Interference coefficients

The contribution of interference elements can be estimated by performing spectral line interference corrections. Calibrators are prepared in which mutually interferent elements are not present in the same solution. These solutions are then used to calibrate the system. Apparent concentrations are obtained by analyzing the ultrapure single element solutions (or solids). The interference coefficients are calculated by dividing the apparent concentration by the concentration of the interferent. In ICP-AES, the corrections are generally linear and thus a single element solution suffices to determine the correction factor. In spark and DC arc emission spectrometry, several samples are required. In practice, the determination of an element may be influenced by several other sample concomitants, and the final corrected concentration must be the summation of all the in-terferents. To complicate matters further, an iterative procedure must be used to deal with mutual interferences. 

A spectroscopic diagnostic has been developed to maintain the optimum conditions of ICP operation, in particular the flow rates of the aerosol carrier. The ratio between an atomic line of copper and an ion line of manganese is used to adjust divergent intensity responses because of unfavorable operating conditions. When this diagnostic is applied, the variability of the interference coefficients is small. The larger the correction factor, the larger the error in the quantitation of the analyte line subject to interference. 

As a result, the interference of the reflectional wave is shown the change for the position both the defects and the interfaces, and the size of the defect. And, the defect detection quantitatively clarified the change for the wave lengths, the reflection coefficient of sound pressure between materials and the reverse of phase. 

A term that is nearly synonymous with complex numbers or functions is their phase. The rising preoccupation with the wave function phase in the last few decades is beyond doubt, to the extent that the importance of phases has of late become comparable to that of the moduli. (We use Dirac s terminology [7], which writes a wave function by a set of coefficients, the amplitudes, each expressible in terms of its absolute value, its modulus, and its phase. ) There is a related growth of literatm e on interference effects, associated with Aharonov-Bohm and Berry phases [8-14], In parallel, one has witnessed in recent years a trend to construct selectively and to manipulate wave functions. The necessary techifiques to achieve these are also anchored in the phases of the wave function components. This bend is manifest in such diverse areas as coherent or squeezed states [15,16], elecbon bansport in mesoscopic systems [17], sculpting of Rydberg-atom wavepackets [18,19], repeated and nondemolition quantum measurements [20], wavepacket collapse [21], and quantum computations [22,23], Experimentally, the determination of phases frequently utilizes measurement of Ramsey fringes [24] or similar" methods [25]. 

A measure of a method s freedom from interferences as defined by the method s selectivity coefficient. 

The selectivity of the method for the interferent relative to the analyte is defined by a selectivity coefficient, Ka,i... 

The selectivity coefficient is easy to calculate if kj and kj can be independently determined. It is also possible to calculate Ka,i by measuring Sjamp in the presence and absence of known amounts of analyte and interferent. 

A method for the analysis of Ca + in water suffers from an interference in the presence of Zn +. When the concentration of Ca + is 100 times greater than that of Zn +, an analysis for Ca + gives a relative error of -1-0.5%. What is the selectivity coefficient for this method ... 

Knowing the selectivity coefficient provides a useful way to evaluate an inter-ferent s potential effect on an analysis. An interferent will not pose a problem as long as the term K/ i X i in equation 3.7 is significantly smaller than or A,i X Q in equation 3.8 is significantly smaller than Ca. 

Even if a method is more selective for an interferent, it can be used to determine an analyte s concentration if the interferent s contribution to Sjamp is insignificant. The selectivity coefficient, Ka,i> was introduced in Chapter 3 as a means of characterizing a method s selectivity. 

An interferent, therefore, will not pose a problem as long as the product of its concentration and the selectivity coefficient is significantly smaller than the analyte s concentration. 

In a particular analysis the selectivity coefficient, Xa.i, is 0.816. When a standard sample known to contain an analyte-to-interferent ratio of 5 1 is carried through the analysis, the error in determining the analyte is +6.3%. (a) Determine the apparent recovery for the analyte if Rj = 0. (b) Determine the apparent recovery for the interferent if Ra = 1 ... 

The amount of calcium in a sample of urine was determined by a method for which magnesium is an interferent. The selectivity coefficient, Rca.Mg> for the method is 0.843. When a sample with a Mg/Ca ratio of 0.50 was carried through the procedure, an error of-3.7% was obtained. The error was +5.5% when a sample with a Mg/Ca ratio of 2.0 was used. 

A sample contains a weak acid analyte, HA, and a weak acid interferent, HB. The acid dissociation constants and partition coefficients for the weak acids are as follows Ra.HA = 1.0 X 10 Ra HB = 1.0 X f0 , RpjHA D,HB 500. (a) Calculate the extraction efficiency for HA and HB when 50.0 mF of sampk buffered to a pH of 7.0, is extracted with 50.0 mF of the organic solvent, (b) Which phase is enriched in the analyte (c) What are the recoveries for the analyte and interferent in this phase (d) What is the separation factor (e) A quantitative analysis is conducted on the contents of the phase enriched in analyte. What is the expected relative erroi if the selectivity coefficient, Rha.hb> is 0.500 and the initial ratio ofHB/HA was lO.O ... 

Plot of cell potential versus the log of the analyte s concentration In the presence of a fixed concentration of Interferent, showing the determination of the selectivity coefficient. 

In most quantitative analyses we are interested in determining the concentration, not the activity, of the analyte. As noted earlier, however, the electrode s response is a function of the analyte s activity. In the absence of interferents, a calibration curve of potential versus activity is a straight line. A plot of potential versus concentration, however, may be curved at higher concentrations of analyte due to changes in the analyte s activity coefficient. A curved calibration curve may still be used to determine the analyte s concentration if the standard s matrix matches that of the sample. When the exact composition of the sample matrix is unknown, which often is the case, matrix matching becomes impossible. 

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