Simultaneous multicomponent determinations

Simultaneous multicomponent determinations, 361 Sine waves, 33, 34, 508,956 mathematical description, 135 superposition. 137 Single-beam computerized spectrophotometers, 358 grating instruments, 357 instruments, 240, 241, 351 for atomic spectroscopy, 240 efl ect of mismatched cells, 343 for molecular absorption measurements, 351 advantages, 358 Singlet state, 216, 400-402,411 excited, 216,400,401,405 Size distributions, measuring, 951. 955, 961... 

Ghasemi J, Abbasi B, Niazi A, Nadat E, Mordai A. Simultaneous spectrophotometric multicomponent determination of folic acid, thiamine, riboflavin and pyridoxal by using double divisor-ratio spectra derivative-zero crossing method. Anal Lett 2004 37 2609-23. 

Models are constructed in analytics to describe the relationship between responses and factors. This is, for example, important for optimization of analytical methods on the basis of response surface methods (cf. Section 4.2). Models are also needed for cahbration of analytical methods. There, calibration of a single analyte in dependence on one or several wavelengths might be of interest. If, in the first example, the straight-line model would be adequate, for the second task of multiwavelength spectroscopy, multivariate approaches are needed. Calibrations in the case of unselective analytical methods must also be performed. These methods are termed simultaneous multicomponent analysis. In near-infrared (NIR) spectroscopy, the contents of water and protein in whole grain wheat are determined that way. 

In many industrial processes, the many components contained in the liquid evaporate simultaneously. Evaporation of individual components is easy to determine. For multicomponent liquid systems, the individual evaporation rates are summed to obtain the total evaporation rate. 

It has proved to be very useful, providing both qualitative and quantitative information derived from mathematical processing of UV/VIS spectra. The principles of derivative spectrophotometry were discussed [15,16]. Obviously, derivatisation of spectra does not provide any additional information to that acquired during the measurement, but allows for easier interpretation. In particular, the possibility of resolving overlapping peaks makes derivative spectrophotometry a valuable tool for multicomponent analysis. Typically, derivative spectrophotometry is useful for the simultaneous determination of two additives in polymeric materials with very closely positioned absorption maxima. In quantitative analysis, derivative spectrophotometry leads to an increase in selectivity. 

Chong et al. [742] have described a multielement analysis of multicomponent metallic electrode deposits, based on scanning electron microscopy with energy dispersive X-ray fluorescence detection, followed by dissolution and ICP-MS detection. Application of the method is described for determination of trace elements in seawater, including the above elements. These elements are simultaneously electrodeposited onto a niobium-wire working electrode at -1.40 V relative to an Ag/AgCl reference electrode, and subjected to energy dispersive X-ray fluorescence spectroscopy analysis. Internal standardisation... 

This approach uses a kinetic sequential principle to carry out multicomponent CL-based determinations. In fact, when the half-lives of the CL reactions involved in the determination of the analytes in mixture are appreciably different, the CL intensity-versus-time curve exhibits two peaks that are separate in time (in the case of a binary mixture) this allows both analytes to be directly determined from their corresponding calibration plots. In general, commercially available chemiluminometers have been used in these determinations, so the CL reaction was initially started by addition of one or two reaction ingredients. Thus, in the analysis of binary mixtures of cysteine and gluthatione, appropriate time-resolved response curves were obtained provided that equal volumes of peroxidase and luminol were mixed and saturated with oxygen and that copper(H) and aminothiol solutions were simultaneously injected [62, 63],... 

Kinetic analysis usually employs concentration as the independent variable in equations that express the relationships between the parameter being measured and initial concentrations of the components. Such is the case with simultaneous determinations based on the use of the classical least-squares method but not for nonlinear multicomponent analyses. However, the problem is simplified if the measured parameter is used as the independent variable also, this method resolves for the concentration of the components of interest being measured as a function of a measurable quantity. This model, which can be used to fit data that are far from linear, has been used for the resolution of mixtures of protocatechuic... 

LC-MS/MS has dramatically changed the way bionalysis is conducted. Accurate and precise quantitation in the pg ml scale is nowadays possible however one has to be aware of certain issues which are specific to mass spectrometric detection such as matrix effects and metabolite crosstalk. With the current growing interest in the analysis of endogenous biomarkers in biological matrices, quantitative bioanalysis with MS has certainly the potential to contribute further in this field with the development of multicomponent assays. Modern triple quadrupole instruments have the feature to use very short dwell times (5-10 ms), allowing the simultaneous determination of more than 100 analytes within the timescale of an HPLC peak. Due to the selectivity of the MS detection the various analytes... 

