3.1.2. Extraction of fat in tree nuts
The percentage of fat content in tree nut samples, varied from
25.3% for cashew nut to 61.4% for walnut. Among the samples
studied in this work, Brazil nuts, almond, walnut and cashew nut
from Spain had high fat content with percentages higher that 50%.
The direct determination of Hg in tree nuts by DMA involved the
production of a high volume of fumes and provided variable Hg
results owing to the thermal decomposition of fat. So, samples
were defatted with a mixture of chloroform and methanol before
measurement based on information from previous reported works
[14,15,29,30].
Samples were analysed before and after fat removal. Table 2
shows that the results obtained for defatted samples does not
always coincide with those obtained directly, probably due to the
interference of fat during the pyrolysis process that directly affects
the results. These differences were, in some cases, up to three times
the concentration found for defatted samples and because of that a
previous treatment of sample with chloroform and methanol was
mandatory to obtain accurate and precise results. Additionally, the
defatting process avoid the smoking of the measurement cells with
the fumes. Assays made on the nut fat evidenced the absence of Hg
in this part of the samples (results not shown).