Standard, external internal

Standardization—External standards, standard additions, and internal standards are a common feature of many quantitative analyses. Suggested experiments using these standardization methods are found in later chapters. A good project experiment for introducing external standardization, standard additions, and the importance of the sample s matrix is to explore the effect of pH on the quantitative analysis of an acid-base indicator. Using bromothymol blue as an example, external standards can be prepared in a pH 9 buffer and used to analyze samples buffered to different pHs in the range of 6-10. Results can be compared with those obtained using a standard addition. 

Internal Plasticizers. There has been much dedicated work on the possibiUty of internally plasticized PVC. However, in achieving this by copolymerization significant problems exist (/) the affinity of the growing polymer chain for vinyl chloride rather than a comonomer implies that the incorporation of a comonomer into the chain requites significant pressure (2) since the use of recovered monomer in PVC production is standard practice, contamination of vinyl chloride with comonomer in this respect creates additional problems and (J) the increasing complexity of the reaction can lead to longer reaction times and hence increased costs. Thus, since standard external plasticizers are relatively cheap they are normally preferred. 

Quantification External standard External and internal standard... 

Unlike GC/MS methods, internai standards are not appropriate for immunoassays. Internal standards that would react with the antibody but would not interfere with the assay are nonexistent. In the place of internal standards, external QC must be maintained. 

Thorium Static, External Standardization (no internal mass fractionation correction) using TIMS Faraday-lon Counter gain determined at the start of the session... 

Chemical standards may be used for calibration in two different ways. They may be used externally , where they are measured in isolation from the samples, or internally , where the standard is added to the sample and both the standard and sample are measured at the same instant, i.e. as a single enriched sample. These two approaches are frequently termed external standardization and internal standardization , (see Sections 5.3.2.1 and 5.3.2.2 below). 

Standardize the reagents prepare the needed calibration (external, internal or standard addition) standards... 

In clinical chemistry, interpretation of the data can be quite simple or complex. In the case of MS/MS applications pertaining to a single analyte, all that is needed is the intensity value from the mass of a peak of interest and its internal standard. Viewing of a spectrum is not necessary. For profile methods such as full-scan acylcarni-tines, amino acids, or other compound families, the interpretation is more complex. With multiple related components, calculation of the concentration of many key metabolites is required. The system generally has multiple internal standards, external standards, or both. In addition to the concentration calculations, examination of a profile is often best achieved by viewing the spectra together with the quantitative information. 

Calibration standards can be of two types external standards and internal standards. With external standards, multiple concentrations of the standards are injected, areas are measured, and a calibration curve is platted. Unknown samples are then injected, chromatograms run, and areas are calculated and compared with the calibration curves to determine amounts of each compound present. With internal standards, known amounts of an internal standard are added to each known concentration of standard compound and areas or peak height response factors relative to those of the internal standard are calculated. When unknowns are run, a known amount of internal standard is added to the unknown sample, response factors are calculated relative to the internal standards, and amounts of each unknown present are calculated from the standards calibration factors. Internal standards are usually used to correct for variations in injection size due to different operators and injection techniques. Internal standards can also be used to correct for extraction variation in GC/MS target compound quantitation, this standard is referred to as a surrogate standard. Generally, an internal standard is used for one purpose or the other, not both at the same time. 

The RF should be determined using standards at various concentrations, and an average RF value should be used in the calculation. Both the external standard and internal standard calibration methods for GC analysis are fully discussed in Chapter 1.3. 

Figure 4.6. Types of calibration curves (a) external standard (b) internal standard (c) standard addition.

Following integration, the analytical response is converted into analyte concentration with the aid of a calibration curve. There are four principal techniques for determining relative composition information about a sample normalization, internal standard, external standard, and standard addition. 

Many of these difficulties can be monitored and overcome with the use of standards, either internal or external (Zevin and Kimmel 1995). For the internal standard method, a known quantity of standard material is added to an unknown mixture, and the ratio of the intensity of the standard component is compared to a previously determined calibration curve to determine the mass fraction of the unknown (e.g. one or more of the polymorphic components). In the external standard method, the entire composition of the unknown sample is determined simultaneously by comparing the measured intensities and respective calibration constants of reference intensity ratios (determined beforehand), which must all be with reference to the same reference standard. 

