Showing papers on "Calibration curve published in 2001"

Validities of mRNA quantification using recombinant RNA and recombinant DNA external calibration curves in real-time RT-PCR

Abstract: Reverse transcription (RT) followed by polymerase chain reaction (PCR) is the technique of choice for analysing mRNA in extremely low abundance. Real-time RT-PCR using SYBR Green I detection combines the ease and necessary exactness to be able to produce reliable as well as rapid results. To obtain high accuracy and reliability in RT and real-time PCR a highly defined calibration curve is needed. We have developed, optimised and validated an Insulin-like growth factor-1 (IGF-1) RT-PCR in the LightCycler, based on either a recombinant IGF-1 RNA (recRNA) or a recombinant IGF-1 DNA (recDNA) calibration curve. Above that, the limits, accuracy and variation of these externally standardised quantification systems were determined and compared with a native RT-PCR from liver total RNA. For the evaluation and optimisation of cDNA synthesis rate of recRNA several RNA backgrounds were tested. We conclude that external calibration curve using recDNA is a better model for the quantification of mRNA than the recRNA calibration model. This model showed higher sensitivity, exhibit a larger quantification range, had a higher reproducibility, and is more stable than the recRNA calibration curve.

Simultaneous Multianalyte ELISA Performed on a Microarray Platform

Abstract: Background: A logical progression of the widely used microtiter plate ELISA is toward a protein array format that allows simultaneous detection of multiple analytes at multiple array addresses within a single well. Here we describe the construction and use of such a multiplex ELISA to measure prostate-specific antigen (PSA), α1-antichymotrypsin-bound PSA (PSA-ACT), and interleukin-6 (IL-6). Methods: We silanized glass plates and printed the appropriate capture antibodies to allow for the construction of “sandwich” ELISA quantification assays. We examined specificity of the assay for appropriate antigen, assembled calibration curves, and obtained PSA concentrations for 14 human serum samples. We compared the serum PSA concentrations derived through the use of our array with values obtained independently using a standard ELISA method. Results: R 2 values generated by our microarray for the PSA and PSA-ACT calibration curves were 0.989 and 0.979, respectively. Analyte concentrations used for the construction of these curves were 0.31–20 μg of protein/L of diluent. IL-6 calibration curve concentrations were 4.9–300 ng of IL-6/L of diluent. The R 2 value for the IL-6 calibration curve was 0.983. The 14 human serum samples screened by this micro-ELISA technique for PSA concentrations generated a regression equation (linear) with a slope of 0.83 ± 0.10 and intercept of 0.74 ± 0.70 ( R 2 = 0.88). Conclusions: Multiplexed ELISA arrays are a feasible option for analyte quantification in complex biologic samples.

Soil Suction Measurements by Filter Paper

Abstract: This paper reports on an evaluation of wetting and drying filter paper suction calibration and soil total and matric suction measurement techniques of filter paper method. Calibration of the method was investigated by constructing two calibration curves; one by using the process of wetting the filter papers through vapor flow and the other by using the method of drying the filter papers through fluid flow. The wetting curve was constructed using sodium chloride (NaCl) salt solutions and Schleicher & Schuell No. 589-WH filter papers. It was found that the change in the wetting suction curve is very sensitive to minor changes in filter paper water content below about 1.5 log kPa (2.5 pF) suction. The drying curve was established by employing both pressure plate and pressure membrane devices and the same filter papers. In developing the filter paper calibration curves, the capabilities, pitfalls, and limitations of the method are also discussed.

Calibration in chemical measurement processes: I. A metrological approach

Abstract: A metrological approach to calibration, from the analytical chemistry point of view, is discussed. The terms referring to calibration, and usually employed in the literature (such as calibration point, correction, calibration factor, calibration curve and calibration function) are explained and clarified. Various definitions of calibration, compiled from several international standards, are placed in a metrological context. Likewise, the different types of calibration, which are not always well established, such as direct and indirect calibration, equipment and process calibration are described. Recovery factors and uncertainty in the calibration are also considered.

Calibrating a test system using unknown standards

Abstract: A method and system for calibrating a test system and a vector network analyzer use models of unknown calibration standards for a standards-based calibration. The models are selected for the unknown standards and performance data for each different calibration standard of the set are measured by the test system. The performance data is used to optimize the models by adjusting element values of constituent elements of the models. The optimized models are used to calibrate the test system such that the test system corrects for any imperfections in performance measurements taken of a device under test measured by the calibrated test system. The present invention further can correct for affects of a test fixture in device under test measurements. The method can also determine calibration coefficients for unknown calibration standards by extracting the calibration coefficients from the optimized models.

