A better idea is to post your article on YOUR OWN website first, then wait for it to be indexed by the search engines before posting to the article directories. Why do this?
By posting original content on your own site that contains your keywords, you are helping build up you own virtual real estate. When you place all of your new articles on the article directory sites first, this is the first place the search engines will find it - which means you are helping to further build the page rank of the article directory instead of your own website!
The most effective thing you can do is to post new content to your own site, wait for about one week, then post your article to the top article directories linking back to your site in the author resource box. No, placing your article on the article directories will NOT mean the "D" word (duplicate content.) There is a huge misconception floating around the web about this subject. Duplicate content is considered to be content on one single website that is repeated on that very same website - not two entirely different websites.
Regardless, article marketing ROCKS for your business - drive traffic and build search engine ranking by linking back to your site with effective keywords. Yes, content IS still king online.