Oscillating capillary nebulizer

#The present invention relates to a method and apparatus for generating an aerosol and, more particularly, an oscillating capillary nebulizer which is capable of nebulizing a liquid flow at microflow liquid flow rates and controlling the particle size and the particle size distribution of the nebulized particles.

#Typical pneumatic nebulizers, such as the Meinhard TR 30-C3 nebulizer, operate at liquid sample flow rates of about 500 .mu.l/min or greater. The Meinhard nebulizer consists of a rigid inner glass capillary tube drawn to a fine tip, surrounded by another glass tube drawn concentrically to a conical tip. The nebulizer operates through the interaction of a liquid stream in the inner capillary and a gas stream in the annular space between the capillary tubes causing droplet formation. The Meinhard nebulizer suffers from a number of drawbacks, including that it tends to block up due to its converging tip. Once blocked, it is usually discarded.

#Nebulizers which employ parallel coaxial tubes tend to avoid blockage problems. One such nebulizer is that of the application GB 2 203 241 to Willoughby et al. In this nebulizer velocity of the entraining gas combined with thermally induced solvent evaporation serves to cause a breakup of the liquid sample jet into liquid particles to produce an aerosol. This nebulizer is described to operate over liquid sample flow rates from 10-2000 .mu.l/min. However, such nebulizers are not known to work well at low liquid flow rates or when the end of the inner capillary tube extends out beyond the end of the outer capillary tube. By low liquid flow rates, we mean 500 .mu.l/min or less. This nebulizer is not described to cause an oscillation of the capillary tube by creating instability in the system, but rather describes that the aerosol is created by the combination of the entraining gas velocity and liquid sample heating. Another example of a known nebulizer which incorporates a coaxial tube arrangement is disclosed in U.S. Pat. No. 4,924,097 to Browner et al.

#FIG. 1 illustrates a cross-sectional side view of the oscillating capillary nebulizer of the present invention.

#FIG. 2 illustrates a cross-sectional view of the coaxial arrangement of the inner and outer capillary tubes of the present invention.

#FIG. 3 illustrates a trace of the ultrasonic wave observed on the inner capillary tip of the oscillating capillary nebulizer of the present invention.

#As shown in FIGS. 1 and 2, the oscillating capillary nebulizer of the present invention is comprised of a pair of coaxial inner and outer capillary tubes 1, 2. The capillary tubes are friction-fit mounted by way of PEEK tubing ferrules 3 and 4 near their proximal ends 10 and 12, respectively. This fitting allows for interchangeability and replacement of capillary tubes. Liquid sample introduction, generally from a liquid chromatography, is provided by liquid flow path 5 via the inner capillary tube 1. A gas flow path is provided by the annular space 6 between the outer diameter of the inner capillary tube 1 and the inner diameter of the outer capillary tube 2. The gas enters the gas flow path through an port 8 in the side of the outer capillary tube. At least the inner capillary tube 1 is made of a flexible material, preferably polyamide coated fused silica (Polymicro Technology, Inc., which adds flexibility and makes the tubing less brittle). The outer capillary tube 2 may also, but need not, be made of a flexible material. The dimensions of the inner capillary tube 1 are such that a flow of the liquid sample is provided at flow rates as low as 50 .mu.l/min. and less.

#A connector 11 is shown for allowing connection of the liquid sample input of the nebulizer to a ZDV union. The nebulizer is further constructed with a rotating connector ring 12 sealed by O-ring 13.

#With reference to FIG. 2, the inner and outer capillary tubes are arranged to provide relative movement between them in the axial directions. Preferably, a rotating connector ring or fitting 9 allows the outer capillary tube to be moved in the axial direction such that the distance that the distal end 40 of the outer capillary tube 2 extends in relation to end 7 of the inner capillary tube 1 can be adjusted.