Fjölrit RALA - 22.03.1979, Blaðsíða 54

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II. Collection of Samples and Methods of Analysis
The staff of the Food Science Department at the ARI
collected samples from Reykjavík and the Eastern Fiords
in October 1977. Other samples were sent to the ARI on
request by the National Institute of Environmental Health
by health representatives in the different communities.
These samples arrived at the ARI in 1978.
The samples were ground and about 5 grams of the ground
meat put in 250 ml digestion tubes. Water was added to the
tubes which were placed in a digestion block preheated to
90-95°C. The samples were heated in this manner for one
hour in order to extract the nitrate and nitrite out of
the meat and into the water. After heating, the solutions
were cooled to room temperature and diluted to the 250 ml
mark with water. They were then filtered through filter
paper and the filtrate collected in a beaker. The filtrate
was then analyzed for nitrate and nitrite.
The Technicon AutoAnalyzer IIR was used to measure the
amount of nitrate and nitrite. Nitrate is reduced to nitrite
on a cadmium column. The nitrite ion then reacts in acid
with sulfanilamide and forms a diazo-compound which binds
to N-l-naphthylethylenediamine dihydrochloride. This bind-
ing causes formation of a pink azo-pigment which is meas-
ured on the spectrophotometer at a wavelength of 550 nm.
This measurement gives nitrate + nitrite. If the Cd-column
in removed nitrite alone is measured. To obtain the nitrate
content, the nitrite concentration is subtracted from the
total concentration of nitrate + nitrite.