Maintenance of ICP-MS cones
Enjoy your Cones longer, practical tips and background information
Introduction
Troubleshooting and maintaining your ICP-MS sample introduction system can be quite a job. However, not following proper maintenance on a regularly scheduled basis can be costly.
This goes for especially for ICP-MS laboratories processing a large number of samples. In this article we emphasize why, when and how to maintain y
our ICP-MS interface Cones, as well as the importance of conditioning the Cone. We also discuss the advantages of platinum (Pt) coated Cone. It should be noted that these are recommended maintenance guidelines, many of which have been borrowed from ICP-MS manufacturers. Always refer to the recommended maintenance guidelines provided by your instrument manufacturer.
Most common problems
The most common type of problems with ICP-MS Cones have to do with clogging of the Orifice or corrosion. The interface cones are also very fragile, especially the tip. Damage to the tip changes the diameter of the Orifice and the performance of the Cone. Using cones that are in poor condition for your ICP-MS can lead to increased background signal, memory effects, loss of sensitivity and poor precision. All of this can lead to interrupted analysis and the need to re-run sample series, resulting in a loss of time and a lower gain.
When to clean?
Frequency
The frequency with which they need to be cleaned strongly depends on the application and the load on the instrument. Excessive cleaning can lead to a shorter life span, so unnecessary cleaning should be avoided. If the samples are clean and usage is low, the Cones may only need to be cleaned monthly. 
However, if, for example, the instrument is in continuous use, and/or the samples contain high levels of dissolved solids or are highly corrosive, the Cones will need to be cleaned daily.
Type of samples
If your laboratory analyses different types of samples, it may be necessary to clean the Cones in between. For example, one sample matrix contains a high concentration of an element to be analyzed and another matrix is the same element at trace level. To avoid cross-contamination, clean the Cones in between.
Visible deposits
If there are visible deposits near the opening or if the opening is blocked or deformed. As mentioned above, a deterioration in the performance of the ICP-MS may also indicate that the Cones may need to be cleaned. Pay particular attention to increased background signal, memory effects, loss of sensitivity or distorted peak shapes.
Change vacuum measurement
A change in the vacuum measurement of the instrument may also indicate problems with the Cones. If the orifice is blocked, the vacuum will increase (pressure drop). A deterioration of the measurement results will already be noticeable for this point. If the vacuum decreases (and the pressure increases), this may indicate that the orifice is worn out and has become larger. If this happens, the Cone must be replaced. Since the Sampler Cone is more exposed to the plasma, it will usually need to be cleaned more often than the Skimmer Cone. If the performance of the instrument does not improve after cleaning, the Cones may need to be replaced or reconditioned (Pt tipped).
Method of Cleaning
The method of cleaning also depends on the application. If the samples are relatively clean, a gentle cleaning is sufficient. In some cases, routine cleaning with a cotton swab and DI water is suitable. However, if the samples contain high levels of dissolved solids or are highly corrosive, a more aggressive cleaning procedure is required. A diluted Citranox solution is a gentle and effective cleaning agent and we recommend that you try this first. If Citranox is not effective, it may be necessary to use a more aggressive cleaning agent such as nitric acid.
However, we recommend using nitric acid only when necessary. Nitric acid is more corrosive than Citranox and prolonged use will shorten the life of the Cones. Even Citranox will corrode the copper Cones, so they should not be exposed to high concentrations of Citranox or prolonged exposure to it.
Thread protection
When cleaning threaded Cones, it is important that the thread does not come into contact with a corrosive solution. If the thread becomes corroded, the Cone may not seal properly or may adhere to the base and be difficult to remove. And with Pt-tipped cones, there is a good chance that the thread for the Pt insert will wear out. It is also important to keep the thread in good condition to avoid the possibility of thread distortion and possible damage to the instrument housing. Glass Expansion has developed the ConeGuard Thread Protector to seal the thread and protect against corrosion during the cleaning process. The ConeGuard is simply screwed onto the thread portion of the Cone and O-ring seals prevent the solution from coming into contact with the thread.
Pre-Soaks
Pre-soaking the Cones in a cleaning agent such as Fluka RBS-25 for cleaning with Citranox or nitric acid helps in the cleaning process. Citranox is produced by Alconox Inc. (www.alconox.com) and Fluka RBS-25 by Sigma-Aldrich. Fluka is available through us (P/N FLUKA25). Always use safety goggles and gloves. Be careful when handling the Cones; the tip is very easy to damage. Hold the Cone by the edge and use only light pressure with your hand when cleaning the tip. Never use tools to clean Cones. The cleaning process does not necessarily have to reproduce the original, newly polished appearance. Sample deposits must be removed, but it is usually not a problem if the Cone is discolored. This can even lead to a more stable signal (see Cone Conditioning).
