There are many reasons to consider using contract labs for analysis with LC/MS. The three primary reasons are 1) you have too few samples, 2) you have too many samples, or 3) you need specialized equipment. Some organizations may not have the sample volume to justify the budget expenditures and resources to perform LC/MS sample analysis in-house. Some organizations may not have the capacity from time to time to handle a given sample load (over-capacity). Some organizations may not have specialized equipment to solve a particular problem (e.g. high resolution).

Above is a list of labs that provide analysis in LC/MS with contact information. Note that most major universities have mass spec facilities and are usually available for analytical support; particularly for a small number of samples. For larger volumes of samples, private labs are usually better equipped to meet your sample and reporting requirements
http://www.lcms.com/samples.htm

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Note added at 5 mins (2005-07-08 09:04:49 GMT)
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et on peut ajouter, comme le mentionne Philippe, sous contrat