Interferences activation analysis

Methods for iodine deterrnination in foods using colorimetry (95,96), ion-selective electrodes (94,97), micro acid digestion methods (98), and gas chromatography (99) suffer some limitations such as potential interferences, possibHity of contamination, and loss during analysis. More recendy neutron activation analysis, which is probably the most sensitive analytical technique for determining iodine, has also been used (100—102). 

To date, a few methods have been proposed for direct determination of trace iodide in seawater. The first involved the use of neutron activation analysis (NAA) [86], where iodide in seawater was concentrated by strongly basic anion-exchange column, eluted by sodium nitrate, and precipitated as palladium iodide. The second involved the use of automated electrochemical procedures [90] iodide was electrochemically oxidised to iodine and was concentrated on a carbon wool electrode. After removal of interference ions, the iodine was eluted with ascorbic acid and was determined by a polished Ag3SI electrode. The third method involved the use of cathodic stripping square wave voltammetry [92] (See Sect. 2.16.3). Iodine reacts with mercury in a one-electron process, and the sensitivity is increased remarkably by the addition of Triton X. The three methods have detection limits of 0.7 (250 ml seawater), 0.1 (50 ml), and 0.02 pg/l (10 ml), respectively, and could be applied to almost all the samples. However, NAA is not generally employed. The second electrochemical method uses an automated system but is a special apparatus just for determination of iodide. The first and third methods are time-consuming. 

After adjusting to 2 mol 1 1 in hydrochloric acid, 500 ml of the sample is adsorbed on a column of Dowex 1-XS resin (Cl form) and elution is then effected with 2 M nitric acid. The solution is evaporated to dryness after adding 1M hydrochloric acid, and the tin is again adsorbed on the same column. Tin is eluted with 2 M nitric acid, and determined in the eluate by the spectrophotometric catechol violet method. There is no interference from 0.1 mg of aluminium, manganese, nickel, copper, zinc, arsenic, cadmium, bismuth, or uranium any titanium, zirconium, or antimony are removed by ion exchange. Filtration of the sample through a Millipore filter does not affect the results, which are in agreement with those obtained by neutron activation analysis. 

Stiller et al. [824] have described the determination of cobalt, copper, and mercury in Dead Sea water by neutron activation analysis followed by X-ray spectrometry and magnetic deflection of /i-ray interference. 

Short reviews appeared on the various MS techniques for quantitation of stable isotopes and long-lived radioisotopes and the application of Mg stable isotopes as tracers in biology and medicine. The radioactive isotope Mg is not usually available and has a short half-life (21.3 h), hence its hmited usefulness as a tracer. The sensitivities and interference problems encountered in activation analysis for Al, Mg, Mo, P, Si and Zr were discussed. Much higher sensitivities were found for cyclotron-produced than for reactor-produced fast neutrons or 14 MeV neutrons. ... 

There are several factors which make neutron activation analysis (NAA) an appropriate technique for investigating potential pollutants in coal and the combustion process. First, the multi-element nature of NAA is useful because of the large number of potential elemental pollutants, such as Se, Hg, As, Zn, Ni, Sb, and Cd. Also, the use of elemental ratios made possible by the multi-element capability facilitates the understanding of chemical behavior during the combustion process. Elemental ratios have been used previously in urban (15) and upper atmospheric (26) studies. Secondly, the sensitivity and selectivity of NAA allows determination of many elements present at very low concentrations (ppm or lower), and the results are unaffected by matrix interferences. This sensitivity also allows analysis of very small samples. Finally, the cost of NAA when conducted as a multi-element analytical tool is competitive with more conventional and less sensitive techniques on the cost-per-element-per-sample basis. 

