Showing papers on "Calibration curve published in 1993"

Stacked modules for micro flow systems in chemical analysis: concept and studies using an enlarged model

Abstract: A valveless flow-injection-analysis system incorporating a series of functional modules, provided by a set of flat elements that are stacked vertically to form a series of internal flow streams, has been developed. A dye is used for sample introduction and injection and the system is coupled to an optical detector. The samples undergo a minimal amount of dilution, retaining 96–97% of their original concentration. Good run-to-run reproducibility is achieved, as indicated by measured standard deviations of less than 1%. A calibration curve has been generated and produces a linear fit to the data. The use of micromachining techniques to produce the set of flat elements and therefore to manufacture large quantities of identical flow-injection systems is discussed.

Absolute quantification of target DNA: a simple competitive PCR for efficient analysis of multiple samples.

Abstract: PCR is an exquisitely sensitive method for detection of minute amounts of target DNA. The exponential nature of DNA amplification, however, is prone to burden the experimental data with significant standard error due to the tube-to-tube inherent variations in amplification efficiency. Therefore the reliable quantitation of DNA or RNA templates by PCR necessitates introduction of an internal standard. Typically, in a series of replicates of analyzed sample the defined range of such standards is coamplified together with constant unknown amount of wildtype template (1, 2) or alternatively both templates are subjected to endpoint dilution (3). Obviously, each of the methods is based on multiple PCR reactions which are to be performed simultaneously with each of the analyzed samples. Such procedure, nevertheless, may become cumbersome when large numbers of samples are to be analyzed. We describe a modification of competitive PCR which is based on standardization of interpolation from a calibration curve. This approach enables accurate analysis of multiple samples by comparison with a single set of standard samples containing known amounts of the wild-type template of interest. Effective compensation for intra-assay variability is achieved using a constant amount of internal standard to spike all samples being analyzed as well as the samples used as standards. The comprehensive equation — logiN^/N^) = \og(N01/Ng^) + nlogieff^effi) defines the yield of the two products in any competitive PCR in terms of the ratio of the two original templates and their relative efficiencies of amplification, and simplifies when the products of both the endogenous wild-type template and the exogenous internal standard are generated with the same efficiency. Provided that this requirement (effi = effd is

Theory of a sequential addition competitive binding immunoassay based on high-performance immunoaffinity chromatography.

Abstract: This study examined the theory and behavior of a chromatographic competitive binding immunoassay with sequential injection of sample and a labeled analyte analog. Based on nonlinear chromatographic theory, an equation was derived to describe the calibration curve for this assay in a system with adsorption-limited kinetics and homogeneous binding sites. This equation related assay response (B/Bo) to the column's binding capacity, the moles of analyte and labeled analog injected, and the flow rate/adsorption kinetics of the system. There was good agreement between this equation and experimental data for the binding of human serum albumin (HSA) to an immobilized anti-HSA antibody column. It was found that the amount of labeled analog injected, when applied in excess vs binding sites in the column, had little or no effect on the relative response or position of the calibration curve. The position of the curve was determined mainly by the number of binding sites on the column; however, this position could be shifted over several orders of magnitude by varying the flow rate used for analyte injection. By varying both the injection flow rate and labeled analog load, this method could be designed for use as either a screening test or quantitative assay.

The determination of unit-cell parameters from Bragg reflection data using a standard reference material but without a calibration curve

Abstract: The procedure for determining unit-cell parameters from Bragg reflection data, using a standard reference material but without a calibration curve, is described. In this procedure, the observation equations for both the sample to be measured (SMP) and a standard reference material (SRM) are solved simultaneously and the unit-cell parameters and a form of error function are determined during the least-squares calculation. The theory, which was first proposed as a linear least-squares procedure [Toraya & Kitamura (1990). J. Appl. Cryst. 23, 282–285], has been extended to create a nonlinear least-squares procedure. The procedure can be used in two different ways. In one approach, the unit-cell parameters of the SMP and the parameters in the error function are refined while the unit-cell parameters of the SRM are fixed during the least-squares calculation. This procedure requires knowledge of the wavelength but it gives a stable solution and the tangent term in the error function gives a perfect correction for the error in wavelength. In the other approach, the unit-cell parameters of both the SMP and the SRM are refined, together with the parameters in the error function. The procedure does not require knowledge of the wavelength. The solution, however, became unstable when the correlation was strong between the unit-cell parameters and the error function and careful selection of the error function was required. The first approach gave the same result as the second and is, therefore, more practical to use. Since the form of the angle-dependent error function is determined using reflection data from both the SMP and the SRM, just one or two reflections from the SRM were enough for the correction of systematic error. The procedure, coupled with high-precision reflection data, can determine accurately the unit-cell parameters in a routine analysis.

