It is now widely known that drug residues can be found in hair long after the actual time of use, and these mills can be used to prepare samples for analysis
Using the planetary ball mills Pulverisette 5 and 6, the planetary micro mill Pulverisette 7, as well as the vibratory micro mill Pulverisette 0, hair samples can be reduced to a fine powder for subsequent analysis.
In most cases, the sample quantities are only 0.3 to 0.5g.
Prerequisite for optimum comminution is the selection of the material for the grinding bowls and balls and the inevitable associated contamination/abrasion during milling.
This can, however, lie below the detection threshold if the milling time is very short. Another important user requirement that must be taken into account is the ease with which the grinding parts can be cleaned: the grinding elements must often be sterilised.
The sample quantity of < 0.5g with a average feed particle size of 1-2cm (for very fine hair this might reach 3-4cm) can be ground in the 45ml grinding bowls of the Pulverisette 7 fitted with 7x15mm balls in zirconium oxide, silicon nitride, sintered corundum or agate within 5-20 min.
down to a final fineness <100µm.
The higher the density of the grinding elements, the shorter the grinding time.
The grinding time is also reduced if the grinding elements have a rough surface.
This may, however, lead to a measurable contamination which should, nevertheless, not cause any problems when an extract of the hair sample is subsequently prepared.
The vibratory micro mill Pulverisette 0 is particularly suitable for milling very small quantities.
The best results are achieved with grinding elements made of sintered corundum; the smooth grinding elements are unsuitable here.
Using this instrument, since the required energy input is small, the time required to reduce a sample of 0.5g to a final particle size <200-300µm is about 20-30min.
A comminution using the variable speed rotor mill Pulverisette 14 is not possible because of the following reasons: due to the very small diameter of the hairs, only 40-60µm, they are able to pass, in part, through the sieve ring used, leading to uneven reduction.
In addition there is a brief but sharp rise in temperature during the grinding process. For the Environmental Sample Bank and other investigation bodies, larger quantities of hair were also ground for their use as standards.
For this, the planetary mill Pulverisette 5 was used with a 500ml grinding bowl and 9x30mm grinding balls made of sintered corundum.
The maximum feed quantity that can be ground at one time is about 25g with a maximum feed particle size of 2-3cm and fills the mortar completely.
After a grinding time of 15min, a fine powder with a particle size of approx.
200µm or less is obtained.
The temperature during the grinding process rises up to approximately 35-38C.
