Nonlinear Calibration Curve Research Articles

Glucose Oxidase Electrode Based on Graphite and Methylthio Tetrathiafulvalene as Mediator

Abstract A glucose sensor based on glucose oxidase and a new mediator - 4,5-dimethyl-4′-methylthio-Δ 2,2′-bi-1,3-dithiole (MTTTF) is described. The background for sensor action is the effective MTTTF cation interaction (apparent bimolecular constant (2.0+/-0.5)∗106 M−1 s−1 at 25°C and pH 7.0) with reduced glucose oxidase and the high electrochemical rate of mediator transformation. A glucose sensor was prepared by adsorbing mediator (MTTTF) and glucose oxidase on graphite rods. The sensor responds to glucose at electrode potentials higher than 50 mV vs SCE, but the maximal activity is obtained at a potential of 250 mV. In air saturated solution the electrode shows a non-linear calibration curve with a half-saturation concentration 10.4 mM and Hill coefficient 2.08 at 250 mV. Sensor response changes little at pH 6.5–8.0. The energy of activation of the sensor response calculated from the Arrhenius equation was 64.5 kJ/mol, and the temperature coefficient at 25°C was 9.2%.

Estimating suspended sediment concentrations in surface waters of the Amazon River wetlands from Landsat images

A method has been developed, based on spectral mixture analysis, to estimate the concentration of suspended sediment in surface waters of the Amazon River wetlands from Landsat MSS and TM images. Endmembers were derived from laboratory reflectance measurements of water-sediment mixtures with a range of sediment concentrations. Using these reference spectra, we applied a linear mixture analysis to multispectral images after accounting for instrument and atmosphere gains and offsets. Sediment concentrations were estimated for individual pixels from the mixture analysis results based on a nonlinear calibration curve relating laboratory sediment concentrations and reflectance to endmember fractions. The uncertainty in the sediment concentrations derived from this analysis for three Amazon images is predicted to be within ±20 mg/ L, and the concentrations fall within a range of concentrations of suspended sediment that were measured at several times and places in the field over the past 15 years. The emphasis of our work is to use the patterns of sediment concentrations to compute the approximate volumes of sediment that are transferred between the main channel and floodplain of the Amazon River. However, the methodology can be applied universally if the optical properties of water and sediment at the site are known, and it is, therefore, useful for the study of suspended sediment concentrations in surface waters of wetlands elsewhere.

Absorption Measurements with an Integrating Plate Photometer Calibration and Error Analysis

In this study, the integrating plate photometer (Lin et al., 1973), used at the University of Vienna, was calibrated with nonabsorbing and absorbing test aerosols to determine the systematical errors of the technique, which can be interpreted as apparent absorption coefficients σa a. A nonlinear calibration curve was obtained from measurements with polystyrene latex particles of various sizes, which includes the scattering properties (expressed in terms of the scattering coefficient σs of the particles) and the area coverage ƒ of the filter. Application of this curve σa a/σs = 0.0398 f −0.441 to polydisperse paraffin aerosols gave satisfactory results. For the soot aerosol, σa a is < 10% of the calculated “true” absorption coefficient

Coupling a particle beam interface directly to a quadrupole ion trap mass spectrometer

A particle beam interface has been coupled to a quadrupole ion trap mass spectrometer. The system allows the collection of electron ionization mass spectra from analyte in solution. The interface incorporates a pneumatic nebulizer, a heated desolvation chamber, and a three-stage separator region. Additional helium, for improved performance, is added through stage 3. The particles formed in the interface are separated from solvent molecules and are transferred directly to the ion trap where they are expected to collide with the hot hyperbolic surface of the end cap. The end cap serves both as a heated target used to vaporize the particles and as an ion-trapping electrode. Mass analysis is achieved with the mass-selective instability scan supplemented with resonance ejection. Electron ionization spectra from 100 ng of caffeine [molecular weight (MW) = 194]; 1-naphthalenol methylcarbamate (carbaryl) (MW = 201), 17α-hydroxyprogesterone (MW = 330), and reserpine (MW = 608) are shown using sampling by a segmented flow analysis. Some charge exchange is evident with methanol as well as self-chemical ionization at higher analyte levels. The interface shows a nonlinear caffeine calibration curve for analyte amounts below 30 ng and a more linear response at higher amounts. Caffeine was detected at 25 pmol (5 ng), with a signal-to-noise ratio of 50, 50-μL loop, full scan.

