Showing papers on "Calibration curve published in 2009"

Method of calibrating an analyte-measurement device, and associated methods, devices and systems

Abstract: The invention relates to a method for calibrating an analyte-measurement device that is used to evaluate a concentration of analyte in bodily fluid at or from a measurement site in a body. The method involves measuring a concentration, or calibration concentration, of an analyte in blood from an “off-finger” calibration site, and calibrating the analyte-measurement device based on that calibration concentration. The invention also relates to a device, system, or kit for measuring a concentration of an analyte in a body, which employs a calibration device for adjusting analyte concentration measured in bodily fluid based on an analyte concentration measured in blood from an “off-finger” calibration site.

Magnetic nanoparticle temperature estimation

Abstract: The authors present a method of measuring the temperature of magnetic nanoparticles that can be adapted to provide in vivo temperature maps. Many of the minimally invasive therapies that promise to reduce health care costs and improve patient outcomes heat tissue to very specific temperatures to be effective. Measurements are required because physiological cooling, primarily blood flow, makes the temperature difficult to predict a priori. The ratio of the fifth and third harmonics of the magnetization generated by magnetic nanoparticles in a sinusoidal field is used to generate a calibration curve and to subsequently estimate the temperature. The calibration curve is obtained by varying the amplitude of the sinusoidal field. The temperature can then be estimated from any subsequent measurement of the ratio. The accuracy was 0.3 degree K between 20 and 50 degrees C using the current apparatus and half-second measurements. The method is independent of nanoparticle concentration and nanoparticle size distribution.

Effect of calibration method on Tekscan sensor accuracy.

Abstract: Tekscan pressure sensors are used in biomechanics research to measure joint contact loads. While the overall accuracy of these sensors has been reported previously, the effects of different calibration algorithms on sensor accuracy have not been compared. The objectives of this validation study were to determine the most appropriate calibration method supplied in the Tekscan program software and to compare its accuracy to the accuracy obtained with two user-defined calibration protocols. We evaluated the calibration accuracies for test loads within the low range, high range, and full range of the sensor. Our experimental setup used materials representing those found in standard prosthetic joints, i.e., metal against plastic. The Tekscan power calibration was the most accurate of the algorithms provided with the system software, with an overall rms error of 2.7% of the tested sensor range, whereas the linear calibrations resulted in an overall rms error of up to 24% of the tested range. The user-defined ten-point cubic calibration was almost five times more accurate, on average, than the power calibration over the full range, with an overall rms error of 0.6% of the tested range. The user-defined three-point quadratic calibration was almost twice as accurate as the Tekscan power calibration, but was sensitive to the calibration loads used. We recommend that investigators design their own calibration curves not only to improve accuracy but also to understand the range(s) of highest error and to choose the optimal points within the expected sensing range for calibration. Since output and sensor nonlinearity depend on the experimental protocol (sensor type, interface shape and materials, sensor range in use, loading method, etc.), sensor behavior should be investigated for each different application.

Rapid Determination of Free Fatty Acid in Extra Virgin Olive Oil by Raman Spectroscopy and Multivariate Analysis

Abstract: We introduce a visible Raman spectroscopic method for determining the free fatty acid (FFA) content of extra virgin olive oil with the aid of multivariate analysis. Oleic acid was used to increase the FFA content in extra virgin olive oil up to 0.80% in order to extend the calibration span. For calibration purposes, titration was carried out to determine the concentration of FFA for the investigated oil samples. As calibration model for the FFA content (FFA%), a partial least squares (PLS) regression was applied. The accuracy of the Raman calibration model was estimated using the root mean square error (RMSE) of calibration and validation and the correlation coefficient (R 2) between actual and predicted values. The calibration curve of actual FFA% obtained by titration versus predicted values based on Raman spectra was established for different spectral regions. The spectral window (945–1600 cm−1), which includes carotenoid bands, was found to be a useful fingerprint region being statistically significant for the prediction of the FFA%. High R 2 and small RMSE values for calibration and validation could be obtained, respectively.

