Kansas Geological Survey, Bulletin 202, pt. 1, originally published in 1971
Originally published in 1971 as part of Kansas Geological Survey Bulletin 201, pt. 1, p. 17. This is, in general, the original text as published. The information has not been updated. An Acrobat PDF version of the complete bulletin (7 MB) is also available.
Described is a method for analyzing small quantities of suspended silica, either airborne or suspended in water. The silica is entrapped on a membrane. The membrane is ashed and the silica fused with Na2CO3 and dissolved in water. The quantity of silica is determined by atomic absorption.
The following steps are used in preparing samples:
Care must be exercised at all steps to avoid loss of silica or contamination. HF cleaning of all platinum and plastic prevents contamination from those sources. Keeping the samples covered at all times prevents airborne contamination. All reagents should be silica free, and use of glassware should be avoided.
Atomic absorption analysis is performed with a nitrous oxide-acetylene flame using the 2516 Å line of silicon. A standard curve is prepared using standards containing 100 to 0.3 ppm Si. A new curve should be prepared after every 10 samples.
The range of the method is 20 to 0.6 mg SiO2. This may be extended by dissolving the fused sample in a greater or lesser volume of water. However, if the amount of silica is much less than 0.6 mg, a colorimetric analysis should be performed or another method more sensitive than atomic absorption should be used.
The standard deviation based on 20 samples of 10-mg quartz was 0.5 mg, and the standard deviation based on 20 samples of 1-mg quartz was 0.06 mg. Recovery was 98 to 99 percent in both cases. After storage for three weeks recovery dropped to 90 percent but was restored to 98 to 99 percent after digestion on the steam bath for 1 hour.
Kansas Geological Survey, Determination of Suspended Silica by Atomic Absorption
Placed on web May 7, 2009; originally published in May 1971.
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