Internal standard procedure

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. 

Fig. 19.11 Calibration plot for internal standard procedure for benzoic acid.

Adequate precision and accuracy are only likely to be achieved if some standardization procedure is employed and the nature of this, internal or external standards or the method of standard additions, needs to be chosen carefully. If internal standardization procedures are adopted then appropriate compound(s) must be chosen and their effect on the chromatographic and mass spectrometry methods assessed. The ideal internal standard is an isotopically labelled analogue of the analyte but, although there are a number of commercial companies who produce a range of such molecules, these are not always readily available. An analytical laboratory is then faced with the choice of carrying out the synthesis of the internal standard themselves or choosing a less appropriate alternative with implications on the accuracy and precision of the method to be developed. 

Hanley, Q. S. and Ramkumar, V. (2005). An internal standardization procedure for spectrally resolved fluorescence lifetime imaging. Appl. Spectrosc. 59, 261-6. 

Define internal standard. Tell why an internal standard is important in a quantitative analysis by GC. Also tell what is plotted on the x- and y-axes when plotting the standard curve in internal standard procedures. 

Variation in sample volume is the factor that most affects the precision of quantitative measurements and the use of an injection valve may overcome this and permit the use of external standards. However, it is still often desirable to use an internal standardization procedure as this will reduce the effects of any variation in the detector responsiveness over a period of time. 

In the internal standard procedure, the analyst identifies a region of the chromatogram that is devoid of peaks (quiet region). The analyst... 

Examples of redox indicators are Indigo Carmine (C.I. 73015 [ 860-22-0] 8), which is frequently employed, and ferroin, an iron(n) complex with three 1,10-phenanthroline ligands (14), which is widely used in water and wastewater analysis in the determination of chemical oxygen demand (COD) in an internationally standardized procedure. For the structure of the organic ligand, see p. 539. 

Proponents of the internal standard procedure have questioned the validity of the substrate standard method to adequately correct for matrix absorption, Leroux and coworkers JLA) have presented data which support the method in addition, several measurements were performed in this laboratory to verify the validity of the method ( ), Mixtures of chrysotile in talc (1-7%) were prepared and various quantities "spiked" on silver filters. Table III illustrates the results obtained after correcting for matrix absorption as compared with the uncorrected data. Overall, there is excellent agreement between the corrected weight and the "spiked" weight. 

The trend in industrial hygiene work is to identify the particular species responsible for an occupational health problem, although assessment of exposures to inorganic materials previously has most often been based on elemental analysis When a solid inorganic compound is to be identified and quantified, X-ray diffraction should be among the approaches considered This paper has outlined the use of X-ray powder diffraction as a tool for the identification and quantitation of crystalline particulates It has been shown that the substrate standard method is the preferred quantitative procedure for several reasons (1) easy adaptability to most analytes (2) fast analysis time (as compared to the internal standard procedure) and (3) accurate determination of matrix absorption effects While there are a number of reasons why a given compound may not be amenable to this technique, it is likely that the list of analytes will be added to in the future ... 

It acts as an internal standardization procedure, negating the need for calculations to be performed to compensate for other sample attributes, such as solids content, specific gravity, matrix interferences, and so on. 

An alternative calibration technique was developed and successfully applied to techniques hyphenated to LA [43-48]. In addition, an increasing number of matrix-independent calibration procedures using external reference materials and/or internal standardization procedures is being developed [49-51]. 

J.E. Silva, F.A. Silva, M.F. Pimentel, R.S. Honorato, V.L. Silva, M.C.B.S.M. Montenegro, et al., A flow-batch internal standard procedure for iron determination in hydrated ethanol fuel by flame atomic absorption spectrometry, Talanta 70 (2006) 522. 

GC Analyses, The n-alkanes in the fuel samples were determined with a 100 meter OV-101 wall coated glass capillary column. The inlet split ratio was 50 1, the column oven was temperature programmed from 80 to 240°C, and the inlet temperature was 310°C. The internal standard procedure was used for quantitation. 

An internal standard procedure is used. The integrator is calibrated to report results in ppm for a 10 liter air sample after correction for desorption efficiency. 

More national and international standardization procedures for mercury porosimetry and the derivation of pore size distributions from adsorption isotherms are in preparation. Regarding the weakness of the two-parameter BET model for surface area determination in addition the three-parameter BET equation or improved approximations [26] should be considered. Competitive evaluation methods, like the method of Dubinin, Horwath-Kawazoe, Kaganer and Radushkevich are being discussed. 

There is no specialised national or international standard procedure to test all the mechanical and physical tests which may be applied to highly dense and compacted materials. A selection of national or international standards allied to bulk powder properties is, however, shown in Table 1.7. 

For coupling of HSGC with MS, the internal standard procedure has proved particularly successful for quantitative analyses. Besides the headspace-specific effects, possible variations in the MS detection are also compensated for. The best possible precision is thus achieved for the whole procedure. The MHE procedure can be used in the same way. 

Figure 3.166 Calibration function using the internal standard procedure. Plot area of the sample/area of the internal standard (ISTD) against concentration in the sample. The dotted lines indicate two standard deviations calibration precision.

The isotope dilution analysis method provides a definitive technique that does not depend on the comparison to one or more external calibration standards for quantitation. The method is similar to the standard addition technique in that a known quantity of analyte material is added to the sample to be analyzed, thereby performing the quantitation in situ. This approach ehminates matrix interference problems. The method is also similar to the internal standardization procedure, with the exception that a form of the analyte itself serves as the internal standard. AU of these factors combine to provide analysis characteristics comparable to the most basic gravimetric methods. 

These test methods are applicable to impurity concentrations in the range of 0.0001 to 0.1000 wt% and for cyclohexane purities of 98 % or higher when using the internal standard procedure. 

Note 1—In case of dispute, the internal standard procedure will be the correct procedure to use. 

Internal Standard Procedure—lasMi the chromatographic column and establish stable instrument operation at the proper operating conditions showm in Table 2. The selected column and conditions must satisfy the resolution requirements as stated in 5.2. Make reference to instructions provided by the manufacturer of the chromatograph, and to Practices E 260 and E 1510. 

Test Method A (Internal Standard Procedure)—In-temal standards are used to compensate for interelement effects of X-ray excitation and fluorescence (see Sections 1 to... 

Test Method A (Interned Standard Procedure)— Internal standards are used with the standards and sample specimens to compensate for the potential interelement effects. 

The internal standard procedure requires that every test solution (sample and standard) have the same concentration (or a known concentration) of an internal standard element that is not present in the original sample. The internal standard is usually combined with the dilution solvent. Internal standard compensation is typically handled in one of two different ways, which can be summarized as follows. 

External Standards—The sulfur compounds and matrices of external standards should be representative of the sulfur compounds and sample matrices being analyzed. Test Methods D2622 and D3120 can be used to analyze materials for calibration of this test method. The internal standardization procedure can also be used for generating external standards. Alternatively, primary standards prepared as described in 6.1.4 can be used for method calibration when it is demonstrated that the matrix does not affect calibration. Only one external standard is necessary for calibration, provided that the system performance specification (7.3) is met. An external standard must contain at least one sulfur compound at a concentration level similar, for example, within an order of magnitude to those in samples to be analyzed. 

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