Why is it necessary to change the micropipette tip when carrying out ten-fold serial dilutions but not when carrying out two-fold serial dilutions?
In this manual, two-fold serial dilutions are used in quantitative assays to indicate the concentration of Newcastle disease virus (HA test) or Newcastle disease virus antibodies (HI test) in each dilution. These data is then used to calculate a titre to the log base 2. In both assays, the small quantities of the antibodies or virus carried over on tips between the two-fold dilutions will not greatly influence the result of the titres. In this manual, ten-fold dilutions are used in quantal assays to titrate viral infectivity. Each dilution is inoculated into eggs and a single viral particle is sufficient to infect the embryo. Infected embryos will give a positive result when the allantoic fluid is tested for the presence or absence of virus after incubation for four days. For this reason even a small number of infective virus particles that are carried over on the pipette tip will falsify the results. The infectivity titres calculated from these results will be erroneously high. By usi
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