96 Well Deepwell
Page 3 of 3
Are your plates whiter than white?
Or do they harbour a dirty secret?
Deep well polypropylene microplates are commonly used for sample storage in life science laboratories. An essential aspect of the manufacture of these plates is the selection of clean raw materials for injection moulding. Polypropylene is an inert and heat resistant material, ideal for sample storage. However, all grades of polypropylene are not the same, for example, Injection moulding grades of polypropylene often have high concentrations of chemicals to aid the moulding process. This allows rapid production of plates and lower costs, but may compromise the integrity of samples or compounds which are stored in such plates for extended periods. The
problem is particularly acute where compounds are stored as solutions in solvents such as methanol or DMSO, as these excellent solvents have a tendency to extract from the polypropylene base material any added extractable compounds such as mould release agents or polymer flow improvers.
Porvair Sciences has carried out tests on many manufacturers’ deep well plates to establish levels of extractables in each. A typical example is illustrated. Extractables testing was performed by adding a volume of methanol, sufficient to half fill the wells to each test plate. An internal standard comprising methanol spiked with 10 mg/ml of caffeine was used to give a consistent peak. Samples were taken from each well and subjected to analysis on a GC-MS system with splitless injection @ 250°C, using an HP - 5MS capillary column. A temperature gradient was programmed such that:
Initial temp: 70°C Hold 2 min
Final temp: 310°C Hold 5 min
Results from the GC-MS showed good performance from the Porvair microplate, with a clean caffeine peak and no significant levels of leachable or extractable compounds. Plate B shown here, is a typical example of the other commercial microplates tested, which included two major German manufacturers and several other well-known suppliers. These variously displayed extra peaks with a variety of retention times across the run, indicating several different contaminants. Further analysis of these extra peaks revealed that they were, indeed, mostly recognized chemicals used as additives in the polypropylene to assist the injection moulding process. From this it can be seen that it is essential to select the correct grade of polypropylene material for storage plate manufacture. The full report can be downloaded from our website.
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