Carryover stock

Prepare 10-fold dilutions of the virus stock in MEM 2%. Dilutions in the range of 10 2-10 7 (for HSV) and in the range 10 1-10 4 (for CMV and VZV) are appropriate for most virus stocks. Use a fresh pipet or tip for each dilution to prevent carryover of virus (which might otherwise result in an anomalously high virus titer). 

Surveys carried out by the Canadian Grain Commission on the erucic acid content of Canadian rapeseed are summarized in Fig. 1. By 1974, the average level of erucic acid in the New Crop Survey had decreased to below 5%. Because of carryover of stocks from previous years, it took until 1976 for the average level of erucic acid in exported seed (carlot and cargo surveys) to fall below 5%. 

Van der Walt (1970) suggests that in the case of fastidious yeast, such as Brettanomyces/Dekkera, cell suspensions be prepared in stock vitamin solution (see 3.5.2 for preparation). In this case, and in general, it is advisable to prepare a control to detect carryover of nitrogen or carbon from the original culture. The control, here, consists of only basal medium and yeast. 

Additional Components Analyte recovery (extraction efficiency) Stock stability Matrix stability Post process stability (extract) Integrity of dilution Carryover and contamination Matrix effects Incurred sample reproducibility Incurred sample stability... 

Several of these constituents can be varied to optimize PCR and overcome problems with inhibition. For example, the final MgCl2 concentration with the aforementioned kit is 1.5 mM, but this can easily be increased by addition from a 25-mM MgCl2 stock solution. The DNA concentration can also be varied if inhibition is a problem due to carryover of something in the sample matrix. This can be tested by inspecting PCR product concentration with different DNA template additions and spiking the sample DNA extraction with a positive-control template. 

---