Advances in second-order calibration

Abstract: Several multivariate methods are now available for the calibration of second-order or hyphenated instruments (e.g. GC/MS). When applied to bilinear data, it has been shown that calibration can be performed in the presence of unknown interferences - a significant advantage over first-order calibration. In this paper, non-bilinear rank annihilation (NBRA), a method which has the potential of handling, second-order non-bi-linear data, is studied through theoretical analysis and computer simulation. It is found that the second-order advantage can be carried over to non-bilinear data if a property defined as net analyte rank (NAR) holds for the analyte of interest. The net analyte signal (NAS) is defined accordingly for second-order calibration and the analogy to and difference from lower-order calibration are discussed. With NAS, some analytical figures of merit such as signal-to noise ratio, selectivity, sensitivity and limit of determination can be calculated for second order calibration. An application to MS/MS data is also given.

The Effect of Curve Fits for the Disdrometer Calibration on Raindrop Spectra, Rainfall Rate, and Radar Reflectivity

Abstract: Peaks in number density observed by many authors using Joss-Waldvogel disdrometers are almost certainly due to the manner in which a best-fit curve was chosen to represent the calibration data. The extreme sensitivity to small changes in the calibration curve was demonstrated with extensive observations of Malaysian tropical rain, which for best-fit calibrations showed multiple peaks; however, when a linear interpolation between calibration points was applied, only single peaks were seen in this first, recalibrated dataset. Hence, field evidence for multiple peak equilibrium distributions obtained in numerical models should be reconsidered. On the other hand, the rainfall and radar reflectivity, calculated from best fits, differ by less than 4% from that based on linear interpolation between calibration points.

Capacitance sensors for measurement of phase volume fraction in two-phase pipelines

Abstract: The effect of phase distribution (flow pattern) is considered for determining the volume fraction in two-phase pipelines. Experiments were performed with a variety of capacitance sensor designs. It was found that for a well-agitated mixture, two flow patterns occur for different compositions of the mixture, resulting in a discontinuous calibration curve. Sensitivity loss was found when the continuous phase was electrically conducting. This results in operational difficulties in applications to oil wells. It is concluded that capacitive sensors are practical only when the continuous phase is nonconductive or as a low electrical conductivity. >

Blood extraction flow control calibration system and method

Abstract: A method and system for calibrating and controlling the withdrawal of a fluid, such as blood, from a fluid source, such as a blood vessel, includes a fluid pump (26), a pressure sensor (24), a flow rate sensor, and a microprocessor based flow control subsystem. The flow control subsystem optimizes the flow rate by sensing zero flow rate pressure within the subject, making a plurality of periodic flow path pressure measurements and extrapolating a calibration flow rate curve (110). A control curve (130) is generated by utilizing the zero-flow rate pressure point (100), the slope of the calibration curve (110), and an empirically predetermined pressure offset value (150). The blood pump (26) is then operated at a maximum speed that is limited by the flow control curve (130) to maximize flow without occlusion or collapse of the blood vessel during blood withdrawal. The method and system of the invention is particularly applicable to automated apheresis system.

