For nocodazole arrest of yeast cells (S.cerevisiae) your stock solution concentration should be 1.5mg/ml and final concentration on culture 15ug/ml, that is 10 ul per ml of culture, so i.e. if you got a 5 ml culture you shoud add 10ul per ml, from a 1.5mg/ml stock solution. What I usually do is to grow cells up to an O.D. of 0.6 or around that, and dilute them to O.D. of 0.2 or 0.3 and leave the cells for at least an hour or two, and after that time adding nocodazole treatment; after 2 hours of nocodazole treatment I add (another) half the amount of the initial concentration,so if at point 0 you added 50ul Nocodazole for a 5 ml culture, 2 hours later you have to add 25ul and wait another hour, so in total cells must be at least 3 hours in nocodazole treatment. One way of checking it, is to see at cell morphology, they should be dumbells with only one nucleus (stained with DAPI), other way is, if you have a Tub1-GFP(tubulin) tagged strain, check for tubulin depolymerization and if you got a Net1-GFP(rDNA marker) you should be able to observe what is called the rDNA loop. In anycase titration is a good option and varies from strain to strain, and you should check the specific conditions for your strain and experiment, but otherwise 3 hours under nocodazole treatment as specified before and controlling your O.D. will do in order to arrest your cells. DMSO final concentration in culture,should not exceed 1%. If you still got problems with that, try to prepare a new stock of nocodazole (nocodazole must be kept in DMSO at -20ºC in aliquots), maybe the batch was old or in bad condition, who knows.
here ther is a link that will help you : http://mcb.berkeley.edu/labs/koshland/P ... yeast.html
hope all this will be helpful, good luck