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101.
Hakvoort G. Hol C. M. van Ekeren P. J. 《Journal of Thermal Analysis and Calorimetry》2001,64(1):367-375
A number of compounds is investigated for DSC calibration during cooling. Adamantane and Zn show fast reversible transitions
and can be applied both for temperature and for heat calibrations. A third compound, namely 4,4’-azoxyanisole, has a liquid
crystal to isotropic liquid transition at 409K. This compound can be used for temperature calibration. Heat calibration with
this compound is more problematic because of the small heat effect and the construction of the baseline. Other compounds like
NaNO3, In, Hg and Pb, show a slight supercooling. Nevertheless they can be used for heat calibration. The use of large samples
of NaNO3 and In gives the possibility to construct the equilibrium onset temperatures of the cooling peaks, so these two compounds
are also appropriate for temperature calibration on cooling.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
102.
An important step in the validation of an analytical procedure is the study of its robustness. In the case of spectrofluorimetric determinations, quenching introduces specific problems which are approached in this paper for the particular case of tetracyclines determination in milk. Quenching can be detected with excitation emission matrices (EEM) signals and a three-way Parallel Factor (PARAFAC) decomposition and modelled by means of a four-way PARAFAC decomposition which reproduces the physical model of this effect.The robustness of the method is evaluated by including changes in seven experimental variables: trichloroacetic acid (TCA) volume solution used in the precipitation of milk proteins, revolutions per minute, time and temperature in the centrifugation step, pH and emission-excitation slit width in the fluorimetric analyte determination and the analyst. The robustness analysis is carried out by means of a Plackett-Burman experimental design as it is suggested by European Decision 2002/657/EC (European Decision (EC) No. 2002/657/EC of 12 August 2002, implementing Council Directive 96/23/EC, concerning the performance of analytical methods and the interpretation of results, Off. J.L 221, 17/8/2002, 8). The analyte concentration will be taken as response in the Plackett-Burman experimental design instead of the signal as it is habitual in these cases. Therefore, a three-way Partial Least Squares (3-PLS) calibration models with EEM signal is needed.When an analogous study is carried out for tetracycline (TC) in the absence of chlorotetracycline (CTC) as interferent, univariate calibration is employed, being able to conclude that in the robustness analysis, different factors are significantly active when quenching exists. 相似文献
103.
104.
105.
Andrei Medvedovici Florin Albu Iuliana Daniela Sora Stefan Udrescu Toma Galaon Victor David 《Biomedical chromatography : BMC》2009,23(10):1092-1100
A sensitive method for determination of free captopril as monobromobimane derivative in plasma samples is discussed. The internal standard (IS) was 5‐methoxy‐1H‐benzimidazole‐2‐thiol. Derivatization with monobromobimane immediately after blood collection and plasma preparation prevents oxidation of captopril to the corresponding disulfide compound and enhances the ionization yield. Consequently, derivatization enhances sample stability and detection sensitivity. Addition of the internal standard was made immediately after plasma preparation. The internal standard was also derivatized by monobromobimane, as it contains a thiol functional group. Preparation of plasma samples containing captopril and IS derivatives was based upon protein precipitation through addition of acetonitrile, in a volumetric ratio 1:2. The reversed‐phase liquid chromatographic separation was achieved on a rapid resolution cartridge Zorbax SB‐C18, monitored through positive electrospray ionization and tandem MS detection using the multiple‐reaction monitoring mode. Transitions were 408–362 amu for the captopril derivative and 371–260 amu for the internal standard derivative. The kinetics of captopril oxidation to the corresponding disulfide compound in plasma matrix was also studied using the proposed method. A linear log–log calibration was obtained over the concentration interval 2.5–750 ng/mL. A low limit of quantitation in the 2.5 ng/mL range was obtained. The analytical method was fully validated and successfully applied in a three‐way, three‐period, single‐dose (50 mg), block‐randomized bioequivalence study for two pharmaceutical formulations (captopril LPH 25 and 50 mg) against the comparator Capoten 50 mg. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
106.
Multiple-component determinations present difficulties which cannot be resolved mathematically when there is severe spectral overlap, as in the determination of rare-earth elements with chromogenic reagents. The interdependence of absorptivities is greatly decreased when absorbance data from procedures based on several chromogenic reagents are used together in the calculations of calibration factors and concentrations. Various features of the method are discussed. 相似文献
107.
