CSV Validation In C# - Making Sure Each Row Has The Same Number Of Commas

I wish to implement a fairly simple CSV checker in my C#/ASP.NET application - my project automatically generates CSV's from GridView's for users, but I want to be able to quickly run through each line and see if they have the same amount of commas, and throw an exception if any differences occur. So far I have this, which does work but there are some issues I'll describe soon:

int? CommaCount = null;

StringBuilder sb = new StringBuilder();
StringWriter sw = new StringWriter(sb);
String Str = null;
//This loops through all the headerrow cells and writes them to the stringbuilder
for (int k = 0; k <= (grd.Columns.Count - 1); k++)
{
sw.Write(grd.HeaderRow.Cells[k].Text + ",");
}
sw.WriteLine(",");
//This loops through all the main rows and writes them to the stringbuilder
for (int i = 0; i <= grd.Rows.Count - 1; i++)
{
StringBuilder RowString = new StringBuilder();
for (int j = 0; j <= grd.Columns.Count - 1; j++)
{
//We'll need to strip meaningless junk such as <br /> and
Str = grd.Rows[i].Cells[j].Text.ToString().Replace("<br />", "");
if (Str == " ")
{
Str = "";
}
Str = """ + Str + """ + ",";
RowString.Append(Str);
sw.Write(Str);
}
sw.WriteLine();
//The below code block ensures that each row contains the same number of commas, which is crucial
int RowCommaCount = CheckChar(RowString.ToString(), ',');
if (CommaCount == null)
{
CommaCount = RowCommaCount;
}
else
{
if (CommaCount!= RowCommaCount)
{
throw new Exception("CSV generated is corrupt - line " + i + " has " + RowCommaCount + " commas when it should have " + CommaCount);
}
}
}
sw.Close();

And my CheckChar method:

protected static int CheckChar(string Input, char CharToCheck)
{
int Counter = 0;
foreach (char StringChar in Input)
{
if (StringChar == CharToCheck)
{
Counter++;
}
}
return Counter;
}

Now my problem is, if a cell in the grid contains a comma, my check char method will still count these as delimiters so will return an error. As you can see in the code, I wrap all the values in " characters to 'escape' them. How simple would it be to ignore commas in values in my method? I assume I'll need to rewrite the method quite a lot.