Showing papers on "Calibration curve published in 1988"

Conversion of logarithmic channel numbers into relative linear fluorescence intensity.

Abstract: We describe a simple, reproducible, and generally applicable method to assess the performance of log amplifiers by using a fluorescent sample that provides multiple peaks of different intensities. The channel differences between multiple peaks are used to evaluate the logarithmic behavior of the fluorescence signal amplifier on the flow cytometer. A calibration curve can be created to correct the channel numbers for deviations from true logarithmic behavior and then convert data into relative linear intensities. By using these linear fluorescent intensities, we compared the capacity of different antisera against HIV-1 (human immunodeficiency virus type 1) peptides to inhibit the binding of HIV-1 to CEM, a CD4-positive T-cell line. A wide range of applications for this calibration procedure can be envisioned and the method is valuable for monitoring instrument performance over time.

The effect of interferences and calbiration design on accuracy: Implications for sensor and sample selection

Abstract: Methods of multivariate calibration use models that relate spectral data or sensor array responses to the concentrations of analytes. The goal is to insure that the calibration model can accurately estimate analyte concentrations in unknown samples not contained in the calibration set. The sensors or spectral channels (e.g. wavelengths) selected for incorporation in the model, as well as the samples selected for the calibration step, are known to have an effect on the accuracy of analysis for unknown samples. This work provides a fundamental treatment of this effect and derives criteria for optimal selection. Additionally, a proof is given for the advantage of having more sensors and calibration samples than analytes—the overdetermined case.

Calibration of eddy current profilometry

Abstract: Calibration of an eddy current probe (24) and associated data acquisition and analysis system (42, 48, 52, 54, 66) is accomplished using a step tube sample (68) having a nominal diameter portion (74) substantially equivalent to a nominal field tube (22). Two readings of eddy current test units are obtained from the step tube sample, and the diameter of the probe is used as a boundary condition on the non-linear response of the probe to variations in tube radius. A calibration curve is generated for use in converting field tube eddy current measurements to field tube radius or profile.

The use of infrared spectroscopy for determination of polypropylene stereoregularity

Abstract: This study examines the application of infrared (IR) spectrometry to the determination of polypropylene (PP) stereoregularity. The use of the absorption bands at 998 cm−1 and 841 cm−1 as indices of isotacticity and bands at 1167 cm−1 and 973 cm−1 as internal references have been explored. Calibration curves relating various absorption ratios to isotacticity as measured by 13C nuclear magnetic resonance are reported. The ratios A998/A973 and A841/A973 are the most useful and provide linear correlations with isotacticity. The effect of instrument type on the calibration has been investigated for both dispersive and Fourier transform type IR spectrometers. For samples annealed at room temperature the average of measurements on the same set of PP films by five instruments provide the calibrations: A998/A973 = 1.08 ± 0.02 (mm)−0.15 ± 0.03; and A841/A973 = 0.84 ± 0.06 (mm)−0.04 ± 0.02. High temperature annealing increases the crystallinity of the samples and the corresponding value of the absorption ratio but is not necessary for obtaining reproducible calibration curves.

Application of ion-exchanger phase absorptiometry to flow analysis. Determination of trace amounts of chromium(VI) in water

Abstract: Ion-exchanger phase absorptiometry was applied to the determination of trace amounts of chromium(VI) in natural waters using flow analysis. The product of the reaction of chromium(VI) with 1,5-diphenylcarbazide was introduced into a carrier solution stream in the flow system. The increase in absorption by the coloured complex sorbed on a cation exchanger, with which the light-path of a flow-through cell had been partly filled, could be measured directly with high precision. When 4.4 cm3 of sample solution were pumped through, the sensitivity obtained was 160 times higher than that of the corresponding solution method. The detection limit was as low as 0.5 ng of chromium(VI). Cations such as calcium and background electrolytes present in natural waters at high concentrations caused a change in the background attenuation. For fresh water, this effect could be removed only by passing the sample solution through a small hydrogen-form cation-exchange column. For sea water, it is necessary to use a calibration graph prepared at similar concentrations to those in the sample solution. Without pre-concentration, the proposed method is directly applicable to the analysis of natural water samples containing chromium(VI) at less than 1 µg dm–3.