Jan Korbel 《Entropy (Basel, Switzerland)》2021,23(1)
The maximum entropy principle consists of two steps: The first step is to find the distribution which maximizes entropy under given constraints. The second step is to calculate the corresponding thermodynamic quantities. The second part is determined by Lagrange multipliers’ relation to the measurable physical quantities as temperature or Helmholtz free energy/free entropy. We show that for a given MaxEnt distribution, the whole class of entropies and constraints leads to the same distribution but generally different thermodynamics. Two simple classes of transformations that preserve the MaxEnt distributions are studied: The first case is a transform of the entropy to an arbitrary increasing function of that entropy. The second case is the transform of the energetic constraint to a combination of the normalization and energetic constraints. We derive group transformations of the Lagrange multipliers corresponding to these transformations and determine their connections to thermodynamic quantities. For each case, we provide a simple example of this transformation. 相似文献
108.
Petr Chocholouš Paweł Świt Joanna Kozak Petr Solich Paweł Kościelniak 《Analytical letters》2017,50(4):617-628
The generalized calibration strategy (GCS), developed and previously applied to chemical analysis, has been adapted to two-component (2C) analysis. According to the 2C-GCS procedure, a set of 10 calibration solutions containing a sample and standards of two analytes in well-defined composition was diluted. The measurements performed at a given dilution stage allow the concentration of both analytes in a sample to be evaluated with six apparent concentrations calculated with various mathematical approaches. As a result, the method allows the detection, examination, and elimination of nonlinear and interference effects with multiplicative and additive characteristics. To perform 2C-GCS automatically and effectively, a dedicated flow sequential injection system was designed to be fully controlled by a computer. Caffeine and paracetamol were determined in synthetic and pharmaceutical samples using this calibration approach. The analytes were determined with good precision and accuracy with low consumption of sample and standard solutions. On the basis of this experimental model, the influence of effects and tendencies in the examined analytical system was detected and evaluated. 相似文献
109.
Summary of ISO/TC 201 standard: ISO 11775:2015 – Surface chemical analysis – Scanning probe microscopy – Determination of cantilever normal spring constants 下载免费PDF全文
Charles A. Clifford 《Surface and interface analysis : SIA》2017,49(3):171-172
This International Standard describes five methods for the determination of normal spring constants for atomic force microscope cantilevers to an accuracy of 5 to 10%. Each method is in one of the three categories of dimensional, static experimental and dynamic experimental methods. The method chosen depends on the purpose, convenience and instrumentation available to the analyst. For accuracies better than 5 to 10%, more sophisticated methods, not described in the standard, are required. Copyright © 2016 Crown copyright. Surface and Interface Analysis © 2016 John Wiley & Sons, Ltd. 相似文献
110.
Anna Maria Orani Petko Mandjukov 《International journal of environmental analytical chemistry》2017,97(8):710-729
Analytical procedure for the determination of As, Cd, Cu, Ni, Co and Cr in marine biota samples using solid sampling high-resolution continuum source atomic absorption spectrometry (HR CS AAS) and accelerated fast temperature programmes has been developed. Calibration technique based on the use of solid certified reference materials similar to the nature of the analysed sample and statistics of regression analysis were applied. A validation approach in line with the requirements of ISO 17025 standard and Eurachem guidelines was followed. Accordingly, blanks, selectivity, calibration, linearity, working range, trueness, repeatability and reproducibility, limits of detection and quantification and expanded uncertainty for all investigated elements were assessed. The major contributors to the combined uncertainty of the analyte mass fractions were found to be the homogeneity of the samples and the microbalance precision. Traceability to the SI system of units of the obtained with the proposed analytical procedure results was also demonstrated. The potential of the proposed analytical procedure based on solid sampling HR CS AAS technique was demonstrated by direct analysis of marine reference biota samples. Overall, the use of solid sampling HR CS AAS permits obtaining significant advantages for the determination of selected trace elements in marine biota samples, such as straightforward calibration, a high sample throughput, sufficient precision, a suitable limit of detection and reduced risk of analyte loss and contamination. 相似文献