The HP/Agilent Co-axial sheath-liquid flow CE-MS interface - 1

Smith and co-workers were the first to propose the co-axial delivery of a solvent to the end of the CE separation capillary as a terminal electrolyte reservoir [see references here].

Based on this work and an already available ESI-sprayer for LC-MS engineers at Hewlett-Packard developed  a triple tube sprayer IF for CE-MS which was introduced to the market in 1995. A pictorial view of the HP/Agilent triple tube sprayer is given in the figure below. The arrows in the l.h.s. picture A, have following meanings: a. introduction of nebulising gas (N2), b. delivery of the sheath solvent, c. standard CE separation capillary (fused silica 365 µm o.d. and 25-100 µm i.d.) filled with BGE, d. SST spray needle (0.5 mm o.d., 0.4 mm i.d.)with electrical ground connection f, e. outer tube. The r.h.s. picture B shows the actual sprayer. The ribbed ring in the middle allows adjustment of the CE capillary in axial direction. The sprayer is placed in an enclosure (source) which is mounted in front of the MS inlet and thus allows to isolate the spray from environmental disturbances (see visualization on following pages).

The HP/Agilent Co-axial sheath-liquid flow CE-MS interface - 2 

The development of Agilent (Hewlett-Packard) CE-MS interface has been paralleled by development of chromatography data system and mass spectrometry software that control CE separation parameters, MS data acquisition, data processing and automation. At introduction of CE-MS in 1995, control of interface parameters, MS data acquisition and data processing was embedded in one of the first graphical users interfaces (GUI) for the G1600 series 3D High Performance Capillary Electrophoresis system. The mass spectrometer in the system was a single quadrupole mass analyzer driven by the ChemStation. The 6000 series of Agilent MS instruments introduced 2006 were driven my the MassHunter software separate from the Chemstation. Meanwhile the MassHunter software controls the Agilent CE as well resulting in two integrated CE-MS platform systems. In the figure below, import details of the Agilent CE-MS system coupled with aTOF MS are displayed.

The HP/Agilent Co-axial sheath-liquid flow CE-MS interface - 3

Important additional aspects of the triple tube CE-MS interface

In the co-axial sheath-liquid flow interface design, sensitivity will become compromised for the following reasons.

  1. Since the sheath-liquid flow rate is high (1-10 µL/min), the benefits of running the separation in the nanoflow rate regime on ESI (20 - 200nL/min), like sensitivity enhancement and reduction of ion suppression are lost.
  2. In addition, depending on the ratio of the sheath-liquid flowrate and EOF, the analytes leaving the CE-capillary will become diluted 10-50 times.