A Direct J-R Curve Analysis of Fracture Toughness Tests

Abstract: A method is proposed to evaluate fracture toughness in a J-R curve format directly from load displacement records without the need for automatic crack length measurement devices. This method uses the calibration curve in which the flow properties of a material for a stationary crack provide the relationships between load, displacement, and crack length. Crack growth is then evaluated by comparing load and displacement pairs for the growing crack case with this stationary crack curve. This is similar to the approach in which a common “key curve” was used to determine crack length; however, in this case, individual calibration curves are developed for each specimen. The calibration curve is described by separate elastic and plastic components of displacement. The relationship between load and elastic displacement is described by a compliance function and between load and plastic displacement by a power term with constant coefficient and exponent. Three methods are suggested for evaluating the power term exponent and coefficient. The first assumes that the exponent coming from a fit of the true-stress true-strain tensile test results can be used, the second determines all information directly from the test record, and a third does the same but uses a plastic zone adjustment. The method is applied to a set of results from an A508 steel in which the J-R curve had previously been determined using the elastic compliance method of crack length measurement. These tests were conducted on compact specimens with a range of sizes varying by a factor of 20 (10T to 1/2T). The method is also applied to a 4340 steel and stainless steel weld metal. The results show that second approach works best. Although further evaluation of the method is needed, it showed promise as a replacement for automatic crack length measurement techniques in the evaluation of J-R curves.

Enhanced performance of ion-selective electrodes in flow injection analysis: non-nernstian response, indirect determination, differential detection and modified reverse flow injection analysis

Abstract: Some general aspects concerning the measuring device, cell design, flow manifold and sensor requirements for the incorporation of ion-selective electrodes (ISEs) in flow injection systems are outlined. The main aim of this paper is to demonstrate how the control of sample dispersion and timing in flow injection analysis (FIA) can be used to attain unique potentialities. The detection limits of ISEs can be decreased, even below the intrinsic solubility of the sensor membrane. The integration of sample processing steps within the manifold improves the reliability of the electrode for reaction products which are unstable or volatile. The series differential detection method is shown to increase the sensitivity (slope of the calibration graph) and to simplify data evaluation. The indirect determination of trace amounts of aluminium with a fluoride ISE can be performed with a simple experimental set-up and high sample throughput. Finally, the modified reverse FIA technique is shown to be a novel method for process analysis, continuous monitoring purposes and high precision calibration.

Determination of trace amounts of aluminium by ion chromatography with fluorescence detection

Abstract: A method is described for the determination of aluminium by high-performance ion chromatography followed by post-column derivatisation with 8-hydroxyquinoline-5-sulphonate and fluorescence detection at 512 nm (excitation at 360 nm). A short (50 mm) low-capacity cation-exchange resin column was used as the analytical column and 0.1 M K2SO4, adjusted to pH 3.0, as the eluent. The calibration graph was linear from 5 to 10 000 µg l–1 of aluminium with a detection limit (3σ) of 1 µg l–1. Typical relative standard deviations were 3.4% at the 250 µg l–1 level. No interference was observed from other commonly occurring metals and aluminium was successfully determined in a certified reference material (Monel Alloy) and in tap water.

A statistical method for estimating rates of soil development and ages of geologic deposits: A design for soil-chronosequence studies

Abstract: A statistical method for estimating rates of soil development in a given region based on calibration from a series of dated soils is used to estimate ages of soils in the same region that are not dated directly. The method is designed specifically to account for sampling procedures and uncertainties that are inherent in soil studies. Soil variation and measurement error, uncertainties in calibration dates and their relation to the age of the soil, and the limited number of dated soils are all considered. Maximum likelihood (ML) is employed to estimate a parametric linear calibration curve, relating soil development to time or age on suitably transformed scales. Soil variation on a geomorphic surface of a certain age is characterized by replicate sampling of soils on each surface; such variation is assumed to have a Gaussian distribution. The age of a geomorphic surface is described by older and younger bounds. This technique allows age uncertainty to be characterized by either a Gaussian distribution or by a triangular distribution using minimum, best-estimate, and maximum ages. The calibration curve is taken to be linear after suitable (in certain cases logarithmic) transformations, if required, of the soil parameter and age variables. Soil variability, measurement error, and departures from linearity are described in a combined fashion using Gaussian distributions with variances particular to each sampled geomorphic surface and the number of sample replicates. Uncertainty in age of a geomorphic surface used for calibration is described using three parameters by one of two methods. In the first method, upper and lower ages are specified together with a coverage probability; this specification is converted to a Gaussian distribution with the appropriate mean and variance. In the second method, “absolute” older and younger ages are specified together with a most probable age; this specification is converted to an asymmetric triangular distribution with mode at the most probable age. The statistical variability of the ML-estimated calibration curve is assessed by a Monte Carlo method in which simulated data sets repeatedly are drawn from the distributional specification; calibration parameters are reestimated for each such simulation in order to assess their statistical variability. Several examples are used for illustration. The age of undated soils in a related setting may be estimated from the soil data using the fitted calibration curve. A second simulation to assess age estimate variability is described and applied to the examples.

