Showing papers on "Calibration curve published in 1997"

Solid-Phase Microextraction for the Analysis of Human Breath

Abstract: Solid-phase microextraction (SPME) has been applied to the quantitative determination of ethanol, acetone, and isoprene in human breath. The method involves extraction and preconcentration with a fused silica fiber coated with a polymeric stationary phase, desorption at 200 °C, and assay by gas chromatography/mass spectrometry. Three different fiber coatings have been evaluated with regard to sensitivity, linear range, precision, and detection limits. Typical RSD values in the range 2%−6% could be obtained, depending on the fiber coating and the compound investigated. The calibration curves for the compounds are reproducible and linear over the concentration ranges found in human breath samples. The method is capable of detecting concentrations of acetone and isoprene reported for healthy subjects. The influence of temperature and humidity on the extraction process has been studied in detail. A linear relationship between log K versus 1/T allows the calibration of the method for any given temperature. The...

Improved infrared spectroscopic method for the analysis of degree of N -deacetylation of chitosan

Abstract: Various infrared spectroscopic techniques for the analysis of degree of N-deacetylation of chitosan were evaluated for accuracy. A new method was proposed which involved development of a calibration curve using the absorbance intensities of the chitosan infrared spectrum at 1655 and 3450 cm−1. The degree of N-deacetylation of various chitosan samples was then determined by using the absorption ratios [A1655/A3450] in the equation of the calibration curve. This method yielded results which were superior to those of any of the previously reported infrared spectroscopic methods tested herein.

Apparatus and method for detection and concentration measurement of trace metals using laser induced breakdown spectroscopy

Abstract: A method and apparatus for in situ detection and concentration measurement of trace elements in an analysis sample is disclosed. The invention uses laser induced breakdown spectroscopy (LIBS) wherein femtosecond pulsed laser energy is employed to produce the plasma. The femtosecond pulsed laser energy is focused on the analysis sample to produce the plasma and the resulting emission is delivered for spectral analysis. Because the method and apparatus of the present invention allow breakdown of the analysis sample without propagation of energy to the sample-air interface, a plasma is produced that consists essentially of sample materials without being contaminated by air plasma formation. Thus, the background emission is reduced and there is no need to wait for the plasma to cool down over time before detecting the spectral lines of the sample. Because there is no need to wait for cooling before spectral measurement, lower detection limits are possible. Furthermore, concentration measurement accuracy is improved using intensity rationing techniques since a calibration curve produced using the method and apparatus of the present invention is substantially more linear than those using the conventional nanosecond pulsed LIBS.

Absolute analysis of particulate materials by laser-induced breakdown spectroscopy.

Abstract: We have developed a new data acquisition approach followed by a suitable data analysis for Laser-induced breakdown spectroscopy. It provides absolute concentrations of elements in particulate materials (e.g., industrial dusts and soils). In contrast to the known calibration procedures (based on the ratio of spectral lines), which are applicable only when one component is constant, this approach requires no constant constituent and results in absolute (rather than relative) concentrations. Thus, the major drawback of this analytical method, namely, the signals' instability (especially when particulate materials are concerned) is partially solved. Unlike the commonly used integrated data acquisition, we use a sequence of signals from single breakdown events. We compensate for pulse to pulse fluctuations in an intrinsic way, and the final results do not depend on the presence of any constant component. Extended linear calibration curves are obtained, and limits of detection are improved by 1 order of magnitu...

A New Method for Automated Dynamic Calibration of Tipping-Bucket Rain Gauges

Abstract: Existing methods for dynamic calibration of tipping-bucket rain gauges (TBRs) can be time consuming and labor intensive. A new automated dynamic calibration system has been developed to calibrate TBRs with minimal effort. The system consists of a programmable pump, datalogger, digital balance, and computer. Calibration is performed in two steps: 1) pump calibration and 2) rain gauge calibration. Pump calibration ensures precise control of water flow rates delivered to the rain gauge funnel; rain gauge calibration ensures precise conversion of bucket tip times to actual rainfall rates. Calibration of the pump and one rain gauge for 10 selected pump rates typically requires about 8 h. Data files generated during rain gauge calibration are used to compute rainfall intensities and amounts from a record of bucket tip times collected in the field. The system was tested using 5 types of commercial TBRs (15.2-, 20.3-, and 30.5-cm diameters; 0.1-, 0.2-, and 1.0-mm resolutions) and using 14 TBRs of a single type (20.3-cm diameter; 0.1-mm resolution). Ten pump rates ranging from 3 to 154 mL min21 were used to calibrate the TBRs and represented rainfall rates between 6 and 254 mm h21 depending on the rain gauge diameter. All pump calibration results were very linear with R2 values greater than 0.99. All rain gauges exhibited large nonlinear underestimation errors (between 5% and 29%) that decreased with increasing rain gauge resolution and increased with increasing rainfall rate, especially for rates greater than 50 mm h21. Calibration curves of bucket tip time against the reciprocal of the true pump rate for all rain gauges also were linear with R2 values of 0.99. Calibration data for the 14 rain gauges of the same type were very similar, as indicated by slope values that were within 14% of each other and ranged from about 367 to 417 s mm h21. The developed system can calibrate TBRs efficiently, accurately, and virtually unattended and could be modified for use with other rain gauge designs. The system is now in routine use to calibrate TBRs in a large rainfall collection network at Yucca Mountain, Nevada.

