Nebulizers - choosing the right one

Whereas most ICP-MS users pump sample from 0.3 to no more than 1.0 mL/min, the majority of ICP-OES users work at 0.8 to no more than 1.5 mL/min. In both cases, it makes sense to user a nebulizer intended for the corresponding flow rate range.

Here in Lab-Club you'll find the most direct equivalent to the product recommended by the instrument manufacturer. For most of our Meinhard nebulizers we do, however, offer numerous options. Where these are available, it's mentioned in the description of the recommended product.

Most ICP-MS manufacturers recommend a nebulizer with a flow rate of either 0.5 mL/min or 1.0 mL/min. Usually, 0.2 (or less), 0.3, 0.5, and 0.7 mL/min are available as options. The recommendation is based on two things:

a) that the user is most likely to find out for himself what is best for his analysis

b) what the instrument manufacturer knows is best to demonstrate that the instrument meets factory specifications for limits-of-detection, etc.

In reality, most ICP-MS use a solution flow that ranges from 0.3 mL/min to as much as 0.7 mL/min. A higher liquid flow is unusual today, but was common up until around the turn of the century.

Can using a nebulizer with a higher flow-rate damage your ICP-MS instrument? The simple answer is No. But, if sample is pumped at more than 2 mL/min, oxides will skyrocket, signals will diminish due to plasma loading and limits of detection will be seriously degraded. The ICP-MS basically responds to mass per unit time and, in general, as the sample delivery rate to the nebulizer falls, the delivery rate to the cones falls much more slowly because nebulizer performance changes.

There are limits to what can be done with a given nebulizer in terms of the rate of sample delivery to it. In general, the nebulizer will become somewhat more efficient as the solution flow rate is decreased from the natural aspiration rate. At some point, however, the aerosol will begin to pulse because the rate of delivery of liquid is too low compared to the dimensions of the nozzle. This typically happens at something less than half the natural aspiration rate. So, for example, a TR-50-C0.5 can be pumped at less than 0.2 mL/min to as much as 1 mL/min with no concern, but outside that range it would be essential to study the noise level.

A primary difference between ICP-MS and ICP-OES is the magnitude of the background, which is much greater in ICP-OES. At the same time, oxide formation is not a concern in ICP-OES. As a result, modern ICP-OES instruments generally use a rate of sample delivery that ranges from 0.7 mL/min to no more than 2 mL/min. There are instances where more than 2 mL/min might be used, as well as analyses where less than 0.7 mL/min might be used (for example, volatile organic solvents). It should also be noted that - while this is less the case in Europe - instrument operators only rarely explore possibilities that lie outside the guidelines provided by the instrument manufacturer. So, while there are many options, we, as previously mentioned, recommend our most direct equivalent to whatever it is that the instrument manufacturer recommends.