Identification of Substance

Lawson Number (LN)-CAS Reg No (RN) Beilstein Pref RN (BPR) Other Source (OS)- 

4 -HYDROXYACETOPHENONE. 99 PERCENT. WHITE. 4-Hydroxyacetophenone. pract ca 97 percent (NT), 4 -hydroxyacetophenone 1-(4-hydroxy-phenyl)-ethanone 136 15 

SpecInfo Database. E.Merck. Darmstadt, Aldrich Fluka. EINECS 

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HPLC systems coupled to mass spectrometers (LC-MS) are extremely important methods for the separation and identification of substances. If not for the costs involved in LC-MS, these systems would be more commonly found in research laboratories. 

Isolation and identification of substances (natural products from nature, protein purification and characterisation, etc). 

For large molecules, at least, Raman spectra contain numerous bands which cannot always completely he assigned to particular vibrational modes. The large number of bands can, however, when measured with appropriate spectral resolution, enable unambiguous identification of substances by comparing the spectral pattern ("fingerprint") with those of reference spectra, if they are available. 

This approach has allowed us to characterize other antimicrobial substances as well (12-14). The application of a similarly designed procedure will facilitate Identification of substances in plants responsible for allelopathy. 

Applications Sollinger and Sawatzki [793] have reported the use of TLC-Raman for routine applications, e.g. TLC of hydroxybenzenes (including hydro-quinone and pyrogallol) on conventional, silica gel and specific Raman-TLC plates (coated with spherical silica gel). Databases were used for identification of substances. Typical detection limits were in the low p,g region per application, Micro-Raman spectrometry has been employed in analysing TLC fractions from polymer additives within a detection limit... 

In a further move to achieve a high degree of consumer protection and to provide adequate information, the Commission is addressing the issue of specific identification of substances in food that cause allergies and symptoms of intolerance and hypersensitivity in certain consumers. A proprosed Directive19 will require declaration of these substances (listed in Annex Ilia) under all... 

The purity of a crystallised organic substance is checked by the melting point. This easily determined constant also serves for the identification of substances and, in the case of new compounds, for their characterisation. The apparatus is a long-necked, round-bottomed flask into which a tested thermometer is fixed by means of a cork a sector is cut out of the cork with a sharp knife in order that the whole of the thermometer scale may be visible (Fig. 31). 

ECHA (2007) Guidance for the preparation of an Annex XV dossier on the identification of substances of very high concern. http //echa. eiuopa.eu/ documents/10162/17230/svhc en.pdf. Accessed 29 Jan 2012... 

The quantity of any given element which could be synthesized in the cyclotron was not great. In most cases only unweighable amounts of the new substances were obtained in it. Specialized techniques had to be developed to identify the traces of the elements by carrying them through a series of reactions with elements which they resembled chemically. This tracer technique has yielded a surprising amount of information as to the chemistry of the new elements, and has made possible the positive identification of substances which are present in amounts too small even to give an X-ray spectrum. 

A simpler means for unequivocal identification of substances by TLC or HPTLC combined with MS, can be provided by online procedures (54, 55). The ability to perform MS on analytes directly on the chromatographic plate removes the need to recover them prior to identification. This greatly reduces the amount of work needed to confirm identity. The determination of midazolam in serum (56) and the identification of tetracycline residues in honey (57) are examples of TLC coupled in situ with FAB-MS. 

The second obstacle this theory offered to chemical development lay in the fact that so long as this theory was maintained, no identification of substances as elements was... 

Some plasticizer mixes require pretreatment, such as saponification, but in most instances chromatographic separations can be accomplished with the mix. In addition to the usual identification of substances by organochemical analysis, other methods now being used include color tests, physical tests (determinations of boiling point and refractive index), and infrared and ultraviolet spectroscopy. 

Analysis The identification of the composition of a substance. Physical methods used for essential oil mixtures include GC-MS. The identification of substances is called qualitative analysis, while the estimation of the amounts of components present is quantitative analysis. 

Apart from toxicity tests involving the use of live animals, there are other ways of evaluating the toxic properties of chemicals that stem from an understanding of their mode of action. For example, the Ames test aids in the identification of substances that act as carcinogens or mutagens in mammals. Also, the study of the relationship between structure and toxicity (i.e., quantitative structure-activity relationships or QSARs) can provide support for the identification of toxic substances. These approaches will become more viable as molecular mechanisms of toxicity become better known, and they can lead to an understanding of the molecular characteristics that cause a chemical to interact adversely with cellular macromolecules. 

Measurement is the heart of modem science, and even the social sciences are becoming more qnantitative. Measurements make identifications of substances more precise and enable more scientific generalities to be made. For example, even ancient peoples knew that when objects were dropped, they fell downward. Measurements involving gravity enabled Sir Isaac Newton (1642-1727) to determine that the same laws of gravity that goveam the fall of an object here on Earth also govern the motions of the Moon and the planets in the solar system. 

H., 2005, Non-targeted multi-component analytical surveillance of plastic food contact materials Identification of substances not included in EU positive lists and their risk assessment, Food Additives and Contaminants, 22, 1012-1022. 

The on-line coupling between TLC and mass spectrometry provides a powerful combination for the detection and identification of substances separated by a planar chromatographic method. The on-line coupling between these two methods has to overcome the problem of vaporizing and introducing the sample into the mass spectrometer. Different methods are reported in the literature, but the analytical principle is the same the sample is ionized from the layer surface by means of a laser beam, under vacuum, and in the presence of an energy-buffering matrix. Once the ions are transferred into the mass spectrometer, more sophisticated methods can be applied for data analysis and interpretation, e.g., MS-MS. 

The use of MS as a detector for TLC concerns identification of substances in a mixture, as well their... 

Method of identification of substances causing side effects (if applicable). 

When the gas chromatograph is attached to a mass spectrometer, a very powerful analytical tool (gas chromatography-mass spectrometry, GC-MS) is produced. Gas chromatography allows the separation of mixtures but does not allow the definitive identification of unknown substances, whereas mass spectrometry is good for the identification of individual compounds of the mixtures of compounds. This means that with GC-MS, both separation and identification of substances in mixtures can be achieved. The spectrometer can be connected to a computer that has a library from which the mass peaks can be compared and is a very powerful analytical tool. Because of the relatively small amounts of material required for mass spectrometry, a splitting system is inserted between the column and the mass spectrometer. This enables only a small fraction of the effluent to enter the spectrometer the rest of the effluent is usually collected or vented to the air. 

Most of the above methods of column chromatography have been, or can be, automated. Devices are available for the automated application of samples to columns which are useful for analytical evaluation of samples, or for repeated analysis or separations to obtain larger amounts of material. The specific fractions of the effluent can be collected. Equipment for these purposes can be obtained from several of the supplier listed at the end of the HPLC section above with the corresponding websites. GC systems coupled with mass spectrometers (GC-MS) and HPLC systems coupled to mass spectrometers (LC-MS) are extremely important methods for the separation and identification of substances. These are invariably linked to a computer with internal libraries which can identify the peaks, and the libraries can be continually updated (see above). With more elaborate equipment LC-MS-MS where the peaks from the first spectrometer are further analysed by a second mass spectrometer provide a wealth of information. If not for the costs involved in GC-MS, GC-MS-MS, LC-MS and LC-MS-MS equipment, these systems would be more commonly found in analytical and research laboratories. [For further reading see Bibliography.]... 

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