INDEX reference standards

The physics of X-ray refraction are analogous to the well known refraction of light by optical lenses and prisms, governed by Snell s law. The special feature is the deflection at very small angles of few minutes of arc, as the refractive index of X-rays in matter is nearly one. Due to the density differences at inner surfaces most of the incident X-rays are deflected [1]. As the scattered intensity of refraction is proportional to the specific surface of a sample, a reference standard gives a quantitative measure for analytical determinations. 

Compare the refractive index of the substance to be examined with the refractive index of the reference standard of valproic acid, which has a known refractive index of 1.422-1.425 [10,11],... 

It is not surprising that the data produced as total petroleum hydrocarbons (EPA 418.1) suffer from several shortcomings as an index of potential ground-water contamination or health risk. In fact, it does not actually measure the total petroleum hydrocarbons in the sample but rather, measures a specific range of hydrocarbon compounds. This is caused by limitations of the extraction process (solvents used and the concentration steps) and the reference standards used for instrumental analysis. The method specifically states that it does not accurately measure the lighter fractions of gasoline [benzene-toluene-ethylbenzene-xylenes fraction (BTEX)], which should include the benzene-toluene-ethylbenzene-xylenes fraction. Further, the method was originally a method for water samples that has been modified for solids, and it is subject to bias. 

NSF-RANN POLLUTANT FILE FDA-PESTICIDE REFERENCE STANDARDS CPSC-CHEMRIC MONOGRAPHS CAMBRIDGE UNIVERSITY CRYSTAL DATA EROICA THERMODYNAMIC DATA MERCK INDEX... 

The peak with the parent ion of m/e 226 was assigned benzo[ghi]flu granthene. The reference standard was not available, but its retention index was in agreement with that reported (389.6) by Lee et al. (6). The presence of benzo[b,j k]fluoranthenes was also confirmed. They appeared as one broad peak, but the presence of all three was established by their GC retention time in the HPLC subfraction S1-C2C. Benzo[ejpyrene and benzo[a]pyrene were also characterized by MS. PAHs with higher ring systems were not detected in this sample. 

It is highly recommended that all retention properties be normalized to one or preferably several reference standards. Retention indexing, first described by Kovats (Kovats, 1965 see Support Protocol), is by far the most useful standardization procedure for aroma chemicals, because there are published databases (see Internet Resources) listing hundreds of aroma chemicals including their Kovats indices on several substrates. 

The samples were analyzed by capillary gas chromatography and gas chromatography/mass spectrometry (GC/MS). Identifications were verified by comparing the component s mass spectmm and experimental retention index (I) with that of an authentic reference standard. The retention system proposed by Kovats (12) was utilized. When standards were not available the identifications were considered tentative. 

The introduction of GC as an analytical technique has had a profound impact on both qualitative and quantitative analysis of organic compounds. Identification of compounds by GC can be accomplished by their retention times on the column as compared to known reference standards, by inference from sample treatment prior to chromatography, " or by the concept of retention index. " The latter method and tables of retention indices " with associated conditions have been reported. " Although qualitative data and analytical techniques for identification of compounds are well-established " and relative retention data for over 600 substances also have been published, " the main utility of GC undoubtedly lies in its powerful combination of separation and quantitative capabilities. Use in quantitative analysis involves the implementation of two techniques being performed concurrently, i.e., separation of components and subsequent quantitative measurement. 

In support of its program for public standards for drugs, the USPC supplies the Reference Standards required by the monograph standards, tests, and assays of both the USP and the NF. Biologic assays in the USP were the first to require use of reference materials. Authoritative sources of these were needed, and the first were adopted in 1926. As an index of the growth of analytical science, 45 were needed in 1950 for the USP and NF and 438 in 1980. As of 2000, there are 1400. 

Had I read it over someone s shoulder on the subway train Probably not, for it would be unusual, indeed, to have read so much under such circumstances. How could I trace this reference The article had been published, to be sure, but I remembered details which were not sufficiently important to have been indexed in standard tools. There was the possibility, too, that the publication was too new to have been picked up by these tools. 

While compendial standards are available for some monographed article impurities, it may be difficult at times to obtain pure standards of impurities. Manufacturers of pharmaceuticals function as a potential source for obtaining reference standards of impurities, which may be synthesis precursors, process intermediates, or degradation products. The characterization and evaluation of these impurities reference standards should be constant with their intended use. In many cases, analytical procedures are developed and validated, where the response of an impurity is compared to that of the new drug substance itself. Response factor evaluation of impurities at the chosen detection wavelength is necessary to determine if a correction factor is needed (when the responses differ). Potentiometric detection, fluorescence/ chemiluminescence detection, and refractive index detection are some examples of detection modes available for compounds that may not be suitable for UV detection. 

In studies of diagnostic accuracy, the results of one test (often referred to as the index test, the test of interest) are compared with those from the reference standard (referred to as the reference test, the best current practice), A test can be any method for obtaining additional information on a patient s health status. This includes not only laboratory tests, imaging tests, and function tests but also data from the history and physical examination, and genetic data. 

In the ideal study, the results of aU patients tested with the test under evaluation are contrasted with the results of a single reference standard. If fewer than all patients are verified with the reference standard, then partial verification exists, and verification bias may occur if the selection of subjects for reference testing is not purely random. For example, if selection is associated with the outcome of the index test, or the strength of prior suspicion, or both, then verification bias is certain. In a typical case, some patients with negative test results (test-negatives) are not verified by the reference standard if this involves a costly or invasive procedure, and these patients are not included in the analysis. This may result in an underestimation of the number of false-negative results. 

Participant recruitment Was recruitment based on presenting symptoms, resuits from previous tests, or the fact that the participants had received the index tests or the reference standard ... 

Data coiiection Was data coiiection pianned before the index test and reference standard were performed (prospective study) or after (retrospective study) ... 

Technical specifications of material and methods involved including how and when measurements were taken, and/or cite references for index tests and reference standard. ... 

Definition of and rationale for the units, cutoffs and/or categories of the results of the index tests and the reference standard. ... 

Whether or not the readers of the index tests and reference standard were blind (masked) to the results of the other test and describe any other clinical information available to the readers. ... 

The number of participants satisfying the criteria for inclusion that did or did not undergo the index tests and/or the reference standard describe why participants failed to receive either test (a flow diagram is strongly recommended). ... 

Test results 17 Time interval from the index tests to the reference standard, and any treatment adminstered between. ... 

The International Sensitivity Index (ISI) is a measure of the thromboplastin s responsiveness compared with the WHO reference standard. Each thromboplastin reagent manufactured has an ISI valne that should be used to calculate the INR. Although the INR system has a number of potential problems, it is currently the best means available... 

To evaluate the behaviour of a stationary phase, a comparison of the Kovats indexes for five reference compounds belonging to different structural classes is made on the studied phase as well as on squalane, chosen as the reference standard phase for this calculation. The five indexes on a column using squalane, the only reproducible apolar phase since it is formed from a pure material, have been established once and for all (Table 2.1). 

The refractive index of DMF is reported in the literature as 1.4280 at 25 °C. Make your normal temperature corrections based upon the value of water as a reference standard. 

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