Analytical figures of merit for tensorial calibration

Abstract: The subject of analytical figures of merit for tensorial calibration is critically reviewed. Tensorial calibration derives its name from tensor algebra, which provides a classification of calibration methods depending on the complexity of the data obtained for one chemical sample. Expressions for net analyte signal, sensitivity (classical model formulation), "inverse sensitivity' (inverse model formulation), selectivity, signal-to-noise ratio and limit of detection (in signal space) are proposed for Nth-order data (N≥2) that are consistent with the accepted zeroth-order definitions and previously proposed definitions for first-order data. Useful relationships between the proposed figures of merit and prediction error variance are described. A selectivity-based rule of thumb is derived to compare data analysis across orders. Central to the currently proposed framework for analytical figures of merit is the reduction of a complex data structure to the scalar net analyte signal. This allows for the construction of a univariate calibration graph (classical or inverse model), independent of the complexity of the data. Enhanced visualization and interpretation are obtained that may help to bridge the gap between Nth-order calibration and the intuitive understanding of zeroth-order data. © 1997 John Wiley & Sons, Ltd.

In-flight calibration of NOAA AVHRR visible and near-IR bands over Greenland and Antarctica

Abstract: A new method for in-flight calibration of NOAA AVHRR visible and near-IR bands is presented. The approach involves using calibrated NOAA-9 near-nadir reflectances over spatially and temporally uniform ice-surfaces from Greenland and Antarctica to produce reflectance calibration curves for AVHRR instruments in all orbits. The reflectance calibration curves consist of second order polynomial regressions of reflectance on solar zenith angle, derived from observations that are spatially uniform in all AVHRR channels over sub-regions of area 68 km by 68 km. By comparing reflectances from uncalibrated AVHRR instruments with these calibration curves, new channel 1 and 2 calibration coefficients are obtained with an accuracy of 5 per cent. The main advantages of this calibration method are: (1) calibration targets are large; (2) it can be applied over multiple years; (3) it is applicable for a wide range of solar zenith angles, and can therefore be used year-round. When calibration coefficients inferred from NOAA...

Quantitative analysis of additives in solid zinc alloys by laser-induced plasma spectrometry

Abstract: In this paper the use of laser-induced plasma spectrometry (LIPS) for the quantitative analysis of Al, Cu, Fe, Pb and Sn components in solid zinc alloys is evaluated. Laser-induced plasmas are characterized using spectroscopic diagnostic techniques that yield the excitation temperature and electron density. Optimal experimental conditions for analysis are evaluated, including time gating parameters and distance from focusing lens to target where it is found that the focus of the laser beam should be positioned behind the target in order to prevent secondary air plasmas from forming in front of the target. Calibration curves are produced for several analytical lines, and the analytical performance of the technique is assessed. While low detection limits (<60 ppm) are found, the precision of measurement could be improved.

Rapid Laboratory Calibration of Time Domain Reflectometry Using Upward Infiltration

Abstract: We propose an upward infiltration method to calibrate a time domain reflectometry (TDR) system. The method is rapid, allows the soil to remain unchanged during the experiment, and provides hundreds of data points. Three experiments were conducted using 18.7-cm-long probes in soils of three textures (nine experiments total). Calibrations also were performed by packing soil cores with soil at progressively higher water contents. The data from the two methods were fitted using regression techniques to two published models of the dielectric constant-water content relationship. The results show that the calibration curves of all three soils, fitted simultaneously to replicate experiments, were similar in shape and statistically the same. A single calibration curve, fitted simultaneously to the replicate experiments of the three soils, was compared with Topps equation and was statistically the same. The results support the conclusion that the upward infiltration method provides a fast and repeatable calibration method, consistent with conventional calibration.

