Showing papers on "Calibration curve published in 2002"

Determination of chlorinity in aqueous fluids using Raman spectroscopy of the stretching band of water at room temperature: Application to fluid inclusions

Abstract: A new analytical method, based on the Raman spectroscopy of the ν(OH) stretching vibration of water, has been developed for the determination of the concentration of chloride in aqueous solutions with the goal of reconstructing the bulk ion content of fluid inclusions that are relics of paleo-fluid circulation in rocks. The method involves calibrating the area of one band of the spectrum difference between pure water and solutions of appropriate composition with respect to the chloride concentration. Calibration curves were constructed for the major geological chemical salts LiCl, NaCl, KCl, CaCl2, and MgCl2, and NaCl-CaCl2 systems. The application to fluid inclusions has been confirmed using synthetic fluid inclusions. For cubic minerals such as fluorite, the calibration curve for the NaCl system correctly estimates the chlorinity. For birefringent minerals, such as quartz, the Raman spectrum of the aqueous solution depends on the orientation of the host crystal. The crystal must be oriented in such a way that one axis of the ellipse of the indicatrix projects parallel to the spectrometer slit. This method complements micro-thermometric data and allows the determination of chlorinity when ice-melting temperature cannot be used.

Rapid, Specific Determination of Iodine and Iodide by Combined Solid-Phase Extraction/Diffuse Reflectance Spectroscopy

Abstract: A new, rapid methodology for trace analysis using solid-phase extraction is described The two-step methodology is based on the concentration of an analyte onto a membrane disk and on the determination by diffuse reflectance spectroscopy of the amount of analyte extracted on the disk surface This method, which is adaptable to a wide range of analytes, has been used for monitoring ppm levels of iodine and iodide in spacecraft water Iodine is used as a biocide in spacecraft water For these determinations, a water sample is passed through a membrane disk by means of a 10-mL syringe that is attached to a disk holder assembly The disk, which is a polystyrene-divinylbenzene composite, is impregnated with poly(vinylpyrrolidone) (PVP), which exhaustively concentrates iodine as a yellow iodine-PVP complex The amount of concentrated iodine is then determined in only 2 s by using a hand-held diffuse reflectance spectrometer by comparing the result with a calibration curve based on the Kubelka-Munk function The same general procedure can be used to determine iodide levels after its facile and exhaustive oxidation to iodine by peroxymonosulfate (ie, Oxone reagent) For samples containing both analytes, a two-step procedure can be used in which the iodide concentration is calculated from the difference in iodine levels before and after treatment of the sample with peroxymonosulfate With this methodology, iodine and iodide levels in the 01-50 ppm range can be determined with a total workup time of approximately 60 s with a RSD of approximately 6%

Comparison of 193, 213 and 266 nm laser ablation ICP-MS

Abstract: There is a widespread discussion concerning the ‘better’ wavelength for laser ablation chemical analysis. Wavelength is believed to be an important parameter based on the sample’s optical penetration depth as well as photon energy for bond breaking. The lasers most widely employed for analytical applications are the excimer, based on an ArF mixture with a wavelength of 193 nm, and the solid state Nd:YAG, with wavelengths of 266 nm and 213 nm. NIST glasses were ablated to test the effects of these wavelengths on fractionation and transport efficiency. Crater geometry and volume were measured by using a white-light interference microscope. For all three wavelengths, linear calibration curves were obtained using NIST glasses as standards. The 208Pb/238U ratio in a tuff rock sample was measured using all three wavelengths; the value obtained using the NIST-glass calibration was compared to that measured using liquid nebulization.

Calibration for vector network analyzer

Abstract: An improved calibration method for a vector network analyzer stores sparse calibration data, interpolates system error data from the sparse calibration data for each measurement by the vector network analyzer, and creates calibrated measurement data from the system error data and uncorrected measurement data at each measurement frequency. The sparse calibration data may be generated by measuring every Nth frequency step over a calibration frequency range greater than a specified measurement frequency range, or by measuring every frequency step over the calibration frequency range and compressing the resulting measurement data. The interpolation may be achieved by using a curve-fit algorithm, such as a parametric polynomial curve fitting algorithm.

Concentration measuring method

Abstract: A concentration measuring method includes selecting a calibration curve optimum for computing the concentration of a measurement target substance from a plurality of calibration curves based on an output from a reaction system containing the target substance and a reactant capable of reacting with the target substance, and computing the concentration of the target substance based on the optimum calibration curve and the output. Each of the calibration curves is prepared based on a plurality of outputs generated upon lapse of a same reaction time from a plurality of standard reaction systems each containing a standard reagent of a known different concentration and the reactant. The plurality of calibration curves differ from each other in reaction time based on which the calibration curves are prepared.

Accommodating subject and instrument variations in spectroscopic determinations

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 or subject-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 or intra-subject 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 or subject.

