Remove all non-ASCII characters from string

I have a C# routine that imports data from a CSV file, matches it against a database and then rewrites it to a file. The source file seems to have a few non-ASCII characters that are fouling up the processing routine.

I already have a static method that I run each input field through but it performs basic checks like removing commas and quotes. Does anybody know how I could add functionality that removes non-ASCII characters too?

Here a simple solution:

public static bool IsASCII(this string value)
{
    // ASCII encoding replaces non-ascii with question marks, so we use UTF8 to see if multi-byte sequences are there
    return Encoding.UTF8.GetByteCount(value) == value.Length;
}

source: http://snipplr.com/view/35806/

string sOut = Encoding.ASCII.GetString(Encoding.ASCII.GetBytes(s))

Do it all at once

public string ReturnCleanASCII(string s)
{
    StringBuilder sb = new StringBuilder(s.Length);
    foreach(char c in s)
    {
       if((int)c > 127) // you probably don't want 127 either
          continue;
       if((int)c < 32)  // I bet you don't want control characters 
          continue;
       if(c == ',')
          continue;
       if(c == '"')
          continue;
       sb.Append(c);
    }
    return sb.ToString();
}