The british archaeomagnetic calibration curve: an objective treatment

Abstract: This paper examines the limitations and deficiencies of the current archaeomagnetic calibration curve in use in Britain and explores a different approach to its construction, drawing on recent advances in this subject, in particular the use of a weighted moving window method of averaging. The main advantage of this method is shown to be its ability to take into account uncertainties in both the magnetic direction and the archaeological date of data used in the calibration curve, leading to a secular variation curve with an associated error estimate. Hence, when dating a magnetic direction, the uncertainties in the calibration curve can be taken into account, as well as the uncertainties in the magnetic direction to be dated.

Determination of Total Mercury in Sediments by Microwave-assisted Digestion-Flow Injection-Inductively Coupled Plasma Mass Spectrometry

Abstract: A method for the determination of total mercury in sediment samples was developed. Extraction of mercury from a sample matrix was carried out in an open vessel microwave digestion system while maintaining mild conditions during digestion in order to avoid any loss of mercury due to volatilization. A complexing agent (EDTA) and a surfactant (Triton X-100) were added to the samples in order to eliminate memory effects associated with mercury determinations and to obtain reproducible linear calibration curves. Standard additions and internal standardization were used for calibration and correction in an FI–ICP-MS detection system. The method was validated using the certified reference material PACS-1 and the reference materials IAEA-356 and S19 and gave results in good agreement with the certified and reference values. Sediment samples from Arcachon Bay were also analysed. Detection limits of 10 ng g -1 for solution and 1 ng g -1 for dry sediment samples were obtained.

Two- and three-parameter calibrations of time domain reflectometry for soil moisture measurement

Abstract: Time domain reflectometry (TDR) is widely used to measure and monitor soil water. The commonly used calibration curve is the third-degree “universal polynomial” of Topp et al. [1980]. The most common refinement is calibration to a specific soil but still using four parameters (coefficients) from fitting a third-degree polynomial. Here we demonstrate that a three-parameter expression, θυ = aKaα + )where the three parameters a, b, and α are determined by fitting water content θυ to the dielectric coefficient Ka). This form is consistent with the well-known mixing model. For an isotropic soil with homogeneous water distribution this expression is further simplified to two parameters by taking α=0.5. When α is 0.5, its calibration is equivalent to the linear calibration between θυ and the travel time along the waveguide. In addition, the simple three-parameter expression can be easily inverted without losing accuracy with regard to the original calibration. The TDR calibration expressed in a three-parameter form not only achieves a good fit but also conveys a physical connotation.

Biological dosimetry in simulated in vitro partial irradiations.

Abstract: The assessment by biological dosimetry of the dose received in cases of partial-body exposure to ionizing radiation can be underestimated because irradiated lymphocytes are mixed with non-irradiated ones. To determine if the exposure affects the whole body or only part of it, it may be useful to know the distribution of cells with more than one dicentric chromosome. We established a dose-effect calibration curve for X-rays by analysis of chromosome aberrations. Moreover, in the present work, 20 partial irradiations for four different doses of X-rays (2, 3, 4 and 5 Gy) have been simulated by mixing irradiated and non-irradiated blood in different proportions. In all cases, the 95% confidence intervals of the estimated dose included the real dose of irradiation. However, some difficulties were found for the estimation of the fraction of irradiated cells. In the present study, D0 3.8 allows to obtain the best fit between the estimated and the real fraction of irradiated cells.

A noniterative polynomial 2-D calibration method implemented in a microcontroller

Abstract: Output signal handling of a smart sensor usually involves a calibration facility to correct for input-output nonidealities which comprise offset, gain errors, nonlinearity errors, and cross sensitivity. In this paper, a calibration method is presented which features a progressive improvement in the sensor calibrated transfer toward the desired transfer as the user proceeds from one calibration point to the next. The method is based on a set of mathematical formulas whereby a calibration coefficient is calculated at a selected calibration point and used to calculate a first correction of the sensor transfer curve. Further improvement in the sensor transfer is obtained by repeating the process for a second calibration point using the transfer resulting from the first calibration, without the need to review the calibration already carried out at the first point. The process can be repeated until the desired error reduction is obtained. Step by step, the calibration method builds up a polynomial transfer correction. Simulation results are shown to demonstrate the performance of the method, A software implementation of the method for two-dimensional (2-D) calibration in an 8-bit microcontroller is presented. The microcontroller with calibration program can be incorporated in a compact smart sensor system.

