Internal standard isotopic

There are a variety of techniques available to aid in the identification of sample components matching retention times, standard addition, internal standard, isotopic labeling, enzyme peak shift, and UV and mass spectral libraries. 

Internal standard Isotope labeled analyte with optimized binding assessment, and verified standard curve IS peak area within 50 % of each analyte 13C6-Estradiol, 16a-Hydroxyestra-diol-rf2, Testosterone-, 13C,-Etheylnylestradiol IS peak area within 50 % of each analyte Testosterone-, Estradiol-rf3 Estron-d4, Estradiol-d3... 

Le Cornec, F. Correge, T. A new internal standard isotope dilution method for the determination of U/Ca and SrjCa ratios in fossil corals by ICP-MS. Varian ICP-MS Applications Note ICP-MS-18, September 1998 (www.varianinc.com). 

The keys to the success of LC-MS in quantitative bioanalysis are (1) typical detection limits in the picogram and in favorable cases even subpicogram range, (2) excellent selectivity against possibly interfering compounds in the biological matrix by the use of the SRM mode, (3) enhanced confidence of identity of the compound(s) analyzed, and (4) the ability to use the ideal internal standards isotopically labeled compounds. LC-MS-MS is often as easy to operate as LC-UV-PDA, but provides better selectivity. As a result, LC-MS-MS has become the method of choice in quantitative bioanalysis within pharmaceutical industries. 

Several strategies are generally incorporated into HPLC-MS method design and development to counter matrix effect problems. When the analytes are known, stable isotope-labeled internal standards (isotope dilution)... 

Typical internal standards Isotopes monitored (refo to Table 20.2 for details)... 

Calibration Internal standard Isotope dilution method, C-labelled... 

As mentioned above, transport effects, suppression effects and drift can cause accuracy problems in ICP-MS. In environmental analysis, this is most commonly corrected for by the use of internal standards. An internal standard can be added to each solution either by volumetric addition or by mixing the flow of the internal standard solution and the sample (pumped separately) using a T- or Y-piece prior to the nebuliser. The latter option is often preferred as it does not require each sample to be accurately dispensed into a test tube. Since suppression and drift effects can be somewhat mass dependent, several internal standard isotopes are normally... 

When multiple internal standards are used, most instrument software packages give the option either to interpolate analyte responses between the internal standards or to reference each analyte to a particular internal standard isotope. This is normally done on the basis of the internal standard that is closest in mass to the target analyte. Sometimes, some analytes behave unlike the internal standard, because of, for example, differences in ionisation. In such cases some analysts attempt to match this behaviour by utilising an internal standard of similar ionisation potential. 

In cases where the internal standard isotope is indigenous in the sample, an enhanced signal for only this internal standard isotope will be observed. Most software packages have functionality to allow the affected isotope to be removed from the calculation for only the affected sample. 

---