Here's an alternative solution to the accepted one, converted from a VB.NET sample:
using System;
using System.IO;
using System.Runtime.InteropServices;
class Test
{
const int OPEN_EXISTING = 3;
const uint GENERIC_READ = 0x80000000;
const uint GENERIC_WRITE = 0x40000000;
const uint IOCTL_STORAGE_EJECT_MEDIA = 2967560;
[DllImport("kernel32")]
private static extern IntPtr CreateFile
(string filename, uint desiredAccess,
uint shareMode, IntPtr securityAttributes,
int creationDisposition, int flagsAndAttributes,
IntPtr templateFile);
[DllImport("kernel32")]
private static extern int DeviceIoControl
(IntPtr deviceHandle, uint ioControlCode,
IntPtr inBuffer, int inBufferSize,
IntPtr outBuffer, int outBufferSize,
ref int bytesReturned, IntPtr overlapped);
[DllImport("kernel32")]
private static extern int CloseHandle(IntPtr handle);
static void EjectMedia(char driveLetter)
{
string path = "\\\\.\\" + driveLetter + ":";
IntPtr handle = CreateFile(path, GENERIC_READ | GENERIC_WRITE, 0,
IntPtr.Zero, OPEN_EXISTING, 0,
IntPtr.Zero);
if ((long) handle == -1)
{
throw new IOException("Unable to open drive " + driveLetter);
}
int dummy = 0;
DeviceIoControl(handle, IOCTL_STORAGE_EJECT_MEDIA, IntPtr.Zero, 0,
IntPtr.Zero, 0, ref dummy, IntPtr.Zero);
CloseHandle(handle);
}
static void Main()
{
EjectMedia('f');
}
}