An improved olive oil overall migration test for plastics using Karl Fischer titration.

Karl Fischer titration has been used to eliminate the need to humidity-condition food contact plastics under test for overall migration into olive oil. The water content of the oil is measured before and after the migration test. This direct measure of the loss (or uptake) of water by the test plastic is then used in calculations of the overall migration. The use of Karl Fischer titration gives faster analysis with reduced labour input. The time savings varied from a few days to several weeks depending on the type of plastic. Karl Fischer titration is particularly useful in the high temperature testing of polar plastics where incomplete humidity conditioning can lead to erroneous results. The technique should be equally valuable when employing sunflower oil or the triglyceride HB307 in place of olive oil.

The manipulation of DNA with restriction enzymes in low water systems.

The cleavage of phage lambda (lambda) DNA by the restriction enzyme HindIII in low water systems has been investigated. Two types of low water systems have been studied--those which contain a surfactant in a reverse micelle environment and a surfactant-free system in which a solid support (celite) is used. The effect of the surfactants themselves in a normal aqueous environment has also been studied. Charged surfactants were found to greatly inhibit HindIII activity in aqueous buffer, while non-ionic surfactants did not affect either the activity or the specificity of the restriction enzyme. The rate of cleavage by HindIII in a reverse micelle system consisting of sodium dioctylsulphosuccinate is very slow, however, in a Triton B system the expected fragments are observed. In a surfactant-free low water environment, cleavage occurs at the expected sites but in a different order to that observed in normal aqueous systems. These results suggest that DNA tertiary structure in low water systems is different to that in aqueous solution and that this influences cleavage by the restriction enzyme HindIII.