Analytical Chemistry of Silicates

Alternative methanol determination by head space chromatography If the facility is available, prepare a series of MeOH solutions in the range 5 x 10 -10 M. Set the head space oven temperature at 60 C. Use a 20 m Carbowax c illary column (at 40 C), with nitrogen gas carrier at a pressure of 8 psi. It is best to have automatic head space sampling from 2 cm vials. Plot the relative peak height against [MeOH] and use the calibration plot to determine unknown [MeOH]. (J.T.S.Irvine, PhD.Thesis, University of Ulster, 1986, p. 123). 

Naturally-found silicates are complex mixtures of minerals which are best characterised by XRD, TGA and DTA. Special methods of chemical analysis are available and are used in special laboratories. However, cement, which is an industrial silicate product, can be analysed more readily than natural silicates. Hie composition of cement is usually expressed as oxides of Si, Ca, Al, S, Fe(III) and Mg besides the alkali metals Na and K. 

Chemical analysis of ordinary Portland cement Determination of Si, Al, Fe(III), Mg, Mn and Ti 

When cement is fused with NaOH and the product dissolved in HCl, the chlorides are determined by atomic absorption. 

Weigh out accurately 0.7 g of dried cement into a 250 cm beaker. Disperse in water, add 10 cm cone. HCl and 150 cm hot water. Bring to the boil and keep hot for 5 minutes. Cool and transfer quantitatively to a 250 cm volumetric flask and make up to the marie. Dissolve in a 100 cm aliquot 0.191 g purest KCI and in another 100 cm aliquot 0.254 g purest NaCl. These chlorides are added as ionisation suppressors. Use the atomic spectrophotometer in the emission mode and measure the readings for the two solutions, using the manufacturer s recommended operating conditions. Use calibration standards to find [K] and [Na]. Calculate from the results of spectrophotometry the percentages of oxides of the elements determined. 

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