Laser ablation—laser induced breakdown spectroscopy (LA-LIBS): A means for overcoming matrix effects leading to improved analyte response

Abstract: Laser-ablation laser-induced breakdown spectroscopy (LA-LIBS) is proposed as a novel analytical scheme with goals of improved analyte response, minimization of sample matrix effects, and use of non-matrix matched standards. A direct comparison of the LA-LIBS approach and a traditional direct LIBS analysis was made for a set of seven reference materials, ranging from nearly pure iron to copper-nickel and aluminum alloys. The precision of each approach was assessed using calibration curves, and the LA-LIBS configuration was demonstrated to consistently produce a superior analytical response, as assessed by the linear least-squares fit correlation coefficient and y-intercept values. Significantly, the normalized (by Fe) response of the four targeted analyte species (Al, Mn, Mg and Cu) was successfully reduced to a single calibration curve with the LA-LIBS approach. In addition, particle size measurements of the laser-ablation plume were recorded along with SEM and white-light interferometry analysis of ablation craters for assessment of the analytical sample as presented to the analytical LIBS plasma. Finally, the effect of carrier gas is explored by substitution of nitrogen with helium.

A bayesian approach to the estimation of radiocarbon calibration curves: The INTCAL09 methodology

Abstract: This article presents a new approach to the construction of radiocarbon calibration curves. The Bayesian methodology was developed specifically to facilitate construction of the 2009 updates to the internationally agreed 14C calibration curves known as IntCal09 and Marine09. The curve estimation approach taken uses Markov chain Monte Carlo sampling, specifically a Metropolis-within-Gibbs sampler, which offers improved flexibility and reliability over the approaches used in the past. In particular, the method allows accurate modeling of calibration data with 14C determinations that arise from material deposited over several consecutive calendar years and that exhibit complex uncertainty structures on their calendar date estimates (arising from methods such as wiggle-matching and varve counting).

A Novel Calibration-Free Method of Measurement of Oxygen Saturation in Arterial Blood

Abstract: In present-day pulse oximeters, oxygen saturation in arterial blood (SpO2) is computed by utilizing an empirical relationship extracted from a calibration curve. The calibration curve is obtained by curve-fitting data acquired from volunteers. A novel method of computation of SpO2 that does not require the use of a calibration curve is presented in this paper. Based on a model for the attenuation of light through skin, tissue, bone, and blood, suitable processing steps are identified so that the analytical expression derived for the estimation of SpO2 becomes free of not only patient but sensor-dependent parameters as well. The experimental results presented in this paper establish the efficacy of the proposed method.

Characterization of a novel calibration method for mineral density determination of dentine by X-ray micro-tomography

Abstract: Laboratory micro-CT systems, although limited by beam hardening effect and instability of the source, have been utilized to measure mineral density in combination with specific image processing methods. However, few attempts have been made to accurately determine mineral density profiles in dentine due to the lack of suitable calibration standards. The aim of this study was to develop a calibration method to evaluate mineral density profiles in dentine including changes associated with dentinal caries. A series of K2HPO4 solution phantoms in a concentration range between 0 and 0.9 g cm−3-coupled to a set of water infiltrated porous solid hydroxyapatite (HA) phantoms, with mineral densities ranging from 1.52 to 2.08 g cm−3, was used in this investigation. First we evaluated the micrometer-scale homogeneity and noise in the HA phantoms using a commercial laboratory micro-CT system. Then an experimental validation was performed of the linearity over the entire density range of these two different calibration materials. The results show the HA phantoms extended the calibration curve obtained from K2HPO4 solution phantoms to densites as high as 2.08 g cm−3; the linearity remains stable at different energy levels. Finally, compared to the reference micro-CT calibration methods, the advantages of this new method are discussed. We conclude that this calibration method allows a more rational assessment of mineral density of dentine by micro-CT and has a promising potential for future studies.

