Water activation analysis

Thorinm-232 is the only non-radiogenic thorium isotope of the U/Th decay series. Thorinm-232 enters the ocean by continental weathering and is mostly in the particulate form. Early measurements of Th were by alpha-spectrometry and required large volume samples ca. 1000 T). Not only did this make sample collection difficult, but the signal-to-noise ratio was often low and uncertain. With the development of a neutron activation analysis " and amass spectrometry method " the quality of the data greatly improved, and the required volume for mass spectrometry was reduced to less than a liter. Surface ocean waters typically have elevated concentrations of dissolved and particulate 17,3 7,62... 

At the Taylor Road landfill (originally intended for the disposal of municipal refuse only), unknown quantities of hazardous wastes from industrial and residential sources were deposited. During the period when the landfill was active, soil and groundwater samples collected at the site were found to contain concentrations of volatile organic compounds and metals above acceptable safe drinking water standards. Analysis of samples collected from private drinking water wells indicated that contamination... 

The HFBR at Brookhaven National Laboratory is a heavy water moderated and cooled reactor designed to provide an intense beam of neutrons to the experimental area. In addition using thimbles i oiitaincd within the vessel, it provides isotopic production, neutron activation analysis, ami muiemi irradiations. It began operation in 1965 at a power of 40 MW to be upgraded to 60 MW m 19S2. 

Cerium was included in a list of 14 elements determined by Lee et al. [627] in seawater using neutron activation analysis. The metals were first precon-centraed on a mixture of Chelex 100 and glass powder. The elements were desorbed from the column by 4 M nitric acid, and aqueous solution was irradiated for 3 days and subjected to y-ray spectrometry method with a Ge(Ii) detector coupled to a 4000-channel analyser. Cerium was found to be present to the extent of 16.7 xg/l in water taken from the Kwangyang Bay (South Korea). 

Iieser et al. [628] studied the application of neutron activation analysis to the determination of trace elements in seawater. The rare earths included in this study were cerium and europium. The element concerned were adsorbed onto charcoal. Between 75% and 100% of the elements were adsorbed onto the charcoal which was then subjected to analysis by neutron activation analysis. Cerium (300 p,g/l) and europium (0.00082 pg/1) were found in North Sea water by this method. 

The chemistry of rare earth elements makes them particularly useful in studies of marine geochemistry [637]. But the determination of rare earths in seawater at ultratrace levels has always been a difficult task. Of the various methods applied, instrumental neutron activation analysis and isotope dilution mass spectrometry were the main techniques used for the determination of rare earths in seawater. However, sample preparation is tedious and large amounts of water are required in neutron activation analysis. In addition, the method can only offer relatively low sample throughputs and some rare earths cannot be determined. The main drawbacks of isotopic dilution mass spectrometry are that it is time-consuming and expensive, and monoisotopic elements cannot be determined as well. 

The average concentration and standard deviation of the Pacific Ocean waters ( xg/l) were 2.00 0.09 by neutron activation analysis, and 1.86 0.12 by atomic absorption spectrometry. For the Adriatic water the corresponding values were about 1.7 xg/l. The difference between the values for the same seawater is within the range to be expected from the standard deviations observed. 

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. 

May et al. [73] used neutron activation analysis to determine 237neptunium in waste waters. The determination used the 237Np(rc,y)238Np reaction. The detection limit was 5 x 10 6 xg of 237neptunium, which corresponds to 2.5 x 10 6 xg/kg for 200 ml seawater samples. 

For a first chemical model, we calculate the distribution of species in surface seawater, a problem first undertaken by Garrels and Thompson (1962 see also Thompson, 1992). We base our calculation on the major element composition of seawater (Table 6.2), as determined by chemical analysis. To set pH, we assume equilibrium with CO2 in the atmosphere (Table 6.3). Since the program will determine the HCOJ and water activities, setting the CO2 fugacity (about equal to partial pressure) fixes pH according to the reaction,... 

Luck, W.A.P. 1981. Structures of water in aqueous systems. In Water Activity Influences on Food Quality (L.B. Rockland and G.F. Stewart, eds), pp. 407 134. Academic Press, New York. Ludescher, R.D., Shah, N.K., McCaul, C.P., and Simon, K.V. 2001. Beyond Tg Optical luminescence measurements of molecular mobility in amorphous solid foods. Food Hydro colloids 15, 331-339. Ludwig, R. 2001. Water From cluster to the bulk. Angewandte Chem. Int. Ed. 40, 1808-1827. Maclnnes, W.M. 1993. Dynamic mechanical thermal analysis of sucrose solutions. In The Glassy State in Foods (J.M.V. Blanshard and PJ. Lillford, eds), pp. 223-248. Nottingham Univ. Press, Loughborough, Leicestershire. 

Due to the complexity and cost of the technique no water laboratory in the UK has its own facilities for carrying out neutron activation analysis. Instead, samples are sent to one of the organizations that possess the facilities, e.g. the Atomic Energy Research Establishment at Harwell or the Joint Manchester-Liverpool University Reactor located at Risley. 

Tablets and capsules Pharmaceutical ingredients Purified water Manufacturing environment Products Periodic after history is established accepted on supplier certificate of analysis Loop daily and taps weekly Quarterly Periodic after history is established due to low water activities of tablets and capsules...

