with different amounts of energy and the respective proportion of the substance is determined by calculation from the measurements of the individual substances and of the stratum or mixture. In the case of measurements of soil moisture, a determination is disclosed which is based solely on a calibration curve.

Calibration curve for GPC analysis of asphalts

Abstract: The work reported in this paper shows that it is possible to approach experimentally the problem of the plotting of a calibration curve in molecular weight for gel permeation chromatography (GPC) on a micro-packing applied to the characterization of asphalts. It is shown that if one determines, for different asphalts, a specific calibration curve relating the number average molecular weight, measured by membrane osmometry, of narrow fractions to their elution volume, one obtains a single curve independent of the origin of the crude and of the manufacturing process. This curve is very close to the polystyrene curve for values between about 1000 and 3000. It moves away toward the higher elution volumes, for small molecular weights, owing to the increase in the aromaticity of the asphalt constituents as molecular weight decreases. It also moves away, and in the same direction, as the weight increases: in this case, molecular weight measurements lead to apparent values higher than the real values owing to the non-ideal behavior of the solutions. This difficulty may be overcome by accepting the hypothesis of the applicability of universal calibration to asphalt fractions and by using a viscosimetric detector to plot a new calibration curve with reference tomore » the calibration curve in hydrodynamic volume. The interpretation of the results makes it possible to establish a calibration relationship of the form: log M (asphalt) = 3.21 - 1.04 X + 0.331 X/sup 2/, in which X = log M (polystyrene), and to elucidate, for asphalt fractions, the relationship between intrinsic viscosity and molecular weight.« less

Characterization of NTD Silicon Crystals by the Photoluminescence Technique

Abstract: The neutron-transmutation-doped (NTD) silicon crystals with a controlled neutron dose have been used as standard samples for the calibration of the photoluminescence (PL) method for the quantitative impurity analysis. The revised calibration curve for determining the P concentration in the range between 1011 and 1015cm−3 is reported. The calibration curve for B is also revised using the results obtained by the accurate PL and resistivity measurements. It is demonstrated that the concentrations of the transmuted P31 and background shallow impurities in commercial NTD crystals are determined precisely by using these calibration curves.