Interferences in determination

Basel et al. [23] have described methods of compensating for chloride, ammonia, and bicarbonate interferences in determining bromide in sabne waters with an automated segmented flow analyser utihsing the phenol red method. 

Hollis B. 1,25-Dihydroxyvitamm D3-26,23-lactone interferes in determination of 1,25-dihydroxyvitamin D by RIA after immunoextraction. CHn Chem 1995 41 1313-14. 

The optimal acidity corresponds to pH 3.0 0.2. Only Au, Hg, and Pt interfere in determination of palladium. The reaction of TMK with Hg(ll) is slower (about 2 h). Oxidants also interfere the reagent behaves as a reductor. Chloride masks silver ions. EDTA can be used to prevent hydrolysis of some metal ions. 

Specificity is a property of monocomponent systems and it occurs when the method is free of interference. Selectivity is related to the complexity of the matrix and it occurs when not more than one ion (molecule) interferes in determination. Enantioselectivity is a relatively new term introduced for the assay of enantiomers.257258 An analytical method is enantioselective when it can discriminate between enantiomers. Enantiospecificity is an extreme case of enantioselectivity. It is possible to create the conditions for a highly enantioselective analysis, and in this case enantiospecificity can also occur. For example, a maltodextrin with dextrose equivalence (DE) of 4.0 to 7.0 was used in capillary zone electrophoresis as a stationary phase for the separation of the enantiomers,259 and also in the design of a potentiometric, enantioselective membrane electrode.260 The method for capillary zone electrophoresis is enantioselective, as it is for the potentiometric method. 

Equation 23 indicates that for mild interfacial slopes the interfacial shear reduces to the quasi-steady value in Equation 14, x . However, as the interface becomes perturbed with (growing) unstable modes, the second term, C 3h/dx, dynamically interferes in determining the interface stability. 

High concentrations of silicate interfere in determining cadmium by flame AAS (5.6.). However, silicates are not significantly soluble in the acid matrix used to prepare the samples. 

Campbell, F.R. and Thomas, R.F., Automated method for determining and removing silica interference in determination of soluble phosphorus in lake and stream waters. Environmental Science and Technology 4, 602,1970. 

Up to 8 mg phosphorus, fluorine, sulphur, do not interfere in determination of 2 mg chlorine... 

What is the role of wave interference in determining whether a molecular orbital is bonding or antibonding ... 

Phase interference in optical or material systems can be utilized to achieve a type of quantum measmement, known as nondemolition measurements ([41], Chapter 19). The general objective is to make a measurement that does not change some property of the system at the expense of some other property(s) that is (are) changed. In optics, it is the phase that may act as a probe for determining the intensity (or photon number). The phase can change in the comse of the measurement, while the photon number does not [126]. 

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 ... 

In the second limiting situation the analyte is a weaker acid or base than the interferent. In this case the volume of titrant needed to reach the analyte s equivalence point is determined by the concentration of both the analyte and the interferent. To account for the contribution from the interferent, an equivalence point for the interferent must be present. Again, if the acid dissociation constants for the analyte and interferent are significantly different, the analyte s determination is possible. If, however, the acid dissociation constants are similar, only a single equivalence point is found, and the analyte s and interferent s contributions to the equivalence point volume cannot be separated. 

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. 

A major advantage of this hydride approach lies in the separation of the remaining elements of the analyte solution from the element to be determined. Because the volatile hydrides are swept out of the analyte solution, the latter can be simply diverted to waste and not sent through the plasma flame Itself. Consequently potential interference from. sample-preparation constituents and by-products is reduced to very low levels. For example, a major interference for arsenic analysis arises from ions ArCE having m/z 75,77, which have the same integral m/z value as that of As+ ions themselves. Thus, any chlorides in the analyte solution (for example, from sea water) could produce serious interference in the accurate analysis of arsenic. The option of diverting the used analyte solution away from the plasma flame facilitates accurate, sensitive analysis of isotope concentrations. Inlet systems for generation of volatile hydrides can operate continuously or batchwise. 

For several reasons — including the complete breakdown of sample into its substituent elements in the plasma and the use of an unreactive monatomic plasma gas (argon) — background interferences in the resulting mass spectra are of little importance. Since there are no or very few background overlaps with sample ions, very precise measurements of sample ion abundances can be made, which facilitate the determination of precise isotope ratios. 

