side a rotating motor shaft induces the eccentric motion with an offset drive pin connected to the drive plate the sample bottle is connected to the drive plate as depicted in fig6 and fig7 a which will be described later the mixing method may use a sealed container to prevent splashing and spilling during the vortex development smooth swirling of a liquid in a container creates a slanted liquid mass as shown in for instance fig1 the slanted liquid mass may reach over the lip of an open bottle when the bottle is nearly full to prevent this possibility the sample bottle can be sealed on top fig1 and fig1 u2014 also described in more detail below u2014 show the preferred embodiment of the sealing system inverting the bottle minimizes the tare volume the tare volume is fluid from the previous sample trapped before the optical particle counter this fluid a passes through the particle counter or other sensor without being counted as part of the current sample and b is discarded the narrower neck 1060 of the sample bottle 1010 in fig1 and fig1 allows nearly the entire sample to be drawn from the bottle when a sample bottle 1010 is placed over sample needle 690 and vent needle 1050 the intake end of sample intake needle 690 resides in neck 1060 of the bottle the system therefore can use all the liquid in the sample bottle except for a portion in the narrow neck below the intake end of sample needle 690 this helps extract the most sample liquid from the.