Copper. In the presence of sulfur dioxide, copper-protein cloudiness may develop in white wines. Only small amounts of copper (about 0.3 to 0.5 mg/liter) cause cloudiness. Widespread use of stainless steel in modern wineries has reduced copper pickup, but many wineries routinely test their wines for copper. Atomic absorption spectrophotometry is the method of choice (51) although reducing sugars and ethanol interfere, and correction tables must be used (107). To reduce this interference, chelating and extracting with ketone is recommended (108). Lacking this equipment colorimetric procedures can be used, especially with di-ethyldithiocarbamate (3, 4, 6, 9,10, 22,109). Neutron activation analysis has been used for determining copper in musts (110). 

Devise an activation analysis scheme for determining the concentration of nitrogen in a sample of plant material. Assume the analysis must be nondestructive and rapid. Suggest an appropriate reaction, irradiation, and counting conditions, and indicate possible interferences in your analysis. 

Imagine you wish to detect ppm levels of A1 in a matrix containing iron, calcium, and silicon. Assume you have access to a modern nuclear reactor. Describe an activation analysis procedure to do this analysis. Be sure to describe the irradiation conditions, any pre- or postirradiation chemistry, and the counting strategy. Indicate how you would deal with any interferences in the analysis. 

Neutron activation analysis techniques are frequently used for trace element analyses of coal and coal-related materials (Weaver, 1978). Precision of the method is 25%, based on all elements reported in coal and other sample matrices. Overall accuracy is estimated at 50%. Neutron activation analysis utilizing radiochemical separations (NAA-RC) is employed by investigators when the sensitivity for a particular element or group of elements is inherently low or when spectral interference for a given element in a specific matrix is too great to be detected adequately. This situation was more prevalent before the advent of Ge(Li) spectrometry when only low-resolution Nal(TI) detectors were available. 

The determination of 129I in low-level radioactive waste was accomplished by radioactive instrumental neutron activation analysis [3]. A different group reported the determination of both 129I and 127I by neutron activation analysis and inductively coupled plasma mass spectrometry [4]. The method was very rapid - a sample could be analysed in three minutes. However, interference from 129Xe resulted in limited sensitivity for 129I detection. 

Discussions of errors associated with the technique of activation analysis in general may be found in many of the books and monographs referenced in the introduction to this paper. Interferences unique to 14 MeV neutron activation techniques have been reviewed by Mathur and Oldham 42> and a discussion of precision has been published by Mott and Orange 43>. 

Selenium forms a volatile derivative, piazselenol, which can be subjected to GC analysis (Scheme 5.39). Young and Christian [612] treated selenium with 2,3-diaminonaph-thalene at pH 2.0 and extracted the resulting piazselenol into -hexane. With the use of an ECD, down to 5 10-I° g of selenium could be detected. The procedure, applied to the analysis of selenium in human blood, urine and river water, led to results equivalent to those obtained by neutron activation analysis. Similarly, Nakashima and Toei [613] performed the reaction of selenium (as selenious acid) with 4-chloro-o-phenylenediamine at pH 1 and extracted the derivative into toluene. They reported a detection limit of 0.04 jug. Shimoishi [614] analysed the content of selenium in metallic tellurium by this method. The sample was dissolved in aqua regia, followed by reaction with 4-nitro-o-phenylenediamine and extraction into toluene. Down to 10 ng of selenium could be determined using only a few milligrams of sample. Common ions did not interfere even when present in a large excess. Selenium in marine water was determined after the same derivatization step [615],... 

Each spectroscopic method has a characteristic application. For example, flame photometry is still applicable to the direct determination of Ca and Sr, and to the determination of Li, Rb, Cs and Ba after preconcentration with ion-exchange resin. Fluorimetry provides better sensitivities for Al, Be, Ga and U, although it suffers from severe interference effects. Emission spectrometry, X-ray fluorescence spectrometry and neutron activation analysis allow multielement analysis of solid samples with pretty good sensitivity and precision, and have commonly been applied to the analysis of marine organisms and sediments. Recently, inductively-coupled plasma (ICP)... 

