C-FLOW Technical Features
The critical design area of a PFA concentric nebulizer is between the end of the capillary (inside the nebulizer body) and the orifice at the tip. With conventional glass concentric nebulizers, liquid sample exits the capillary at the nebulizer tip, where the flow of carrier gas shears the liquid in a process called prefilming, creating a thin film of liquid. The gas flow then converts the liquid into an aerosol by the venturi effect. With PFA concentric nebulizers, the capillary terminates several mm behind the nebulizer tip, and so prefilming takes place inside the nebulizer body [1]. The more efficient gas-liquid interaction results in a smaller mean droplet size (~9um) with a narrower size distribution, so transport to the plasma and drying and decomposition are more efficient than with glass concentric, V-groove, cross flow and parallel path nebulizers [2]. In designing the C-Flow, special attention was paid to the positioning of the capillary inside the nebulizer tip - to optimize performance and reproducibility in sample uptake rate.
C-Flow Design - Body
Unlike all other PFA nebulizers, the C-Flow is unique in that the body assembly is comprised of two parts: an outer body and an inner support (both are molded PFA) that supports the capillary. Savillex’s molding expertise allows for the parts to be manufactured to extremely tight tolerances. The photograph below shows the two components prior to assembly. Note the quality of the molding and finish. The 4mm nebulizer gas fitting is shown connected to the outer body.
C-Flow nebulizer prior to assembly, showing outer body and inner capillary support.
C-Flow Design - Tip
The C-Flow is unique among PFA nebulizers in that the capillary is physically supported all the way to the inside of the nebulizer tip and the capillary is positioned centrally within the body, making it the only PFA nebulizer that is a true concentric nebulizer. The design requires highly accurate moldings to ensure the inner support axially aligns with the orifice. Savillex’s unique molding expertise and design capabilities make this design possible. Because the capillary is positioned with very high accuracy and precision, it enables the shape of the orifice to be optimized to give uniform, high gas velocity around the capillary, which makes the C-Flow resistant to salting at the tip. This is especially important with the C-Flow 700 high solids version. The benefits of the unique tip design of the C-Flow are also important at ultra low flow rates where reproducibility in performance is critical. Operating at 50uL/min, the C-Flow 50 offers reliable, reproducible performance not seen in other ultra low uptake rate nebulizers. The design is shown in detail in the drawings below.
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C-Flow drawing showing inner support (blue) |
Close up of C-Flow tip, showing the capillary (red) protruding into the space behind the orifice. |
Ar carrier gas flows around the inner support, forming an annular gas stream around the end of the capillary. The capillary protrudes into space behind the tip, several mm from the orifice itself. As sample liquid exits the capillary, the annular gas stream shears the liquid, causing prefilming around the complete inner circumference of the tip. Liquid/gas interaction and energy transfer is optimized, resulting in a very fine aerosol with narrow droplet size distribution. The high, annular gas velocity around the end of capillary also prevents salt deposition – even with very high TDS solutions.
High TDS Capability
The C-Flow 700 is designed for high solids use with ICP-OES and ICP-MS and has a large ID capillary, and a nominal uptake rate of 700uL/min. Below is a demonstration of the ability of the C-Flow 700 to tolerate high total dissolved solids (TDS) samples. A C-Flow 700 was pumped at approx. 500uL/min with a peristaltic pump. The nebulizer aspirated 25% w/v NaCl solution (saturated solution) from a container on a balance. The rate of aspiration of the salt solution was calculated by measuring the weight loss of the container with time, measured at intervals over 4 hours (see table). No humidifier was used. As can be seen from the consistent flow rate, no clogging or salt deposition occurred. The photographs below show the aerosol produced by aspiration of 25% NaCl solution, taken after 4 hours, and also the nebulizer tip directly after the completion of the experiment. No deposits were observed.
| 25% Salt Solution | |
| Time (hrs) | Uptake rate (g/min) |
| 0 | 0.487 |
| 0.5 | 0.482 |
| 1 | 0.481 |
| 1.5 | 0.480 |
| 2 | 0.478 |
| 2.5 | 0.478 |
| 3 | 0.475 |
| 3.5 | 0.474 |
| 4 | 0.475 |
Aspiration rate of C-Flow 700 vs. time: 25% NaCl
Aerosol (left), and nebulizer tip (right) after 4hrs aspirating 25% NaCl
A second experiment, designed to test the capability of the C-Flow 700 to aspirate particulate containing samples, was performed. Using the same set up as the salt test, the nebulizer aspirated a 5% solution of a NIST-traceable Megabead particle size standard containing 80uM diameter polystyrene microspheres. The solution was pumped at approx. 400uL/min and the weight loss of the container was measured over 4 hours. The rate of aspiration of the particle solution was calculated by measuring the weight loss of the container with time (see table). Photographs of the aerosol produced by the particle standard solution and the nebulizer tip after 4 hours are shown below. As can be seen, the solution aspirated cleanly with no loss in aspiration rate over the test period, demonstrating that the C-Flow 700 can handle samples containing particles up to 80uM in diameter - exceeding the specification of high solids glass nebulizers.
| 80uM Particulate Solution | |
| Time (hrs) | Uptake rate (g/min) |
| 0 | 0.409 |
| 0.5 | 0.407 |
| 1 | 0.405 |
| 1.5 | 0.405 |
| 2 | 0.402 |
| 2.5 | 0.401 |
| 3 | 0.399 |
| 3.5 | 0.398 |
| 4 | 0.400 |
Aspiration rate of C-Flow 700 vs. time: 80uM particulate standard
Aerosol of 5% w/v 80uM Megabead particle standard (left), and nebulizer tip (right) – both after 4hrs.
Constant ID Uptake Tubing
A limitation of most concentric nebulizers is the potential for blockages due to particulates in the sample. The C-Flow has an integrated uptake line and is unique in having constant ID uptake tubing from the sample, all the way to the tip. This is because the uptake tubing itself is actually the capillary at the tip. There are no connectors in the sample flow path, and no constriction near the tip, so the possibility of clogging is greatly reduced. If a blockage did ever occur, the C-Flow can be easily cleared by backflushing with nebulizer gas. With nebulizer gas switched on, a gloved finger is placed over the nebulizer tip which forces gas back down the uptake tube. Because the capillary is supported at the tip, it is not damaged by backflushing. And because there is no constriction at any point in the uptake line, any blockage would occur at the end of the tubing connected to the autosampler.
The C-Flow has zero dead volume because the sample uptake line is also the capillary. Unlike glass nebulizers there is no connection between uptake line and nebulizer body – so no additional dead volume to be washed out, which is a significant benefit for high throughput labs.
References
1. J.L. Todolí, J.M. Mermet, Spectrochimica Acta Part B 61 (2006) 239–283.
2. Liquid Sample Introduction in ICP Spectrometry. A Practical Guide. J.L. Todolí and J.M. Mermet, Elsevier. ISBN: 978-0-444-53142-1