ARGON HUMIDIFIER continued Concentric Nebulizer with 25% TDS Tolerance Nebulizer without Elegra Figure 3 – Elegra nebulizer stress test (see text for details).
dilution of the sample prior to introduction into the plasma greatly improves the plasma robustness, enabling improved analysis of high-matrix samples by ICP-MS. High-matrix samples also need to be diluted for ICP-MS analysis to prevent the rapid buildup of salt deposits on the interface cones, which would otherwise result in signal drift and frequent cleaning. Use of aerosol dilution rather than offline dilution of the samples4
prevents errors
associated with manual sample preparation. The Elegra Dual model allows for humidifica- tion of both the nebulizer gas and dilution gas for these types of ICP-MS setups. This helps
to prevent nebulizer and injector blockages, while the moisture added to the dilution gas further improves plasma robustness.3
Experimental As mentioned above, it is important to select
the proper nebulizer when dealing with high TDS. The SeaSpray and DuraMist concentric- style nebulizers are well-suited for handling high dissolved solids. A self-washing tip on the SeaSpray tolerates up to 20% for the most common salts. The DuraMist is a PEEK nebulizer capable of handling up to 30% TDS and is resis- tant to hydrofl uoric acids (HF).5
Nebulizer with Elegra
To evaluate performance, a nebulizer stress test was performed by aspirating a 25% NaCl solution while monitoring the nebulizer gas flow with and without the Elegra (Figure 3). The NaCl solution was aspirated continuously with no rinsing. Typically the Conikal nebulizer (Glass Expansion) would not be recommended for use with a high-TDS matrix because it has a tolerance of up to 5% TDS. However, it was used here to demonstrate the Elegra’s performance. As expected, the nebulizer was completely clogged after only 5 minutes of aspirating the salt solution without the Elegra. In contrast, the nebulizer held a relatively constant gas flow throughout the entire test (over 30 minutes) with the Elegra; the added moisture from the humidifier prevented the nebulizer from clogging.
Matrices like lithium metaborate fusions can pose a challenge even when a suitable high- TDS nebulizer is used. The high amount of dissolved solids in such matrices often requires frequent nebulizer maintenance. Extended analyses are often rerun due to a drift in signal from the slow buildup of salts. An easy way to eliminate drift and frequent nebulizer mainte- nance is to add the Elegra. A high-throughput contract laboratory evaluated the Elegra with its lithium metaborate method on an ICP optical spectrometer. The stability of three internal standard (IS) lines was compared with and without the humidifi er (Figure 4). Without the Elegra, the IS signal began to drift after
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