On C# - How to capture the Serial Port received data to Global Variable?

Hi Guys.
I've using serialPort and written a small method to read the SerialPort. The SerialPort being read!  I need to separate the string the get Particles Counters. The devices send the string in this format: ?01,00000,00000,00000,n/a,n/a I try to capture the string to separate in the commas, but unfortunately, so capture the end of the string or "n/a". How to capture the entire string to global variable and treat this variable in another method?
Thanks in advance
My method:

private void serialPort1_DataReceived(object sender,System.IO.Ports.SerialDataReceivedEventArgs e)
{
	if(serialPort1.DataBits==8)
    {
    RxString=serialPort1.ReadExisting();
    this.Invoke(new EventHandler(DisplayText));
    }
}

private void DisplayText(object sender,EventArgs e)
{
	textBox1.AppendText(RxString);
}

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