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A Look at the Most Critical Component of ICP-MS

What are sample and skimmer cones, why do they matter, and how can you reduce your operating costs without sacrificing performance?

by Alpha Resources
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A wide range of industries, from pharmaceutical to environmental and QC for metals, materials, and chemical industries rely on inductively coupled plasma mass spectrometers (ICP-MS) for high-sensitivity elemental analysis. These instruments use 9-10,000°C argon plasma to atomize samples and cone interfaces to transport those ions into high vacuum where the mass analyzer separates a selected element and allows detection at parts per trillion levels. 

This incredible sensitivity comes at a cost—cones, tubes, torches, tips, and lenses all require regular replacement. Replacement cones form a major operational expense for labs. Purchasing aftermarket replacements can help reduce costs, but the quality of replacements is critical to exacting performance. Here we examine cone design, maintenance, what to look for in replacements, and why.

What are cones, and how do they work?

ICP-MS cones form the interface between sample and plasma at atmospheric pressure and the high-vacuum mass spectrometer (MS) chamber. They extract ions from the plasma through narrow orifices and focus them into the MS through progressively higher vacuum. This is often a two-stage reduction—a sample cone with an approximately 0.5-1 mm diameter aperture gates the initial drop in pressure (down to 1-10 mbar), followed by a skimmer cone, typically with 0.2-0.5 mm diameter apertures, which leads into the detection chamber (10-6 mbar). Some MS instruments include a third cone, called a hyper skimmer cone, to provide a more gradual pressure drop through a three-stage reduction with larger orifices. 

Samples are normally prepared with acidic or alkaline diluents to reduce salt and solvent loads. Over time, cones will wear down and/or accumulate buildup that obscure the signals with high background and may considerably impact performance. Cones must be regularly cleaned and replaced to maintain data integrity. 

Clean or replace?

Cleaning frequency depends on cone design, instrument configuration, and sample type. Sample cones, exposed to plasma and a higher concentration of “dirty” samples, require more frequent cleaning than skimmer cones, while smaller apertures clog more readily than larger apertures. Three-stage instruments can usually run longer between cleans than two-stage instruments, sample dependent. Cones will accumulate common ions like lithium, boron, and magnesium, particularly if running any samples with high concentrations. Salts quickly build up—seawater samples, for example, can cause visible salt deposits within hours of running.

Illustration showing how ICP-MS works
Alpha Resources

The manufacturer-recommended cleaning protocols should be followed. These may involve a combination of DI water, cotton swabs, metal cleaners, nitric acid, isopropyl alcohol, and ultrasonic treatment depending on the type and degree of contamination. Blockages should never be cleared with force, which is highly likely to deform or erode the orifice geometry.

Often, visual checks for damage, especially to orifice geometry, during cleaning can indicate whether the cone needs to be replaced. The ICP-MS is a harsh environment with extreme temperatures, acids, and damaging solvents and sample compositions. This leads to vitrification, corrosion, cracking, and other visible damage indicating replacement need. Other indicators include drops in sensitivity or performance, or increased background levels post-cleaning. Replacement intervals depend on application and materials. Generally, labs that operate around the clock will need to replace cones every month or two, while labs with more moderate operation of their ICP-MS are likely to replace cones a few times per year. 

“What did you do?”

Cones are extremely delicate. User error is another major driver for replacement. Rough handling, aggressive cleaning, and dropping are some of the leading causes of damage to the tip, making adequate training worth the time and expense. Users should always wear gloves and use proper installation tools when manipulating cones.

Do you have to buy OEM cones?

How do you choose? The simplest answer is to consider your application need and then to match the manufacturer’s part number for your ICP-MS cone to suppliers’ offerings. While quality is always of utmost importance, reliability and performance can be achieved with aftermarket cones. Even with the precise requirements of ICP-MS cone geometry for analysis performance, aftermarket cones from reputable suppliers can offer a more cost-effective solution to the higher-priced OEM cones while still providing the needed quality and reliability to meet high performance standards. 

Alpha Resources® offers OEM-quality cones, as determined by customer testing, at approximately 30-40 percent less than the cost of OEM ICP-MS cones. As a production lab with years of experience manufacturing quality aftermarket products for elemental analysis, Alpha’s cones are produced in an ISO 9001:2015 accredited quality system and are a guaranteed quality match to an OEM product. Alpha’s cones are equal in durability to OEM cones with consistently reliable analytical output throughout their life.