Capillary electrophoresis–mass spectrometry

[1] CE–MS combines advantages of both CE and MS to provide high separation efficiency and molecular mass information in a single analysis.

There are two common techniques to load the sample into CE–MS system, which is similar to approaches for traditional CE: hydrodynamic and electrokinetic injection.

[11] One of the main advantages of hydrodynamic injection is also that it is unbiased to molecules with high or low electrophoretic mobility.

The major problem faced when coupling CE to MS arises due to insufficient understanding of fundamental processes when two techniques are interfaced.

CE has been coupled to MS using various ionization techniques like FAB, ESI, MALDI, APCI and DESI.

Another key factor for successful CE–MS interface is the choice of buffer solution which must be suitable for both CE separation and ESI operation.

[14] Because no sheath liquid is used, the system has high sensitivity, low flow rates and minimum background.

The latest sheathless interface design features porous ESI emitter through chemical etching.

This porous emitter interface has been explored to couple of CITP/CZE (or transient ITP) which greatly improves sample loading capacity of CE and enabled ultrasensitive detection of trace analytes.

[15] High reproducibility, robustness and sensitivity were achieved in sheathless transient capillary isatochophoresis (CITP)/capillary zone electrophoresis (CZE) -MS interface, where conductive liquid was used.

In most popular commercial CE-ESI-MS interfaces an additional outer tube (three-tube coaxial design) with sheath gas is used, which help to improve electrospray stability and solvent evaporation.

Electrokinetic method allows one easily operate in nanoelectrospray regime (ESI flow rates at nl/min) and thus to improve sensitivity.

The outlet end of the separation capillary was treated with hydrofluoric acid to decrease thin of the wall and to taper the tip.

[18] Using nanoflow electrospray regime (with small emitters and ESI flow rates below 1000 nl/min) also helps in increase sensitivity, reproducibility and robustness.

For making this interface, borosilicate emitter with tapered tip and the separation capillary with etched end may be utilized.

[20] This technique uses a stainless steel tee to mix separation electrolyte from CE capillary with make up liquid.

The CE capillary and ESI needle are inserted through opposite sides of the tee and a narrow gap is maintained.

Body fluids like blood and urine have been analyzed with CE–MS to identify biomarkers for renal diseases and cancer.

Analysis of cells usually includes extraction of molecules with small amount (several μl) of organic solvent prior to the CE–MS.