Internal standards amounts

When a reference standard is available and is calibrated against an internal standard in the TIC mode, six-point calibration curves of either individual or closely related analytes (for example, the isomers ethylmalonic acid, 2-methyIsuccinic, and glutaric acid) are run according to the standard/internal standard amount ratio shown in Table 3.1.5. Variations of this basic scheme may be indicated depending on the intensity of target ions ([M-15]+ species), the level of excretion in normal and disease states, and the linearity limit. 

Content = internal standard amount x amount ratio = 10 X 0.4 = 4gl ... 

The internal standard can perform several functions. Its most common purpose is to correct for sample and standard injection volume. Since each sample and standard contains a constant internal standard amount, the injected amount is proportional to the internal standard concentration and the analyte concentration is proportional to the ratio of the analyte to internal standard signals. Likewise, the sample and standard dilution volume can be compensated for by use of an internal standard. 

Physicochemical properties of the samples were examined by means of XRD, ESR, and XANES. A quantitative analysis of Cr203 phase was performed on Rigaku-Denki D-9C X-ray diffractometer using Cap2 as an internal standard. Amounts of Cr loaded were measured on Phillips PW-1404 X-ray fluorescence spectrometer. ESR spectrum was obtained by using Varian E-3 Spectrometer at room temperature or liquid nitrogen temperature. X-ray absorption experiments in the transmission mode were carried out on EXAFS facilities installed at BL10B at the Photon Factory in Tsukuba, Japan. 

The method is based on the international standard ISO 4053/IV. A small amount of the radioactive tracer is injected instantaneously into the flare gas flow through e.g. a valve, representing the only physical interference with the process. Radiation detectors are mounted outside the pipe and the variation of tracer concentration with time is recorded as the tracer moves with the gas stream and passes by the detectors. A control, supply and data registration unit including PC is used for on site data treatment... 

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

Calibration curves must be made using a series of standards to relate emission intensities to the concentration of each element of interest. Because ICP-OES is relatively insensitive to matrix effects, pure solutions containing the element of interest often are used for calibration. For thin films the amount of sample ablated by spark discharges or laser sources is often a strong function of the sample s composition. Therefore, either standards with a composition similar to the sample s must be used or an internal standard (a known concentration of one element) is needed. 

Quantitative analysis using the internal standard method. The height and area of chromatographic peaks are affected not only by the amount of sample but also by fluctuations of the carrier gas flow rate, the column and detector temperatures, etc., i.e. by variations of those factors which influence the sensitivity and response of the detector. The effect of such variations can be eliminated by use of the internal standard method in which a known amount of a reference substance is added to the sample to be analysed before injection into the column. The requirements for an effective internal standard (Section 4.5) may be summarised as follows ... 

The procedure comprises the addition of a constant amount of internal standard to a fixed volume of several synthetic mixtures which contain varying known amounts of the component to be determined. The resulting mixtures are chromatographed and a calibration curve is constructed of the percentage of component in the mixtures against the ratio of component peak area/standard peak area. The analysis of the unknown mixture is carried out by addition of the same amount of internal standard to the specified volume of the mixture from the observed ratio of peak areas the solute concentration is read off using the calibration curve. 

Standard addition. The sample is chromatographed before and after the addition of an accurately known amount of the pure component to be determined, and its weight in the sample is then derived from the ratio of its peak areas in the two chromatograms. Standard addition is particularly useful in the analysis of complex mixtures where it may be difficult to find an internal standard which meets the necessary requirements. 

To use KBr discs for quantitative measurements it is best to employ an internal standard procedure in which a substance possessing a prominent isolated infrared absorption band is mixed with the potassium bromide. The substance most commonly used is potassium thiocyanate, KSCN, which is intimately mixed and ground to give a uniform concentration, usually 0.1-0.2 per cent, in the potassium bromide. A KBr/KSCN disc will give a characteristic absorption band at 2125 cm 1. Before quantitative measurements can be carried out it is necessary to prepare a calibration curve from a series of standards made using different amounts of the pure organic compound with the KBr/KSCN. A practical application of this is given in Section 19.9. 

In the internal standard method the intensity of the unknown line is measured relative to that of an internal standard line. The internal line may be a weak line of the main constituent. Alternatively, it may be a strong line of an element known not to be present in the sample and furnished by adding a fixed small amount of a compound of the element in question to the sample. The ratios of the intensities of these lines — the unknown line and the internal standard line — will be unaffected by the exposure and development conditions. This method will provide lines of suitable wavelength and intensity by variations of the added element and the amount added, due regard being paid to the relative volatility of the selected internal standard element. It is important to use as internal standard pairs only those lines of which the relative intensities are insensitive to variations in excitation conditions. The line selected as standard should have a wavelength close to that of the unknown and should, if possible, have roughly the same intensity. 

Accurate quantitation in GC/MS requires the addition of a known quantity of an internal standard to an accurately weighed aliquot of the mixture (matrix) being analyzed. The internal standard corrects for losses during subsequent separation and concentration steps and provides a known amount of material to measure against the compound of interest. The best internal standard is one that is chemically similar to the compound to be measured, but that elutes in an empty space in the chromatogram. With MS, it is possible to work with isotopically labeled standards that co-elute with the component of interest, but are distinguished by the mass spectrometer. 

In addition to meeting the foregoing requirements, a good internal standard will be easy to add uniformly and precisely, and (preferably) no appreciable amount of the element St (free or combined) will be present in the sample before the addition. Cope29 provides an excellent illustration of these points. He found that yttrium nitrate dissolved in ethyl alcohol could be added to a powdered uranium mineral in a mortar, whereupon grinding immediately to dryness dispersed the internal standard (yttrium) so uniformly that uranium could be satisfactorily determined in certain minerals. But the mineral euxenite is an exception, for it contains both yttrium and uranium, and this complicates the uranium determination with yttrium as internal standard. 

Step 2. Add to the weighed sample an amount of reference material that contains the internal standard in an amount equal to the estimated amount of the element sought. This mixture is the diluted sample. 

To enable qnantitative measurements to be made, the analyst requires the ability to determine the areas or heights of the detector responses of analyte(s) and any internal standard that may be present and then, from these figures, to derive the amount(s) of analyte(s) present in the unknown sample. The software provided with the mass spectrometer allows this to be done with a high degree of automation if the analyst so desires. 

Internal standard A method of relating the intensity of signal from an analyte measured in an unknown to the amount of analyte present. In this approach, a known amount of an internal standard is added to both calibration and... 

Lipid Screening. The problems of lipid analysis in the newborn is difficult because of the fact that most methods for analysis for lipids require substantial amounts of serum, yet a total lipid determination is very important in various types of disease. This problem can be solved by thin-layer chromatography (59). Figure 38 shows a typical pattern obtained when an extract 7rom 10 microliters of serum is subjected to thin-layer chromatography. If these specimens are scanned, and an internal standard is run, one can obtain a rough approximation of the distribution of the various lipids in the serum. This is shown in Figure 39, in which a normal specimen is run in an adult. 

Normal Neutralization tests In cell cultures or In animals Measurable amounts of one bacterial antibody and of one viral antibody for which there are International standards... 

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