High-performance liquid chromatography method for determination of carnosic acid in rat plasma and its application to pharmacokinetic study

Abstract: A sensitive and reproducible high-performance liquid chromatography method with ultraviolet detection (UV) was developed for the determination of carnosic acid (CA) in rat plasma. After simple acidification and liquid-liquid extraction of plasma samples using gemfibrozil as an internal standard, the supernatant was evaporated to dryness under a gentle stream of nitrogen. The residue was reconstituted in 200 microL before being injected into the chromatographic system. The analysis was performed on a C(18) column protected by an ODS guard column using acetonitrile-0.1% phosphoric acid (55:45, v/v) as mobile phase, and the wavelength of the UV detector was set at 210 nm. The calibration curve was linear over the range of 0.265-265.0 microg/mL with a correlation coefficient of 0.9997. The recovery for plasma samples of 0.530, 13.25, 132.5 and 265.0 microg/mL was 72.2, 87.9, 90.4 and 94.7%, respectively. The intra-day and inter-day relative standard deviations for the measurements of quality control samples were less than 3.1%. The stability of the plasma samples was also validated. This method was successfully used to study the pharmacokinetics and bioavailability of CA in rats.

A portable capillary electropherograph equipped with a cross-sampler and a contactless-conductivity detector for the detection of the degradation products of chemical warfare agents in soil extracts.

Abstract: A fully portable CE device equipped with a capacitively coupled contactless-conductivity detector and a cross-injection device is put to the test in laboratory conditions. The portable device is capable of working on batteries for at least 4 h. After that, its performance is strongly affected by the drop in the high-voltage output and analysis may be interrupted if its length exceeds a reasonable time. The concentration of the BGE affects both ionic strength and conductivity. Choosing an optimal concentration of BGE is therefore about finding a good compromise between selectivity and sensitivity. All experiments were performed using a mixture of histidine and MES with a concentration of 15 mM as BGE. The performance of the cross-injection device is optimized by the use of internal standards. Satisfactory reproducibility is gained as the RSD of peak areas is reduced to 8% or less. LODs for different phosphonic acids are in the range of 2.5-9.7 microM. For the analysis of adsorption of phosphonic acids in sand and loamy soil samples, calibration curves are constructed. Linearity in a measured concentration range of 10-100 microM is excellent, as the squares of correlation constants are approximately 1. The concentration analysis of phosphonic acids in soil extracts demonstrates that their adsorption curves in sand and loamy soil follow different adsorption isotherms.

Applicability of standardless semiquantitative analysis of solids by high-irradiance laser ionization orthogonal time-of-fight mass spectrometry.

Abstract: A compact high-irradiance laser ionization time-of-flight mass spectrometry system has been developed for the multielemental analysis of solids. Helium was introduced into the ion source as a buffer gas to cool high kinetic energy ions and suppress the interference of multicharged ions. A special pulse train repelling mode was used to achieve explicit spectra. Two quantitative methods are described for the laser ionization mass spectrometry in this paper. The first of these is the routine calibration curve quantitation, in which various matrix-matched standards are required; the second method, which is based on the uniform correlation between the signal and elemental concentration of different samples, is more convenient and covers a typical dynamic range of 6 orders. All the investigations and results indicate satisfactory performance of the newly developed instrument and its applicability for simultaneous multielemental analysis of solid samples.

An optical fibre reflectance sensor for p-aminophenol determination based on tetrahydroxycalix[4]arene as sensing reagent

Abstract: A fibre-optic sensor for p-aminophenol (PAP) based on the use of 25,26,27,28-tetrahydroxycalix[4]arene (CAL4) immobilised onto Amberlite XAD-16 and reflectance spectrometry has been developed. The sensor is based on the reaction of PAP with CAL4 in presence of an oxidant to produce an indophenol dye. The reflectance measurements were carried out at a wavelength of 620 nm since it yielded the largest divergence different in reflectance spectra before and after reaction with the analyte. A highly linear calibration curve (r2 = 0.992) was observed in the PAP concentration range of 0.5–35 ppm (linear within 0.5–5.5 ppm) with a calculated limit of detection (LOD), defined as the lowest concentration level of analyte that the proposed method can detect to be statistically different from an analytical blank (i.e., yielding an analytical response greater than three times the standard deviation of a blank), of 0.109 ppm. The sensor response from different probes (n = 5) gave an RSD of 1.8% at 10.9 ppm PAP concentration. The response time of the optical one-shot sensor was 5 min for a stirred solution. The intra- and inter-assay variability (as relative standard deviation: RSD) was approximately 2 and 4%, respectively. The lifetime of the blank sensor (CAL4 adsorbed onto XAD-16) was at the order of weeks–months when protected from light, while of the analyte sensor (XAD-16 + CAL4, to which the oxidation product of PAP is coupled) was at the order of days when protected from air and light. Using the optical sensing probe, PAP in urine, pharmaceutical and pharmaceutical wastewater was determined. Although aminophenols showed serious interference, the method was not affected from common ions and from various important drug active constituents present in urine and pharmaceutical effluents such as acetaminophen, acetylsalicylic acid, sorbitol, and caffeine. The proposed technique was tested by replicate analysis of several complex samples with spiked PAP, with recoveries ranging between 97 and 102%.

