C#

// Constants used in DLL methods
        const uint GENERICREAD = 0x80000000;
        const uint OPENEXISTING = 3;
        const uint IOCTL_STORAGE_EJECT_MEDIA = 2967560;
        const int INVALID_HANDLE = -1;
        const uint DRIVE_CDROM = 5; 

        // File Handle
        private static IntPtr fileHandle;
        private static uint returnedBytes;

        // Use Kernel32 via interop to access required methods

        // Get a File Handle
        [DllImport("kernel32", SetLastError = true)]
        static extern IntPtr CreateFile(string fileName,
        uint desiredAccess,
        uint shareMode,
        IntPtr attributes,
        uint creationDisposition,
        uint flagsAndAttributes,
        IntPtr templateFile);

        [DllImport("kernel32", SetLastError = true)]
        static extern int CloseHandle(IntPtr driveHandle);

        [DllImport("kernel32", SetLastError = true)]
        static extern bool DeviceIoControl(IntPtr driveHandle,
        uint IoControlCode,
        IntPtr lpInBuffer,
        uint inBufferSize,
        IntPtr lpOutBuffer,
        uint outBufferSize,
        ref uint lpBytesReturned,
        IntPtr lpOverlapped);

        [DllImport("kernel32", SetLastError = true)]
        static extern int GetDriveType(string driveLetter);

...

public static void Eject(string driveLetter)
        {
            try
            {
                // Create an handle to the drive
                fileHandle = CreateFile(driveLetter,
                GENERICREAD,
                0,
                IntPtr.Zero,
                OPENEXISTING,
                0,
                IntPtr.Zero);

                if ((int)fileHandle != INVALID_HANDLE)
                {
                    // Eject the disk
                    DeviceIoControl(fileHandle,
                    IOCTL_STORAGE_EJECT_MEDIA,
                    IntPtr.Zero, 0,
                    IntPtr.Zero, 0,
                    ref returnedBytes,
                    IntPtr.Zero);
                }

            }
            catch
            {
                throw new Exception(Marshal.GetLastWin32Error().ToString());
            }
            finally
            {
                // Close Drive Handle
                CloseHandle(fileHandle);
                fileHandle = IntPtr.Zero;
            }
        }