Mass fraction of analyte

Figure 6.2. Horwitz horn curve of relative standard deviation as a function of mass fraction of analyte (x). The solid curve is log2(J ) = 1-0.5 log10(x) (Horwitz et al. 1980). Dotted lines at the extremes are modifications suggested after the original paper (Thompson 2004).

Smith and Udseth [154] first described SFE-MS in 1983. Direct fluid injection (DFT) mass spectrometry (DFT-MS, DFI-MS/MS) utilises supercritical fluids for solvation and transfer of materials to a mass-spectrometer chemical ionisation (Cl) source. Extraction with scC02 is compatible with a variety of Cl reagents, which allow a sensitive and selective means for ionising the solute classes of interest. If the interfering effects of the sample matrix cannot be overcome by selective ionisation, techniques based on tandem mass spectrometry can be used [7]. In these cases, a cheaper and more attractive alternative is often to perform some form of chromatography between extraction and detection. In SFE-MS, on-line fractionation using pressure can be used to control SCF solubility to a limited extent. The main features of on-line SFE-MS are summarised in Table 7.20. It appears that the direct introduction into a mass spectrometer of analytes dissolved in supercritical fluids without on-line chromatography has not actively been pursued. 

In this case, the first reason for deviation from linearity is that the exponent on the scan rate is not 1/2, but some other fraction. If the exponent is greater than 1/2, then we assume that an additional means of mass transport supplements the diffusion - with either convection or migration also being involved. Conversely, if the exponent is much less than 1/2, then we usually assume that the analyte is adsorbed at the electrode, implying that there is little mass transport of analyte at all. 

If it is not possible to involve additional laboratories for the determination of the between-laboratory reproducibility, then the within-laboratory reproducibility may be used to get an estimate of the between-laboratory reproducibility. The reproducibility of the method may be dependent upon the mass fraction of the analyte in the test sample. It is therefore recommended, when studying the reproducibility, to investigate whether a relation exists between concentration and reproducibility. The measurement series should be greater than 8. 

Certified reference materials offer the chance to limit the impact of most of the factors described above. They are certified to the mass fractions of the plant materials (typically seeds) used [16]. This makes these standards fully traceable to SI units. The materials are produced under highly standardized and well-characterized conditions and their homogeneity is confirmed. Every analyst calibrating his/her method using these standards will have an analytical system that is traceable to SI units. 

This book describes the fundamental operating characteristics of the most common inorganic mass spectrometers. At the heart of this discussion is a description of the various ionization sources that generate a representative analyte population for mass analysis. The initial chapters introduce the mass spectrometric hardware that separates the ionized fractions of analytes, one mass from another. The detection schemes used to measure this ion population, and the data processing systems that permit this information to be of value to the chemical analyst, are also discussed. 

Synergism caused by the addition of Group C particles was found from both SEM microscopy and video macroscopy (Xia and Kwauk, 1985) to be associated with adhesion of these line particles on the coarse particle. Nevertheless, more appropriate analytical, or even theoretical, ground needs to be found to account for the initial rise and later fall in the value of the dimensionless time 0 as the mass fraction of fines increases from zero to unity. 

Using equations (3) and (4), equations (2a-2c) can be written as depending on only one variable. This variable should be easily monitored experimentally. Such a variable is the mass fraction of the gas G or the mass fraction of the solid residue (1 - G). The three equations (2a-2c) can be initially used to calculate the values for k-, k2 and a-). This can be done using a best-fit technique for experimental data that are assumed to be described by equations (2) in isothermal conditions. Once the values for k-, k2 and a- are known, the kinetics equations can be integrated and solved for any time t. This model has been successfully applied, for example, to describe the pyrolysis of cellulose and of pine needles [8]. In anal ical pyrolysis this model can be used to determine the amount of gas generated during pyrolysis. Also, analytical pyrolysis data can be used to fit the kinetics model for use in other practical applications. 

J. de Boer, M. Lohman and E.A. Maier, The certification of the contents (mass fractions) of eight polychloro biphenyls (CB lUPAC No 28, 52, 118, 138, 149, 153, 170 and 180) in fresh mussel tissue — (CRM 682), Report EUR J78S9 EN. CEC Luxembourg (1999). Quantifying uncertainty in analytical measurement. English Edition. EURACHEM. DTI-VAM Crown Copyright 1995 UK, ISBN 0-948926-08-2 (1995). 