A technique for the determination of Tc amounts as little as 4 x 10 g by neutron activation analysis has been described by Foti et al. . Tc in triply distilled water is irradiated in a thermal neutron flux of 5 x 10 neutrons per cm and per second to produce °°Tc. Other radionuclides are removed by co-precipi-tation with Fe(OH)j. Then, °°Tc is co-precipitated twice with tetraphenylarsonium perrhenate which can be removed by sublimation. The chemical purification of °°Tc requires 40-45 s and the technetium yield is about 53%. 

A method has been developed for the determination of technetium-99 in mixed fission products by neutron activation analysis Tc is separated from most fission products by a cyclohexanone extraction from carbonate solution, the stripping into water by addition of CCI4 to the cylohexanone phase, and the adsorption on an anion exchange column. Induced Tc radioactivity is determined using X-ray spectrometry to measure the 540 and 591 keV lines. The sensitivity of the analysis under these conditions is approximately 5 ng. The method has been successfully applied to reactor fuel solutions. 

Greenberg RR, Kinston HM. 1982. Simultaneous determination of 12 trace elements in estuarine and sea water using pre-irradiation chromatography. In 1981 International Conference Modern Trends in Activation Analysis, Part 3, Toronto, Ont, Canada, June 15-16, 1981. J Radioanal Chem 71 147-168. 

As mentioned in Section 4, the analysis of rate data resulting from unimolecular reactions is considerably easier than the analysis of such data for bimolecular reactions, and the same is true for pseudounimolecular reactions. Kinetic probes currently used to study the micellar pseudophase showing first-order reaction kinetics are almost exclusively compounds undergoing hydrolysis reactions showing in fact pseudofirst-order kinetics. In these cases, water is the second reactant and it is therefore anticipated that these kinetic probes report at least the reduced water concentration (or better water activity in the micellar pseudophase. As for solvatochromic probes, the sensitivity to different aspects of the micellar pseudophase can be different for different hydrolytic probes and as a result, different probes may report different characteristics. Hence, as for solvatochromic probes, the use of a series of hydrolytic probes may provide additional insight. 

Cadmium in acidified aqueous solution may be analyzed at trace levels by various instrumental techniques such as flame and furnace atomic absorption, and ICP emission spectrophotometry. Cadmium in solid matrices is extracted into aqueous phase by digestion with nitric acid prior to analysis. A much lower detection level may be obtained by ICP-mass spectrometry. Other instrumental techniques to analyze this metal include neutron activation analysis and anodic stripping voltammetry. Cadmium also may be measured in aqueous matrices by colorimetry. Cadmium ions react with dithizone to form a pink-red color that can be extracted with chloroform. The absorbance of the solution is measured by a spectrophotometer and the concentration is determined from a standard calibration curve (APHA, AWWA and WEF. 1999. Standard Methods for the Examination of Water and Wastewater, 20th ed. Washington, DC American Public Health Association). The metal in the solid phase may be determined nondestructively by x-ray fluorescence or diffraction techniques. 

The isotope cahfomium-252 undergoes spontaneous fission generating neutrons. It serves as a convenient source of neutrons for neutron activation analysis, neutron moisture gages, and in the determination of water and oilbearing layers in well-logging. It is expected to have many other potential applications, including synthesis of other heavy isotopes. 

Palladium metal is digested in aqua regia, evaporated to near dryness. This is followed by addition of concentrated HCl and distdled water and the solution is warmed until dissolution is complete. The solution is aspirated directly into an air-acetylene flame. Palladium is detected by flame-AA spectrophotometry. Other instrumental techniques such as ICP/AES, x-ray fluorescence, and neutron activation analysis are used also. 

Ruthenium and its compounds are analyzed by flame AA method using nitrous oxide-acetylene flame. ICP-AES, ICP/MS, and neutron activation analysis are also applicable. The metal or its insoluble compounds may be solubilized by fusion with alkah and leached with water. 

Over the last 20-30 years not too much effort has been made concerning the determination of standard potentials. It is mostly due to the funding policy all over the world, which directs the sources to new and fashionable research and practically neglects support for the quest for accurate fundamental data. A notable recent exception is the work described in Ref. 1, in which the standard potential of the cell Zn(Hg)jc (two phase) I ZnS O4 (aq) PbS O4 (s) Pb(Hg)jc (two phase) has been determined. Besides the measurements of electromotive force, determinations of the solubility, solubiKty products, osmotic coefficients, water activities, and mean activity coefficients have been carried out and compared with the previous data. The detailed analysis reveals that the uncertainties in some fundamental data such as the mean activity coefficient of ZnS04, the solubility product of Hg2S04, or even the dissociation constant of HS04 can cause uncertainties in the f " " values as high as 3-4 mV. The author recommends this comprehensive treatise to anybody who wants to go deeply into the correct determination of f " " values. 

The solubility of water in a water-immiscible solvent at water activity 1 can be determined by equilibrating the solvent with pure water, followed by water analysis, for example, by Karl Fischer titration. At water activities lower than 1, lower amounts of water dissolve in the solvents, as shown in Figure 1.3. It should be noted that the solubility of water in the solvent changes when solvent composition is changed, for example, by dissolving substrates (Figure 1.3). In a hydrophobic solvent the increase in solubility of water can be substantial when substrates are dissolved in it. 

---