Determination of bismuth using on-line preconcentration by trapping on resistively heated W coil and hydride generation atomic absorption spectrometry

Abstract: A novel analytical system was developed to trap and preconcentrate bismuth from the vapour phase stream. Bismuthine formed by sodium tetrahydroborate reduction was trapped on a tungsten coil previously heated to 270 °C. The analyte species were re-volatilised by increasing the coil temperature to 1200 °C and then transported to an externally heated silica T-tube by using a mixture of argon and hydrogen as the carrier gas. The base width of the transient signal was less than 0.5 s. The reproducibility of the analytical signal was influenced by the rate of heating of the tungsten coil at the releasing stage. The precision of the analytical system was found to be 5.8% RSD (n = 13) for 0.010 ng ml−1 Bi when peak height was used. Due to sharp signals, peak area readings gave higher RSD values but they could be used for quantitation. The relationship between the analytical signal and the sample volume was found to be linear between 0.5 ml and 60 ml when using 0.100 ng ml−1 Bi. When the sample volume was increased to 25 ml, the blank values became significant. The calibration plot for an 18 ml sampling volume was linear between 0.030 and 0.500 ng ml−1 Bi. A limit of detection of 0.0027 ng ml−1 (3s) was obtained with 18 ml of sample volume. The concentration limit of detection achieved was comparable with or better than those obtained by techniques such as ICP-MS and HG-ETAAS. When the distance between the trap and atomiser was increased to 200 cm, a 72% and 24% decrease was observed in the peak height and peak area, respectively. In order to validate the accuracy of the method, two geological standard reference materials and one certified water standard reference material were analysed and the results were found to be in good agreement with the certified values at the 95% confidence level.

Polarographic behaviour of meloxicam and its determination in tablet preparations and spiked plasma.

Abstract: Meloxicam is a new non-steroidal anti-inflammatory drug (NSAID), which has a higher activity cyclooxygenase-2 (COX-2) than against cyclooxygenase-1 (COX-1), with potentially high anti-inflammatory and analgesic action. The voltammetric behaviour of meloxicam was studied using direct current (DC), differential pulse polarography (DPP) and cyclic voltammetry (CV). The influence of several variables (including nature of the buffer, pH, concentration, modulation amplitude, scan rate, drop size, etc.) was examined in DPP method for meloxicam. The best DPP response was obtained in acetate buffer pH 4.88. The peak currents were measured with a static mercury drop electrode at −1.49 V versus Ag/AgCl. Calibration curve for meloxicam was linear at a concentration range from 0.38 to 15.0 μg ml−1. The method was validated and applied to the determination of meloxicam in tablets, which were in two different dosage forms. A spectrophotometric method reported in the literature was utilized as a comparison method. There were no significant differences between the results obtained by two methods. DPP method is also available and applicable for the determination of mentioned substance in plasma. Mean recovery was 99.20±0.37%. It was concluded that the developed method was accurate, sensitive, precise, reproducible and useful for the quality control of meloxicam in pharmaceuticals and spiked plasma.

Field demonstrations of a direct push FO-LIBS metal sensor.

Abstract: A direct push, FO-LIBS sensor probe for real-time, in-situ measurement of metals in soils has been built and its capabilities demonstrated at three sites. The response of the FO-LIBS sensor is affected by the soil matrix conditions of grain size, composition, and water content. For each site, uncontaminated soil was collected and spiked with known quantities of the metal under investigation. These calibration standards were used to generate a site-specific calibration curve, which compensates for variations in soil matrix conditions of grain size, composition, porosity, etc. To compensate for moisture content, extra laser pulses are used to volatilize the water, higher power densities and/or shortened acquisition delay times are used. The LIBS experiment inherently exhibits poor precision since it is a point measurement. When multiple spectra are taken of a single, homogenized soil sample, there is a significant amount of variability in the peak intensities. There is no internal standard available to corr...

Method for lifetime-based chemical sensing using the demodulation of the luminescence signal

Abstract: A novel method for measuring the phosphorescence decay time of optical sensors is presented. It is based on the frequency domain measurement of the demodulation of luminescence signals. Two lock-in amplifiers are used in the set-up. The ratio of two amplitudes simultaneously measured at different modulation frequencies (f1 and f2) corresponds to the luminescence demodulation and therefore to the decay time. The feasibility of the new method is demonstrated for an optical oxygen sensor. The decay time data obtained from the demodulation measurement are compared with those derived from the conventional phase detection. The well established two-site model for description of intensity calibration curves for oxygen partial pressure, was found to be also suitable to describe the decay time based calibration curves derived from the demodulation and from phase angles.

Time-resolved laser-induced plasma spectrometry for determination of minor elements in steelmaking process samples

Abstract: A pulsed Nd:YAG laser operating on the fourth (266 nm) and second (532 nm) harmonics has been used to generate plasmas on the target surface in air at atmo- spheric pressure. The influence of wavelength on quanti- tative analysis of 4 minor elements in stainless steel sam- ples (Si, Ti, Nb and Mo) was investigated. Stainless steel samples with different elemental concentrations were pre- pared and analyzed by laser-induced plasma spectrometry (LIPS). The effect of laser wavelength on analytical fig- ures of merit (calibration curves, correlation coefficients, linear dynamic ranges, analytical precision, and accuracy values) was found to be negligible when internal stan- dardization (an Fe line) and time-resolved laser-induced plasma are employed. For both wavelengths, the calibra- tion curves presented a good linearity and an acceptable linear dynamic range in the concentration interval investi- gated. For the four elements studied, limits of detection lower than 150 µg g -1 were achieved. To evaluate the in- fluence of wavelength on precision and accuracy, a set of fifteen high-alloyed steel samples from different stages of steelmaking process have been analyzed. Finally, the long-term stability of the analytical measurements for Mo with 532 nm wavelength has been discussed. RSD values were lower than 5.3% for the elements studied.

