Yes, you should not post the same content in two places. Why i am saying means, the content which has been crawled by the search engnine bots in second will be deducted as duplicate by the search enginebots. So, it is best to use unique content in blog and for article submission.
Actually, it is not recommended to use the same content on two different places (Blog and Article), because it will never help you in SEO tactices and also it will definitely affect your website's reputation/page rank during the Google Panda Update. So, try to utilize high quality unique contents to avoid unnecessary Google penalties.
As all member suggest, you should not submit same content for blog and article both. It is the case of the duplicate content. You should either choose one. I will suggest you to go with blog post rather than article submission.
You should not at any cost copy your blog content and use it for article because it will be considered as duplicate content by Google and moreover if someone after reading your article visit your blog and finds the same content then it will not be appropriate. So avoid doing it.
If you want to promote your blog, it's best to write different content for an article you want to submit to some popular website. It doesn't make sense to post the same content at two or more different places. It happens sometimes that different websites just take your content and usually they put a link to your website. This confuses me a bit. I would never do that, but I don't think I would tell them to take down my content.