Chapter 4

Capillary zone electrophoresis (CZE) offers an alternative to agarose gel electrophoresis for the detection and quantification of serum proteins. Protein separation is performed in a liquid buffer system running through narrow-bore capillaries made of fused silica. The separated proteins pass an ultraviolet detector that measures absorbance at 200 to 215 nm to determine the protein concentration.

Electrophoretograms generated by CZE are similar in appearance to those produced by SPE, and can be used for monoclonal protein quantitation (in combination with serum total protein measurements) (Figure 4.2). Katzmann and colleagues [123] reported a good correlation between monoclonal protein concentration obtained by CZE and SPE for values <20 g/L, but above 20 g/L, values for CZE tended to be greater.

The main advantage of CZE over SPE is that it is an automated technique with faster throughput. In addition, most [123][124][125], but not all [126] reports conclude that capillary-based methods have slightly higher sensitivity than agarose gel-based electrophoresis (Table 4.1). The superior sensitivity of CZE over SPE has been shown to identify additional cases of monoclonal serum free light chains (sFLCs) and small monoclonal protein peaks in either the β-region or on a polyclonal background [123][124][125].

MethodAnalytical sensitivity
SPE ~0.5 g/L
sIFE 0.1 g/L
UPE 20 mg/L
uIFE 3 - 5 mg/L
CZE 0.25 g/L
Total κ and λ ~4 g/L
sFLC 0.25 - 3 mg/L*

Table 4.1. Detection limits for various methods used to detect monoclonal immunoglobulins. Based on manufacturers’ information and published studies [119][127][128]. UPE: urine protein electrophoresis. * This is the analytical sensitivity of FLC measurement and not the limit for detection of monoclonal FLC, which is dependent upon the presence of an abnormal κ/λ sFLC ratio.