What is national interest?

Joseph Stiglitz has a hard hitting article on trade agreements and interests that need to be protected while negotiating them in this piece in the Guardian. What caught my attention is the commercial interests versus national interest argument that I have tried to grapple with in many pieces of this blog:

"...no trade agreement should put commercial interests ahead of broader national interests, especially when non-trade-related issues like financial regulation and intellectual property are at stake. ... 

If negotiators created a genuine free trade regime that put the public interest first, with the views of ordinary citizens given at least as much weight as those of corporate lobbyists, I might be optimistic that what would emerge would strengthen the economy and improve social well-being. The reality, however, is that we have a managed trade regime that puts corporate interests first, and a process of negotiations that is undemocratic and non-transparent."

Some food for thought for trade policy negotiators around the world? Whose interests are at stake? Are not domestic business interests national interest? national interest may be a broader term but is not pursuing the interest of one's domestic industry part of national interest? Is it antithetical to common citizen's interests? Can they go together? Sometimes they do sometimes they dont? Who decides and on what terms? How does one do the balancing act? What if one's national business interest is impacting local citizen's interest in the trading partner? Is international trade about advancing one's own domestic business interest or addressing the issue of inequity worldwide? Can national interest be an amalgam of domestic corporate interest and the interest of a number of stakeholders? Like one trade policy maker stated recently can it combine the interest of the "worker, farmer, rancher, manufacturers, service providers, innovators, investors and consumers" all at once?