X509Certificate Perfomance Issue

I'm new to .NET development, but have been a programmer for 16 years, so I'm not new to coding.  I developed this code as a C# COM object (dll) for a lotus notes application.  The COM Object  gets instantiated, and I pass the encoded data to the objects "CertificationData" attribute. It then loops through 4000+ records and calls the "GetCertExpirationDate" method for each record, passing in the "CertificationData" attribute as Bytes.  After some investigating I noticed the X509Certificate object takes 4 seconds to be created.  Everything else including the interop takes milliseconds to complete. I noticed when I first installed the code it ran at warp speed, then degraded over time to the 4 seconds I see now.  I'm worried the object may have a memory leak.  How can I make sure the object is removed, and memory cleared? Deos anybody have example code that would allow me to make sure there are no memory leaks? I've tried a few things that I've commented out.  I've been hitting my head against a stone wall for days.  I'm stuck, and need help!  Heres my code mentioned above: 

using System;
using System.IO;
using System.Security.Cryptography.X509Certificates;
using System.Text;
using System.Runtime.InteropServices; //Need for API
namespace CertificationInfo
{
    //Certification Class
    public class CertificateInformation
    {
        //Class Attributes
        public string CertificateData; 
        public string ExpirationDate;
        public string NotesUNID;
        public Boolean LoggingOn;
        public String LogFile;
        public Boolean ErrLoggingOn;
        public String ErrFile;
        private MemoryManagement MemMngr;
        private DLLLog Logging;
        private String DateString;
        //Constructor
        public CertificateInformation()
        {
            //Reset Expiration Date
            this.ExpirationDate = "";
            this.LoggingOn = false;
            this.ErrLoggingOn = false;
            DateTime TodaysDate = DateTime.Today;
            this.DateString = (TodaysDate.Year.ToString())+(TodaysDate.Month.ToString())+(TodaysDate.Day.ToString());
            this.LogFile = "DLLLog"+this.DateString+".txt";
            this.ErrFile = "DLLErrors"+this.DateString+".txt";
            this.MemMngr = new MemoryManagement();
            this.Logging=new DLLLog();
        }
        //Method
        public string GetCertExpirationDate(string rawdata)
        {
            try
            {
                this.Logging.LogMe(this.LogFile, "Start Logging - UNID: "+this.NotesUNID,this.LoggingOn);
                //Clean Up Memory
                //this.MemMngr.ReleaseMemory();
                //Reset Expiration Date Property
                this.ExpirationDate = "";
                //Check for data
                if (rawdata == "" && this.CertificateData == "")
                {
                    this.Logging.LogMe(this.LogFile, "Variables rawdata and certificatedata blank!", this.LoggingOn);
                    //Nothing is passed & property is blank
                    this.ExpirationDate = "";
                }
                else
                {
                    //Check for Raw Data value
                    if (rawdata != "")
                    {
                        this.Logging.LogMe(this.LogFile, "Using variable rawdata!", this.LoggingOn);
                        this.CertificateData = rawdata;
                    }
                    //Convert Property Array
                    //Might be best to use unicode Under Encoding namespace
                    //System.Text.UnicodeEncoding Encoding=new System.Text.UnicodeEncoding();
                    //Byte[] bytedata=Encoding.GetBytes(this.CertificateData);
                    this.Logging.LogMe(this.LogFile, "Converting Cert Data: " + this.CertificateData, this.LoggingOn);
                    //Convert Property to byte array
                    System.Text.ASCIIEncoding Encoding = new System.Text.ASCIIEncoding();
                    Byte[] bytedata = Encoding.GetBytes(this.CertificateData);
                    this.Logging.LogMe(this.LogFile, "Cert Data Converted!", this.LoggingOn);
                    //Create Encoding Object
                    this.Logging.LogMe(this.LogFile, "Creating X509 Object...", this.LoggingOn);
                    X509Certificate CertificateObject = new X509Certificate(bytedata);
                    //X509Certificate2 CertificateObject = new X509Certificate2(bytedata);
                    //this.CertificateObject = new X509Certificate(bytedata);
                    this.Logging.LogMe(this.LogFile, "X509 Object Created!", this.LoggingOn);
                    //Might have to check to see iff cert object is null though catch should pick it up 
                    //Get Expiration date
                    //this.ExpirationDate = CertificateObject.GetExpirationDateString();
                    this.Logging.LogMe(this.LogFile, "Get expirationdate...", this.LoggingOn);
                    this.ExpirationDate = CertificateObject.GetExpirationDateString();
                    this.Logging.LogMe(this.LogFile, "Expiration Date: " + this.ExpirationDate, this.LoggingOn);
                    //Reset Object & Certificate Data Property
                    //this.Logging.LogMe("DLLLog", "Nulling Out Objects!");
                    //CertificateObject = null;
                    //Encoding = null;
                    //this.Logging.LogMe("DLLLog", "Resetting Certificate...");
                    //CertificateObject.Reset();
                    //this.CertificateData = "";
                    //Clean Up Memory
                    //this.Logging.LogMe("DLLLog", "Memory Manager Clean-up!");
                    //this.MemMngr.ReleaseMemory();
                }
            }
            //Error Trapping in case of error still returns something
            catch
            {
                this.Logging.LogMe(this.ErrFile, "Start Error Logged - UNID: " + this.NotesUNID, this.ErrLoggingOn);
                this.Logging.LogMe(this.ErrFile, "Error Data -: " + this.CertificateData, this.ErrLoggingOn);
                this.Logging.LogMe(this.ErrFile, "End Error Logged - UNID: " + this.NotesUNID, this.ErrLoggingOn);
                this.ExpirationDate = "";
            }
            //this.Logging.LogMe("DLLLog", "Returning expiration date!");
            this.Logging.LogMe(this.LogFile, "End Logging - UNID: " + this.NotesUNID + " Returning expiration date!", this.LoggingOn);
            return this.ExpirationDate;
        }
    }
    //Debug Log Code
    public class DLLLog
    {
        //Constructor
        public DLLLog()
        {
        }
        //Methods
        public void LogMe(String Filename,String LogMeMessage,Boolean LogOn)
        {
            if (LogOn==true)
            {
                using (StreamWriter w = File.AppendText(Filename))
                {
                    WriteLog(LogMeMessage, w);
                }
            }
        }
        public static void WriteLog(string logMessage,TextWriter w)
        {
            w.Write("\r\nLog Entry: ");
            w.WriteLine("{0} {1}", DateTime.Now.ToLongTimeString(), DateTime.Now.ToLongDateString());
            //w.WriteLine("  :");
            w.WriteLine("  :{0}", logMessage);
            w.WriteLine("-------------------------------");
        }
        public static void ReadLog(StreamReader r)
        {
            string line;
            while ((line = r.ReadLine()) != null)
            {
                Console.WriteLine(line);
            }
        }
    }
    //API Class to Clean up Memory threads
    public class MemoryManagement
    {
        //Memory Management API
        [DllImport("kernel32.dll")]
        public static extern bool SetProcessWorkingSetSize(IntPtr proc, int min, int max);
        //Method
        public void ReleaseMemory()
        {
            GC.Collect();
            GC.WaitForPendingFinalizers();
            if (Environment.OSVersion.Platform == PlatformID.Win32NT)
            {
                SetProcessWorkingSetSize(System.Diagnostics.Process.GetCurrentProcess().Handle, -1, -1);
            }
        }
    }
}