Attenuated Total Internal Reflection Fourier Transform Infrared Spectroscopy: A Quantitative Approach for Kidney Stone Analysis

Abstract: The impact of kidney stone disease is significant worldwide, yet methods for quantifying stone components remain limited. A new approach requiring minimal sample preparation for the quantitative analysis of kidney stone components has been investigated utilizing attenuated total internal reflection Fourier transform infrared spectroscopy (ATR-FT-IR). Calcium oxalate monohydrate (COM) and hydroxylapatite (HAP), two of the most common constituents of urinary stones, were used for quantitative analysis. Calibration curves were constructed using integrated band intensities of four infrared absorptions versus concentration (weight %). The correlation coefficients of the calibration curves range from 0.997 to 0.93. The limits of detection range from 0.07 +/- 0.02% COM/HAP where COM is the analyte and HAP is the matrix, to 0.26 +/- 0.07% HAP/COM where HAP is the analyte and COM is the matrix. This study shows that linear calibration curves can be generated for the quantitative analysis of stone mixtures provided the system is well understood especially with respect to particle size.

Spectral filtering modulation method for estimation of hemoglobin concentration and oxygenation based on a single fluorescence emission spectrum in tissue phantoms.

Abstract: Purpose: Hemoglobin concentration and oxygenation in tissue are important biomarkers that are useful in both research and clinical diagnostics of a wide variety of diseases such as cancer. The authors aim to develop simple ratiometric method based on the spectral filtering modulation (SFM) of fluorescence spectra to estimate the total hemoglobin concentration and oxygenation in tissue using only a single fluorescence emission spectrum, which will eliminate the need of diffuse reflectance measurements and prolonged data processing as required by most current methods, thus enabling rapid clinical measurements. Methods: The proposed method consists of two steps. In the first step, the total hemoglobin concentration is determined by comparing a ratio of fluorescence intensities at two emission wavelengths to a calibration curve. The second step is to estimate oxygen saturation by comparing a double ratio that involves three emission wavelengths to another calibration curve that is a function of oxygen saturation for known total hemoglobin concentration. Theoretical derivation shows that the ratio in the first step is linearly proportional to the total hemoglobin concentrations and the double ratio in the second step is related to both total hemoglobin concentration and hemoglobin oxygenation for the chosen fiber-optic probe geometry. Experiments on synthetic fluorescent tissue phantoms, which included hemoglobin with both constant and varying oxygenation as the absorber, polystyrene spheres as scatterers, and flavin adenine dinucleotide as the fluorophore, were carried out to validate the theoretical prediction. Results: Tissue phantom experiments confirm that the ratio in the first step is linearly proportional to the total hemoglobin concentration and the double ratio in the second step is related to both total hemoglobin concentrations and hemoglobin oxygenation. Furthermore, the relations between the two ratios and the total hemoglobin concentration and hemoglobin oxygenation are insensitive to the scattering property of the tissue model for the chosen probe geometry. Conclusions: A simple two-step ratiometric method based on the SFM of fluorescence spectra is proposed to estimate the total hemoglobin concentration and oxygenation in a tissue model using only a single fluorescence emission spectrum. This method is immune to the variation in system throughput caused by inconsistent optical coupling because of its ratiometric nature. Calibration curves are insensitive to the scattering coefficient for the chosen probe geometry. Moreover, since only fluorescence intensities at a few wavelengths in a single fluorescence emission spectrum are needed in this method, the SFM method minimizes the amount of required data and reduces the data acquisition time. Finally, since this method does not use nonlinear regression, it can dramatically save computation time in data processing. The high sensitivity of the proposed method to superficial tissue volumes makes it ideal for fluorescence based oximetry and medical diagnostics in applications such as early epithelial cancer diagnosis or wherever the measured tissue volume is exposed to the outside such as in open surgery.