Determination of Nitrate in Water Containing Dissolved Organic Carbon by Ultraviolet Spectroscopy

Abstract: Direct measurement of ultraviolet (UV) light absorption by nitrate in the 200–205 nm wavelength band offers a reliable, accurate and rapid method of nitrate determination in natural waters. However, UV light is also strongly absorbed by organic matter at these wavelengths. A two-wavelength approach was adopted and evaluated for the correction of absorbance that organic matter might have contributed. The measurements were made at 205 nm and 300 nm. The relationship between absorbance at 205 nm and 300 nm due to organic matter was incorporated into traditional nitrate calibration curve to make allowance for the organic matter contribution. The method developed has a detection limit of 0.04 mg NO3-N dm−3 and is capable of determining nitrate concentration in the range of 0.08 – 4.0 mg NO3-N dm−3. In terms of accuracy and reproducibility, the method compares well with the hydrazine-reduction method, with matching precision (1.14% over the concentration range) and accuracy (± 2%). This two-wavelength ...

Rapid Quantitative Determination of Ciprofloxacin in Pharmaceuticals by Use of Solid-State FT-Raman Spectroscopy

Abstract: FT-Raman spectroscopy based on band intensity or band area measurements was used for the quantitative determination of ciprofloxacin in pharmaceutical solid dosage forms. Univariate calibration was used for quantitative analysis. Bands observed at 1708, 1624, 1548, 1493, 1273, 1253, 1238, 1024, 805, 787, 752, 718, 665, and 638 cm-1 were used. Calibration curves were linear in the concentration range of 3-100% w/w with correlation coefficients of 0.99-0.996 and 0.991-0.9993 for band intensity and band area measurements, respectively. Precision ranged from 0-11 and 0.4-12% relative standard deviation (RSD) (n = 3) for band intensity and band area measurements, respectively, and results were in good agreement with the results obtained by the current United States Pharmacopoeia (USP 24) and National Formulary (NF 19) method. Multivariate calibration was also used for quantitative analysis. Multiple linear regression using the intensities of the 1545 and 1272 cm-1 bands gave results in accordance with those obtained by the current United States Pharmacopoeia (USP 24) and National Formulary (NF 19) method. As measurement takes just 30 s using the analytical readout from a single band, the proposed method can be used to replace tedious and time-consuming methods.

Methods and apparatus for spectroscopic calibration model transfer

Abstract: A method and apparatus for measuring a biological attribute, such as the concentration of an analyte, particularly a blood analyte in tissue such as glucose. The method utilizes spectrographic techniques in conjunction with an improved instrument-tailored calibration model. In a calibration phase, calibration model data is modified to reduce or eliminate instrument-specific attributes, resulting in a calibration data set modeling intra-instrument variation. In a prediction phase, the prediction process is tailored for each target instrument separately using a minimal number of spectral measurements from each instrument.

A rapid method for peroxide value determination in edible oils based on flow analysis with Fourier transform infrared spectroscopic detection.

Abstract: The development of an automated, rapid and highly precise method for determination of the peroxide value in edible oils based on a continuous flow system and Fourier transform infrared (FTIR) spectroscopic detection is described. The sample stream was mixed with a solvent mixture consisting of 25% (v/v) toluene in hexanol which contained triphenylphosphine (TPP). The hydroperoxides present in the sample reacted stoichiometrically with TPP to give triphenylphosphine oxide (TPPO) which has a characteristic and intense absorption band at 542 cm−1. A 10% (m/v) TPP solution in the solvent mixture and a 100 cm reaction coil were necessary for complete reaction. FTIR transmission spectra were recorded using a flow cell equipped with CsI windows having an optical pathlength of 100 μm. By using tert-butyl hydroperoxide spiked oil standards and evaluation of the band formed at 542 cm−1 a linear calibration graph covering the range 1–100 PV (peroxide value; mequiv O2 kg−1 oil) was obtained. The relative standard deviation was 0.23% (n = 11) and the throughput 24 samples h−1. The developed system was also applied to the determination of PV in olive, sunflower and corn oils, showing good agreement with the official reference method of the European Community which is based on titration using organic solvents. The results obtained clearly show that the developed method is superior to the standard wet chemical method, hence suggesting its application in routine analysis and quality control.

