On-line sequential injection-capillary electrophoresis for near-real-time monitoring of extracellular lactate in cell culture flasks

• Automated sequential injection capillary electrophoresis for bioprocess monitoring.
• Determination of lactate in media with intraday electrophoretic mobility RSD 0.07%.
• Requires only 1.99 mL of sample for 228 analyses (every 20 min over 3 days).
• Special sampling interface for sampling of cell-free media from adherent cell cultures.
• Provides a unique insight in changes in metabolism and cell health over time.

Cell culture has replaced many in vivo studies because of ethical and regulatory measures as well as the possibility of increased throughput. Analytical assays to determine (bio)chemical changes are often based on end-point measurements rather than on a series of sequential determinations. The purpose of this work is to develop an analytical system for monitoring cell culture based on sequential injection-capillary electrophoresis (SI-CE) with capacitively coupled contactless conductivity detection (C4D). The system was applied for monitoring lactate production, an important metabolic indicator, during mammalian cell culture. Using a background electrolyte consisting of 25 mM tris(hydroxymethyl)aminomethane, 35 mM cyclohexyl-2-aminoethanesulfonic acid with 0.02% poly(ethyleneimine) (PEI) at pH 8.65 and a multilayer polymer coated capillary, lactate could be resolved from other compounds present in media with relative standard deviations 0.07% for intraday electrophoretic mobility and an analysis time of less than 10 min. Using the human embryonic kidney cell line HEK293, lactate concentrations in the cell culture medium were measured every 20 min over 3 days, requiring only 8.73 μL of sample per run. Combining simplicity, portability, automation, high sample throughput, low limits of detection, low sample consumption and the ability to up- and outscale, this new methodology represents a promising technique for near real-time monitoring of chemical changes in diverse cell culture applications.