Dry Ashing without Retaining Aids

Ashing of samples may be defined as heating a substance to leave an ash that is noncombustible and that is soluble in most dilute acid or base solutions. The resulting solution is analysed for elemental composition against certified standards prepared in the same acid 

The second consideration for quantitative analysis is that if the elements are present in trace quantities the problems of multiple sample preparation by ashing increase. A vicious circle is endured when the quantity and percentage recovery of the element cannot be determined until the quantity of the element present is known for dilution limits and range of standard calibration curve required. If the quantity is known, the percentage recovery may be determined by calibration curve or by standard addition. The percentage recovery results should be 100% 2% to allowing for errors and loss. Drawbacks to this method are  

The ashing of a sample is usually easy to perform but not all resulting ashes are soluble in acid, bases, etc. It may be possible to analyse these samples for elements in the ash that will dissolve in 1.0-2.0 M HC1 and separate the unwanted ash by filtering. The insoluble products in these cases usually indicate mainly sand, talc and silica. If analysis is required for the complete ash a stronger acid or acid mixtures may be required, e.g. H2SO4, HC1, HNO3, HF, etc. This method works well for most alkali, alkaline and transition elements including some refractory elements. 

The vessels used for ashing, particularly for trace elements, must be carefully cleaned (usually in 1-2 M boiling HC1 for 10 or 15 min), rinsed with de-ionised water and dried 

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