Thermochemical effects in hexafluoroethane (Freon 116) modified argon inductively coupled plasmas

Hexafluoroethane (Freon 116), added to the argon nebulizer gas, has been investigated as a potential volatilization aid for refractory materials in slurry nebulization inductively coupled plasma atomic emission spectrometry (ICP-AES). The introduction of Freon 116 resulted in apparently unusual plasma spectrochemistry, which yielded non-linear calibration curves. These were attributed to classical mass action buffering involving highly stable metal fluoride species. This dictated against the use of Freon 116 as a volatilization aid in slurry nebulization ICP-AES.

Percentage vegetation cover of a degrading rangeland from SPOT

Abstract Multispectral SPOT imagery is used to map percentage vegetation cover in the Mackenzie Basin of the South Island, New Zealand. Twenty ground measurements of quadrats 60 by 60 m2 relate percentage vegetation cover to normalized vegetation index. The non-linear calibration curve is C = 50 tanh (6·1(NV1-0·22))+ 50 (1) where C is percentage vegetation cover and NVI is normalized vegetation index. The vertical spread of quadrat points about the calibration curve gives the accuracy of a percentage cover prediction from NVI. In the linear part of the calibration curve the upper and lower prediction limits (80 per cent confidence interval) are plus or minus 15 per cent cover.

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.

Determination of Surfactants Using Ion Pair Extraction of Near-infrared Laser Dyes

Abstract Ionic surfactants and near-infrared laser dyes formed complexes which were extracted into organic solvents as ion pairs. Surfactants were determined spectrophotometrically by measuring the near-infrared absorbance and fluorescence of the ion pair in the organic solvent. Several of the commercially available near infrared dyes have been found suitable for surfactant determination in water using this technique. The excess near-infrared dye coextracted into the organic solvent was determined by blank extractions. The calibration curves were linear within two orders of magnitude of surfactant concentrations. Non-linear calibration curves are obtained for wider concentration range of surfactants. This method using the recently developed near-infrared laser diode intracavity technique was applied to the determination of SDS in water. Lower detection limits and ease of operation are the major advantages of using this new laser diode technique. The extraction efficiency of different solvent systems was e...

Calibrating detector responses using chromatographic peak shapes

A new method for calibrating time-independent detector responses using only a series of chromatographic peak shapes is presented. The method provides an alternative to steady-state detector calibration which may be difficult experimentally, as in gas chromatography, or too expensive or material-intensive, as in preparative chromatography. In the new method a calibration-curve model function is adopted, and model parameter values are determined. The values used as those that minimize the difference between the analyte amounts injected into the chromatography and the analyte amounts computed from applying the calibration curve to the experimental peak shapes. Examples of applications to linear and nonlinear calibration curves are given.

Spectrophotometric Determination of Chloride Ion Using Mercury Thiocyanate and Iron Alum

Small amounts of chloride ion have been determined spectrophotometrically by means of iron(III) alum (NH4Fe(SO4)2• 12H2O) reagent solution in nitric acid and thiocyanate reagent solution in methanol. Previously developed methods using iron(III) alum and thiocyanate for determining chloride ion are not sensitive enough and/or have non-linear calibration curves. Therefore, attempts to improve these methods were made in the present work. The results are as follows. Higher linearity and better sensitivity of calibration curves were obtained with higher concentrations of iron(III) alum (150-300g/dm3 in 6M HNO3, 2ml) and mercury thiocyanate reagents (9g/dm3 in MeOH, 2ml, or 4g/dm3 in MeOH, 4ml) in the chloride ion concentration of up to 20mg/dm3. The influence of light on absorbance of the solution was very small, although the temperature dependence on absorbance was relatively great. Effects of nitric acid concentration and stirring conditions were also studied.

Quantitative computed tomography in measurement of vertebral trabecular bone mass

Measurement of bone mineral concentration (BMC) can be done by several modalities. Quantitative computed tomography (QCT) can be used for measurements at different sites and with different types of bone (trabecular-cortical). This study presents a modified method reducing the influence of fat. Determination of BMC was made from measurements with single-energy computed tomography (CT) of the mean Hounsfield number in the trabecular part of the L1 vertebra. the method takes into account the age-dependent composition of the trabecular part of the vertebra. as the amount of intravertebral fat increases with age, the effective atomic number for these parts decreases. This results in a non-linear calibration curve for single-energy CT. Comparison of BMC values using the non-linear calibration curve or the traditional linear calibration with those obtained with a pixel-by-pixel based electron density calculation method (theoretically better) showed results clearly in favor of the non-linear method. the material ...

