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Why does the height of one or more peaks change between different runs?

a.) One or more sample components deteriorated or column activity changed.

Solution: Use fresh sample or standard to confirm sample as source of problem. If some or all peaks are still smaller than expected, replace column. If new column improves analysis, try to restore the old column, following appropriate procedure. If performance does not improve, discard old column. b.) Changes in the sample preparation process. Differences in the matrix can affect peak heights. Solution: Check sample preparation process and eliminate matrix effects as cause of problem. c.) Leak, especially between injector port and column inlet. (Retention also would change.) Solution: Check system for loose fitting. Check pump for leaks, salt build-up, and unusual noises. Change pump seals if necessary. d.) Inconsistent sample volume. Solution: Be sure samples are consistent. For fixed volume sample loop, use 2-3 times loop volume to ensure the loop is completely filled. Be sure automatic sampler vials contain sufficient sample. Check syringe-type injectors for air. In systems with wash or flushing step, be sure wash solution does not precipitate sample components. e.) Detector or detector setting changed. Solution: Please check the settings. f.) Weak detector lamp. Solution: Please replace the lamp. g.) Contamination in detector cell. Solution: Please clean the cell.

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Based in Berlin, KNAUER has been serving the sciences since 1962. We develop and manufacture scientific instruments of superior quality for liquid chromatography systems and components, including:

Analytical HPLC / UHPLC
Preparative HPLC
Fast protein liquid chromatography (FPLC)
Multi-Column Chromatography / SMB
Osmometry

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