Evaluation of frozen plasma calibrants for enhanced standardization of the international normalized ratio (INR): a multi-center study.

Abstract: Local ISI calibration has been proposed to improve INR accuracy and inter-laboratory precision. We evaluated the affect of local PT calibration on INR precision and accuracy using six levels of frozen plasma calibrants prepared and pooled from normal donors and patients stabilized on sodium warfarin (coumarin) based oral anticoagulant therapy (OAT). Reference prothrombin time (PT) and INR values were assigned to these calibrants in accordance with World Health Organization (WHO) procedure using rTF 95 international reference preparation (IRP) of thromboplastin (human recombinant). These calibrants, along with five similarly characterized individual OAT patient plasmas, were distributed to 127 laboratories in a multi-center study. Calibrant plasmas were evaluated and INR’s subsequently determined on the 5 OAT test samples using: 1) the ISI and MNPT in place before the study (the local system), 2) the locally calibrated ISI value (local system with ISI calibration) and 3) a PT-INR calibration curve. Precision of INR results improved across the study group using the local system with ISI calibration and the PT-INR calibration curve methods, while accuracy of INR results improved using the PT-INR calibration curve approach only and not the local ISI calibration. The authors conclude that frozen plasma calibrants can be used locally to enhance precision and accuracy of PT results as reported in INR. These calibrants are effective over a range of reagents and instrument combinations. Furthermore, the PT-INR calibration curve appears to be the superior method for local calibration.

Direct impurity analysis of semiconductor photoresist samples with laser ablation ICP-MS

Abstract: A high-throughput method involving laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) was developed for the determination of critical elements in semiconductor photoresist samples. An innovative procedure, including a sequence of spiking, mixing, spin-coating, and baking, was developed for the preparation of photoresist film standards to be used for calibration in the direct analytical process. The homogeneity of the photoresist sample was then evaluated using the radiotracer technique, and the effects of silicon substrate reflection, spin rate and baking temperature on the signal response of the analytes in the photoresist film were subsequently studied. The results indicated that sample pretreatment conditions (i.e., spin rate and baking temperature) strongly influenced the signal intensity. The signal variations with respect to photoresist thickness, due to the changes in spin rate, could be corrected by using an internal standard, while those due to the changes in baking temperature could not. Visual evidence of shock-wave motion, via a laser induced plasma, on the photoresist film was presented in the SEM images using a Nd-YAG laser in the Q-switched mode. For direct determination of impurities in photoresist samples, various calibration methods, including a matrix-matched external calibration curve, an internal standard with the major matrix element (i.e., carbon), and an internal standard with metal spiking (i.e., Co and Tl), were evaluated independently. The recoveries of spike metals (Al, Cu, Pt, Au, Th and U) ranged from 81 to 112%, with detection limits in the 20–285 ng mL−1 range for all elements except Al. The analytical throughput of the developed method was up to 12 samples per hour.

Automated constant voltage anemometer for measurements with fluid temperature drifts

Abstract: An automated procedure has been developed for a constant voltage anemometer to obtain in situ heated and cold resistances of a hot wire in each measurement cycle. From these parameters mean velocity can be deduced in the presence of ambient flow temperature variations, using a calibration curve based on, e.g., King’s law with the assumption of constant coefficients over a given temperature range. The method requires only one hot wire. This is a definite advantage over previous methods established for constant current or constant temperature anemometers where an additional temperature sensor is needed, with a separate temperature calibration of the hot wire. Results from a typical test are presented to demonstrate the procedure. The prototype tested was a 400 kHz bandwidth unit and the measurement cycle can be changed through software commands to suit each test requirements.

Prompt gamma-ray activation analysis for determination of boron in aqueous solutions

Abstract: Prompt gamma-ray activation analysis (PGAA) is a nuclear analytical technique for the determination of trace and other elements in solid, liquid or gaseous samples. The method consists in observing gamma rays emitted by a sample during neutron irradiation. Of particular importance for PGAA is the measurement of boron. Indeed, this technique gives the opportunity to detect boron concentration down to the ppm or ppb level depending on the sample matrix. Furthermore, boron cannot be easily measured by other methods without risks of contamination. Trace analysis of boron in liquids has been performed and characterized at the PGA facility of the neutron spallation source SINQ (Paul Scherrer Institute, Switzerland). First, a calibration curve was determined with standard boron solutions. Then, the PGAA was applied for the determination of boron in geological water samples. The results were compared with ICP-MS measurements. Finally, the method yielded promising results to measure the concentration of boron taken up by cells in a new treatment for rheumatoid arthritis.