Secondary reference substance

The procedure employed for the establishment of the chemical reference substances used in these assays has been previously published (Sandrin et al. 1997). The CRSs for the microbiological assays of antibiotics are first submitted to the chemical tests of the monograph. If the results are satisfactory, a collaborative microbiological assay is carried out, using the International Standard as calibrator. Thus, these reference substances are considered to be secondary reference substances since they are calibrated against existing standards. Potency is expressed in International Units. If an International Standard does not exist, European Pharmacopoeia Units are used. 

The preliminary draft guidelines for the establishment of secondary reference substances were presented to the Committee. The Committee endorsed the general approach and agreed that a definition of a pharmacopoeial reference standard should be included before the text was circulated for comment. 

In 1975 the World Health Organization produced a guideline for the establishment, maintenance and distribution of chemical reference substances (WHO 1975). This document was intended to foster collaboration and harmonization of approval for the provision of reference substances by national authorities and organizations responsible for reference substances collections. This guideline was revised in 1982 (WHO 1982) and a further revision was completed more recently (WHO 1999) to take into account progress in pharmaceutical analysis. The latest guidehne defines both primary chemical reference substance and secondary chemical reference substance as follows ... 

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 . 

Figure 2.8, is generated, presenting peaks correspondent to functional groups, such as epoxide, primary and secondary amines, and hydroxyl. The values of the absorption bands for these groups can be found in the papers referenced earlier. The basic principle of all these methods is the comparison between the spectrum of reference substances and spectra of the reactants and products of a curing reaction subjected to radiation. A qualitative and quantitative identification of the components is then possible. 

SI is the term given to cases of insomnia that appear to be secondary to other distressful conditions or secondary to substance use. Secondary in this context means that another condition causes and maintains the insomnia. Insomnia cases where no causal link exists, but where insomnia and another condition co-occur yet function independently, are referred to as co-morbid . If an insomnia state is clearly secondary to another condition, then presumably, the insomnia will subside if the primary condition is successfully treated, but data to support this SI conceptual scheme are scarce, calling into question the concept of causal influence in supposed SI. 

An alternative method for referencing Li shifts in organolithium compounds has recently been proposed by Jackman et al. [45]. It takes advantage of the multiple frequency probes and radio frequency systems of modem spectrometers and is independent of volume susceptibility difference and the nature of the lock substance. The spectrometer has to be calibrated with, for example, a 0.3 M solution of LiCl in [D]methanol containing 5% TMS. The methanol C signal (secondary reference) is then referenced to the primary standard (TMS) which yields... 

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.

Nucleus Reference substance Secondary reference compound Shift from the primary compound (ppm)... 

Raw Material Assignment. Raw material samples are sent to the reference substances service where registered, indexed and stored in appropriate preservation conditions (temperature, moisture, etc.) these products cem be selected for further analysis as substances of secondary reference. 

International Chemical Reference Substances (ICRS) are established upon the advice of the WHO Expert Committee on Specifications for Pharmaceutical Preparations. They are supplied primarily for use in physical and chemical tests and assays described in the specifications for quahty control of medicines published in The International Pharmacopoeia or proposed in draft monographs. The International Chemical Reference Substances are mainly intended to be used as primary standards to calibrate secondary standards. 

Reference standard, secondary A substance of established quality and purity, as shown by comparison with a primary reference standard, used as a reference standard for routine laboratory analysis. 

Samples of reference substances specified in the current instructions for testing should be obtained. Reference standards and any secondary standards prepared from them should be dated and be stored, handled and used so as not to prejudice their quality. 

Reference substances and preparations Reference substances and preparations secondary standard preparations and standards specific to the company must be acquired or prepared, preserved and used according to define procedures which ensure the maintenance of quality. 

Absolute Shielding Scales. - For lighter elements, the way to the absolute shielding involves a non-relativistically valid relation between the spin-rotation constant, C, and shielding a, applied to at least one primary reference molecule. A review of how spin-rotation constants relate to shielding constants was provided by Bryce and Wasylishen. The C and a tensors for the primary reference are corrected for rovibrational effects and then connected to a commonly used secondary reference (usually a neat liquid substance) via an NMR measurement in the gas phase at the limit of zero density and in the liquid... 

Dethier, V. G. (1980b) Evolution of receptor sensitivity to secondary plant substances with special reference to deterrents. Am. Nat., 115, 45-66. 

We make no attempt to characterize these chemicals beyond the generalizations that (i) wide ranges of both primary and secondary plant substances act as excitatory stimuli (ii) inhibition of investment behaviors is triggered mainly by secondary substances but sometimes by unfavorable balances of primary nutrients and (iii) because they are relatively non-volatile and effectively compartmentalized, many phytochemicals generating the inhibitory inputs influence insect behavior only during or after the examining phase when direct contact has been established. Readers are referred to Hedin et al. (1974) for analysis of behaviorally active phytochemicals by chemical class. 

A big step forward came with the discovery that bombardment of a liquid target surface by abeam of fast atoms caused continuous desorption of ions that were characteristic of the liquid. Where this liquid consisted of a sample substance dissolved in a solvent of low volatility (a matrix), both positive and negative molecular or quasi-molecular ions characteristic of the sample were produced. The process quickly became known by the acronym FAB (fast-atom bombardment) and for its then-fabulous results on substances that had hitherto proved intractable. Later, it was found that a primary incident beam of fast ions could be used instead, and a more generally descriptive term, LSIMS (liquid secondary ion mass spectrometry) has come into use. However, note that purists still regard and refer to both FAB and LSIMS as simply facets of the original SIMS. In practice, any of the acronyms can be used, but FAB and LSIMS are more descriptive when referring to the primary atom or ion beam. 

Air pollution can be considered to have three components sources, transport and transformations in the atmosphere, and receptors. The source emits airborne substances that, when released, are transported through the atmosphere. Some of the substances interact with sunlight or chemical species in the atmosphere and are transformed. Pollutants that are emitted directiy to the atmosphere are called primary pollutants pollutants that are formed in the atmosphere as a result of transformations are called secondary pollutants. The reactants that undergo transformation are referred to as precursors. An example of a secondary pollutant is O, and its precursors are NMHC and nitrogen oxides, NO, a combination of nitric oxide [10102-43-9] NO, and NO2. The receptor is the person, animal, plant, material, or ecosystem affected by the emissions. 

In titrimetry certain chemicals are used frequently in defined concentrations as reference solutions. Such substances are referred to as primary standards or secondary standards. A primary standard is a compound of sufficient purity from which a standard solution can be prepared by direct weighing of a quantity of it, followed by dilution to give a defined volume of solution. The solution produced is then a primary standard solution. A primary standard should satisfy the following requirements. 

One approach to providing secondary RMs is the NIST Traceable Reference Material (NTRM) program for gas standards (Jenks et. al. 1998 NIST 1997). The NTRM program is to be extended to metals, trace elements and pure substances. It may be possible to extend this concept to other types of RM, but it is difficult to see how it can easily be applied to the production of complex matrix CRMs. 

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