Mass, of sample

Accurate enthalpies of solid-solid transitions and solid-liquid transitions (fiision) are usually detennined in an adiabatic heat capacity calorimeter. Measurements of lower precision can be made with a differential scaiming calorimeter (see later). Enthalpies of vaporization are usually detennined by the measurement of the amount of energy required to vaporize a known mass of sample. The various measurement methods have been critically reviewed by Majer and Svoboda [9]. The actual teclmique used depends on the vapour pressure of the material. Methods based on... 

Treating a population as though it contains only two types of particles is a useful exercise because it shows us that the relative sampling variance can be improved by collecting more particles of sample. Furthermore, we learned that the mass of sample needed can be reduced by decreasing particle size without affecting the relative sampling variance. Both are important conclusions. 

Each of the f2 samples had a nominal weight of O.f g. Determine the approximate value for fQ, and the mass of sample needed to achieve a percent relative standard deviation of 2%. 

The effective use of column volume overload for preparative separations was experimentally demonstrated by Scott and Kucera [1]. These authors used a column 25 cm long, 4.6 mm I.D. packed with Partisil silica gel 10 mm particle diameter and employed n-heptane as the mobile phase. The total mass of sample injected was kept constant at 176 mg, 8 mg and 0.3 mg of benzene, naphthalene and anthracene, respectively, but the sample volumes used which contained the same mixture of solutes were 1 pi, 1 ml, 2 ml and 3 ml. The chromatograms of each separation are... 

To demonstrate the effect in more detail a series of experiments was carried out similar to that of volume overload, but in this case, the sample mass was increased in small increments. The retention distance of the front and the back of each peak was measured at the nominal points of inflection (0.6065 of the peak height) and the curves relating the retention data produced to the mass of sample added are shown in Figure 7. In Figure 7 the change in retention time with sample load is more obvious the maximum effect was to reduce the retention time of anthracene and the minimum effect was to the overloaded solute itself, benzene. Despite the reduction in retention time, the band width of anthracene is still little effected by the overloaded benzene. There is, however, a significant increase in the width of the naphthalene peak which... 

It is often desirable to calculate the mass of sample from the gas laws. Pressure and temperature must then be known. 

Mass of sample = amount in moles X mass per mole... 

Mass spectrometry allows us to measure masses of individual atoms. Still, there is an enormous difference between the mass of one atom and the masses of samples measured in the laboratory. For example, a good laboratory balance measures mass values from about 10 to 10 g. An atom, on the other hand, has a mass between 10 and... 

As micro-analytical techniques (performing direct analysis on a <10 mg sample mass) have a particularly distinct demand for very homogeneous CRMs, it becomes necessary to provide element-specific homogeneity information in the CRM certificates. The distribution of elements in a material can be evaluated experimentally by repetitive analysis. The scattering of results from a method with known intrinsic precision is related to the mass of sample consumed for individual analysis. The... 

Different analytical procedures have been developed for direct atomic spectrometry of solids applicable to inorganic and organic materials in the form of powders, granulate, fibres, foils or sheets. For sample introduction without prior dissolution, a sample can also be suspended in a suitable solvent. Slurry techniques have not been used in relation to polymer/additive analysis. The required amount of sample taken for analysis typically ranges from 0.1 to 10 mg for analyte concentrations in the ppm and ppb range. In direct solid sampling method development, the mass of sample to be used is determined by the sensitivity of the available analytical lines. Physical methods are direct and relative instrumental methods, subjected to matrix-dependent physical and nonspectral interferences. Standard reference samples may be used to compensate for systematic errors. The minimum difficulties cause INAA, SNMS, XRF (for thin samples), TXRF and PIXE. 

Such nuclear reactions are controllable by keeping the sample size small. Most of the neutrons escape from the sample instead of causing further reactions. The smallest mass of sample that can cause a sustained nuclear reaction, called a chain reaction, is called the critical mass. Another way to control the nuclear reaction is to insert control rods into the nuclear fuel. The rods absorb some of the neutrons and prevent a runaway reaction. 

Fig. 1.6. Absolute masses of samples and analytes (a) and relative analyte amounts (b) relevant in analytical investigations...

The experimental procedure for conducting phase solubility analysis is rather simple it consists of mixing increasing amounts of sample with a fixed volume of solvent and then determining the mass of sample that has dissolved after each addition. It is not necessary to exceed the solubility limit of the analyte species, but attainment of this condition makes it easier to recognize trend within the plots. An experimental protocol for phase solubility analyses is available [39]. The data are most commonly plotted with the system composition (total mass of sample added per gram solvent) on the x axis, and the solution composition (mass of solute actually dissolved per gram of solvent) on the y axis. 

In many industrial areas, as well as food and agriculture, the amount of sample available to the analyst is not normally a limiting factor. However, in clinical chemistry the opposite applies, as no patient is willing to donate large volumes of blood for analysis Similarly in forensic work, the sample material may also be limited in size. Sample size is linked to the limit of detection. Improved detection levels can sometimes be achieved by taking a larger mass of sample. However,... 

This question requires use of the general expression substance (mol) = mass of sample (g) molar mass (g mol 6 (a) Mass of sulphur dioxide (g) =... 

Test Equipment Typical Mass of Sample (g) Typical Sensitivity (W/kg) Thermal Inertia of System Possible Data Acquired... 

The energy of combustion of benzoic acid determined by standardizing laboratories normally refers to the following certification conditions [21,25,39-43] (1) The benzoic acid sample is burned in a bomb at constant volume, in pure oxygen at an initial pressure of 3.04 MPa (2) the mass of sample burned, expressed in grams, is equal to three times the internal volume of the bomb in dm3 (3) the amount of water inside the bomb, expressed in grams, is also equal to three times the internal volume of the bomb in dm3 (4) the combustion reaction is referred to 298.15 K. If calibrations are not made strictly under the certification conditions, the value of Acm(BA) under the actual bomb conditions should... 

The results of the calibration and reaction experiments are shown in table 8.1 [142]. In this table, t is the time during which a current of intensity /flows through the calibration resistance, V the measured potential drop across the resistance, and m the mass of sample. The values of ATad for the calibration and reaction experiments were determined from the corresponding temperature-time data, using the Regnault-Pfaundler method with 7], Tf, k, and Tc0 calculated from equations 7.12-7.15 (section 7.1). 

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