Low-pressure vaporization for graphite furnace atomic absorption spectrometry

Abstract: A low-pressure graphite furnace atomic absorption spectrometry technique is presented which, for aqueous Pb samples at 0.15 Torr, results in a 2 orders of magnitude reduction in sensitivity and a working range that extends to about 1 ..mu..g. The limit of detection is 5 ng of Pb. Sticking is diminished for refractory analytes (e.g., V), thus reducing memory effects and peak tailing. Solid sample analysis is demonstrated for Pb in a phosphorized Cu alloy, for which low-pressure atomization minimizes Cu vaporization while allowing for quantitative determination of Pb when compared to a calibration curve prepared from aqueous standards. In addition, the appearance of multiple peaks suggests the use of the technique for differentiating between various forms or locations of Pb within the sample. This is in contrast to atmospheric vaporization where only one broad peak is observed.

Determination of ionic surfactants by flow injection pseudotitration

Abstract: Two flow-through surfactant-selective electrodes have been developed which are selective for anionic and cationic surfactant ions. They employ PVC membranes containing appropriate ion-exchanging salts, coated on the internal wall of a graphite tube. The performance of the electrodes as sensors in a flow injection pseudotitration has been evaluated. By relating peak width to the logarithm of the concentration of a series of standard surfactants, a linear calibration graph may be produced. This permits the determination of unknowns by extrapolation. The system is of particular value when applied to the control analysis of known standards.

Determination of chromium in human urine by graphite furnace atomic absorption spectrometry with Zeeman-effect background correction

Abstract: A rapid and direct method for the determination of chromium in human urine using graphite furnace atomic absorption spectrometry with Zeeman-effect background correction is described. No reagent or sample pre-treatment (except for straightforward dilution of concentrated samples with distilled water) was necessary, thereby reducing the risk of contamination. The concentration of chromium in urine was evaluated directly from a calibration graph constructed from a metal-spiked human urine pool. Hence, the time consuming method of standard additions was avoided, which permitted an increased sample throughput (100–120 samples per day) with minimum attention of the analyst. In routine use, the reproducibility (both within-day and day-to-day) and limit of detection were in the order of ±10% and 0.09 µg l–1 of Cr, respectively. With a minor alteration in charring temperature the method may also be used for the determination of chromium in whole blood and serum. The method described is suitable for the biological monitoring of chromium in the general population or in occupationally exposed persons.

Automated continuous monitoring of inorganic and total mercury in wastewater and other waters by flow-injection analysis and cold-vapour atomic absorption spectrometry.

Abstract: An automated continuous monitoring system for the determination of inorganic and total mercury by flow-injection analysis followed by cold-vapour atomic absorption spectrometry is described. The method uses a typical flow-injection manifold where digestion and reduction of the injected sample takes place. Mercury is removed by aeration from the flowing stream in a specially designed air-liquid separator and swept into a silica cell for absorption measurement at a wavelength of 253.7 nm. A calibration curve up to 10 μg Hg ml-1 using three different path length cells is obtained with a detection limit of 0.02 μg Hg ml-1. The sampling rate of an injection every 3 min produces 20 results per hour from a flowing stream.

Calibration of Minority Carrier Lifetimes Measured with an ac Photovoltaic Method

Abstract: Calibration curves for estimating true lifetimes from the measured ones are theoretically obtained for getting the long lifetimes of relatively thin Si wafers, where lifetimes measured with an ac photovoltaic method are limited by the sample thickness. Apparent lifetimes of 7.2 through 14 µs in 475 µm thick p-type Si wafers are calibrated to be 9.6 through 65µs, respectively, using the calibration curves. As a result, it is found that lifetimes in the samples oxidized after dipping in HF solution are longer than those oxidized without dipping in HF solution. This is because contaminated natural oxide films on the sample, which are formed by alkaline rinse, are eliminated by the HF dipping.

