Known subtraction technique

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. 

Potentiometric titration is actually a form of the multiple known subtraction method. The main advantage of titration procedures, similar to multiple addition techniques in general, is the improved precision, especially at high determinand concentrations. ISEs are suitable for end-point indication in all combination titrations (acid-base, precipitation, complexometric), provided that either the titrand or the titrant is sensed by an ISE. If both the titrant and the titrand are electro-inactive, an electrometric indicator must be added (for example Fe ion can be titrated with EDTA using the fluoride ISE when a small amount of fluoride is added to the sample solution [126]). 

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 liquids in general, it is very helpful to note if the sample is known to be a single material, a mixture, or a solution. If the sample is a solution, the major solvents, if known, should also be recorded, preferably during the same time frame. In this way, it is possible to differentiate the solute and solvent, especially with the aid of computer subtraction techniques. Other issues relevant to knowledge of the sample include the following It is important to know if the sample is wet , especially if salt optics (KBr, NaCl, or Csl) are used, and it is beneflcial to know if there are volatile components present. Sometimes a special treatment is required for volatile materials (see Section 3.4). 

The techniques of known addition and known subtraction may be used with certain electrode instrumentation to avoid the use of ionic strength adjustors and calibration curves. These techniques are instrument-related and do not submit to general discussion. Orion (1973) treats this and other manufacturer-related electrode techniques. 

What is special for the PLSR compared to, for example, the more well-known statistical technique of principal component regression (PCR) is that the y variable is used actively in determining how the regression factors ta,a= 1,2,..., A are computed from the spectra X. Each PLSR factor t<, is defined so that it describes as much as possible of the covariance between X and y remaining after the previous a - I factors have been estimated and subtracted. 

This method of evaluation can also be used when the concentration of the measured ion in the test solution is reduced by a precisely known amount (preciptitate or com-plexation, subtraction technique) rather than increased. 

To evaluate die position of the equilibrium, p is determined by the equation pAeq = pA a (reactant acid) —pAa (product acid). For the above example pA), = 17 — 10 = 7, and based on the definition of pA, Aeq = 10 7 for this equilibrium. Thus the equilibrium lies far to the reactant side that is, very litde isopropoxide ion or ethyl ammonium ion is present at equilibrium. This technique is applicable for virtually any acid-base equilibrium. The three required steps are to (a) write a balanced equation that describes the equilibrium to be analyzed, (b) identify the species which is acting as an acid on each side of the equilibrium and write down its pAa, and (c) subtract the pAa of the product acid from the pAa of the reactant acid to give the pAeq for the equilibrium in question. It is a requirement that the pAy s of the acids on each side of the equilibrium are known or can be estimated reasonably well. Furthermore, the pA eq that is determined refers to the equilibrium in the direction it is written. It is therefore important to write the chemical equilibrium as you wish to analyze it. 

It has been known for many years that the surface hydroxyl groups can be readily converted to OD simply by repeated exposure to D20. Early experiments with this type of exchange were used in order to manipulate vibrational modes to portions of the spectrum which were more transparent. Thus, for instance, isotopic substitution of D for H in surface silanol groups moves the fundamental stretching frequency from 3747 to 2750 cm 1. Peri (15) used this technique before computer subtraction was so readily available in order to determine the bond angle of the surface Sis-OH group. By recording... 

Rather than describing changes in expression of a known class of genes, several studies have utilized unbiased approaches to determine changes in expression of a large number of genes in association with arousal state using cDNA arrays, DNA chips, or other molecular techniques. Subtractive hybridization was used to isolate two mRNAs whose expression was altered in forebrain after 24-hr SD... 

Equation 9 represents the IR spectmm (intensity versus wavenumber), which can be derived from expression (8) using a mathematical technique known as Fourier transformation. Needless to say, this requires spectrometer-interfaced computing power, which additionally provides the capacity for spectral manipulation such as deconvolution, smoothing, and subtraction. 

The combined limitations of direct and Green-Kubo simulations mean that neither may be satisfactory if one is interested in the small, but nonzero, field limit. To accomplish this, two simulation techniques have been developed. The first is commonly known as the subtraction method because it is based on... 

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