Dating techniques ratios

Davio et al. (43) report efforts to obtain monoclonal antibodies (mAbs) to STX. Because STX is a small molecule of approximately 300 daltons, well below the size necessary for immunogenicity, a carrier molecule must be conjugated to the hapten (STX). This technique must minimize alterations of the antigenic form. For the anti-STX antibodies tested to date, the ratios of immunoassay response factor to pharmacological potency for various STX derivatives differ substantially, the immunoassay being virtually unresponsive to some of the common natural derivatives (44). 

L and the D/L ratio approaches zero. After the death of the living organism, proteins start to spontaneously break down. An inter-conversion of the amino acids occurs from one chiral form (L) to a mixture of D- and L- forms following protein degradation this process is called amino acid racemisation. The extent of racemisation is measured by the ratio of D/L isomers and increases as a function of time and temperature. The longer the racemisation process continues the closer to 1 the ratio between the D- and L-forms becomes. If the D/L ratio is <1 it may be possible to use it to estimate age. The D/L ratio of aspartic acid and isoleucine are the most widely used for this dating technique [104]. Dates have been obtained as old as 200 000 years. However, it has been used mainly to date samples in the 5000 100 000 year range. Recent studies [ 105] mention an estimation of the method accuracy to be around 20%. 

With respect to interpretation, the existence of alternative dating techniques has made clear the necessity for and the difficulty of this step. That is, nature seldom provides ideal dating systems with fixed injection rates, negligible losses, and constant temperature. As a result, simple dates based upon observed isotopic ratios and nuclear half-lives, for example, frequently require cautious interpretation before they can serve as accurate... 

During the past several years exciting advances have taken place in radioactive dating techniques—advances which have made it possible to determine unusually small isotope ratios and to determine the radioisotopic composition of individual chemical fractions and particle size fractions of extremely small samples. 

A dating technique for fossils is based on the measurement of the d l ratio of amino acids extracted from the fossil sample. The hypothesis is that over very long periods... 

The essential difference between K-Ar and Ar-Ar dating techniques lies in the measurement of potassium. In K-Ar dating, potassium is measured generally using flame photometry, atomic absorption spectroscopy, or isotope dilution and Ar isotope measurements are made on a separate aliquot of the mineral or rock sample. In Ar-Ar dating, as the name suggests, potassium is measured by the transmutation of to Ar by neutron bombardment and the age calculated on the basis of the ratio of argon isotopes. 

GC-(high resolution)MS after enzymatic hydrolysis of the glucuro- and sulphoconjugates and trimethyl-silylation is the most widely used method for the determination of anabolic steroids and their metabolites in the urine of athletes. The most up-to-date technique for the solution of the difficult problem of differentiating between endogenous and exogenous testosterone is gas chromatography - combustion/ isotope ratio (C /C ) mass spectrometry (GC-C-IRMS). 

A second radiometric dating technique, used to measure much longer periods of time, involves U-238. U-238 decays with a half-life of 4.5 X 10 yr through a number of intermediates, and eventually ends as lead. As a result, all rocks on Earth that contain uranium also contain lead. If a rock is assumed to have been only uranium when it was formed (which can be determined by the relative amounts of different lead isotopes in the rock), the ratio of uranium to lead can be used to date the rock. For example, if one half-life has passed, the rock would contain 50% uranium atoms and 50% lead atoms. After two half-lives, the rock would be 25% uranium atoms and 75% lead atoms. 

How is the uranium to lead ratio in a rock used to estimate its age How does this dating technique provide an estimate for Earth s age How old is Earth according to this dating method ... 

Rubidium-87 emits beta-particles and decomposes to strontium. The age of some rocks and minerals can be measured by the determination of the ratio of the mbidium isotope to the strontium isotope (see Radioisotopes). The technique has also been studied in dating human artifacts. Rubidium has also been used in photoelectric cells. Rubidium compounds act as catalysts in some organic reactions, although the use is mainly restricted to that of a cocatalyst. 

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