Showing papers on "Calibration curve published in 1991"

A generalized theory and new calibration procedures for network analyzer self-calibration

Abstract: A general theory for performing network analyzer calibration is presented. Novel calibration procedures are derived which allow for partly unknown standards. The most general procedure derived is called TAN and allows for five unknown parameters in the three calibration standards. The values of the unknown parameters are determined during the calibration procedure via eigenvalue conditions. The good performance of all the procedures has been shown experimentally. This wide spectrum of procedures using different calibration standards makes it possible to choose an optimal algorithm for any environment. >

Reheating of a Laser-Produced Plasma by a Second Pulse Laser

Abstract: Focused radiation of a Nd:YAG laser was used for ablation and production of free sample atoms from electrically conducting and nonconducting solids for analytical purposes The microplasmas were generated in an argon buffer gas atmosphere at reduced pressure In order to increase the intensities of analyte lines the microplasmas were reheated by a second Nd:YAG laser after the process of atomization was completed It is demonstrated for aluminum and manganese in glass and steel samples and for magnesium and manganese in glass, copper, and aluminum that by internal standardization a common calibration curve can be obtained

Simple photon diffusion analysis of the effects of multiple scattering on pulse oximetry

Abstract: Photon diffusion theory is used to derive analytical expressions that relate the AC-DC intensity ratios measured by transmission-mode and reflectance-mode pulse oximeters to arterial oxygen saturation (S/sub a/O/sub 2/). The effects of multiple scattering are examined by comparing the results of the photon diffusion analysis with those obtained using an analysis is based on the Beer-Lambert law which neglects scattering. It is shown that the difference between the average lengths of the paths traveled by red and infrared photons makes the calibration curve of oximeters sensitive to the total attenuation coefficients of the tissue in the two wavelength bands, as well as to absorption by the pulsating arterial blood. Therefore, the shape of the calibration curve is affected by tissue blood volume, source-detector placement, and other variables that change the wavelength dependence of the attenuation coefficient of the tissue. After evaluating the relationship between S/sub a/O/sub 2/ and the red/IR AC-DC ratio under a variety of physiological conditions, it is concluded that for oximeters utilizing fixed calibration curves based on measurements obtained from normal subjects, errors introduced by interfering variables should be less than a few percent when S/sub a/O/sub 2/ exceeds 70%. >

Comparisons of standard curve-fitting methods to quantitate Neisseria meningitidis group A polysaccharide antibody levels by enzyme-linked immunosorbent assay.

Abstract: We examined several of the more commonly used models (log-log, two forms of the logit-log, and the four-parameter logistic-log transformations) for forming standard or calibration curves by using a standardized enzyme-linked immunosorbent assay (ELISA). Assay range, accuracy, and error for each function were measured and compared. Antibody levels to Neisseria meningitidis group A polysaccharide were estimated by calculating antibody concentrations of a serially diluted standard reference serum of known concentration. Each function achieved a high squared correlation coefficient (r2 greater than 0.97), indicating a high degree of accuracy in forming the standard curves. However, when predicted antibody concentrations were compared with the known values, the log-log function exhibited the least precision, with extreme percentages of error occurring at several dilutions. A partially specified logit-log transformation performed better than the log-log model over a reduced range of standard dilutions. This indicated that a high r2 alone was not a reliable measure of the accuracy of the standard curve. Of the methods surveyed, the logistic-log and fully specified logit-log functions were the most accurate models for forming standard curves and for interpolating antibody concentrations from the standard curve. The accuracy of the fully specified logit-log function is highly dependent on the precise specification of two unknown quantities, the optical densities at zero and infinite concentrations, prior to fitting the model to a typical set of calibration data. The four-parameter logistic-log function was the preferred choice for quantitating N. meningitidis group A total polysaccharide antibody by using a standardized ELISA. The function does not require prespecification of any parameters before estimating the standard curve, and the four parameters are readily interpretable in terms of identifiable physical quantities. This model also has the advantage that it is easiest to visualize since it does not incorporate complex transformations of the optical density scale.