Quantitative analysis with d.c.- and r.f.-glow discharge spectrometry

Abstract: Glow discharge spectrometry (GDS) is a technique for rapid depth profiling and bulk analysis of materials. The latest instruments can be operated in either d.c. or r.f. modes. The d.c. mode provides analysis of conductive materials only, while the r.f. mode allows analysis of both conductive and non-conductive samples. Until now, no theory for r.f.-GDS has been available. The recently proposed d.c. theory, which assumes that emission yield depends only on pressure, is extended to r.f.-GDS and is shown to be valid for the r.f. mode as well. A key to the success of the theory is that, in support of Duckworth and Marcus, the two modes are shown to have similar analytical characteristics, e.g. in comparing the two modes most elements examined had similar sensitivity factors and background equivalent concentrations. This will facilitate calibration of the light elements hydrogen, oxygen and nitrogen for use in the d.c. mode. Recommended procedures for bulk analysis, in either d.c. or r.f. modes, are presented and illustrated for manganese in steel. Both modes provide calibration curves of high linearity. Quantitative depth profiles of three commercial metallic-coated steel samples are compared in d.c. and r.f. modes and the similarity of the quantitative profiles, given the very different lamp parameters operating between the modes, confirms that the theory works for both d.c. and r.f. The theory is then applied to data from a commercial prepainted metallic-coated sample to provide the first quantitative GDS depth profile of a non-conductive material.

Quantitative analysis in capillary zone electrophoresis using ion-selective microelectrodes as on-column detectors

Abstract: Inorganic and organic cations can be quantified using capillary zone electrophoresis with an ion-selective microelectrode as on-column detector. This is illustrated by determining the linear calibration plots for potassium, sodium, rubidium, calcium, and dopamine in the range of 10 -4 -10 -3 M and for histamine in the range of 10 -5 -10 -4 M, where imidazole and potassium were used as internal standards. Quantification of the potassium concentration in blood plasma is shown by use of both internal standard and external calibration plot. By delogarithmizing the emf values of the ISME response and integrating the resulting curve, a linear relationship between integral and analyte quantity is obtained

Method and analytical system for performing fibrinogen assays accurately, rapidly and simply using a rotating magnetic field

Abstract: A method of performing a quantitative fibrinogen assay is provided which uses a dry reagent chemistry in combination with a rotational magnetic field and which has excellent correlation with the Fibrometer, the gold standard in the industry. Additionally, an apparatus for conducting the assay, a qualitative fibrinogen assay and a method for preparing a calibration curve for use with the quantitative fibrinogen assay are provided.

Quantitative Analysis of Peptides by Matrix-Assisted Laser Desorption/Ionization Time-Of-Flight Mass Spectrometry

Abstract: Quantitative analysis of peptides using internal standards was carried out with the use of matrix-assisted laser desorption/ionization (MALDI) on a time-of-flight mass spectrometer in a ferulic acid matrix Spectra were collected and averaged over several areas of the sample surface at constant laser energy, and a defocused beam was used to improve reproducibility A calibration curve was plotted, showing a correlation coefficient of 0992 and a relative standard deviation of 183% The accuracy and precision of this technique were sensitive to the crystal structure of the matrix and saturation effects of the instrument's detector

Determination of trace amounts of beryllium in water by solid-phase spectrophotometry

Abstract: A method for the determination of trace amounts of beryllium has been developed, based on solid-phase spectrophotometry. Beryllium reacts with Eriochrome Cyanine R in the presence of ethylenediaminetetraacetic acid to give a highly absorbent complex, which is fixed on a dextran-type anion-exchange gel. The absorbance of the gel, at 580 and 750 nm, packed in a 1 mm cell, is measured directly. The calibration graph is linear over the concentration range 0.1–1.2 µg l–1 and the relative standard deviation is 2.3%. The detection limit of the 1000 ml sample method is 6 ng l–1 for 0.030 g of anion-exchange gel. The sensitivity can be enhanced by increasing the sample volume. The method has been applied to the determination of beryllium in tap and natural waters.

Analysis of silicon carbide powder by ETV-ICP-AES

Abstract: A direct “tandem” atomic spectroscopic method for the determination of Ca, Fe and Ti impurities in SiC powders with various grain size (0.78

New use of size exclusion chromatography in kinetics of mechanical degradation of polymers in solution

Abstract: A new method to investigate the mechanical degradation of polymers in solution is described that uses size exclusion chromatograms of the initial polymer and of the degraded sample. The incipient parts of these chromatograms are analyzed to obtain kinetic data about degradation at the level of infinitesimal fractions. The procedure is based on the fact that mechanical degradation of the polymers is a first-order reaction and macromolecules are cleaved mostly in their central region. The rate constant and the variation in the rate constant with molecular weight are determined in a single experiment, avoiding additional fractionation steps. Moreover, the slope of the size exclusion chromatographic calibration curve is derived, opening new ways to determine polydispersities or even to make rapid calibration for unknown polymers. To verify the method, the rate constant and the molecular weight dependence of the rate constant were determined for the sonic degradation of polystyrene in toluene. The rate constant is found to vary with the square of the molecular weight, and its value is in good agreement with results reported using much more laborious methods. © 1993 John Wiley & Sons, Inc.

