Hydrogen phosphide as a fumigant for foods, feeds and processed ...

142 W. H. D1ErER1CH, GERO MAYR, KARL HILA, ) . B. SULLIVAN, and J . MURPHY
toxic byproducts would be formed by chemical reaction . The first approach
toward the solution of this problem was the use of a method shown to be
practicable with raw agricultural commodities. This was described by BRUCE
of al. in 1962 and was shown to be sensitive in the range of parts per billion
(p.p.b.) ; apparent phosphene residues in flour and bread were in the
range of less than 60 p.p.b. A limiting factor in this method was the concentration
of phosphorus in the analytical reagents used, including the
water; for this reason the authors emphasized the need for funning control
or blank samples.
In an attempt to increase the overall sensitivity of the original method,
SULLIVAN and MURPHY (1966) modified BRUCE's procedure ; specific details
of this new procedure are to be published at a later date .
Utilizing this modified procedure, SULLIVAN and MURPHY (1966)
analyzed the following products for phosphine residues following fumigation
and aeration according to the recommended schedule : green coffee beans,
cocoa powder, nonfat instant dry milk powder, malted barley flour, institu .
tional doughnut mix, pie crust mix, oat flour, gluten concentrate, high fat
soy flour, rice flour, gluten flour, bran buds, primary yeast, beet pulp, cornstarch,
deer pellets, mink conditioner, raisins, dried apples and apricots, pecan
pieces, and Kellogg's Corn Flakes, Rice Krispies, Concentrate, Special K,
Apple Jacks, and Shredded Wheat. After fumigation at the recommended
level with 48 hours' aeration, the highest level of phosphine found in any
product was 0 .017 p .p.m. (see Table III) . Data from a shorter aeration
interval and at an exaggerated dosage level indicate the rapidity with which
phosphine disappears .
Because of the trace levels of phosphorus and related compounds which
might normally be found in foodstuffs, as previously mentioned, an indirect
method for the analysis of phosphine residues was developed by MAYR and
HILD (1966). By demonstrating that all of the phosphine which had been
generated by a measured amount of Phostoxin could be recovered at some
period following the completion of fumigation, they excluded the possibility
of any reaction with or adsorption by the fumigated foodstuffs. Accuracy
of the method was ± 0.07 percent . A description follows :
The fumigation chamber (desiccator) is connected with the equipment for
the phosphine determination, which consists of two bubble towers; the first is
filled with dilute sulfuric acid and the second with mercuric chloride . The
final connection is to a vacuum pump. A stream of nitrogen is drawn through
the desiccator with a speed of eight 1./fir. to wash the phosphine into the mercuric
chloride. Precautions are taken to retain every trace of phosphine and
to pass the nitrogen stream slowly enough to allow the total absorption of the
phosphine. In order to remove the gas from the interstitial spaces of the treated
commodity, the latter is stirred during the nitrogen wash . Nitrogen can be replaced
in this method by air, either hot or cold .
Should there be tablet residues in the fumigated commodity, dilute sulfuric
acid is added to the latter and boiled; the phosphine is completely driven out
and absorbed in the mercuric chloride .
Phosphine reacts with the mercuric chloride to form free hydrochloric
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