Errors from incomplete elution

The zone elution quantification method is tedious and time consuming and is likely to be inaccurate because of difficulties in locating the exact zone boundaries, loss of sorbent during scraping and collection, nonreproducible or incomplete elution from the sorbent, and background interferences due to eluted impurities from the sorbent. These errors are minimized if standards and samples are chromatographed, scraped, and eluted together as consistently as possible, and if an equal-size blank... 

The elution method involves scraping off the separated zones of samples and standards and elution of the substances from the layer material with a strong, volatile solvent. The eluates are concentrated and analyzed by use of a sensitive spectrometric method, gas or liquid column chromatography, or electroanalysis. Scraping and elution must be performed manually because the only commercial automatic micropreparative elution instrument has been discontinued by its manufacturer. The elution method is tedious and time-consuming and prone to errors caused by the incorrect choice of the sizes of the areas to scrape, incomplete collection of sorbent, and incomplete or inconsistent elution recovery of the analyte from the sorbent. However, the elution method is being rather widely used (e.g., some assay methods for pharmaceuticals and drugs in the USP Pharmacopoeia). 

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