Calibration of Radiotracer Method to Study Protein Adsorption at Interfaces

Abstract: Radiolabeled stearic acid, β-casein, and lysozyme were used to construct cpm versus surface radioactivity calibration curves to study the kinetics of adsorption of proteins at the air-water interface by the radiotracer method. It was observed that quantification of the rate and extent of adsorption of lysozyme was profoundly affected by the choice of the standard curve used. Whereas the calibration curve based on spreading 1-14C-stearic acid at the air-water interface underestimated the surface concentration of lysozyme, that based on spreading of lysozyme resulted in overestimation. Even though 1-14C-stearic acid and β-casein formed stable insoluble spread films at the air-water interface, the surface cpm versus surface radioactivity calibration curves were different. These differences presumably arose from differences in the depth of the 14 C nuclide from the air-water interface as well as from possible quenching of β- radiation by the protein matrix. Based on the observations it is proposed that the calibration curve obtained by spreading 14 C-labeled β-casein might be a better reference curve than the others to quantify the rate and extent of adsorption of proteins at the air-water interface using the radiotracer method.

SEC–viscometer detector systems. I. Calibration and determination of mark–houwink constants

Abstract: Five different types of calibration curve currently used in size exclusion chromatography-differential viscometer (SEC–DV) systems were identified and their use summarized. A simple method of deriving weighting factors for fitting local intrinsic viscosity calibration curves was shown to greatly improve the precision of calculated molecular weight distributions. The problem of reliably extrapolating the fitted curves to allow for differences in sensitivity among detectors has yet to be examined. With regard to Mark—Houwink constants, a method of fitting data from the SEC–DV system to obtain more statistically sound values was derived. For the data used here, the new method involves fitting a plot of logarithm of the local intrinsic viscosity of the sample vs. logarithm of the universal calibration curve parameter, Ji. Results for the data obtained appeared only slightly more precise than those for the traditional method. However, the new method promises improved reliability. © 1993 John Wiley & Sons, Inc.

Coupled solid phase extraction–supercritical fluid extraction–on-line gas chromatography of explosives from water

Abstract: A method has been developed for the quantitative extraction of nitrotoluenes (2,3-dinitrotoluene, 2,4-dinitrotoluene and trinitrotolugene) from water using a BakerbondTM phenyl sorbent. The average solid phase extraction recoveries for spiked standards ranged from 80 to 95 percent for reagent water and 52 to 95 percent from well and surface water in the low ppb and ppt levels. After the nitrotoluenes had been trapped on the solid sorbent they were quantitatively eluted using SFE. Adding toluene to the extraction cell increased the rate of extraction, but did not improve analyte recovery versus unmodified CO2. The extracts were analyzed off-line with GC–ECD using an internal standard. Extraction losses were due to analyte breakthrough, and not from poor SFE recoveries. This demonstrates that supercritical fluid extraction is a suitable elution technique for analytes trapped on solid phase extraction sorbents. Also, a method for the direct on-line coupling of SPE to GC, using SFE, has been developed and evaluated. Supercritical CO2 is ideal for directly coupling SPE to GC, since carbon dioxide is a gas under ambient conditions. One potential problem of on-line SPE–SFE–GC is the presence of residual water trapped on the active sites of the Bakerbond13 phenyl sorbent. This problem was dealt with by using a split interface previously described by Hawthorne. From the results of this study, the relative standard deviation of the on-line SPE–SFE–GC interface was determined to be between 4 and 10 percent. In addition, there was no significant difference in the precision of the method with or without the use of an internal standard. A calibration curve was also constructed (r2 = 0.995) from spiked controls, demonstrating that the method is quantitative.

