In recent years, the use of PFA concentric nebulizers has grown rapidly, due to their greater efficiency, inertness and applicability to microvolume samples. Until now, they have been used predominantly for semiconductor applications, with ICP-MS. In designing the C-Flow PFA concentric nebulizer, Savillex have used all their PFA molding expertise to make a range of nebulizers more reproducible in performance and more rugged than other PFA nebulizers. And with the new C-Flow 700d and 400d/e, they have produced the first truly universal nebulizers – tolerant of very high matrix samples and with a wide sample uptake range, in addition to the usual C-Flow benefits of high sensitivity, ultralow blank, zero dead volume, fast washout and unmatched chemical inertness.
C200 showing aerosol formation
The design features that set the C-Flow apart from other nebulizers are:
The Savillex C-Flow PFA concentric nebulizer range features two general purpose d-type versions: C400d/e for ICP-MS and C700d for ICP-OES. These nebulizers are suitable for all non-semiconductor applications, feature removable uptake lines (80cm long) (except for C400e) for maximum flexibility and are designed to be pumped. The C400 is optimized for operation with ICP-MS at 400uL/min sample uptake rate and 1SLPM gas flow. The C700d is optimized for operation with ICP-OES at 700-1000uL/min sample uptake rate and 0.6SLPM gas flow. Completing the C-Flow range are four low flow rate “microconcentric” versions: the C200, C100, C50 and C35, with free aspiration uptake rates of 200, 100, 50 and 35 uL/min respectively. The microconcentric versions are used exclusively with ICP-MS and predominantly in free aspiration mode, for semiconductor analysis and other low sample volume applications (typically in geochemistry), and also with desolvation devices such as the CETAC Aridus II. The microconcentric versions are also available with integrated autosampler probes and different uptake line lengths for use with the following autosamplers: Agilent I-AS (70cm uptake line), ESI SC (90cm uptake line) and CETAC ASX110/112 (90cm uptake line). All C-Flows have a 6mm outer diameter body to fit standard spray chamber end caps.
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 . 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 . 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.
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. Our 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.
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.
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.
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.
Clearing a blockage by backflushing a C-Flow – no need for tools or wires. Simply place a gloved finger over the tip while Ar nebulizer gas is flowing.
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