Extended Path-Length Capillaries

In CE detection is performed on-column, so the detection cell is defined by the diameter of the capillary. Because sensitivity is proportional to the path length, sensitivity of absorbance methods is limited. Thus, capillary 

Polymer Hydrophobicity/ hydrophilicity Hydrogen-bonding capacity 

Poly(ethylene-propylene glycol) (Ucon) Weakly hydrophilic Low 

Poly(hydroxypropyl cellulose) (HPC) Strongly hydrophilic High 

Many of the detectors used in HPLC have been adapted for use in CE. This has been a major challenge, as the highly efficient separations afforded by CZE are a direct result of employing extremely narrow separation columns. Narrow inner diameter capillaries are required to provide effective dissipation of the heat generated by the passage of electrical 

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Figure 4 Separation of a standard sample containing 13 food additives. Peak identification , caffeine 2, aspartame 3, sorbic acid 4, benzoic acid 5, saccharin 6, green S 7, acesulfame K 8, sunset yellow FCF 9, quinoline yellow 10, brilliant blue FCF 11, carmoisine 12, ponceau 4R 13, black PN. Conditions fused-silica capillary 50 m i.d. x 48.5cm with x3 extended path length detection cell separation buffer, 20mmoll carbonate, pFI 9.5, containing 65mmoll SDS applied voltage, 20kV temperature, 25°C.

Ro, K.W., Shim, B.C., Lim, K., Hahn, J.H., Integrated light collimating system for extended optical-path-length absorbance detection in microchip-based capillary electrophoresis. Micro Total Analysis Systems, Proceedings 5th pTAS Symposium, Monterey, CA, Oct. 21-25, 2001, 274-276. 

Ro KW, Lim K, Shim BC, Hahn JH (2005) Integrated light collimating system fra- extended optical-path-length absorbance detectirai in microchip-based capillary electrophOTesis. Anal Chem 77(16) 5160-5166... 

Z-cell introduces a flow through chamber parallel to the excitation beam, extending the path length to 1 mm. The ID of the bubble cell is widened at the detection point. The surface of the capillary can be coated with a reflective coating to make a detection cell where the excitation beam crosses the capillary multiple times. All these approaches offer a modest improvement in sensitivity at the expense of an increased detection volume, which can increase the observed width of the analyte peaks. 

Detection in electromigration techniques is normally carried out by UV detection. In spite of its widespread use, UV detection offers limited concentration sensitivity for CE and related techniques, owing to the extremely short optical path lengths afforded by the small inner diameters of the capillaries. To maximize sensitivity, detection is often performed at low wavelengths such as 200 nm or using an extended Ught path (bubble cell) or high sensitivity cells. "- ... 

Farina et have used both CE and HPLC for the determination of Ceftazidime (cephalosporin antibiotic) and its degradation products. The CE separation was performed using a micellar media. Specifically, separation was achieved using a 64.5-cm (56-cm effective length) x 50- JLm fused-silica capillary with extended light path, a buffer consisting of 25 mM sodium borate, pH... 

In Reference 53, a CD-modified CE method was developed for the separation of frovatriptan using SBE- -CD as CS. A 50-p,m i.d., bare fused-silica capillary with an extended light path (bubble-cell capillary) and an effective length of 72 cm was used. At optimized conditions, a BGE with a 50-mM phosphate buffer with pH 7.0/ACN 90/10 (v/v), containing 20-mM SBE- -CD, and the frovatriptan enantiomers were separated with a resolution above 3. 

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