Standard reference substances

Table 1.3. Standard reference substances for the quadrupolar and integer-spin nuclei, with compounds commonly used as secondary references and their shift relative to the primary reference.

Comparing the S13C-values of the standard reference substances (see Tables 1 to 4) with the data analysed in the water samples consistent values were observed for di-n-butylphthalate and bis(2-ethylhexyl)phthalate. In addition the standard deviations of the water analyses ranging from 0.2 %o to 3.1 %o were very similar compared to the variations obtained from the recovery experiments (see Table 2). 

If the source substance and absorber are different, the spectral absorption line is shifted along the velocity axis that is caused by the additional energy (8.2.9). The energy denominated in units of velocity, is called in TRS the chemical shift (Figure 8.5b). The sodium nitroprusside Na2[Fe(CN)(N0)5]-2H20 is mostly used as the standard (reference) substance in Mossbauer spectroscopy. Indication of the reference substance in scientific publications is obligatory. 

The values of fH° and Ay.G° that are given in the tables represent the change in the appropriate thermodynamic quantity when one mole of the substance in its standard state is formed, isothermally at the indicated temperature, from the elements, each in its appropriate standard reference state. The standard reference state at 25°C for each element has been chosen to be the standard state that is thermodynamically stable at 25°C and 1 atm pressure. The standard reference states are indicated in the tables by the fact that the values of fH° and Ay.G° are exactly zero. 

If a sample substance (S) has been compared against one standard compound (A) to give but comparison with another standard (B) is required (5sb)> then this change can be effected easily if the relation between the two standards 5, 8 is known (Figure 48.4). For delta values, the order in which the suffixes appear is important. For a sample S measured against reference substance A, delta is written as 5sa- This is not the same as 6 5, as can be seen in Figure 48.4. 

There are no estabHshed specifications for the standard reference samples used in general chemical analysis. Many such substances, however, are analyzed and certified by the National Institute of Standards and Technology (NIST), formerly the National Bureau of Standards (NBS). Specific reference standards are required for many of the analyses included in the USP and NE standards for dmgs. 

Laser based mass spectrometric methods, such as laser ionization (LIMS) and laser ablation in combination with inductively coupled plasma mass spectrometry (LA-ICP-MS) are powerful analytical techniques for survey analysis of solid substances. To realize the analytical performances methods for the direct trace analysis of synthetic and natural crystals modification of a traditional analytical technique was necessary and suitable standard reference materials (SRM) were required. Recent developments allowed extending the range of analytical applications of LIMS and LA-ICP-MS will be presented and discussed. For example ... 

Quantitative analysis using the internal standard method. The height and area of chromatographic peaks are affected not only by the amount of sample but also by fluctuations of the carrier gas flow rate, the column and detector temperatures, etc., i.e. by variations of those factors which influence the sensitivity and response of the detector. The effect of such variations can be eliminated by use of the internal standard method in which a known amount of a reference substance is added to the sample to be analysed before injection into the column. The requirements for an effective internal standard (Section 4.5) may be summarised as follows ... 

In flame spectrophotometric measurements we are concerned with solutions having very small concentrations of the element to be determined. It follows that the standard solutions which will be required for the analyses must also contain very small concentrations of the relevant elements, and it is rarely practicable to prepare the standard solutions by weighing out directly the required reference substance. The usual practice therefore is to prepare stock solutions which contain about 1000 ig mL 1 of the required element, and then the working standard solutions are prepared by suitable dilution of the stock solutions. Solutions which contain less than 10 igmL 1 are often found to deteriorate on standing owing to adsorption of the solute on to the walls of glass vessels. Consequently, standard solutions in which the solute concentration is of this order should not be stored for more than 1 to 2 days. 

Throughout this book the use of a number of standard analytical samples is recommended in order that practical experience may be gained on substances of known composition. In addition, standard reference materials of environmental samples for trace analysis are used for calibration standards, and pure organic compounds are employed as standard materials for elemental analysis. 

The amounts of the standard isotopic species and the tracer isotopic species are represented by X and X for the sample and the reference material. The reference substance is chosen arbitrarily, but is a substance that is homogeneous, available in reasonably large amounts, and measurable using standard analytical techniques for measuring isotopes (generally mass spectrometry). For instance, a sample of ocean water known as Standard Mean Ocean Water (SMOW) is used as a reference for and 0. Calcium carbonate from the Peedee sedimentary formation in North Carolina, USA (PDB) is used for C. More information about using carbon isotopes is presented in Chapter 11. 

C16-0057. State the standard (reference) concentration for each substance appearing in the equilibria of Problem. 

Members of the Association of South-East Asian Nations (ASEAN), Malaysia included, have yet to formulate common rules for dmg regulation. Nonetheless, efforts have been made towards harmonization in terms of voluntary standards. Through the ASEAN Technical Cooperation Project in Pharmaceuticals, a number of reference substances and guidelines have been developed (17). Furthermore, agreements made for the ASEAN Free Trade Area have harmonized and reduced import tariffs on a number of goods, including pharmaceutical raw materials and finished products. 

A secondary chemical reference substance is a substance whose characteristics are assigned and/or calibrated by comparison with a primary chemical reference substance. The extent of characterization and testing of a secondary chemical reference substance may be less extensive than for a primary chemical reference substance. This definition may apply to some substances termed Working Standards . 

The employment of reference substances in the related substances test as external standards for the determination of the content of impurities is often used. The impurities themselves may be described for this purpose but also a... 

Pharmacopoeial reference substances are increasingly employed as assay standards since assay of content is determined more and more frequently by separation techniques. 

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