Definition of a sample

In this chapter the word sample has been introduced and used in its statistical sense of a group of objects selected from the population of all such objects, for example a sample of 50 measurements of nitrate ion concentration from the 

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Sample The term sample refers to a single chemical sample as is understood by a chemist. This is in contrast to the statistical definition of a sample, which is a collection of observations from a population. 

The temperature compensator on a pH meter varies the instrument definition of a pH unit from 54.20 mV at 0°C to perhaps 66.10 mV at 60°C. This permits one to measure the pH of the sample (and reference buffer standard) at its actual temperature and thus avoid error due to dissociation equilibria and to junction potentials which have significant temperature coefficients. 

C (250° F) on a filtering medium. The sampling apparatus, however, may have to be modified to conform with the states definition of a particulate. For example, a state may define pai ticulate as any material collectible at stack conditions, a definition that would allow the filtering medium to be located in the stack. 

It is important to recognize that the following analytical methods essentially determine EO-PO ratio ( H NMR, IR, cleavage methods) or even simply alkylene oxide content (compleximetric methods) of the analyte, and as such are not specific quantitative or qualitative methods for poloxamers, since EO-PO copolymers of a different structure (for instance, random copolymers, or PO-EO-PO block copolymers) may respond to the methods in a way indistinguishable from poloxamers. The principal technique that permits definitive identification of a sample as a poloxamer is C NMR, which allows structural details, such as the distribution of EO and PO units along the polymer chain, to be elucidated [10]. 

Definition of a method for obtaining samples for a source of kinetic data on this reactive extmsion must take several factors into account o Extremely small initiator to polymer ratios are involved, o The rate of dispersion of the initiator and the degree of dispersion obtained is likely itiq>ortant to both the homogeneity of the product and the efficiency of the initiator. 

Definition of the reference material, i.e. the matrix, the properties to be certified, and their desired levels Design of a sampling procedure Design of a sample preparation procedure... 

In a widely accepted definition, an analytical method can be defined as the series of procedures from receipt of a sample to the production of the final result. Often, not all procedures can be validated in an adequate way. However, even in such cases, where all procedures of a method are validated, the performance characteristics obtained do not reflect all sources of error. In a recent paper,the complete ladder of errors is described in the following way ... 

Several methods of measurement of the thermal expansion have been developed as a function of the material, dimension and shape of the sample, temperature range and requested accuracy. The measurement of the linear expansion coefficient a = 1/L (AL/A7) of a sample is done by recording the length change AL (in a definite direction) due to a temperature variation AT. 

The microcomputer should incorporate a VDU and have high-density colour graphics capability (up to 1760(x) x 1280(y)). This enables IR-spectra to be displayed on the screen of the VDU with excellent definition so that comparisons, the results of scale expansions and other spectral manipulations can immediately be seen. Parameters such as range, scan time, data point interval, etc., are set and monitored under microprocessor control and stored along with the spectrum. During the scanning of a sample, several thousand data points may be collected and stored in RAM which should be able to accommodate and display at least three spectra simultaneously. There is a wide range of manipulations that can be performed by the analyst on stored spectra, e.g. 

The definition of the sample covariance is also important. Given a set of N pairs of... 

It is a common practice to describe mass dependent isotope fractionation processes by a single linear curve on a three-isotope-plot (Matsuhisa et al. 1978). The resulting straight lines are referred to as terrestrial mass fractionation lines and deviations from it are used as indicating nonmass-dependent isotope effects. The three-isotope-plot is based on the approximation of a power law function to linear format. To describe how far a sample plots off the mass-dependent fractionation line, a new term has been introduced A 0, A Mg, A S, etc. Several definitions of A have been introduced in the literature, which have been discussed by Assonov and Bren-ninkmeijer (2005). The simplest definition is given by ... 

The usual goal of the STS experiment is to probe the DOS distribution of a sample surface. Eq. (14.4) means that this measurement is meaningful only when the tip DOS as a function of energy over the range of measurement is known a priori. Otherwise, the sample DOS does not have a definitive relation to the tunneling spectrum. If the tip DOS is a constant, then Eq. (14.4) implies... 

Semiaqueous or Nonaqueous Solutions. Although the measurement of pH in mixed solvents (e.g., water/organic solvent) is not recommended, for a solution containing more than 5% water, the classical definition of a pH measurement may still apply. In nonaqueous solution, only relative pH values can be obtained. Measurements taken in nonaqueous or partly aqueous solutions require the electrode to be frequently rehydrated (i.e soaked in water or an acidic buffer). Between measurements and after use with a nonaqueous solvent (which is immiscible with water), the electrode should first be rinsed with a solvent, which is miscible with water as well as the analyte solvent, then rinsed with water. Another potential problem with this type of medium is the risk of precipitation of the KC1 electrolyte in the junction between the reference electrode and the measuring solution. To minimize this problem, the reference electrolyte and the sample solution should be matched for mobility and solubility. For example, LiCl in ethanol or LiCl in acetic acid are often used as the reference electrode electrolyte for nonaqueous measurements. 

By definition, concentration of a sample implies an alteration of its composition, often aimed at a specific removal of the major matrix constituent (water, soil material, air). A concentration procedure should... 

Distribution constant. KQ(K). The ratio of the concentration of a sample component in a single definite form in the stationary phase to its concentration in the mobile phase at equilibrium. Both concentrations should be calculated per unit volume of the phase. IUPAC recommends this term rather than partition coefficient. 

If the analyst cannot cite a definite physical reason for failure to include a specific sample measurement, such as evident instrument malfunction, sample container leakage, or sample loss on transfer or injection, then there is no justification for deleting a measurement from subsequent evaluation of a total sample series. If, on injection of a sample into the chromatograph, the operator believes that septum leak is evident, the resulting chromatogram should be marked immediately and never measured or included in the subsequent results. Conversely, if he cannot cite such a reason, the resulting chromatogram must be measured and included in the overall evaluation of the study. 

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