Just a thought: If there is any backflushing going on in the system (sheath flowing back through the sample lines in between samples), the first events from a new sample will be exposed to pure water. Cell lysis may occur. The lysed particles are likely to be near the wall of the sample tubing where the sample buffer equilibrates last. Consequently one can expect a prolonged release of lysed cells into the sample that is being measured. Alternatively, low salt concentrations could induce protein denaturation and aggregation. Could sample / sheath fluid mixing be an explanation for increased background particles? If so the noise shoulf slowly disappear. In my experience equilibration in narrow sample lines is a slow process. It can easily take 10-20 minutes before a sample has pushed all sheath fluid remnants out of the sample tubing. Ger van den Engh UW Seattle
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