Determination of Trace Impurities in High-purity Quartz by Electrothermal Vaporization Inductively Coupled Plasma Mass Spectrometry Using the Slurry Sampling Technique

Abstract: A method has been developed for the determination of 14 relevant trace impurities in high-purity quartz based on ETV-ICP-MS using slurry sampling. The ETV device consisted of a double layer tungsten coil. Experimental conditions were optimized with respect to the temperature program, the carrier gas flow, the i.d. of the aerosol tubing, ICP-MS measurement parameters and internal standardization. Excluding U, calibration had to be carried out by the standard additions method because of non-spectral matrix interferences. For U, simple quantification via calibration curves, recorded with aqueous standards, was possible. The observed interferences also aggravated the background evaluation, which seriously limited the determination of Al and Fe. The method was applied to the determination of Al, Ba, Co, Cr, Cu, Fe, Li, Mg, Mn, Na, Pb, Sr, U and Zn in two quartz samples of different grades of purity. The accuracy of the results was checked by their comparison with those obtained by independent methods including instrumental neutron activation analysis. The achievable detection limits are between 2 ng g -1 (Li, U) and 70 µg g -1 (Al).

Quantitative Electrospray Mass Spectrometry of Halides andHalogenic Anions

Abstract: A quantitative study of the determination of halides and halogenic anions by negative ion electrospray mass spectrometry (ES-MS) is presented. Calibration plots were found to be linear over a range of 2.5–4 orders of magnitude for F - , Cl - , ClO 3 - , ClO 4 - , Br - , I - and IO 3 - when a 1.0×10 - 4 mol l -1 level of external electrolyte was added to the standard solutions. Detection limits ranged from 0.5 ng ml -1 for the perchlorate ion up to a blank limited 35 ng ml -1 for chloride. An attempt was also made to determine the level of fluoride present in mouthwash samples. Measurement of the fluoride content utilizing a calibration curve produced excellent agreement with results obtained by measurement with a fluoride ISE for two synthetic mouthwash samples but poor agreement for two commercial samples. However, excellent agreement between the two methods was obtained for the commercial samples using the method of standard additions with ES-MS.

Chemometric protocol to validate an analytical method in the presence of corrigible constant and proportional systematic errors

Abstract: A statistical methodology to verify the trueness of an analytical method in the presence of corrigible systematic errors is presented. This protocol enables detection of constant and proportional components of error. By using the data set obtained in the Youden calibration with different sample test portions, the constant component of the error (Youden blank) can be determined. An analysis of covariance was applied to 3 calibration curves established with standard solutions and with standard additions to 2 different sample test portions. The slopes were compared, and the presence of any matrix-analyte interaction was detected. A method for removing the numerical components of systematic errors is proposed: a calculation procedure to obtain a correct analytical result and a statistical test to verify the correctness of analyte contents obtained from different calibrations. For demonstration purposes, the protocol was applied to spectrofluorometric determination of oxalates in spinach leaves.

Flow cytometric measurement of intracellular pH.

Abstract: A number of fundamentally important biological processes, such as cell signaling and the initiation of mitosis, are accompanied by a change in intracellular pH. Flow cytometric measurement of pH is a generally straightforward procedure that can be done with any instrument equipped with a 488-nm argon laser. The overall approach is similar to that for calcium: generation of a calibration curve by imparting known changes in pH and interpolation of the test sample pH. This unit presents the traditional calibration method using high-potassium buffers and the proton ionophore nigericin and a more recently developed technique, the pseudo null method, which involves resuspension of cells in defined mixtures of weak acids and weak bases.

Error Analysis of an Evaporation Method for Determining Hydrodynamic Properties in Unsaturated Soil

Abstract: Solving soil unsaturated flow problems requires knowledge of the water retention θ(h) and unsaturated hydraulic conductivity K(θ) relationships. The purpose of this study was to investigate more thoroughly the properties and accuracy of an evaporation method described by Wind (1969) for determining θ(h) and K(θ) from laboratory cores. Evaporation from a vertical column of soil was first simulated using numerical solution of Richards equation for a given set of soil hydraulic properties. The simulated data were then used to evaluate the ability of Wind's method to provide estimations of the retention and unsaturated conductivity curves when measurement errors were taken into account. The main sources of error were (i) errors due to the position of the tensiometers in the sample, (ii) errors due to the calibration of the transducers used for the pressure head measurements, and (iii) errors due to layering in the soil column. The estimated water retention curves were sensitive only to soil layering. On the other hand, small uncertainties in the position of the tensiometers (1 or 2 mm) and in the calibration curve of the transducers for the pressure head measurements (1-5%) had a great influence on the estimated hydraulic conductivity curves. A correction procedure was proposed and was satisfactory when errors of position in the tensiometers were taken into account. Results also showed that temperature corrections related to viscosity of liquid water were large. Finally, this method gives poor estimates of hydraulic conductivities when raw tensiometric data are corrupted with small errors in their position or calibration.