Determination of total tin in silicate rocks by graphite furnace atomic absorption spectrometry

A method is described for the determination of total tin in silicate rocks utilizing a graphite furnace atomic absorption spectrometer with a stabilized-temperature platform furnace and Zeeman-effect background correction. The sample is decomposed by lithium metaborate fusion (3 + 1) in graphite crucibles with the melt being dissolved in 7.5% hydrochloric acid. Tin extractions (4 + 1 or 8 + 1) are executed on portions of the acid solutions using a 4% solution of trioctylphosphine oxide in methyl isobutyl ketone (MIBK). Ascorbic acid is added as a reducing agent prior to extraction. A solution of diammonium hydrogenphosphate and magnesium nitrate is used as a matrix modifier in the graphite furnace determination. The limit of detection is > 10 pg, equivalent to > 1 μg l^?1 of tin in the MIBK solution or 0.2–0.3 μg g^?1 in the rock. The concentration range is linear between 2.5 and 500 μg l^?1 tin in solution. The precision, measured as relative standard deviation, is < 20% at the 2.5 μg l^?1 level and < 7% at the 10–30 μg l^?1 level of tin. Excellent agreement with recommended literature values was found when the method was applied to the international silicate rock standards BCR-1, PCC-1, GSP-1, AGV-1, STM-1, JGb-1 and Mica-Fe. Application was made to the determination of tin in geological core samples with total tin concentrations of the order of 1 μg g^?1 or less.     

Reactions of 1,3-Dibromo-1,1-difluoro Compounds with 1,8-Diazabicyclo[5.4.0]undec-7-ene

Difluorodienes result from the double dehydrobromination of 4-aryl-1,3-dibromo-1,1-difluorobutanes with DBU. Attempted syntheses of analogous 4-alkyl or 4-alkoxy dienes yield monoelimination products under mild conditions and unexpected trifluoro compounds under more vigorous conditions. 4-Aryl-1,1-difluoro-1,3-butadienes react rapidly with 4-phenyl-1,2,4-triazoline-3,5-dione in Diels-Alder reactions, but these dienes are unreactive toward several other electron-deficient and electron-rich dienophiles.     

The free energy of a reaction coordinate at multiple constraints: a concise formulation

The free energy as a function of the reaction coordinate (rc) is the key quantity for the computation of equilibrium and kinetic quantities. When it is considered as the potential of mean force, the problem is the calculation of the mean force for given values of the rc. We reinvestigate the PMCF (potential of mean constraint force) method which applies a constraint to the rc to compute the mean force as the mean negative constraint force and a metric tensor correction. The latter allows for the constraint imposed to the rc and possible artefacts due to multiple constraints of other variables which for practical reasons are often used in numerical simulations. Two main results are obtained that are of theoretical and practical interest. First, the correction term is given a very concise and simple shape which facilitates its interpretation and evaluation. Secondly, a theorem describes various rcs and possible combinations with constraints that can be used without introducing any correction to the constraint force. The results facilitate the computation of free energy by molecular dynamics simulations.     

Complexometric determination of gallium with calcein blue as indicator

A metalfluorechromic indicator, Calcein Blue, has been used for the back-titration of milligram amounts of EDTA in presence of gallium complexes. The indicator was used in conjunction with an ultraviolet titration assembly equipped with a cadmium sulphide detector cell and a microammeter for enhanced end-point detection. The result is a convenient and rapid method with an accuracy approaching 0.1% and a relative standard deviation of about 0.4% for 10 mg of gallium.     

Microcoulometric measurement of water in minerals

A DuPont Moisture Analyzer is used in a microcoulometric method for determining water in minerals. Certain modifications, which include the heating of the sample outside the instrument, protect the system from acid gases and insure the conversion of all hydrogen to water vapor. Moisture analyzer data are compared to concurrent data obtained by a modified Penfield method. In general, there is a positive bias of from 0.1 to 0.2% in the moisture analyzer results and a similarity of bias in minerals of the same kind. Inhomogeneity, sample size, and moisture pick-up are invoked to explain deviations. The method is particularly applicable to small samples.     

The determination of tin,chlorine, and fluorine in six japanese sedimentary standards

Concentrations of tin, chlorine, and fluorine in six new Geological Survey of Japan (GSJ) sedimentary standards are reported. Tin was determined using graphite furnace atomic absorption spectrometry (GFAAS), following a lithium metaborate (LMB) fusion of the rock material. Chlorine and fluorine were determined using ion-selective electrode (ISE) potentiometry following an acid digestion and a LMB fusion, respectively. The methods employed are briefly described and determination limits in the rock of 0.2 g/g for tin, 10 g/g for chlorine, and 100 g/g for fluorine are reported. The precision obtained for the six sedimentary standards, expressed as %relative standard deviation, averaged 5.3% over the range of 2-200 g/g tin, 5.8% over the range of 20–65 g/g chloride, and 1.7% over the range of 100–4500 g/g fluoride, all in the rock. This compares favorably to the precision obtained for international geologic reference materials determined concurrently with the GSJ sedimentary standards. The values of tin, chloride, and fluoride obtained for the international reference materials were in favorable agreement with the recommended literature values.