Method of internal standards

When possible, quantitative analyses are best conducted using external standards. Emission intensity, however, is affected significantly by many parameters, including the temperature of the excitation source and the efficiency of atomization. An increase in temperature of 10 K, for example, results in a 4% change in the fraction of Na atoms present in the 3p excited state. The method of internal standards can be used when variations in source parameters are difficult to control. In this case an internal standard is selected that has an emission line close to that of the analyte to compensate for changes in the temperature of the excitation source. In addition, the internal standard should be subject to the same chemical interferences to compensate for changes in atomization efficiency. To accurately compensate for these errors, the analyte and internal standard emission lines must be monitored simultaneously. The method of standard additions also can be used. 

The amount of camphor in an analgesic ointment can be determined by GC using the method of internal standards. " ... 

V) Verifying results by different methods of analysis (v) Method of standard deviation (vi ) Method of internal standards. 

The method of internal standard can also be used as it corrects for variable sample viscosities for both standards and sample. 

In this method a standard substance of known concentration is added to the unknown sample. The sample composition is determined by comparing the peak areas of standard and sample component. This method does not require all signals to be eluted and detected. Therefore, the method of internal standard is also suited for samples in which not all of the components must be determined. 

Products were identified by QPEX 1000 GCMS SPECTROPHOTOMETER. Quantitative analyses were done on a NUCON 5700 GAS CHROMATOGRAPH using an OV-17 column and FID mode. IR spectra were recorded on a SHIMADZUIR-470 spectrophotometer. NMR spectra were recorded on a JEOL-JNM-GSX400 spectrometer. Catalytic oxidation products were analysed by the method of internal standard. 

Generally, the method of internal standardization is used for the determination of the fatty acid composition, i.e. it is assumed that all the components of the sample are represented on the chromatogram, so that the total of the areas under the peaks represents 100% of the constituents (total elution). If the equipment includes an integrator, the figures obtained therefrom are used. If not, the area under each peak is determined by triangulation. 

The method of internal standardization is used, i.e. it is assumed that all the sterols present in the solution of the sterol fraction are represented by the chromatogram (total elution). 

The method of internal standardization is widely used in spectroscopy, chromatography, MS, and other instrumental methods. The use of internal standards can correct for losses of analyte during sample preparation, for mechanical or electrical drift in the instrument during analysis, for volume change due to evaporation and other types of interferences. The internal standard must be chosen carefully, usually so that the chemical and physical behavior of the internal standard is... 

In this method, a standard substance of known concentration that is not a sample constituent is added to the unknown sample. The sample composition is determined by comparing the peak areas of the standard and the sample component. This method does not require all constituents to be eluted and detected. Therefore, the method of internal standard is suited for samples in which not all of the components have to be determined. Moreover, analytical results based on internal standard calibration are used for control purposes. If the internal standard is added after all sample preparation steps, right before the measurement, the analytical results can be used to control the sample injection or even the detection system, whereas the addition of the standard prior to the sample preparation allows the specific control of the sample preparation steps. 

Virtually all published uncertainty evaluations of mass spectrometric methods assume independent ion currents or isotope amount ratios for all simultaneously measured isotopes [62, 63]. It is unclear why this paradigm has received such widespread acceptance. Isotopic signals in mass spectrometry are always correlated, provided that they are well above the background noise. The method of internal standardization is made possible precisely because mass spectrometric signals are correlated. 

Decylphenol monoethoxylate has been used as an internal standard to correct for incomplete recovery of nonionics (82). An elegant method of internal standard calibration for LC-MS determination of AE uses an ethoxy late of a fully deuterated fatty alcohol (134). 

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