Standard subtraction technique

As an example of the use of AES to obtain chemical, as well as elemental, information, the depth profiling of a nitrided silicon dioxide layer on a silicon substrate is shown in Figure 6. Using the linearized secondary electron cascade background subtraction technique and peak fitting of chemical line shape standards, the chemistry in the depth profile of the nitrided silicon dioxide layer was determined and is shown in Figure 6. This profile includes information on the percentage of the Si atoms that are bound in each of the chemistries present as a function of the depth in the film. 

In the incremental or decremental technique, another designation for the standard addition (or subtraction) technique, one adds increments of standard solution to the sample, or vice versa. (In the decremental technique the standard precipitates or complexes the ion under test.) When the sample itself is incrementally added to the standard, the latter may have received a previous addition of ISA and/or pH adjuster, but in the reverse method this addition may be made to the sample. However, for the specific example of a univalent anion we shall show how the normal incremental method works38 and that in fact the addition of ISA is not necessary. 

Patticini [55] has described an IR method for the determination of 1 to 8% of mineral oil in PS. In this method the PS sample is dissolved in carbon tetrachloride, together with known mineral oil standards. The solutions are evaluated by measurements made between 3,100 and 3,000 cm using a spectral subtraction technique. 

For materials in which a large proportion of glassiness is formed, DSC can lead to an estimate of the crystalline or amorphous (by subtraction) content provided the heat of fusion of the fully crystalline material is known. The heat of fusion of a sample can be percentified as a function of the heat of fusion of a standard giving the crystalline content. Clearly, the same polymorphic form should be present in both sample and standard. The technique has errors and can not be used to estimate the amorphous content when this is low, perhaps less than 5%. Re-scanning a glassy material may determine if it is subject to polymorphic modifications. 

Concentration determinations with a single standard addition (addition or subtraction techniques, as well as indirect analyses) 1 to 10% 4 to 20%... 

Despite the potential problems, two recent studies provide positive results. Matthews et al. (2000) analyzed the 5D of fluid inclusions in present-day cave carbonates from Soreq cave (Israel) using the method of thermal vacuum extraction and standard techniques on cave pool water from the same cave to estimate isotopic fractionation during measurement (Aex = 5Dextracted water - 8Dcave water). After subtracting Aex from 5D... 

A second major estimating technique is the materials balance approach—the original focus of this paper. A chemical engineering standard, the materials balance can reduce to the simple mass balance, as when the measured mass of a chemical in products leaving the plant is subtracted from the raw material entering the plant to yield the loss. This loss is then partitioned among releases to various media or other sinks. If... 

Separation of Adverse Reactions from Placebo Reactions. Since adverse non-drug symptoms are common (Reidenberg and Lowenthal, 1968) and are not easily separated from drug-induced symptoms, both must be collected for analysis if a complete profile of adverse reactions is to be made. However, this technique can only be used in controlled studies, ideally with placebo, as well as with other standard drugs. The temptation to subtract the number of the particular AR in the placebo group from the number in the active drug group as follows ... 

In the mass balance approach, all impurities are quantified and subtracted from the absolute value of 100%. This approach will result in a purity value that, if all impurities are accounted for, is more accurate than the external or internal standard methods. However, the ability to identify all impurities in a given drug substance may require the use of hyphenated detection techniques and could be extremely costly to complete on a regular basis. Therefore, a related approach, called Area Normalization, is often used where the majority of the impurities can be identified and quantified in a single chromatogram. In the simplest case, all of the impurities would be assumed to have the same relative response... 

In addition techniques, the test substance concentration is determined from the difference in the ISE potentials obtained before and after a change in the sample solution concentration. The main advantage Ues in the fact that the whole measurement is carried out in the presence of the sample matrix, so that results with satisfactory accuracy and precision can be obtained even if a substantial portion of the test substance is complexed. Several addition techniques can be used, namely, single, double or multiple known addition methods, in which the sample concentration is increased by additions of a test substance standard solution single, double or multiple known subtraction methods, in which the sample concentration is decreased by additions of a standard solution of a substance that reacts stoichiometrically with the determinand and analyte addition and subtraction methods, in which the sample is added to a test substance solution or to a reagent solution. 

Mineral standards were hand crushed to -1/4 inch, then ground to a fine powder in a ball mill (alumina elements) or Bleuler Model 526/LFS678 puck mill. The resultant powder was aerodynamically classified in a Bahco Model 6000 micro particle classifier and the finest fraction ( 18 throttle) was collected. A size criterion of 90% or more by weight of particles 5 micron and smaller in diameter was used for the mineral standards. Sizes were verified by Coulter Counter. Duplicate 13 mm KBr pellets were prepared and the spectra were weight-scaled by techniques similar to those reported by Painter (3) and Elliot (4). With one exception, all the mineral standard spectra were averages of spectra from duplicate pellets. The one exception was the iron sulfate spectrum, which was obtained as the difference spectrum by subtracting the spectrum of HCl-washed weathered pyrite from that of the weathered pyrite. A weight correction was applied to the difference spectrum. 

In this section, the subtractive multipulse techniques DMPV and SWV are applied to reversible ion transfer across different liquid-liquid systems with one or two polarizable interfaces. These electrochemical techniques allow the accurate and easy determination of standard potentials directly from the peak potentials of the current-potential curves since non-faradaic and background currents are minimized [12, 35-40]. 

The possibilities of quality control in polymer industry have been considerably enhanced by the introduction of computer assisted IR and FT-IR spectrometers. One of the most frequently used techniques in this field is the difference spectroscopy. Difference spectroscopy involves subtracting the digitally stored spectrum of a standard from, for ex-... 

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