diluter (plural diluters)
1. (chemistry) A device that adds a measured amount of sample to a measured amount of diluent.
http://en.wiktionary.org/wiki/diluter

e.g.:
The ultimate Dilumat 4 diluter offers superior
performance in traceability and automation to
microbiology laboratories
http://www.dksh.com.au/htm/620/en_AU/Microbiology-Dilumat-4-...

BIO DILUTOR BASIC with handgrip for tips, complete liquid circuit with bottle,10 ml syringe and box
http://www.lennox.ie/pp/Microbiology/Bio_Dilutor/Bio_Dilutor...

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Note added at 55 mins (2011-06-02 10:50:23 GMT)
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The Compu-pet 100 diluter/dispenser is a versatile and accurate instrument which can be employed for a wide variety of microbiological tests and techniques. Time in performing tests is often more than halved when the diluter is used. Large numbers of tests can be performed with minimal fatigue.
http://jcp.bmjjournals.com/content/28/1/37.abstract

The Smart Dilutor is a gravimetric dilutor and liquid dispenser. The device makes initial sample diluting in microbiology labs a fast, precise, and easy process.
http://www.youtube.com/watch?v=Bc8CgpCD3Ys