Method for the analytical determination of the concentration of a component of a medical sample

Abstract: Method for the analytical determination of the concentration of a component of a medical sample, in which a reaction of the sample with reagents leads to a time-dependent change S(t) in a measured quantity S and the concentration C correlates according to an evaluation curve C(X) with an input variable X derived from S(t), in which the calibration curve is ambiguous for at least a portion of the possible X values. In order to assign an input variable X to one of the sub-sections and thereby to obtain an unambiguous correlation to a particular concentration C, a training run and an analysis run are performed. In the training run, a discrimination algorithm is performed at least once, in which a discriminator set is generated from measurements of S(t), a score is generated in each case from the latter with a multivariate statistical technique and it is checked whether the scores can be divided into separate subsets, in which the concentrations are correctly assigned to the sub-sections of the calibration curve. The discrimination algorithm is repeated with different discriminator sets generated according to different generation methods from the measurements of S(t), in order to establish an operative discrimination algorithm. In the analysis run, an analysis score is calculated from measurements of S(t) according to the operative discrimination algorithm, the analysis score is compared with the boundary score and the measurement result is assigned to one of the sub-curves of the calibration curve by comparison of the analysis score with the boundary score.

Process for determining carbon black concentration and distribution in rubber compounds and other carbon black containing materials and device to carry out the process

Abstract: A method & apparatus for determining carbon black in rubber composites (e.g. for tyres) based on time-resolved laser breakdown spectroscopy (TREUBS) are described. A laser beam (4a) is raster scanned across the sample surface (1a), and atomic or molecular emission from the laser excited plasma (4c) is collected from measuring points (4b), spectrally dispersed by grating (11) and detected using the photodiode array (12). To determine the carbon black distribution, spectral line intensity ratios relative to carbon acting as internal standard, for elements present in the sample are measured at two different delay times after the exciting laser pulse. At short delay times < 0.5 NS, carbon emission is due largely to carbon black; at longer delay times the signal represents total carbon present in the matrix. Comparison of the intensity ratios with calibration curves then yields the concentration of carbon black at the measuring point.

Multi‐detector size‐exclusion chromatography: a novel approach to calibration eliminating lag time estimation

Abstract: In order to obtain the correct calibration of molecular-weight sensitive detectors (such as on-line viscometers or light scattering detectors) in size-exclusion chromatography, it is necessary to account for the (molecular) non-uniformity of the calibration standards. This is true even in the case of the narrow molecular weight distribution standards typically commercially available for calibration. Methods of taking this non-uniformity into consideration are presented. For a multi-detector size-exclusion chromatography system calibrated in this way, independent calibration curves can be established for each detector. Thus, at a given hydrodynamic volume, corresponding signals from the different detectors can be obtained. This eliminates the need to estimate additional parameters such as interdetector volumes or lag times for matching signals from different detectors. The practicability of this approach in the analysis of (molecularly) non-uniform polymers is demonstrated by combining on-line viscometer and concentration signals (to obtain intrinsic viscosity versus molecular weight information) for two different polymers, viz. polystyrene and poly(methyl methacrylate). The resultant intrinsic viscosity versus molecular weight data is then compared to that predicted from the literature.

Calibration of a point-counting technique for estimation of biogenic silica in marine sediments

Abstract: The simple technique of point counting is very quick and is suitable for shipboard use, or in any study where high accuracy is not necessary. Point-counting smear slides yields results different from measurements of weight-percent silica if there are systematic differences in shape and density of biogenic and terrigenous grains. In this note I present calibration curves for synthetic biogenic-terrigenous mixtures, to show how the accuracy of point counting may be improved.

Lidar-inversion technique based on total integrated backscatter calibrated curves

Abstract: The integrated backscatter signal from a smoke cloud contained in a chamber is studied as function of the measured concentration. An analysis based on the total backscattered signal leads to the determination of calibration curves specific to the material and to the lidar system. This procedure leads to a lidar inversion technique based on a calibrated total integrated backscatter curve. The limitation of the technique is discussed in terms of the maximum optical depth permitted for acceptable results.