Split letters and numbers

using System;
using System.Text;
using System.Text.RegularExpressions;

namespace Program
{
    public class App
    {
        static void Main(string [] args)
        {
            string strtemp ="AB324hgdf89dfg";
            string strpart;
            Nullable<int> npart;
            SplitLettersAndNumbers(strtemp,out strpart,out npart);
            Console.WriteLine("{0} : {1} - {2}",strtemp,strpart,npart);
        }

        /// <summary>
        /// This method extracts all numerals and alphabets from a given string
        /// </summary>
        /// <param name="instr">String input</param>
        /// <param name="strpart">all alphabets as string</param>
        /// <param name="intpart">all numerals as string</param>
        /// <returns>return if success else false<returns>
        public static bool SplitLettersAndNumbers(string instr, out string strpart, out Nullable<int> intpart)
        {

            string strtemp = null; //buffer to hold letters
            string nstrtemp = null;//buffer to hold numbers

            if (instr == null) // invalid option
            {
                strpart = null;
                intpart = null;
                return false;
            }

            string[] m1 = Regex.Split(instr, @"\d");//All letters
            string[] m2 = Regex.Split(instr, @"\D");//All numbers

            //Concatenate all strings
            StringBuilder sb = new StringBuilder(instr.Length);
            foreach (string si in m1)
            {
                //Do extra processing if needed
                sb.Append(si);
            }
            strtemp = sb.ToString();

            //Concatenate all Numbers.
            foreach (string si in m2)
            {
                //Do extra processing if needed
                nstrtemp += si;
            }

            //Update out parameter for letters
            if (strtemp != "")
            {
                strpart = strtemp;
            }
            else
            {
                strpart = null;
            }

            //Update out parameter for numbers
            if (nstrtemp != "")
            {
                intpart = int.Parse(nstrtemp);
            }
            else
            {
                intpart = null;
            }

            return true;
        }
    }
}