Calibration natural abundance isotopic

Natural abundance data are nearly always reported as delta values, 5 in units of per mil ( mil = 1000), written %o. This is a relative measurement made against a laboratory s own reference material, a working standard , calibrated against an international standard. Delta values are calculated from measured isotope ratio as ... 

The procedure described in Section 3.8.4 is illustrated using the determination of p,p -DDE in 2,2,4-trimethylpentane. This example shows how the sample and calibration solutions may be prepared so that the natural and isotopically labelled analogue concentrations and their isotope amount ratios are as close to being identical as possible. Additionally, to obtain high accuracy the measured isotopic ion abundance ratios should be as close to unity as possible. For the highest accuracy to be achieved, all solutions should be prepared gravimetrically except where identified below. Conventional volumetric techniques will limit the accuracy attainable by this IDMS method. The symbols used in this example should be read in conjunction with Equation 11 (Annex 3) which was used for the calculation of results. 

Although quantitative and semiquantitative analysis methods are suitable for the majority of applications, there are other calibration methods available, depending on your analytical requirements. For example, if your application requires even greater accuracy and precision, the isotope dilution technique may offer some benefits. Isotope dilution is an absolute means of quantitation based on altering the natural abundance of two isotopes of an element by adding a known amount of one of the isotopes, and is considered one of the most accurate and precise approaches to elemental analysis. - ... 

Abundances of lUPAC (the International Union of Pure and Applied Chemistry). Their most recent recommendations are tabulated on the inside front fly sheet. From this it is clear that there is still a wide variation in the reliability of the data. The most accurately quoted value is that for fluorine which is known to better than I part in 38 million the least accurate is for boron (1 part in 1500, i.e. 7 parts in [O ). Apart from boron all values are reliable to better than 5 parts in [O and the majority arc reliable to better than I part in 10. For some elements (such as boron) the rather large uncertainty arises not because of experimental error, since the use of mass-spcctrometric measurements has yielded results of very high precision, but because the natural variation in the relative abundance of the 2 isotopes °B and "B results in a range of values of at least 0.003 about the quoted value of 10.811. By contrast, there is no known variation in isotopic abundances for elements such as selenium and osmium, but calibrated mass-spcctrometric data are not available, and the existence of 6 and 7 stable isotopes respectively for these elements makes high precision difficult to obtain they are thus prime candidates for improvement. 

ICP-MS can provide semiquantitative analysis for about 70 elements by using element response functions built into the instrument software and calibration of only a few elements [205,206]. Most elements are more than 90% ionized in the ICP (with the exception of elements with ionization potentials greater than about 8 eV). Ion transmission efficiency is a smooth function of mass. The natural isotopic abundances of the elements are well known. Therefore, it is possible to predict the relative sensitivities of the elements and any isobaric overlaps. 

This mathematical equation corresponds to the equation of a curve. The straight line represents only a special case. The nature of the calibration curve that is obtained depends on the normalized relative isotopic abundances and thus on the nature of the isotopes that are introduced, on the increase in the molecular weight and on how enriched the labelled compound is. 

If ICP-MS is used to measure Pb levels,care must be taken to sum the masses of 206, 207, and 208 m/z to account for the natural isotopic variation of Pb in the environment. Failure to sum masses can skew results above or below the actual concentration, as the isotopic abundance of a particular mass in the calibrator might not match the sample. However, this isotopic variation can be exploited to determine the source of Pb exposure. By determining the relative abundances of Pb in blood and also of potential sources of exposure (e.g., paint chips and soil), a matching pattern can be identified. The exposure source with the same ratio of major Pb isotopes as the blood should then be avoided or removed from the patient s environment. 

All data refer to natural isotopic abundance of the elements except that Kr I and Kr II lines below 11,000 A given to three decimal places are for Kr. Also, Hg I lines given to three decimal places are for Hg these are frequently used for calibration. 

Lutetium is unique in having only two isotopes with an abundance ratio of 37-61, with the odd mass numbered isotope 175 being the most abundant. Thus all interferences due to multiply charged ions are insignificant. When 50 ppm LU2O is added, densities of the two Lu isotope lines 175 and 176 lie on the linear portion of the photoplate calibration curve for a wide range of exposures. Thus Lu is usable for short exposures (1-50 x 10 C) while Lu is at appropriate density levels for the longer exposures of 50-2000 x 10" C. On the short exposures, there are no interferences on the Lu line. Interferences due to Hf, Yb and natural Lu are present on the Lu line. These are corrected for as follows ... 

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