Check user agent for IE version and Trident version, like in this article:
string userAgent = Request.UserAgent; //entire UA string
string browser = Request.Browser.Type; //Browser name and Major Version #
if (userAgent.Contains("Trident/5.0")) //IE9 has this token
{
if (browser == "IE7")
{
mode = "IE9 Compatibility View";
}
else
{
mode = "IE9 Standard";
}
}