Measurement of mass

Suppose that for a particular total analysis method the signal is a measurement of mass using a balance whose smallest increment is 0.0001 g. If the method s... 

The measurement of mass using a quartz crystal microbalance is based on the piezoelectric effect.When a piezoelectric material, such as a quartz crystal, experiences a mechanical stress, it generates an electrical potential whose magnitude is proportional to the applied stress. Gonversely, when an alternating electrical field is... 

In a gravimetric analysis a measurement of mass or change in mass provides quantitative information about the amount of analyte in a sample. The most common form of gravimetry uses a precipitation reaction to generate a product whose mass is proportional to the analyte. In many cases the precipitate includes the analyte however, an indirect analysis in which the analyte causes the precipitation of another compound also is possible. Precipitation gravimetric procedures must be carefully controlled to produce precipitates that are easily filterable, free from impurities, and of known stoichiometry. 

Another type of ion is formed almost uniquely by the electrospray inlet/ion source which makes this technique so valuable for examining substances such as proteins that have large relative molecular mass. Measurement of m/z ratios usually gives a direct measure of mass for most mass spectrometry because z = 1 and so m/z = m/1 = m. Values of z greater than one are unusual. However, for electrospray, values of z greater than one (often much greater), are quite coimnonplace. For example, instead of the [M + H]+ ions common in simple Cl, ions in electrospray can be [M + n-H]- where n can be anything from 1 to about 30. 

Two dimensionless variables play key roles in the analysis of single transition systems (and some multiple transition systems). These are the throughput parameter [see Eq. (16-129)] and the number of transfer units (see Table 16-13). The former is time made dimensionless so that it is equal to unity at the stoichiometric center of a breakthrough cui ve. The latter is, as in packed tower calculations, a measure of mass-transfer resistance. 

The amount of work performed fixed W. Measurements of mass and velocity of the rubber band tell us, experimentally, the magnitude of (KE),. How do we know (PE)%1 How are we sure that (PE)2 is equal to W and to (KE),1 The evidence we have is that we put an amount of energy into the system and can recover all of it later at will. It is natural to say the energy is stored in the meantime. Then we can say that the rubber band is just like the billiard ball collision energy is conserved at all times. 

One of the commonest procedures carried out by the analyst is the measurement of mass. Many chemical analyses are based upon the accurate determination of the mass of a sample, and that of a solid substance produced from it (gravimetric analysis), or upon ascertaining the volume of a carefully prepared standard solution (which contains an accurately known mass of solute) which is required to react with the sample (titrimetric analysis). For the accurate... 

The techniques referred to above (Sects. 1—3) may be operated for a sample heated in a constant temperature environment or under conditions of programmed temperature change. Very similar equipment can often be used differences normally reside in the temperature control of the reactant cell. Non-isothermal measurements of mass loss are termed thermogravimetry (TG), absorption or evolution of heat is differential scanning calorimetry (DSC), and measurement of the temperature difference between the sample and an inert reference substance is termed differential thermal analysis (DTA). These techniques can be used singly [33,76,174] or in combination and may include provision for EGA. Applications of non-isothermal measurements have ranged from the rapid qualitative estimation of reaction temperature to the quantitative determination of kinetic parameters [175—177]. The evaluation of kinetic parameters from non-isothermal data is dealt with in detail in Chap. 3.6. 

Precipitation reactions have many applications. One is to make compounds. The strategy is to choose starting solutions that form a precipitate of the desired insoluble compound when they are mixed. Then we can separate the insoluble compound from the reaction mixture by filtration. Another application is in chemical analysis. In qualitative analysis—the determination of the substances present in a sample—the formation of a precipitate is used to confirm the identity of certain ions. In quantitative analysis, the aim is to determine the amount of each substance or element present. In particular, in gravimetric analysis, the amount of substance present is determined by measurements of mass. In this application, an insoluble compound is precipitated, the precipitate is filtered off and weighed, and from its mass the amount of a substance in one of the original solutions is calculated (Fig. 1.6). Gravimetric analysis can be used in environmental monitoring to find out how much of a heavy metal ion, such as lead or mercury, is in a sample of water. 