Quantitative Computed Tomography in Measurement of Vertebral Trabecular Bone Mass

Measurement of bone mineral concentration (BMC) can be done by several modalities. Quantitative computed tomography (QCT) can be used for measurements at different sites and with different types of bone (trabecular-cortical). This study presents a modified method reducing the influence of fat. Determination of BMC was made from measurements with single-energy computed tomography (CT) of the mean Hounsfield number in the trabecular part of the L1 vertebra. The method takes into account the age-dependent composition of the trabecular part of the vertebra. As the amount of intravertebral fat increases with age, the effective atomic number for these parts decreases. This results in a non-linear calibration curve for single-energy CT. Comparison of BMC values using the non-linear calibration curve or the traditional linear calibration with those obtained with a pixel-by-pixel based electron density calculation method (theoretically better) showed results clearly in favor of the non-linear method. The material consisted of 327 patients aged 6 to 91 years, of whom 197 were considered normal. The normal data show a sharp decrease in trabecular bone after the age of 50 in women. In men a slower decrease was found. The vertebrae were larger in men than in women.

Quantitative Analysis of Coexisting Byproducts in Orthorhombic YBa2Cu3Ox by X‐ray Diffraction

BaCuO2, Y2Cu2O5, and Y2BaCuO5 as well as YBa2Cu3Ox were synthesized and nonlinear calibration curves for mole fraction versus integrated intensity ratio of X‐ray diffraction peaks were obtained for BaCuO2‐, Y2Cu2O5‐, and Y2BaCuO5‐YBa2Cu3Ox systems. It is shown that the amount of BaCuO2 contained in orthorhombic YBa2Cu3Ox is not negligible, even if the relative intensity of the strongest diffraction peak of BaCuO2 is negligibly weak.

One-point recalibration of heterogeneous enzyme immunoassays with non-linear calibration curves.

We have investigated one-point recalibration of heterogeneous enzyme immunoassays involving nonlinear calibration curves. By using a factor determined from a single standard we updated calibration curves obtained earlier by means of multiple-point determination. The prerequisite for this method is a reproducible working procedure, i.e., as ensured by a fully mechanized system. In our investigations with Enzymun-Test system ES 600 (Boehringer Mannheim) we determined alpha 1-fetoprotein, carcinoembryonic antigen, digoxin, ferritin, thyroxin-binding globulin, triiodothyronine, and thyroxin in human serum pools over a period of two weeks with both full calibration and one-point recalibration. Comparisons of the results thereby obtained show that the means of the concentrations and the CVs for the alternative calibration procedures differed negligibly, even if we used reagents exposed to different temperatures for different periods of time. With the one-point recalibration procedure presented here, therefore, one can considerably reduce the time and effort spent on calibration.

4713611 Burn-in apparatus for integrated circuits mounted on a carrier tape

High-performance, size-exclusion chromatography columns were calibrated in average root-mean-square radii of gyration (μRgz) by a combination of commercial “narrow” pullulan and “broad” dextran standards. The nonlinear calibration-curves were fitted by a computer-aided, iterative, least-squares procedure. Values of (μRgz), obtained from a point-by-point transformation of the respective pullulan and dextran chromatograms by utilizing universal calibration, were compared with inputted μRgz calibration values. For standards ranging in μRgz value from 20.1 to 389 Å, the accuracy ranged from 1 to 15.3%. Furthermore, from relationships in the literature, μRgz values were transformed to μMw. These values of μMw were comparable to, but generally less accurate than, μMw values from direct, molecular-weight calibration.