Examples are EU and/or FDA for a pharmaceutical industry selling products to the European Union and the United States, respectively EPA for environmental issues in the United States, military, hospital, and nuclear standards for these industries. Some standards are voluntary, e.g., standardization/accreditation programs such as ISO. Here the industry has asked for a certification or accreditation according to the standard. There may also be internal standards in any company based on a combination of external standards and internal standards. 

Internal standard External standard Calibration method Number of calibration standards Finear range of calibration direct/standard additions... 

Three primary methods are used for calibration external standard calibration, internal standard calibration, and standard addition. Figs. 1-3 show the typical response curves for each method. 

Using a calculator or personal computer program, use the appropriate data from the second and third segments of Table 11.1 to calculate the slopes for all five peaks used for both the external standard and internal standard calibration calculation. Check your values against those reported for peaks 2 and 3 in Table 11.2. 

Three modes of instrument calibration exist external standard (ES), internal standard (IS), and standard addition (SA). Each mode will be discussed in sufficient detail to enable the reader to acquire a fundamental understanding of the similarities and differences among all three. 

Determination of Lead in Drinking Water Using Graphite Furnace Atomic Absorption Spectroscopy (GFAA) External Standard Versus Internal Standard Caubration Mode... 

Of the three modes of calibration used in instrumental analysis, external, internal, and standard addition, the latter provides for the most accurate analytical results for samples which exhibit a matrix interference. The external mode of calibration is used to convert instrumental response to concentration when matrix interferences are not considered a factor. A series of standard solutions which contain the metal of interest are prepared from precise dilution of a certified standard stock solution. The calibration curve is obtained and a least squares regression is performed on the x, y data points. The best-fit line is used to establish the calibration curve. Samples which contain the metal at an unknown concentration level in a sample matrix nearly identical to that used to prepare the serial standards can be run and the data interpolated to give the concentration. In contrast, the standard addition mode of calibration requires that calibration and analysis... 

Saturated solution of PH3 in CDCI3. Standards are internal Si(CH3)4 and external PO(CH3)3. Infinitely diluted solutions of PH3 at 294 K. Shifts referenced to Si(CH3)4. Variations of 5( H) and J(P-H) with temperature (294 to 249 K) were given. Additional coupling constants J(P-H) ranging from 182 to 189 Hz were measured for PH3 in various isotropic and liquid-crystal solvents [13]. 

Standard BASIC allows both the function definitions and the named subroutines to be either internal or external. Internal defined functions and subroutines are useful in breaking up large programs into more easily managed pieces. External defined functions and subroutines are necessary for building libraries of routines that can be used as black boxes, without worrying about the details. 

For pesticide separations by LC, different calibration approaches were studied. Among external solvent solubilized standard , internal standard , external matrix-matched standard , and echo peak internal standard approaches, the last two procedures generate better results. The echo peak internal standard is a novel technique based on the possibility of producing a delayed injection of an internal standard having the same identity as the target compound. 

Most integrators perform area percent, height percent, internal standard, external standard, and normalization calculations. For nonlinear detectors, multiple standards can be injected, covering the peak area of interest, and software can perform a multilevel calibration. The operator then chooses an integrator calibration routine suitable for that particular detector output. 

Since, In practice, the efficiency frequently varies, it is necesseuy to determine the counting efficiency before one can compare different samples. A radioactive standard of acciirately known activity is essential for the determination of the efficiency counting. The use of radioactive standards is in principle similar to that of standards in colorimetric or spectrophotometric assays. There are two types of standards (i) internal standard (this is usually a p-emitter of accurately known activity which, when dissolved in unquenched scintillation mixture, provides a reference standard), and (ii) external standard (ay-emitter incorporated in most instruments). 

The three other methods - standard addition, external standard, and internal standard - give more accurate quantitation. 

Comparison of internal standard, external standard, and area normalization methods... 

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