The water mass fraction of the material varied considerably from 7.3 to 10.9% (one participant even reported values around 3%). The water content may change with the humidity of the ambient air therefore, it must be measured at the beginning of each analytical session and corrections to dry mass must systematically applied. 

Young and Russell (1998) suggested that the CCAM line is a secondary and not a primary (i.e. nebular) mixing line in that it results from the inclusion of both altered and unaltered components in mineral separate analyses. As indicated in (a), alteration shifts data off the Y R line along a mass-fractionation trajectory. Analytical uncertainties are smaller than the symbol sizes laser ablation data are from Young and Russell (1998),... 

We began modeling under the assumption that the introduction of the tracer (mass) into the system did not affect the mechanisms present for metabolism of the tracee. The compartmental model was compatible with the assumption that non-steady-state mechanisms for metabolism of /3-carotene were not induced by the tracer because the model prediction of the tracer state, the tracee state, and the steady state could be achieved using the same set of fractional transfer coefficients (FTCs). The appropriateness of this assumption is discussed again under Statistical Considerations. FTC is the fraction of analyte in a donor compartment that is transferred to a recipient compartment per unit of time, in this case per day. 

The composition of carbon-chain polymers with monomeric units having widely differing analytical composition, characteristic elements or groups, or radioactive labels can be readily determined. Chemical (microanalysis, functional group determination, etc.) and spectroscopic methods (infrared, ultraviolet, nuclear magnetic resonance, etc.), as well as the determination of radioactivity, yield the average composition of the polymer. The mean composition can also be determined from the refractive indices of solid samples. The composition can be calculated from the principle that the copolymer is considered to be a solution of one unipolymer (from one of the monomeric units) in the other. The composition can also be found by means of the refractive index increment dw/dc in solution, which gives the variation in refractive index with concentration. The mass fraction of the monomeric unit A can be calculated from... 

Pure substances or solutions used for calibration purposes and/or the identification of substances, or aimed at testing part or the totality of an analytical procedure. They are characterized by the establishment, in mass fractions, of (i) the remaining impurities in the purified substance and/or (ii) its isotopic composition. 

Thus 8 measures the product of the ionization efficiency (fraction of analyte molecules delivered as ions to the entrance from the API source into the MS) with the transmission efficiency of ions from the MS entrance aperture to the detector. The first experiments, conducted at flow rates of tens of nL.min, gave 8 values of about 1/1000 (Wilm 1994), later improved to 1/390 (Wilm 1996) using a quadrupole mass spectrometer operated with very high peak widths to improve transmission efficiency the sampling efficiency... 

In the relative method, the mass fraction of the analyte element in the unknown sample is obtained using the mass fraction of the same element in the standard. The equation takes into account the peak areas obtained in the unknown and in the standard the sample weight (mass), W the decay factors S, D, and C (see Eq. (30.26)) differences in neutron flux and differences in detection efficiency due to slightly different counting geometries. 

Several empirical correlation schemes similar to those appearing elsewhere [1, 2] were applied to the two-phase experimental heat-transfer results. In Reference [1] the Martinelli parameter, Xtt, and an analytical Reynolds number involving the mass fraction of vapor jc were used in establishing the correlation. Similar parameters were chosen for the correlation of the hydrogen data. 

Equation 17 can be solved numerically for any specified temperature history. However, the mesophase temperature history is a function of both time and position (see Fig. 4), and so the transient temperature distribution T(x, t) must be specified in order to obtain an analytic solution for equation 17. If the temperature distribution is static during steady burning of a thick sample as the surface x = 0 recedes at constant velocity v = (dx/df)r and the mesophase is a thin surface layer, then the rate of temperature rise of the mesophase is constant, (dT/df)a =o = -v(dT/dx)t = The assumption of a constant heating rate for the mesophase transforms the independent variable in equation 17 from time to temperature and allows for a solution in terms of the mass fraction of polymer remaining at temperature T... 

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