Standard subtraction method

A variety of infrared methods have been available for the simple problems of verifying the purity of the initial resin components and mixtures of those components. The simplest possible test of the purity of a reactant is to compare its spectrum with a known standard. Subtractive methods may be employed to emphasize the most significant intensity changes 19). Composition analysis of the blended resins and hardeners becomes more difficult. In some cases, one may simply select characteristic isolated absorption bands for each component and estimate the composition by comparison to standard spectra of known composition 20,21). 

A reverse method is based on the removal of the determinand and is called the known (or standard) subtraction method. The removal of the determinand is based on its precipitation or complexation. The necessary condition is that the reaction must be as complete as possible. 

A standard cell potential depends only on the identities of the reactants and products in their standard states. As you will see in the next Sample Problem, you do not need to consider the amounts of reactants or products present, or the reaction stoichiometry, when calculating a standard cell potential. Since you have just completed a similar Sample Problem, only a brief solution using the subtraction method is given here. Check that you can solve this problem by adding a reduction potential and an oxidation potential. 

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. 

The simplest addition methods are the known addition method (KAM) and known subtraction method (KSM). Two potential values are obtained in the sample solution, before the addition (Ei) and after the addition (E2 ) of volume 1 of a standard solution to sample volume Vq. The sample concentration is Cx, the standard solution concentration is c. In KAM, the standard solution contains... 

The known addition method has an advantage in greater rapidity and somewhat improved precision compared with calibration with two standards. It is claimed that it requires about half the time necessary for two-standard calibration [17] and that the relative error is about 2% [22]. A disadvantage is the necessity of determining the value for most systems. The method should be used only for concentrations corresponding to the linear part of the calibration curve. To eliminate the effect of a change in the ionic strength, it has been recommended [19] that a mixture of a standard with the test solution be added to the sample. The known subtraction method is much less used in practice. 

The analyte addition method (AAM) involves adding the sample solution to a standard solution of the determinand, whereas in the analyte subtraction method (ASM) the sample is added to a standard solution of an ion that reacts stoichiometrically with the test substance and is sensed by an ISE. These methods are advantageous for determinations on small samples for which microelectrodes would otherwise have to be used. pH adjustment and masking of interferents in the sample is unnecessary because all these operations can be done beforehand on the standard solution. Furthermore, the analyte subtraction method widens... 

Quality assurance is what we do to get the right answer for our purpose. We begin by writing use objectives, from which specifications for data quality can be derived. Specifications could include requirements for sampling, accuracy, precision, specificity, detection limit, standards, and blank values. For any meaningful analysis, we must first collect a representative sample. In an analysis of standards, the method must produce a result that is acceptably close to the known value. A method blank contains all components except analyte, and it is taken through all steps of the analytical procedure. We subtract the response of the method blank from the response of... 

The standard test method for proximate analysis (ASTM D-3172) covers the methods of analysis associated with the proximate analysis of coal and coke and is, in fact, a combination of the determination of each of three of the properties and calculation of a fourth. Moisture, volatile matter, and ash are all determined by subjecting the coal to prescribed temperature levels for prescribed time intervals. The losses of weight are, by stipulation, due to loss of moisture and, at the higher temperature, loss of volatile matter. The residue remaining after ignition at the final temperature is called ash. Fixed carbon is the difference of these three values summed and subtracted from 100. In low-volatile materials such as coke and anthracite coal, the fixed-carbon value equates approximately to the elemental carbon content of the sample. 

This formula is called electrostatic layer correction (ELC) term [22] forces can be obtained by simple differentiation. Since this yields - up to a desired precision - the contribution of all periodic image layers, they can be subtracted from the result of a standard 3d-method with slabwise summation order to obtain the result for two periodic coordinates. In addition, the error estimates for MMM2D can be adapted for ELC, giving a maximal pairwise error of... 

H. Li, Improvement of Gran s Plot Method in Standard Addition and Subtraction Methods by a New Plot Method, Anal. Lett., 24 (1991) 473. 

The wall thickness of the prosthesis is measured using a fabric thickness tester as per the ASTM Standard Test Method D1777 under a small but known appHed pressure. In order to remove the crimps the prosthesis is flattened by mounting between two glass sHdes and the thickness, h, is calculated by subtracting the thickness of the slides. 

The trade-off between clad and nnclad dielectric materials follows a benefit analysis similar to that used for subtractive versus additive processing. Copper-clad-based material is fabricated using standard practices familiar to most shops. However, it innately generates more waste and has a higher cost due to the subtractive nature of the manufacturing sequence. In addition, copper-clad materials demonstrate limitations in fine-line capability similar to those seen with standard manufacturing methods used today. 

In the linear range of the electrode function, a standard addition or sample subtraction method can also be used successfully. An automatic monitoring method, for example, was worked out by Nagy et al. [45] using coulometric sample subtraction for continuously measuring the chloride content of tap water. 

D of 0.2 100. The quantitative method consisted of subtracting the extinction at 270 mjx of solutions treated with iodine from that at 270 mji of the corresponding untreated solutions, and computing from values established with known quantities of a standard. This method, however, was not applicable to low-potency preparations or to those containing vitamin A. At best the cisjtrans isomerization gives the irons form in 75% yield (Verloop et al., 1959) althou in this authors laboratory only 40-50% yields (Nair and deLeon, 1965) were obtained under die same conditions. However, on employing the trifluoroacetates of the cis form in the iodine-catalyzed reaction, we were able to obtain quantitative yields of the trans vitamins D (see Section V). 

The curing of four UV-curable clearcoats was studied by confocal Raman microscopy. The disappearance of the C C line near 1636/cm provided the signature for the curing of the samples, but quantification of the degree of cure by standard peak fitting and baseline subtraction methods did not work well because of sample fluorescence, baseline shifts and overlapping peaks. A smoothed second-derivative processing approach overcame all of these difficulties and provided a simple. 

This procedure allows the determination of species which are not directly indicated by an electrode, but which react quantitatively with some indicated ion. The comparison solution contains an ion indicated by an ion-selective electrode in position C The ion to be measured quantitatively combines (precipitate, complex) with this indicator ion. A lower activity of this indicator ion results at point B, Examples of this are the determination of Al " ions as already mentioned, of sulfate ions by means of two lead-selective electrodes and a Pb(C104)2 standard solution or phosphate ions with two fluoride-selective electrodes and a L2l(NOs)s standard solution. The calculation corresponds to that of the subtraction method. 

Various methods can be used to analy2e succinic acid and succinic anhydride, depending on the characteristics of the material. Methods generally used to control specifications of pure products include acidimetric titration for total acidity or purity comparison with Pt—Co standard calibrated solutions for color oxidation with potassium permanganate for unsaturated compounds subtracting from the total acidity the anhydride content measured by titration with morpholine for content of free acid in the anhydride atomic absorption or plasma spectroscopy for metals titration with AgNO or BaCl2 for chlorides and sulfates, respectively and comparison of the color of the sulfide solution of the metals with that of a solution with a known Pb content for heavy metals. 

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... 

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. 

---