Monitoring of biologically active substances in clinical samples by capillary and microchip electrophoresis with contactless conductivity detection: A review.

Contactless conductivity detection (C4D) as a universal detection technique plays an important role in combination with efficient electrophoretic separation carried out in capillaries (CE) or on microchips (ME) in the analysis of clinical samples. C4D is particularly sensitive in the quantification of low molecular weight biogenic substances such as inorganic cations and anions, amino acids, amines, low molecular weight organic acids, saccharides and many drugs such as antibiotics, analgesics, anaesthetics or antiepileptics. Biogenic substances are determined in CE/C4D or ME/C4D directly in their native form without derivatization and sample matrix treatment is often based only on dilution or addition of an organic solvent. The limit of detection for most CE/C4D determinations is at the micromolar concentration level, which is sufficient to monitor physiological or therapeutic levels of most of low molecular weight biogenic substances. Therefore, CE/C4D and ME/C4D are widely used for sequential monitoring of nutrients, metabolites and waste products at the level of individual tissues and organs, low-invasive detection of inborn errors of metabolism and cystic fibrosis, pharmacokinetic monitoring and therapeutic drug monitoring. Innovative trends such as electrophoretic stacking, microdialysis, electromembrane extraction, portable and disposable CE instruments and minimally invasive clinical sampling techniques are mentioned. A critical evaluation of the positives and negatives of this technique is presented, covering the main applications published over the last 10 years.