Spectroscopic instrument calibration

Abstract: A calibrated spectrometer can indirectly determine a physical or chemical property of a sample based upon spectral responses measured by the spectrometer with respect to the particular sample. This invention is directed to a method for calibrating or recalibrating a first spectrometer in light of a second spectrometer, or itself, respectively. The calibration employs a unique selection and manipulation of spectral data obtained from both the first and the second instrument. The recalibration employs a unique selection and manipulation of spectral data from the same first instrument, that is obtained both before and after the need for recalibration arises. Instead of modifying the respective responses of the first and second instrument, or the first instrument before and after the need for calibration arises, this invention modifies the calibration equation of the second, or recalibrated instrument, to yield consistent results to those obtained by the first instrument, or the first instrument before it goes out of calibration. A calibration equation is an equation which transforms spectral data of a particular sample at a variety of wavelengths to a calculated value for a chemical or physical property. Generally, the form of such calibration equations is that of a linear combination of absorbances or mathematical transforms of absorbances measured by the first and second instrument for each sample. The accuracy of the calibrated or recalibrated instrument is maintained and in some instances improved.

Method for validation of calibration standards in an automatic chemical analyzer

Abstract: In an automated analyzer that measures concentration of samples by comparing changes in a detector response caused by said samples to a calibration curve or factor based on one or more different calibration standards stored in the analyzer, a replacement calibration standard is validated automatically by processing a portion of said replacement calibration standard as a sample prior to accepting the new calibration standard as a valid standard.

Two improved methods for low-speed hot-wire calibration

Abstract: Two improved methods for hot-wire anemometer calibration in the low-speed range (15-95 cm/s) are described: a laminar pipe-flow method, and a shedding-frequency method. For the laminar pipe-flow method the calibration is performed in the exit plane of a fully-developed laminar pipe flow. For the shedding-frequency method the shedding frequency of a parallel mode cylinder wake is measured; the velocity is then obtained from a continuous Strouhal-Reynolds number relationship. Calibration results from the present methods were compared with each other and with results from a commercially available calibration jet. The present methods were demonstrated as a simple, but accurate means for low-speed hot-wire calibration.

Analysis of Flow Cytometry Data

Abstract: This unit provides several approaches to flow cytometry data analysis. Frequency determinations based on analysis of single-parameter fluorescence histograms and dual-parameter contour plots are presented. Next, steps are described for calculating values for signal-to-noise ratios when logarithmic amplification is used for data collection. This calculation can be used to compare the amounts of antigenic determinants per cell between different cells stained with the same reagent. Finally, a procedure is described for constructing a calibration curve for logarithmic amplifiers. This calibration curve is required for calculation of signal-to-noise values and can also be used to determine if the amplifiers are working properly.

The matrix effect in particle beam liquid chromatography/mass spectrometry and reliable quantification by isotope dilution.

Abstract: The transport efficiency of the particle beam liquid chromatography/mass spectrometer interface is influenced by analyte concentration contributing to a widely reported non-linearity In this work, coeluting, isotope-labeled internal standards were investigated as 'carriers' to improve the transport efficiency and linearity Three styrene metabolites--mandelic, phenylglyoxylic and hippuric acids--and their pentadeutero analogs were separated by reversed-phase liquid chromatography (LC) with an ammonium acetate-acetonitrile mobile phase Selected positive ions produced by electron ionization were monitored to generate particle beam LC/MS calibration curves The present study demonstrates that particle beam LC/MS not only is non-linear, but also is subject to a matrix effect presumably by the same mechanism responsible for non-linearity Coeluting, isotope-labeled internal standards were ineffective at linearizing the particle beam liquid chromatograph/mass spectrometer detector response Isotope dilution quantification, however, compensates for variable transport efficiencies, linearizes calibration and compensates for the matrix effect, affording reliable quantification of the styrene metabolites

Method and apparatus for imaging porous media and method for fabricating novel optical materials

Abstract: A method and apparatus is described for determining petrophysical properties of porous media by the use of light transmission through the media. Specifically, by using a highly collimated light source, preferably a laser, the permeability, grain size, wettability, porosity and clay swelling behavior of a sample can be determined on the scale of millimeters. A calibration curve or function is first established to correlate light transmission through a slab of sandstone on the order of 5 to 10 mm under known conditions. This curved is then used to determine unknown conditions by measuring light transmission and comparing the values to those on the curve. Other applications for the phenomenon of light transmission through porous media are disclosed whereby conditions in a flowing stream of liquid can be monitored by use of light transmission. Specifically, changes in the refractive index and immiscible contamination can be detected. Finally, the phenomenon described can be used to model subterranean hydrocarbon bearing reservoirs, particularly fluid flow at different points in the reservoir, using light rather than hydraulic flows to simulate fluid flow patterns.

