A260/A280 ratios of oligonucleotide

[nhwu at PUBLIC3.BTA.NET.CN]

I know DNA has an A260/A280 ratio of 1.6~1.8, while as RNA has ratio of 
1.8~2.0. But what about oligonucleotide? I want to check the puriety of 
some primers systhesised, but I don't know what range of A260/A280 ratio is 
all right.
any help will be appriciated!
Xiao-yu Liu