StrConv - vbProperCase in C#

public static string ProperCase(string stringInput)
{
System.Text.StringBuilder sb = new System.Text.StringBuilder();
bool fEmptyBefore = true;
foreach (char ch in stringInput)
{
char chThis = ch;
if (Char.IsWhiteSpace(chThis))
fEmptyBefore = true;
else
{
if (Char.IsLetter(chThis) && fEmptyBefore)
chThis = Char.ToUpper(chThis);
else
chThis = Char.ToLower(chThis);
fEmptyBefore = false;
}
sb.Append(chThis);
}
return sb.ToString();
}