Calibration of Time Domain Reflectometry for Water Content in Peat Soil

Abstract: Since peat soil differs from mineral soil in several respects, mineral-soil calibration functions for time domain reflectometry (TDR) are not necessarily applicable. This paper evaluates a number of calibration functions, both empirical polynomial and theoretical mixing models, on the basis of laboratory measurements on undisturbed Sphagnum peat samples. Deviations between different samples within this study indicate dissimilarities in dielectric properties between peats with different degrees of humification. Connections to physical properties such as amount of bound water and structural orientation are likely to exist. There is, however, a lack of methods to measure and quantify parameters expressing these properties. Therefore, until further studies on physical properties are accomplished, empirical or semi-empirical calibration curves are preferred. The best fit was obtained by an empirical, third order polynomial model. This model also gave a better fit than the mixing models when data were grouped into humification classes. However, all models reproduced pooled data with an r 2 better than 0.93.

On-line incorporation of cloud point extraction to flow injection analysis.

Abstract: The on-line incorporation of cloud point extraction (CPE) to flow injection analysis (FIA) is demonstrated for the first time. The technical difficulties of inducing the cloud point phenomenon, separating the surfactant-rich phase from the aqueous phase, and detecting trace amounts of analyte(s) in the presence of the highly scattering surfactant medium in an on-line FIA system were resolved by the following: (1) mixing the sample solution containing the analyte(s) and CPE surfactant with an appropriate salting-out agent, (2) using a collection column to entrap the analyte-containing surfactant aggregates, and ( 3) employing the peroxyoxalate chemiluminescence reaction for the sensitive and selective determination of the analyte(s) in the presence of surfactant micelles. The figures of merit for the determination of coproporphyrin in pretreated urine samples were as follows: precision, 1.1−2.2% (RSD); limit of detection, 2.0 μg/L; and the calibration curve was linear from 46 to 2319 (μ/L (r = 0.9996).

Application of laser-induced breakdown spectrometry for direct determination of trace elements in starch-based flours

Abstract: Spatially resolved laser-induced breakdown spectrometry (LIBS) was investigated to evaluate the feasibility as a quick and simple method to analyze trace elemental concentrations in starch-based flour samples. A Nd∶YAG laser beam (λ = 1064 nm, 30 mJ pulse−1) has been used for generation of laser-induced plasma on sample surface under reduced pressure of argon atmosphere. A series of starch powder samples containing different concentrations of Sr, Mg, Al, Cu, Cr, K, Mn, Rb, Cd, and Pb were used to construct the calibration curves and estimate detection limits of measurements. The calibration graphs for all elements show good linearity (correlation coefficient, r > 0.99) in the range 0–160 µg g−1 or within three orders of magnitude. Detection limits achieved were below 18 µg g−1 for all elements studied in this work. The lowest detection limit (0.3 µg g−1) was obtained from Sr measurement. Precision (%RSD) for the selected analysis was in the range 2–10%. The standard addition method was applied to assess the accuracy of LIBS using a NIES standard rice sample. The concentrations of Mg and Mn in NIES standard rice sample determined by spatially resolved LIBS technique have good agreements with those of certified value within an error range. The results indicate that spatially resolved LIBS has been shown to be an accurate technique for determining trace elements of ppm (µg g−1) level in starch-based food samples directly with an acceptable precision without any tedious digestion and dilution procedure.

Calibração de um equipamento de TDR para medida de umidade de solos

Abstract: The aim of this study was to obtain the calibration curves for a TDR (Time Domain Reflectometry) equipment using five soils from the Piracicaba, SP, Brazil. The suitability of the built-in and generic calibration curves was also tested. Individual fitted curves for each soil showed determination coefficients (R2) of about 0.99 and the fitted curve for all five soils together showed a value of R2 = 0.976. The standard error of estimate analysis has pointed out that generic curves are not suitable for more sensible applications, such as for absolute determination of soil water content. Comparison tests among fitted curves, generic curve and the equipment curve, pointed out that the first one is superior to the others. This study showed also that the equipment built-in calibration curve is not suitable for soil water content determinations for the five studied soils.

Application of solid-phase microextraction in the determination of diazepam binding to human serum albumin.

Abstract: In this paper, protein-drug interactions were studied by solid-phase microextraction (SPME) using diazepam binding to human serum albumin as a model system. Since drug compounds are normally polar and nonvolatile by nature, direct SPME is used in this work. The SPME extraction is an equilibrium process among the concentrations of the analyte partitioned onto the SPME fiber, free and bound drug in the solution. A calibration curve was first constructed by employing the amount of the analytes partitioned on the fiber versus the free analyte concentration in the solution in the absence of protein. In method I, the extraction was performed in the protein solution with known diazepam concentration. In method II, diazepam was first loaded onto the fiber by extracting in solution with known diazepam concentration. This fiber was subsequently transferred into the protein solution for desorption. The amount of the analyte left on the fiber was analyzed after the system reached equilibrium. The free drug concentration was then obtained from the calibration curve for both methods. The Scatchard plot was finally employed to obtain the number of binding sites and the equilibrium binding constants. Since only a very small amount of the protein solution is required (150 microL for each extraction), method II is very useful for circumstances where the protein amount is very limited. The direct measurement method proposed in this paper does not need a GC response factor, which significantly decreases the experimental error. The only measurement needed is the area count change (ratio) of the fiber injections before and after the protein was introduced into the solution. The difference between the direct measurement method for method I and method II is discussed. The result illustrated that the SPME direct measurement method provided both theoretical accuracy and simplicity in such applications.

