| dc.description.abstract | In the recent past there has been an increasing interest
in the determination of the fluoride content in foods. The
fluoride analysis has been carried out using mainly the fluoride
ion selective electrode. This interest has arisen due to the
need to evaluate the total fluoride intake per day from both
water and food and hence establish any correlation with
incidences of dental fluorosis or caries. This has led to the
development of various methods for the release of fluoride ions
which may exist in inorganic or organic forms. The methods
include ashing in the furnace, acid digestion, oxygen bomb,
Schoniqer oxygen flask combustion, pyrohydrolysis and direct
diffusion. The latter method has gained popularity especially
for low fluoride conce'ntrations . Available literature shows
different values of fluoride content even for the same foods and
this may be attributed to methodology, accuracy and/or the
processinq of the foods.
These methods of fluoride analysis are discussed and
compared in this work. In order to handle many samples an
open ashing method has been developed. This involves ashing
in an open flame using calcium hydroxide as a fixative followed
by microdiffusion at 60°C for 20 hours. The results obtained
by this method compared well with those obtained using
Schoniqer oxygen flask method. Direct diffusion (without ashing)
gave much lower values than the ashing method .
The effect of aluminium and silicon on diffusion has been
studied. In order to minimise interference, it was found
necessary to use perchloric acid and low amounts of sample
<0.5g) for diffusion.
The use of different buffers in the measuring solution has
also been investigated. It was found that TISAB II alone is
not effective in presence of aluminium ()2mg) but 1. 4M sodium
citrate plus TISAB II buffer was effective even in presence of
up to 50mg aluminium.
Fluoride content in different types of soils has been
analysed. For mobile fluoride ammonium lactate was used as the
extracting medium. Values obtained with ammonium lactate were
compared with. those obtained using either water, 1M hydrochloric
acid or sodium citr-ate ,plus EDT A. Ammonium lactate was found
to give higher values than either water or sodium citrate plus
EDT A but it was selected for fluoride extraction because of it+s
wide use as extracting media for other common ions in the soil.
The extraction time, pH of the extracting media and amount of
the sample were found to be impor tant factors in fluoride
extraction while clay content, or qanie matter and soil pH play
important roles in fluoride accumulation in the soil. Analysis of
soils from different localities showed the fluoride concentration
-1 to range from 21-282 ~g g fluoride. High concentrations were
recorded for those soils collected near cement and diatomite
industries.
Analysis of fluoride in plants and vegetables collected from
various parts in Kenya has been done. It was found that
there was variation of fluoride content in the same type of
vegetable grown at different places. For example, Solanum
-1 .
nigrum from Lake Bogoria contained 29.98 119 9 while that
-1
from Kiambu contained 3.82 119 9 fluoride. Vegetables of
the same family grown in the same locality accumulated
almost the same amount (Cucurbita sps
-1
Cucurbi.ta pepo 7.32 119 9 fluoride) .
-1
7. 16 119 9 and
Plants picked from the shores of Kenyan lakes were
found to have higher fluoride concentrations for example
Euperus laevigatus (from Lake Nakuru, 140 mg 1-1) contained
1049 119 9 -1 fluoride, while those grown at a distance from
-1
the same lake especially Bequaertia robyns contained 32.06 119 g
fluoride. It was found that, up to 98% of fluoride in tea was
acid labile and the amount of fluoride in tea was found to
depend 'on the age of the tea plant. The older the tea plant,
the higher the, fluoride concentration. | en |