The two monomers enter into the copolymer in overall amounts determined by their relative concentrations and reactivities. The simultaneous chain polymerization of different monomers can also be carried out with mixtures of three or more monomers. Such polymerizations are generally referred to as multicomponent copolymerizations the term terpolymerization is specifically used for systems of three monomers. 

The electronic tongue concept has been successfully proved to be a feasible alternative for multiple analyte determinations, specially suited for monitoring applications, where it can provide real-time multicomponent information, simultaneously compensating matrix effects when used in a dynamic manner. For its proper set-up, the main effort is related with the large amounts of training information needed. In this... 

Gonzalez et al. [8] have applied micelle analysis in the kinetic multicomponent analysis for the simultaneous determination of thiocyanate, sulphite and sulphide in non saline waters. The method involved reaction of the anions with S,S dithiobis(2-nitrobenzoic acid) in aqueous cetyltrimethyl ammonium bromide micelles. Cyanide, sulphide and sulphite were determined at concentrations, respectively, down to 0.5-1.5/10 4M 0.2-1 xl0 4M and 0.2-1.5><10 4M with a relative error of less than 5%. 

Diffusion measurements under nonequilibrium conditions are more complicated due to the difficulties in ensuring well defined initial and boundary conditions. IR spectroscopy has proved to be a rather sensitive tool for studying simultaneously the intracrystalline concentration of different diffusants, including the occupation density of catalytic sites [28], By choosing appropriate initial conditions, in this way both co- and counterdiffusion phenomena may be followed. Information about molecular transport diffusion under the conditions of multicomponent adsorption may also be deduced from flow measurements [99], As in the case of single-component adsorption, the diffusivities arc determined by matching the experimental data (i.e. the time dependence of the concentration of the effluent or the adsorbent) to the corresponding theoretical expressions. 

In the late 1800s, the development of the kinetic theory of gases led to a method for calculating multicomponent gas diffusion (e.g., the flux of each species in a mixture). The methods were developed simultaneously by Stefan and Maxwell. The problem is to determine the diffusion coefficient Dim. The Stefan-Maxwell equations are simpler in principle since they employ binary diffusivities ... 

The general VLE problem involves a multicomponent system of N constituent species for which the independent variables are T,P,N -I liquid-phase mole fractions, and N - I vapor-phase mole fractions. (Note that = 1 and yi = 1, where Xi and yi represent liquid and vapor mole fractions respectively.) Thus there are 2N independent variables, and application of the phase rule shows that exactly N of these variables must be fixed to establish the intensive state of the system. This means that once N variables have been specified, the remaining N variables can be determined by simultaneous solution of the N equilibrium relations ... 

Electroanalytical methods have been used repeatedly in HTSC studies for the quantitative determination of the chemical composition of ceramics and films, their precursors, and also the degradation products. To analyze a multicomponent non-stoichiometric oxide it is necessary to determine independently with sufficient accuracy, the content of individual components that are simultaneously present in the samples [282]. The independent quantitative determination of oxygen is most essential (difference analysis introduces noticeable errors in the values of the important parameter 6). Also important is the determination of the valence of copper. Certain theories of superconductivity of cuprate systems consider Cu " as the principal essential component of HTSCs [9,10], which attracts special attention to this problem. 

Catalytic systems are inherently multicomponent. An attractive method for determining the difFusivities in multicomponent systems is Fourier transform (FT) PFG NMR spectroscopy, which allows the simultaneous determination of the self-difFusivities of the individual components in a. mixture. If the chemical shifts of the individual species are sufficiently different, the Fourier transform of the spin echo yields separate peaks for the various adsorbates, and then similar to normal PFG NMR the attenuation of the separate peaks with increasing applied field gradient intensity yields the self-diffusivities. Because the technique can also be applied at elevated temperatures, it provides the opportunity for in-situ diffusion measurements under reaction conditions. The experiment also yields the time dependence of the relative concentrations of the reactant and product molecules and thus the intrinsic reaction rate. 

Today two models are available for description of combined (diffusion and permeation) transport of multicomponent gas mixtures the Mean Transport-Pore Model (MTPM)[21,22] and the Dusty Gas Model (DGM)[23,24]. Both models enable in future to connect multicomponent process simultaneously with process as catalytic reaction, gas-solid reaction or adsorption to porous medium. These models are based on the modified Stefan-Maxwell description of multicomponent diffusion in pores and on Darcy (DGM) or Weber (MTPM) equation for permeation. For mass transport due to composition differences (i.e. pure diffusion) both models are represented by an identical set of differential equation with two parameters (transport parameters) which characterise the pore structure. Because both models drastically simplify the real pore structure the transport parameters have to be determined experimentally. 

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