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The Enhanced Parallel Path Method

US Patent # 6,634,572, Canadian Patent # 2,384,201

Burgener Nebulizers use the patented Enhanced Parallel Path Method. They work on the basic principal that any body of liquid can be used to produce a fine mist with a gas stream, if they are in close proximity to each other. It is not necessary to have a critical alignment of the gas stream and the liquid. This understanding allows us to produce a nebulizer with a very large opening for the liquid path, preventing the common problem of tiny particles in the liquid from plugging the sample path. Our nebulizers actually have the sample path increase in size near the gas stream, so that plugging is rare.

The Enhanced Parallel Path Method is a significant advancement on our original Parallel Path Method of atomizing liquids. Instead of just having the liquid near the gas stream and being inducted into the gas flow, the Enhanced Method uses a spout protruding into the gas stream. The surface tension of the liquid draws the liquid into the spout and the gas stream impacts the liquid, causing it to break up into small droplets.

The Enhanced Method does not use gravity or induction. As such, it has zero back pressure and zero suction, and operates equally well in any orientation. Babington V Groove designs use gravity to deliver the liquid to the gas stream. The Enhanced Parallel Path Method is not a Babington design.

This enhancement enables the liquid to interact with the gas stream in the central portion of the gas stream. Gas streams in capillaries have velocity gradients across the diameter of the capillary, with the slowest gas moving at the edges of the capillary and the fastest at the center. The central gas flow is 3 to 10 times as fast as the gas at the edge of the stream. If the central portion of the gas stream can impact the liquid, then the gas impacts the liquid with much more energy. Energy is related to the square of the velocity, so 3 to 10 times the speed is 9 to 100 times the energy. With such an increase in energy transfer from the gas to the liquid, the liquid is broken up into much smaller droplets. This produces a mist with average droplet sizes much smaller than any other method for the same gas flow and pressures. This significantly improves sample throughput to the torch, enables much lower flow rates than previously possible, and produces a more stable mist than previously possible.

Our design also allows us to fabricate the nebulizer out of TeflonŽ (PTFE, FEP & PFA). Teflon is essentially inert to laboratory chemicals, acids and solvents, and is practically non-wetting. This enhances the nebulizer's ability to operate with high dissolved solids. The common problem of salts forming around the gas stream does not occur with Teflon. Teflon does not wet and the salts do not form. There can be some salting with very high Sodium (Na) salts. This is a reaction between Na ions with the Fluorine in the Teflon, and can produce an insoluble salt in some instances. This is RARE: less than 1% of our nebulizer customers have reported this occurrence. For those that do experience this salting, it occurs at rates that are very much slower than with glass or sapphire nebulizers. And the salts can usually be washed off with a dilute HF acid wash.

Peek Mira Mist Tip closeup
Here is a comparison of a Burgener Enhanced Parallel Path nebulizer tip with a concentric nebulizer tip:

. Note that the gas orifice on the Enhanced Parallel Path Nebulizer is very much larger than the gas orifice on the concentric. Any salts forming on the concentric will easily plug part of the orifice. Any salts forming in the parallel path orifice have to be very large to have any effect on the gas flow, and usually such salts simply blow away.

Also note that the Enhanced Parallel Path design has a gas orifice is actually circular, and the path you see in the photographs is a spout that dips into the middle of the gas stream much like a tea-pot spout. The surface tension of the liquid fills the end of the liquid passage and also the spout, so that the liquid is touching the gas stream, and interacting directly with the center area of the gas stream.

Phenomenal Stability!
Smaller drop sizes is one benefit, but without consistency, it does not help. The Enhanced Parallel Path method allows a smooth, continuous flow of the liquid into the gas stream, pretty well regardless of how much liquid is flowing. For smaller flows, the spout needs to be more exactly made, but the method is the same for tiny or great flows.

Data from many tests show the benefits of the method. Following is a graph produced by Nathalie Le Corre, of JY Horiba, France. The test was run on a PEEK Mira Mist with 3% NaCl solution, for over 4 hours. In this test, the %RSD variation is always less than 1%. In comparison, most nebulizers are glass concentrics, and they generally plug up as the salts precipitate in the gas orifice. Typically a glass nebulizer will be unable to run 3% salt for more than an hour without plugging up totally, and they always drift badly as the salts form. To run for 4 hours without any drift, nor any loss in sensitivity, and to be able to maintain less than 1% RSD is unheard of with other nebulizers.

Smaller is Better!
Droplet size is very important in analytical and many other applications. For ICP and ICP/MS instruments, the droplet size determines both how much travels to the torch, and also how quickly the droplets vaporize in the plasma. The stability and intensity of the results improves significantly as the drops vaporize more quickly. Data from work by Akbar Montaser, of George Washington University and by John Olesik, of Ohio State University show the smaller droplet sizes of the Mira Mist compared to a standard Glass Concentric nebulizer.

Greater Sample Transport!
With smaller droplets, the vaporization is faster which improves the stability and sensitivity. It also can increase the amount of sample that is delivered to the torch. As the intensity and sensitivity of the instrument is directly related to the number of atoms in the plasma, higher transport rates improve the sensitivity as long as the droplets are small enough to easily vaporize. With the Mira Mist nebulizers, both factors are present: smaller droplets (as shown above) and higher transport rates as shown by the following comparison data from work by John Olesik, of Ohio State University:

For the above graphs, the nebulizers tested are:
Mira Mist: Burgener Parallel Path TR-50: Meinhard Concentric AR-35: Glass Expansion Concentric LFGC: Low Flow Gemcone GC: Gemcone

Note that although the % transport rates decrease as the sample flow increases, the actual total amounts delivered generally do increase. 4.3% of 0.5 ml is 21 ul; 3.3% of 0.75 ml is 25 ul; 2.9% of 1 ml is 29 ul; 2.1% of 1.5 ml is 31.5 ul; 1.7% of 1.8 ml is 30.5 microliters.

Note also that between 1 ml and 2 ml, the amount delivered to the torch is almost CONSTANT. This also helps improve stability as even large variations in the sample flow have very small effects on the amount of sample delivered to the torch, so the system stability is very high if the sample flow rate is in the 1.2 - 1.8 ml/min range.

Transport and size Data reported at FACSS 2002, by John Olesik, Ohio State University.