HF Resistant Introductory System for ICP-OES

We have been working with Glass Expansion for almost two years now and have adopted their HF resistant sample introduction components for our Spectro Arcos and Ciros ICP-OES instruments. Working with an HF resistant introductory system has made our lives much easier in terms of analyzing samples with HF in the matrices. When using the all glass sample introduction system, we neutralized HF in the samples by adding triethanolamine (TEA). This approach worked well for us. Analyses returned accurate values for boron and silicon, which would have leached from the glass components without the neutralization step. On the other hand, the TEA neutralization step added extra work to the sample preparation and also left the ICP torch coated with the TEA residue. The HF resistant sample introduction system has allowed us to eliminate the TEA neutralization step, and still achieve very accurate boron and silicon results.

The main components of the HF resistant sample introduction system are the torch, transfer tube, spray chamber and the nebulizer.

Currently we are using the Glass Expansion D-TorchTM with alumina injector and ceramic outer tube on the Spectro Arcos (EOP). The D-Torch is a demountable ICP torch design that incorporates a ceramic intermediate tube for greater robustness and provides the analyst with an outer tube (quartz or ceramic) that can be replaced when it fails rather than replacing the entire torch. The ceramic outer tube is of particular benefit for the analysis of difficult sample matrices such as high total dissolved solids (TDS) and HF. The D-Torch also features an interchangeable injector, allowing you to choose a specific injector for each application whether aqueous, organics, high TDS or HF. Having a demountable torch also allows for easy maintenance and cleaning. On the Spectro Arcos we are currently using a 2.4mm i.d. alumina injector for HF containing samples. We can switch to a quartz injector if we are not concerned about HF, and are in the process of experimenting with a sapphire injector for higher purity. The D-Torch with alumina injector and ceramic outer tube has been a boon to our work with high TDS samples. We saw approximately 40% improvement in uncertainties, comparing a 2.2% TDS sample to a 3% TDS sample for the elements examined, when we switched to the fully ceramic D-Torch configuration from a semi-demountable torch (quartz torch body). You can see a full report of our collaboration in the Glass Expansion October 2013 Newsletter article, see link below.

http://www.geicp.com/site/GE_Newsletter/GlassExpansionNewsOct13

The interior surface of the PuraFlex transfer tube and Tracey TFE cyclonic spray chamber are treated with a proprietary process that makes the surface more hydrophilic so that a smooth liquid sheeting action results. The StediFlow treatment is exclusive to Glass Expansion, allowing for wetting of the surface, efficient drainage and minimizing carryover. We especially like the Helix nebulizer interface in the spray chamber, which eliminates O-rings, with use of an inert and chemically resistant PFA seal. The nebulizer fits very securely eliminating a source of leakage and the collar of the locking screw provides optimum nebulizer positioning.

The first step in installing the HF resistant components was to reduce the sample uptake rate. This was a necessary step because the HF resistant DuraMistTM nebulizer has a maximum flow rate of 1mL/min. Reducing the flow rate to 0.5mL/min or less, reduces the amount of sample necessary and also gave better relative standard deviation (RSD) for replicates. There are other HF resistant nebulizers available, but the DuraMist nebulizer was recommended to us for our applications, which include working with higher nitric or hydrochloric acid concentrations, dilute HF and high TDS. The DuraMist is a concentric nebulizer with a PEEK body and PFA capillary that can handle up to 5% HF and up to 30% TDS. To reduce our sample flow rate and maintain optimum precision, we reduced the i.d. of the peristaltic pump tubing from 1.02mm i.d. (white/white) to 0.38mm i.d (orange/green). We calibrated the peristaltic pump for an accurate determination of the sample flow rate, followed by optimizing the intensities and RSDs of a solution containing 2ppm Mn, As, and Pb. Optimum performance was achieved using a sample flow rate of 0.5mL/min = 40rpm on the Spectro Arcos. The RSDs for all elements in the optimization solution are below 0.5.

The most important product used in the cleaning and maintenance of the complete sample introduction system is Fluka RBS-25. This is a basic solution available through Sigma Aldrich or Glass Expansion. Glass Expansion recommends rinsing with 2.5% solution of the RBS-25 followed by deionized water rinse before shutting down the ICP. The StediFlow treatment on the transfer tube and spray chamber will deteriorate over time and with extended exposure to acids. We have found that performing the 2.5% RBS rinse at the end of analyses followed by an extended deionized water rinse, extends the life of the treatment and reduces daily maintenance. The lifetime of the treated surface will vary; for our laboratory we average one to two retreatments per year. You will know when the treatment is deteriorating by a worsening of the optimization solution elements’ RSDs and sensitivity. The components needing retreatment are sent to Glass Expansion and the process typically takes 2-3 weeks. We keep a backup set of the transfer tube and spray chamber on hand, so that we can continue to run our samples when sending out parts for retreatment. For thorough cleaning of all intro system parts, including your glass components, soak them overnight in a 25% RBS solution.

For the sake of full disclosure, we have observed some carryover issues with boron and silicon that may be coming from the alumina injector. This is still being investigated by switching to a sapphire injector.

The link below will take you to the Glass Expansion website (www.geicp.com) where you can view the components described here.

http://www.geicp.com/cgi-bin/site/wrapper.pl?c1=Productsbyinstrument&inst=Spectro%20EOP&appno=6

We hope this information is of help to you. Please contact us if you have any questions.