Quantitative Analysis of Polymorphic Mixes of Zirconia by X‐ray Diffraction

Nonlinear calibration curves of weight fraction vs integrated intensity ratio arc obtained for polymorphic mixtures of ZrO2 by means of powder X‐ray diffraction. The (C + M) and (T + M) ZrO2 systems are analyzed using the {111} reflections. Intensity ratios in mixtures prepared with an ultrafine m‐ZrO2 powder agree well with theoretical values. The observed nonlinearity of the intensity‐concentration curve is explicable from the differences in reflecting power of corresponding reflections in the three polymorphs. Considerable deviations from theoretical intensity ratios are observed in mixtures prepared with coarser commercially available m‐ZrO2 powders. This effect is attributed to an anomalously high absorption behavior of those monoclinic materials and can be suppressed by quenching in liquid nitrogen, which is believed to cause the particles to shatter. The (C + T) ZrO2 system is analyzed using the {200} reflections rather than the more usual high‐angle reflections and the derived nonlinear calibration curve agrees well with theoretical prediction. In the ternary system (C + T + M) ZrO2 the presence of tetragonal phase can be confirmed by microphotometric tracing of the {111} and {200} reflection profiles on Guinier photographs, but in this case a quantitative analysis would be difficult.

The use of gel chromatography for the determination of sizes and relative molecular masses of proteins. Interpretation of calibration curves in terms of gel-pore-size distribution.

The separation of proteins by gel-exclusion chromatography has been explained in terms of partitioning of the macromolecules within the gel by a distribution of pores of various radii. The assumption that the distribution of pore sizes is Gaussian has led to the prediction of a linear relationship between the molecular Stokes radius (RS) of the protein and the function erf-1 (1-KD), where KD is the partition coefficient [Ackers (1967) J. Biol. Chem. 242, 3237-3238]. Since careful calibrations of classical (agarose and dextran) gels and h.p.l.c. gels have shown that such a linear relationship is not verified experimentally over a wide range of native protein sizes, we have reinvestigated the model of Ackers (above reference). We show that Ackers' (above reference) derivation is not valid except for a particular Gaussian distribution of pore sizes centred at the origin. Relaxation of this restriction to allow for other types of Gaussian distributions cannot account for the non-linear calibration curves that we have obtained. Instead we show that the pore-size distribution can be calculated from the experimentally determined function KD = f(RS) and that this distribution is bimodal (non-Gaussian). One distribution is centred below 2 nm, whereas the mean value of the second one is around 6-8 nm. The minimum in this bimodal distribution corresponds, for some gels, to a region of poor resolution, which needs to be appreciated for the proper use of gel chromatography in the determination of molecular size.

Evaluation of root-mean-square radius of gyration as a parameter for universal calibration of polysaccharides

High-performance, size-exclusion chromatography columns were calibrated in average root-mean-square radii of gyration (μ R gz) by a combination of commercial “narrow” pullulan and “broad” dextran standards. The nonlinear calibration-curves were fitted by a computer-aided, iterative, least-squares procedure. Values of (μ R gz), obtained from a point-by-point transformation of the respective pullulan and dextran chromatograms by utilizing universal calibration, were compared with inputted μ R gz calibration values. For standards ranging in μ R gz value from 20.1 to 389 Å, the accuracy ranged from 1 to 15.3%. Furthermore, from relationships in the literature, μ R gz values were transformed to μ M w. These values of μ M w were comparable to, but generally less accurate than, μ M w values from direct, molecular-weight calibration.

Tandem thermal-conductivity and electron-capture detectors and non-linear calibration curves in quantitative nitrous oxide analysis

A gas chromatographic system with a thermal-conductivity detector and an electron-capture detector in series was designed to measure carbon dioxide and nitrous oxide evolved from soil at concentrations from ambient atmospheric levels to several per cent. The response of the electron-capture detector to different partial pressures of nitrous oxide was linear up to only 2.5 Pa. Electron-capture response to nitrous oxide at partial pressures up to 40 Pa was found to be closely approximated by representing nitrous oxide partial pressure as a fourth-degree polynomial function of peak area without an intercept. A two-point calibration method for adjusting the coefficients of the polynomial to compensate for day-to-day variations in electron-capture detector sensitivity is described.

Quantitative Analysis of Monoclinic‐Stabilized Cubic ZrO2 Systems by X‐Ray Diffraction

An equation for a nonlinear calibration curve of volume fraction vs integrated intensity ratio is presented for monoclinic‐stabilized cubic ZrO2 systems containing YO1.5, CaO, and MgO. A parameter in the equation was evaluated theoretically and is given for a range of cubic solid solution compositions.