Knowledge on the plasma species can be obtained by the use of plasma diagnostics techniques, such as optical emission spectroscopy (OES) and mass spectroscopy (MS). Both techniques are able to probe atomic and molecular, neutral or ionized species present in plasmas. OES is based on measuring the light emission spectrum that arises from the relaxation of plasma species in excited energy states. MS, on the other hand, is generally based on the measurement of mass spectra of ground state species. 

It is common to achieve accuracies of 1 part in 105 in using equation (1.1) with pycnometers as small as 5 cm3 and routine measurements can achieve 1 part in 104. However the main sources of error in assigning density to a particular compound in a particular state arise from factors other than the measurment of mass and volume. See Section 1.4.1... 

Electrochemical measurements of mass-transfer rates by the limiting-current technique have been employed with increasing frequency in the last 20 years. This chapter offers a discussion of the underlying principles, conditions of validity, and selected applications. 

In this chapter the theory and practice of limiting-current technique for the measurement of mass-transport coefficients have been described. The selective discussion and tabular compilation of results of investigations that used limiting-current measurements should be indicative of the widespread use of this relatively novel method. 

Mass Loss Rate as a Function of External Heat Flux. The technique for the measurement of mass loss rate as a function of heat flux was developed in 1976 at FMRC using the Small-Scale Flammability Apparatus (8 ). Several other flammability apparatuses are now available for such measurements, such as OSU Heat Release Rate Apparatus (13) and NIST Cone Calorimeter (1 4). 

Describe measurements of mass loss rates of various electrical PVC products, by thermoanalytical experiments. 

The required concentration of detergency is extremely important in the field of washing machines and detergency. Two kinds of monitoring methods can be distinguished - direct determination of active substances in the washing liquor and indirect methods, which rely on the measurement of masses and flows. 

Paces, T., 1983, Rate constants of dissolution derived from the measurements of mass balance in hydrological catchments. Geochimica et Cosmochimica Acta 47,1855-1863. 

As just described, the most precise measurements of masses come from double neutron star systems. There are currently five such systems known, three of which will coalesce due to gravitational radiation in less than the age of the universe, 1010 yr (Taylor 1994). These three systems in particular allow very precise measurements of the masses of the components, which are between 1.33 M and 1.45 M0 (Thorsett Chakrabarty 1999). The other two double neutron star systems also have component masses consistent with a canonical 1.4 M . It has been suggested that the tight grouping of masses implies that the maximum mass of a neutron star is 1.5 M0 (Bethe Brown 1995). However, it is important to remember that double neutron star systems all have the same evolutionary pathway and thus the similar masses may simply be the result of a narrow selection of systems. 

The thickness of wire often is measured using a system called the American Wire Gauge (AWG) standard. The smaller the gauge number, the larger the diameter of the wire. For example, 18-gauge copper wire has a diameter of about 0.102 cm 12-gauge copper wire has a diameter of about 0.205 cm. Such small diameters are difficult to measure accurately with a metric ruler. In this experiment, you will plot measurements of mass and volume to find the density of copper. Then, you will use the density of copper to confirm the gauge of copper wire. 

One difficulty in making measurements of transfer coefficients is that equilibrium is rapidly attained between particles and fluidising medium. This has in some cases been obviated by the use of very shallow beds. In addition, in measurements of mass transfer, the methods of analysis have been inaccurate, and the particles used have frequently been of such a nature that it has not been possible to obtain fluidisation of good quality. 

The limitations discussed above also apply approximately to measurements of mass dependent Ca isotope effects. The additional problem is to separate mass dependent fractionation in nature from mass dependent fractionation in the mass spectrometer. The maximum observed natural fractionation is about +0.1% per mass unit, whereas instrumental fractionation is about +0.5% per mass unit (for TIMS and much larger for ICPMS). The separation is accomplished with the use of a double spike (Russell et al. 1978b). The approach is illustrated here using the methods of Skulan et al. (1997), but other researchers have used slightly different algorithms and double spike isotopes (Zhu and MacDougall 1998 Heuser et al. 2002 Schmitt et al. 2003a). 

MALDI measures the mass very accurately, and it gives an absolute measurement of mass. Still, sample and solution conditions must be optimized for the best performance of the matrix and therefore, it cannot yet be used as a routine method. Also, characterization of synthetic polymers by MALDI is sometimes... 

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