Gravity meter calibration at LaCoste and Romberg

Abstract: An ideal gravity meter has a linear response so that its calibration is represented by a single scale factor. Microscopic variations in manufacturing lead to significant departures from this ideal. These variations from linearity are measured by observing the response of the gravity meter to the addition of a test mass to the gravity meter beam at various intervals throughout the meter’s range. This procedure measures the slope of the calibration curve at these points and therefore serves to define its shape. A compromise between accuracy, reading resolution, and cost needs to be reached. High accuracy requires a large mass difference which causes low resolution, requiring many overlapping observations which in turn leads to higher cost. The current procedure provides precision and resolution consistent with a precision of 10 μGals (1microgal=10nm/s2) over short ranges. The resulting calibration curve is scaled to gravity units with repeated observations over a 241.9‐mGal gravity range at Cloudcroft, New ...

Evaluation of water activity measurement with a dew point electronic humidity meter

Abstract: A statistical evaluation of a psychrometric electronic device (Decagon CX-1) for measuring water activity was conducted in order to determine its precision, accuracy, calibration, stability of calibration and hysteresis effect of sensor, using a set of saturated salt solutions to span the whole a w range, at 30 and 40 o C. Results indicated that this instrument, when properly operated and calibrated, and providing that measured values are corrected by a calibration curve, constitutes a precise, accurate and remarkably fast means of determining water activity

Spectrophotometric method for high biomass concentration measurements.

Abstract: Continuous monitoring of concentration is important in the optimal control of bioreactors. Spectrophotometry provides a simple, accurate, and rapid way for measuring cell concentration of unicellular microorganisms, based on either Beer's law or calibration curves prepared using standard solutions. However, this method is limited to a low range of microbial concentrations, because Beer's law deviates significantly at high concentrations. In the present investigation, based on experimental work, a new technique is posed to monitor the concentration of microbial cells as high as 100 g DW/L. this is achieved by using a mixture of known concentration as reference, rather than the "ideal blank" with zero concentration of analyte. As a result, a new equation is developed that, although applied here only to microbial concentration, in principle can be used for monitoring the concentration of any optically sensitive material.

Dilute-solution characterization of poly(dihexoxyphosphazene)

Abstract: Four fractions of poly(dihexoxyphosphazene) with molecular weights M w =2.3, 0.92, 0.25, and 0.026×10 6 , were studied in THF solutions at 25°C. The second virial coefficient decrease with increasing molecular weight. Two iterative numerical procedures were employed to combine all the experimental results, seeking the best choice of the parameters defining both the SEC calibration curve and the Mark-Houwink equation. The K and a constants of the Mark-Houwink equation allow the determination of the viscosity-average molecular weight of the four fractions and their molecular dimensions

Automated determination of sulphide by gas-phase molecular absorption spectrometry

Abstract: An automated method for the determination of sulphide in solution that involves the interfacing of an automatic sampler, a proportioning pump and a gas–liquid separator to an atomic absorption spectrometer is described. Sulphide ions react with 3 mol dm–3 hydrochloric acid and the released hydrogen sulphide is swept into a gas–liquid separator by an air stream. The absorbance was measured at 200 nm using a deuterium hollow cathode lamp. The method is relatively free from interference with a detection limit for sulphide of 0.06 µg ml–1 and relative standard deviations of 1.4–3.3% for repeated analyses. The calibration graph is linear up to 100 µg ml–1 of sulphide. Twenty samples can be analysed in 1 h. The method has been applied to the determination of sulphate-sulphur in plants.

Determination of aluminum in foods by stabilized temperature platform graphite furnace atomic absorption spectrometry

Abstract: The linear calibration curve ranged from 0.24 to 250 mg. The detection limit of aluminium was 0.24 ng. The accuracy of the method was evaluated was evaluated by using NBS pine needles and spinach leaves as standard reference materials.