A iridine traces in aqueous solution can be determined by reaction with 4-(p-nitroben25l)pyridine [1083-48-3] and potassium carbonate [584-08-7]. Quantitative determination is carried out by photometric measurement of the absorption of the blue dye formed (367,368). Alkylating reagents interfere in the determination. A iridine traces in the air can be detected discontinuously by absorption in Folin s reagent (l,2-naphthoquinone-4-sulfonate) [2066-93-5] (369,370) with subsequent chloroform extraction and hplc analysis of the red dye formed (371,372). The detection limit is ca 0.1 ppm. Nitrogen-specific thermal ionisation detectors can be used for continuous monitoring of the ambient air. 

Cyanide compounds are classified as either simple or complex. It is usually necessary to decompose complex cyanides by an acid reflux. The cyanide is then distilled into sodium hydroxide to remove compounds that would interfere in analysis. Extreme care should be taken during the distillation as toxic hydrogen cyanide is generated. The cyanide in the alkaline distillate can then be measured potentiometricaHy with an ion-selective electrode. Alternatively, the cyanide can be determined colorimetricaHy. It is converted to cyanogen chloride by reaction with chloramine-T at pH <8. The CNCl then reacts with a pyridine barbituric acid reagent to form a red-blue dye. 

The methods of choice for beryUium oxide in beryUium metal are inert gas fusion and fast neutron activation. In the inert gas fusion technique, the sample is fused with nickel metal in a graphite cmcible under a stream of helium or argon. BeryUium oxide is reduced, and the evolved carbon monoxide is measured by infrared absorption spectrometry. BeryUium nitride decomposes under the same fusion conditions and may be determined by measurement of the evolved nitrogen. Oxygen may also be determined by activation with 14 MeV neutrons (20). The only significant interferents in the neutron activation technique are fluorine and boron, which are seldom encountered in beryUium metal samples. 

Following this procedure urea can be determined with a linear calibration graph from 0.143 p.g-ml To 1.43 p.g-ml and a detection limit of 0.04 p.g-ml based on 3o criterion. Results show precision, as well as a satisfactory analytical recovery. The selectivity of the kinetic method itself is improved due to the great specificity that urease has for urea. There were no significant interferences in urea determination among the various substances tested. Method was applied for the determination of urea in semm. 

The spatial resolution of the CI SEM mode depends mainly on the electron-probe size, the size of the excitation volume, which is related to the electron-beam penetration range in the material (see the articles on SEM and EPMA), and the minority carrier diffusion. The spatial resolution also may be afiFected by the signal-to-noise ratio, mechanical vibrations, and electromagnetic interference. In practice, the spatial resolution is determined basically by the size of the excitation volume, and will be between about 0.1 and 1 pm ... 

Take photographs, as appropriate, and detailed notes concerning visible airborne contaminants, work practices, potential interferences, movements, and other conditions to assist in determining appropriate engineering controls. 

In multiresidue analysis, where more analytes with a wide polarity range need to be determined, large transfer volumes are required, and consequently, the selectivity is lower. However, since the major interferences in water analysis are the polar humic and fulvic acids, removing this early eluting interference in coupled-column RPLC will also be feasible in multiresidue methodology. 

Note. Under the above conditions of determination the following elements interfere in the amount specified when the amount of Mo is 10 fig (error greater than 3 per cent) V, 0.4 mg, yellow colour [interference prevented by washing extract with tin(II) chloride solution] Cr(VI), 2 mg, purple colour W( VI), 0.15 mg, yellow colour Co, 12 mg, slight green colour Cu, 5 mg Pb, 10 mg Ti(III), 30 mg (in presence of sodium fluoride). 

Traces of many metals interfere in the determination of calcium and magnesium using solochrome black indicator, e.g. Co, Ni, Cu, Zn, Hg, and Mn. Their interference can be overcome by the addition of a little hydroxylammonium chloride (which reduces some of the metals to their lower oxidation states), or also of sodium cyanide or potassium cyanide which form very stable cyanide complexes ( masking ). Iron may be rendered harmless by the addition of a little sodium sulphide. 

These are the primary process interactions that the designer must be aware of in order to determine process interference in product performance and design. Specific materials may introduce other problem areas as, for example, air entrapment, differential expansion, and the problem of a level of crystallinity in a crystalline plastic that exceeds the allowed level for stability of a product. 

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