My guide:
If we provide routine services at a cost, it is normal to be cited in the
Materials and Methods section for the purposes of reproducing an experiment.
We usually work with the investigator on the wording to get the machines
right.
"Oligonucleotides were synthesized by the Biopolymer Facility of..."
If we provide routine services free (rare) or heroic extra service (but
routine procedures) against tight deadlines or such, it is an appropriate
courtesy to mention the heroic technician or staff member in acknowledgments.
"We would like to thank Ms. Jane Jones for her special efforts to
meet..."
Only in the cases where we develop original procedures or protocols of
significant importance to the experiments (and without our input the
experiment would be _CONCEPTUALLY_ impossible) is co-authorship expected.
"A New Method of Selenium Incorporation in Peptides..."
At least, that's the way we do it.
clark riley, baltimore