Explanation in German but the code is a well-tested in-place implementation:
Private Sub QuickSort(ByVal Field() As String, ByVal LB As Long, ByVal UB As Long)
Dim P1 As Long, P2 As Long, Ref As String, TEMP As String
P1 = LB
P2 = UB
Ref = Field((P1 + P2) / 2)
Do
Do While (Field(P1) < Ref)
P1 = P1 + 1
Loop
Do While (Field(P2) > Ref)
P2 = P2 - 1
Loop
If P1 <= P2 Then
TEMP = Field(P1)
Field(P1) = Field(P2)
Field(P2) = TEMP
P1 = P1 + 1
P2 = P2 - 1
End If
Loop Until (P1 > P2)
If LB < P2 Then Call QuickSort(Field, LB, P2)
If P1 < UB Then Call QuickSort(Field, P1, UB)
End Sub
Invoked like this:
Call QuickSort(MyArray, LBound(MyArray), UBound(MyArray))