Electrochemical Determination of Tricyclic Antidepressants

Abstract: Electrochemical detection of tricyclic antidepressants was conducted with glassy carbon, carbon paste and antimony doped tin oxide electrodes. We find that glassy carbon electrodes undergo passivation due to an adsorption process. Reliable calibration curves can only be obtained by polishing the electrode surface between scans. Carbon paste electrodes result in nonlinear calibration curves due to partitioning of the analyte and/or oxidized products of the analyte into the organic phase of the carbon paste. The extent of partitioning is dependent on the number of scans in the presence of the analyte. Antimony doped tin oxide yielded reproducible, linear calibration curves in the flow injection analysis mode as well as with differential pulse polarography.

Automated determination of sulphite by gas-phase molecular absorption spectrometry

Abstract: Conditions for the automated determination of sulphite in aqueous solution based on measuring the absorbance of sulphur dioxide evolved upon acidification of samples are described. The proposed method has a detection limit of 0.20 µg ml–1 and relative standard deviations of 2.3 and 1.8% for 20 and 10 µg ml–1 of sulphite, respectively. The calibration graph is linear up to 120 µg ml–1 and samples can be analysed at the rate of 20 per hour. The method has been applied to the determination of sulphur dioxide in synthetic samples and in white wines.

Isotope dilution mass spectrometry: definitive methods and reference materials in clinical chemistry.

Abstract: The application of gas chromatography-mass spectrometry (GC-MS) for the quantitative analysis of endogenous compounds as well as drugs in clinical biochemistry is taken into account. For this purpose, it is of the utmost importance the choice of a good internal standard (IS). It is demonstrated that the best IS in GC-MS is a stable isotope-labelled analogue of the analyte. In this case only we can speak of isotope dilution mass spectrometry. All the advantages and disadvantages inherent to the use of such a molecule as IS are discussed. The use of a calibration curve to perform the quantitative analysis is described, together with the criteria applied for the definition of the reliability of a method (precision, accuracy and limit of quantification). Examples taken from the literature are described.

Determination of zinc in human milk by electrothermal atomic absorption spectrometry

Abstract: An electrothermal atomic absorption spectrometric method has been developed for determining zinc in human milk. Milk samples were analysed after 1+99 dilution with 0.1% Triton X-100. The within-run precision was found to be 4.6%. The accuracy was ascertained by recovery of standard additions, and was found to be 96 ± 10%(n= 85 milk samples). The accuracy was also checked against National Institute of Standards and Technology Standard Reference Material 1549 Non-Fat Milk Powder. The results were 713 ± 35 µmol g–1(n= 38)(certified value: 705 ± 34 µmol g–1). The detection limit was found to be 0.052 µmol l–1. The calibration graph was linear up to 3 µmol l–1. The choice of experimental parameters (diluent, dilution rate, background correction, graphite furnace tube, etc.) are discussed. Normal values for colostrum and transitional milk varied from 45 to 318 and from 30 to 146 µmol l–1, respectively.

Apparatus for in-situ calibration of instruments that measure fluid depth

Abstract: The present invention provides a method and apparatus for in-situ calibration of distance measuring equipment. The method comprises obtaining a first distance measurement in a first location, then obtaining at least one other distance measurement in at least one other location of a precisely known distance from the first location, and calculating a calibration constant. The method is applied specifically to calculating a calibration constant for obtaining fluid level and embodied in an apparatus using a pressure transducer and a spacer of precisely known length. The calibration constant is used to calculate the depth of a fluid from subsequent single pressure measurements at any submerged position.

Automation of photochemical kinetic determinations without irradiation of the detection cell.

Abstract: This paper reports on the development of an open-closed configuration for continuous kinetic methods based on photochemical reactions; the configuration removes the need to use special flow cells for simultaneous irradiation and detection. The sample plug was recirculated through a circuit including the detector and a coil irradiated with an ultra-violet source. A multipeak recording per injected sample was obtained which allowed signal increments between peaks (whether successive or not) to be measured. The configuration was applied to the fluorimetric determination of thioridazine. The log-log calibration curve obtained was linear in the range over 0.1-20.0 μg/ml of the analyte. The sampling frequencies achieved were between 24 and 13 h-1, depending on the peaks which were selected for measurement. The method was applied to the determination of the analyte in pharmaceuticals.