Method for analyzing components of iron ore by using X-ray fluorescence spectrum

Abstract: The invention discloses a method for analyzing the components of iron ore by using an X-ray fluorescence spectrum, which comprises before-analysis preparation (1) and analysis report submission (5), and the steps between the before-analysis preparation (1) and the analysis report submission (5) including molten sample manufacturing (2), detection by an internal standard method (3) and analysis by a calibration curve method (4), wherein in the before-analysis preparation (1) step, a working curve (16) is built; in the detection by an internal standard method (3) step, an internal standard line of a molten sample is measured; and in the analysis by a calibration curve method (4) step, the measurement results of the molten sample are obtained. The method completes the measurement of all elements in the iron ore by melting once, is high in measurement accuracy, simplifies process and time for measurement, reduces cost of the analysis of the components of the iron ore, and is suitable to be applied to the iron and steel industry and researches.

Determination of toxic trace impurities in titanium dioxide by solid sampling-electrothermal vaporization-inductively coupled plasma mass spectrometry

Abstract: This paper reports on the performance of solid sampling-electrothermal vaporization-inductively coupled plasma mass spectrometry (SS-ETV-ICPMS) for the direct multi-element determination of six toxic trace impurities (As, Cd, Hg, Pb, Sb and Zn) in three different TiO2 samples. Careful selection of the most suitable target nuclides for the different analytes and temperature program optimization permit the reliable monitoring of the analytes of interest, while avoiding the occurrence of potentially relevant spectral interferences. A pyrolysis-free program, in which simultaneous vaporization of all the analytes is carried out at a relatively low temperature (1700 °C), was used. In this way, sample matrix and analyte co-vaporization is avoided, considerably reducing matrix effects and allowing the determination of Zn, which would otherwise be hampered by a spectral overlap with TiO+ ions. Calibration against aqueous standards was found to be feasible. Addition of 50 ng Pd as carrier agent improved the linearity of the calibration curves. Two different internal standards (105Pd+ and 125Te+) were used to compensate for matrix effects. The method thus developed exhibits interesting features: low limits of detection (ng g−1 range) for all of the elements, at least an order of magnitude lower than those for digestion-based procedures; high sample throughput (maximum 35 min per determination), contrasting with the 2 h required for sample digestion and subsequent analysis; low sample consumption (a few milligrams only); precision values usually in the 9–13% RSD range; and last but not least, the absence of any sample pre-treatment, with the subsequent lower risk of analyte losses, contamination or personal and instrumental harms derived from the necessity of using hazardous reagents for sample digestion. SS-ETV-ICPMS therefore seems to be a promising alternative for industrial control analysis of TiO2 samples with analyte contents ranging from a few ng g−1 to several hundreds of µg g−1.

Validated High-Performance Liquid Chromatographic Technique for Determination of 5-Fluorouracil: Applications to Stability Studies and Simulated Colonic Media

Abstract: A simple isocratic stability-indicating high-performance liquid chromatographic method with UV detection using thymine as an internal standard is developed The method is validated and the degradation products are determined The method is applied for the assessment of the stability of 5-fluorouracil in rat caecal content as a simulated colon medium under anaerobic conditions The drug decomposes under acidic, alkaline, thermal, and oxidative stress The drug is highly susceptible to acidic, alkaline, and oxidative hydrolysis as compared to alkaline conditions Separation of the drug from major and minor degradation products is successfully achieved on a C 18 analytical, μ-bondapak column The detection wavelength is 260 nm The method is validated, and the response is found to be linear in the drug concentration range of 01-20 μg/mL The high linearity of the standard calibration curve of 5-fluorouracil in the rat content is found to be R 2 = 0998 in the concentration range from 05 to 5 μg/mL No degradation occurred after incubation of 5-fluorouracil in the rat caecal contents The standard deviation and coefficient of variation values for intra- and inter-day precision study exhibit acceptable accuracy and precision data throughout the concentration range investigated