NEWS Figure 6: All glass spray chamber with broken nebulizer While this design was generally satisfactory, there was a tendency for the o’ring to bond to the glass nebulizer. If this happened, the nebulizer could be difficult to remove, and it was not uncommon for the ICP analyst to break either the spray chamber arm or the nebulizer, see Figure 6. The introduction of the plastic nebulizer adaptor, as shown in Figure 5B, made the spray chamber much more robust and alleviated the problem of the spray chamber arm being broken. However, this design still relied on o’rings, and the problem of the o’rings bonding to the nebulizer remained. Also, there is no o’ring material that is impervious to all of the solvents used with an ICP. In particular, some organic solvents cause the o’rings to degrade rapidly, leading to potential contamination and necessitating frequent o’ring replacement. The new Helix, shown in Figure 5C, eliminates all of the problems with the previous designs. A smooth lock and release mechanism enables the nebulizer to be simply and easily inserted or removed (visit our video page for an instructional video). The Helix seal is made from Teflon, which is totally inert to all of the organic solvents and strong acids normally used in ICP analyses. This minimizes any possibility of contamination. The collar of the Helix provides a positive stop for optimal and reproducible nebulizer positioning. Helix Washout: Another important design feature of the Helix is the elimination of dead volume around the nebulizer seal. Eliminating dead volume leads to faster washout times and higher sample throughput. Figure 7 compares the time required to washout a 10ppm Molybdenum standard with a Glass Expansion spray chamber (Helix interface) and a “Brand-X” spray chamber with an o’ring interface. The results show that with the Helix nebulizer interface a 10ppm standard can be washed out in as little as 4 seconds, whereas “Brand-X” takes 16 seconds. One can expect this time to significantly increase for more troublesome or “sticky” elements that are more prone to carryover issues. Spray Chamber Maintenance Glass and Quartz Spray Chambers: It is good practice to always start and finish use of a glass spray chamber by nebulizing a mildly-acidic blank solution for several minutes. This ensures that sample deposits or crystals don’t form inside a spray chamber when the solvent inside the chamber dries out. To avoid the risk of breakage, washing glass spray chambers in an ultrasonic bath is not recommended. If you notice a degradation in performance (such as poorer precision or detection limits), then clean the spray chamber with Fluka ‘RBS- 25’ (P/N FLUKA25). In the first instance, aspirating a 2.5% Fluka solution for 15 minutes will probably be sufficient to recover the performance. However, if this is not effective, the spray chamber should be soaked overnight in a 25% Fluka solution. If you see droplets collecting on the internal surfaces of your spray chamber, this is a sure sign that stability is suffering - such ‘resident’ droplets in the spray chamber are the most common and visible indication of spray chamber instability, and they should be removed. A long soak in 25%-strength RBS-25 solution is recommended. PTFE and PFA Spray Chambers: The PTFE and PFA spray chambers have an internal surface that is specially treated to ensure that it wets evenly and provides consistent drainage. The treatment turns the surface a characteristic brown color. It should be noted that the treatment actually changes the molecular structure of the PTFE and PFA. It is not a coating and it does not introduce any potential contaminants. While the surface treatment is long lasting, it may degrade after prolonged use. The lifetime of the treated surface depends on the type of samples used and could range from several months to several years. To ensure that you get the best performance from your PTFE and PFA spray chambers, we recommend the following: Do not use H2O2 for cleaning the spray chambers as this will accelerate the degradation of the surface. Do not make physical contact with the chamber interior surface with any instrument, including your hands or a brush. Do not be concerned if the brown color fades over time. This is normal and does not necessarily lead to a degradation in performance. If you notice a degradation in performance (such as poorer precision or detection limits), then clean the spray chamber with Fluka ‘RBS- 25’. In the first instance, aspirating a 2.5% Fluka solution for 15 minutes will probably be sufficient to recover the performance. However, if this is not effective, the spray chamber should be soaked overnight in a 25% Fluka solution. Eventually the surface may degrade to the point where it does not recover after soaking in Fluka. At this point the spray chamber needs to be returned to Glass Expansion where the surface can be Figure 7: 10 ppm Mo Washout comparison between Helix and non-Helix spray chambers re-treated for a nominal cost. www.geicp.com Glass Expansion Newsletter | Issue 35 4
GE0283 GE Newsletter October 2014
To see the actual publication please follow the link above