Simple procedures that require only a dilution of serum or urine have been reported by Schattenkirchner and Grobenski [95], and by Ward et al. [96]. The former diluted samples of sera 1 + 4 with 0.1% Triton X 100 and urine samples 1 + 9 with 0.01 M HC1 and the latter used a 1 + 9 dilution of serum in water. In both cases calibration was by standard additions to compensate for the considerable matrix interferences. Ward et al. [96] demonstrated an excellent correlation (r = 0.98) between neutron activation analysis (NAA) and ETA—AAS analysis of the total plasma Au and albumin bound Au, which contains up to 90% of the total. There was however, a bias towards higher values (10%) by NAA. This difference did not appear to be pre-atomisation losses during ETA—AAS, the recoveries of added Au ranged from 90—105%, nor over-correction by continuum source background corrector. 

EUTRON ACTIVATION ANALYSIS IS A VERY SENSITIVE TECHNIQUE for trace element determinations in various samples. If there are no elements that mutually interfere, the purely instrumental version of this method is often chosen for its established advantages such as accuracy, speed, sensitivity, simultaneous multielement determination, and sample preservation (1). For these reasons, instrumental neutron activation analysis (INAA) was applied to samples taken from a series of metal-working residues excavated at Tel Dan, Israel, from 1985 to 1986. 

Fifteen trace elements were identified by neutron activation analysis Hg, Ag, Sm, Eu, Se, Ca, Th, Cr, Au, As, Sb, Fe, Sc, Co, and La. A problem encountered in this analysis is the interference in gamma-ray spectra caused by the high silver content of the native ore samples. Because of this eflFect, some elements in some samples may have gone undetected, and other elements may have been analyzed only semi-quantitatively. 

Alfassi, Z.B., Probst, T.U., Rietz, B. Platinum determination by instrumental neutron activation analysis with special reference to the spectral interference of scandium-47 on the platinum indicator nuclide gold-199. Anal. Qiim. Acta 360, 243-252 (1998)... 

Carboxylesterase from the liver, butyryl cholinesterase and acetyl cholinesterase from erythrocytes do not interfere with analysis, i.e. they do not exercise any activity in respect of the substrate. Contamination of the sample by glycerol, soap and hand cream must be avoided. 

Oxygen may also be determined by neutron activation analysis (Anders and Briden, 1964). This approach determines inorganic oxygen as effectively as organic oxygen. Fluorine presents a serious interference with this method. Of course, the considerations of moisture are still important. 

Instrumental Neutron Activation Analysis (INAA) was applied to the determination of the platinum metals as part of a study of their uptake, accumulation and toxicity in plants. Long irradiations are described for iridium, osmium and ruthenium determinations in specially grown plant materials. An interference in the determination of platinum in plant matrices by this method is reported also. Short irradiations, utilising thermal and epithermal fluxes are investigated for rhodium and palladium determinations, with further studies using cyclic activation analysis. 

Arsenic levels below 10 ng/g can be readily detected in petroleum by instrumental neutron activation analysis. The most convenient technique involves direct gamma counting based on the 75As (n, y) 76As reaction with a principle radiation of 559 keV. After a 1-hr irradiation at a neutron flux of 1012 n cm"2 sec-1, the arsenic may be counted in a relatively short time. The method requires a high resolution Ge(Li) detector to avoid interference from bromine (550 keV) or antimony (564 keV). 

A number of instrumental methods have been used to determine ppb levels of cobalt in water (4,5,6), biological tissues (7,8), and air particulates (9, 10). Kinetic methods are capable of measuring sub-parts-per-billion (11,12). Potentially any of these techniques could be used in the analysis of petroleum, but only neutron activation analysis (I, 3) and atomic absorption spectroscopy (13,14) have been applied to any appreciable extent. Flame and heated vaporization atomic absorption techniques were selected for more detailed study by the Project because atomic absorption is sensitive, subject to relatively few interferences, and is rather generally available. 

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