A novel pressure array sensor based on contact resistance variation: Metrological properties

Abstract: The working principle and the metrological performances of a novel array sensor devoted to pressure map measurements are experimentally analyzed here. The physical principle on which the sensor elements are sensitive to the pressure is the variation of the contact resistance. Pressure maps from 1 up to 500 kPa can be measured. The prototype here utilized for the metrological characterization has been an 8×8 matrix sensor with a 5 mm spatial resolution over both x and y direction and a total thickness of 150 μm. The materials that have been chosen to assemble the prototype yielded to a very flexible and robust sensor which can easily be fitted over round surfaces without being damaged or leading to an alteration of its measuring properties. The static and the dynamic metrological performances of the sensor that have been studied and discussed are the response function and the calibration curve, the repeatability, the sensitivity, the time drift, the hysteresis, and the dynamic response. In spite of its fun...

NIR transmittance pulse oximetry system with laser diodes

Abstract: A transmittance pulse oximetry system based on near-infrared laser diodes (LD) for monitoring arterial blood hemoglobin oxygen saturation (So 2 ) has been previously reported. In this work we present the results obtained after improvements in the sensor configuration, signal processing algorithm and calibration procedure. The pulse oximetry system also comprises the sensor electronics, and a data acquisition board installed on a handheld personal computer. The two LD chips are mounted on a single metal heat-sink and as photo- detectors are used silicon p-i-n photodiodes with the first amplifier stage situated in their back side. The real time calculation of the parameters related to So 2 is carried out through a numeric separation of the pulsatile and non- pulsatile components of the photoplethysmographic signals for both wavelengths and a non-linear filtering. Patients with respiratory failure conditions were monitored as a part of the calibration procedure in order to cover a wide range of So 2 -values. A calibration curve have been derived through the determination of in vitro arterial So 2 with a significant quantity of experimental points ranging from 60 to almost 100%. The obtained results demonstrate that it is possible to apply the proposed system to monitoring a wide range of oxygen saturation levels.

An iterative EPID calibration procedure for dosimetric verification that considers the EPID scattering factor

Abstract: There has been an increasing interest in the application of electronic portal imaging devices (EPIDs) to dosimetric verification, particularly for intensity modulated radiotherapy Although not water equivalent, the phantom scatter factor of an EPID, Spe, is generally assumed to be that of a full phantom, Sp, a slab phantom, Sps, or a mini phantom This assumption may introduce errors in absolute dosimetry using EPIDs A calibration procedure that iteratively updates Spe and the calibration curve (pixel value to dose rate) is presented The EPID (Varian Portal Vision) is irradiated using a 20 x 20 cm2 field with different beam intensities The initial guess of dose rates in the EPID is calculated from ionization chamber measurements in air, multiplied by Sp or Sps The calibration curve is obtained by fitting EPID readings from pixels near the beam central axis and dose rates in EPID to a quadratic equation The Spe is obtained from EPID measurements in 10 X 10 cm2 and 20 x 20 cm2 field and from the calibration curve, and is in turn used to adjust the dose rate measurements and hence the calibration curve The above procedure is repeated until it converges The final calibration curve is used to convert portal dose to dose in the slab phantom, using the calibrated Spe, or assuming Spe = Sp or Spe=Sps The converted doses are then compared with the dose measured using an ionization chamber We also apply this procedure to off-axis points and study its dependence on the energy spectrum The hypothesis testing results (on the 95% significance level) indicate that systematic errors are introduced when assuming Spe = Sp or Spe=Sps and the dose calculated using Spe is more consistent with ionization chamber measurements Differences between Spe and Sps are as large as 2% for large field sizes The measured relative dose profile at dmax using the EPID agrees well with the measured profile at dmax of the isocentric plane using film in a polystyrene phantom with full buildup and full backup, for open and wedged fields, and for a broad range of field sizes of interest The dependence of the EPID response on the energy spectrum is removed once the calibration is performed under the same conditions as the actual measurements