Analytical Performance and Transport Studies Using Spark Sampling Followed by ICP Excitation with a Sequential Spectrometer

Abstract: It was established that a high-voltage spark is a viable method of sampling iron and aluminum-based alloys using a sequential spectrometer ICP. Calibration curves were linear over at least four orders of magnitude, detection limits were in the parts per million range in the solid, and precisions of 1–3% were readily demonstrated when the base metal was used as an internal standard. Fifteen elements could be determined in a three-minute burn. The best analytical performance was obtained when the gas flow sweeping particles to the plasma passed through the counter electrode. Experiments with a cascade impactor showed that most of the material reaching the plasma was in small particles (<0.4 μm), with a total sample transport rate of about 0.5 μg/s. Particles reaching the plasma were examined by the scanning electron microscope and appeared to be mostly aggregates of very small spheres of 500-1500 A diameter. Under nonoptimum conditions, large spheres (∼1–5 μm diameter) and ablated material of irregular shape made up a significant amount of the transported material. The analytical performance is affected by particle size distribution, particle type, and sample transport rates.

Antimony determination by hydride generation — UV-visible molecular absorption spectrophotometry with diode-array detection

Abstract: A method for antimony determination is described comprising hydride generation and transport into a flow-cell placed in a UV-visible molecular absorption spectrophotometer with diode-array detection. Nitrogen is employed as carrier gas. The measurement is performed at 198 nm. The calibration curve is linear from 3 to 440 μg/ml of antimony. The method was successfully applied to the analysis of PVC.

Mathematical simulation of an amperometric enzyme-substrate electrode with apO2 basic sensor

Abstract: In the first part of the paper a mathematical model of the enzyme-substrate electrode with a pO2 basic sensor was outlined. This model is used to simulate the dependencies of the measuring characteristics (calibration curve, measuring range, sensitivity, response time) on the design parameters (geometric arrangement, membrane properties, enzyme kinetic quantities) of an enzyme-based glucose sensor. The simulated and measured calibration curves are in good agreement with each other. With decreasing pO2 a stoichiometric limitation occurs, and the linear range of measurement is reduced. If catalase is co-immobilised together with glucose oxidase the oxygen consumption is halved and the measuring range is doubled. The infuences of the diffusion coefficients and of the specific enzyme activity on sensitivity and response time are simulated. The results are in good correspondence with the theoretical statements and the experimental results. The limits of the model are determined by its convergence properties.

Problems with Interval Estimation When Data are Adjusted via Calibration

Abstract: The analysis of adjusted data arising from a linear calibration curve is considered. Although it is obvious that adjusted values contain errors due to estimation of the calibration curve, some investigators may be tempted to analyze such data as if they..

High Performance Liquid Chromatography Assay of Itraconazole in Human Plasma

Abstract: A high performance chromatographic method, using internal standard quantification, for the analysis of Itraconazole in human plasma is described. The standard curve was linear over the concentration range tested. The detection limit of the method was 250 ng. An authentic sample of both Itraconazole and the internal standard (ketoconazole) were used to establish the calibration curve.

Quantitative size exclusion chromatography of polypropylene II: Analysis systems

Abstract: Quantitative size exclusion chromatography (SEC) was considered a system with the following components: sample preparation, fractionation, detection, calibration, and resolution correction. Four systems were evaluated: I was 3 columns with “conventional single detector interpretation”; II was 4 columns with concentration correction and detector assessment; III was concentration correction applied to the data of I; IV was two development “mixed bed” columns. Analysis of polystyrene standards included calculation of their molecular weight averages and use of the Glockner “T” measure of resolution as well as “specific resolution index.” Systems I and III provided the best high molecular weight results. System IV allowed 12–20 min analysis times and provided a highly linear calibration curve with very good reproducibility; however, it showed significantly worse resolution at high molecular weights. Plots of molecular weight averages determined from SEC versus their known true values were particularly useful. Concentration correction using the Rudin model moved different concentration data toward a common universal calibration curve and generally lowered molecular weight averages. Narrow polystyrene standards required relatively high concentrations for precise molecular weight averages and therefore, their averages were not good indicators of the need for concentration correction. Analysis of polypropylene samples corroborated the lower high molecular weight resolution of System III. Concentration correction did significantly change the polypropylene molecular weight distribution but did not affect the result of the kinetic model fitting.

Calibration and applications of polarized neutron thermometry at milli- and microkelvin temperatures

Abstract: We have utilized the polarized neutron scattering technique for the determination of the nuclear temperature in copper from 20 mK down to 100 μK. Using a cooling facility where two adiabatic demagnetization stages work in series we have calibrated the flipping ratio of neutrons scattered from the (200) Bragg-peak against the nuclear polarization over the whole polarization range. The observed calibration curve deviates considerably from the curve expected for an extinction-free sample. The polarized neutron thermometer is discussed and applied in measurements of the spin-lattice relaxation in copper.