Cleaning methods
There are three common methods of cleaning Cones. The recommended concentrations of Citranox and nitric acid, and cleaning times, should only be used as a guideline. Given the wide range of ICP-MS applications and samples, you may need to experiment a little to find the best cleaning procedure for your application. We recommend that you do not use more nitric acid than necessary as it will corrode the Cone. If nitric acid is used excessively, the size of the Cone opening may be increased. If this happens, or if the tip is damaged or deformed, the Cone must be replaced.
The following cleaning methods are listed, from the simplest and softest, Method A, to the most thorough and aggressive, Method C.
Method A: Week in Citranox, daily or weekly, depending on the application.
1. Soak the Cones overnight in a 25 % solution (4x dilution) of Fluka RBS-25. 2. Rinse with deionised water. 3. Place the Cones in a 2 % Citranox solution and soak for about 10 minutes. 4. Wipe the Citranox solution with a soft cloth or with Kimwipe dipped in the Citranox solution. 5. Wash thoroughly with deionised water. 6. Place the Cones in deionised water and soak for 2 minutes to remove any remaining Citranox. 7. Replace the deionised water and repeat step 6 at least twice – the Cones should be washed at least three times, each time with fresh deionised water. 8. Rinse with deionised water and leave to dry or blow-dry with clean argon or nitrogen. Make sure the Cones are completely dry. It may help to heat them in a laboratory oven at about 60 °C.
Method B: Ultrasonic cleaning in Citranox, daily or weekly, depending on the application.
1. Soak Cones overnight in a 25 % solution (4x dilution) of Fluka RBS-25. 2. Rinse with deionised water. 3. Be very careful to avoid damaging the tip of the Cone. The Cone must not be placed in the ultrasonic bath without being supported or enclosed. To prevent damage, place the Cone in a sealable plastic bag half filled with a 2% Citranox solution and allow the bag to float in the ultrasonic bath. Make sure the bag floats so that the Cone does not rest on the bottom or touch the walls of the bath. This also minimises the volume of the Citranox used because the bath can be filled with water. 4. Place in an ultrasonic bath for 5 minutes. 5. Wipe with a soft cloth or Kimwipe dipped in the Citranox solution. 6. Wash thoroughly with deionised water. 7. Replace the Citranox with deionised water and sonicate for 2 minutes to remove any remaining Citranox. 8. Replace the deionised water and repeat step 6 at least twice – the Cones should be washed in the ultrasonic bath at least three times, using fresh deionised water each time. 9. Rinse with deionised water and allow to dry or blow-dry with clean argon or nitrogen. Ensure that the Cones are completely dry. It may help to heat them in a laboratory oven at about 60 °C.
Method C: Ultrasonic cleaning in nitric acid, weekly or monthly, depending on the application.
1. Soak the Cone overnight in a 25 % solution (4x dilution) of Fluka RBS-25. 2. Rinse with deionised water. 3. Be very careful to avoid damaging the tip of the Cone. The Cone must not be placed in the ultrasonic bath without being supported or enclosed. One way to prevent damage is to place the Cone in a sealable plastic bag half filled with 5% nitric acid and allow the bag to float in the ultrasonic bath. Make sure the bag floats so the Cone doesn’t rest on the bottom or touch the walls of the pool. This also minimizes the volume of nitric acid used, as the bath can be filled with water. 4. Place in ultrasonic bath for 5 minutes. 5. Wipe with a soft cloth. 6. Wash thoroughly with deionised water. 7. Replace the nitric acid with deionised water and sonicate for 2 minutes to remove any residual nitric acid. 8. Replace the deionised water and repeat step 6 at least twice (the Cones must be washed in the ultrasonic bath at least three times), using fresh deionised water each time. 9. Rinse with deionised water and leave to dry or blow-dry with clean argon or nitrogen. Ensure that the Cones are completely dry. It may help to heat them in a laboratory oven at about 60 °C. After cleaning your Sampler and Skimmer Cone, it is also important to check the condition of the Cone’s consumables. Many Sampler and Skimmer Cones depend on a gasket or O-ring for a good seal. Installing a new or recently cleaned Cone with a worn gasket or O-ring can prevent a good vacuum and result in rapid overheating of the Cone. Some Cones require additional screws for installation within the interface. Heavily corroded screws can lead to the same problems and in some cases result in an elevated iron background as many of the screws are made of steel. You do not want to ruin a Cone for an O-ring or gasket. We therefore recommend replacing the gasket on the Sampler every time you replace the Sampler Cone to ensure a good seal. Check the condition of the O-rings regularly and replace them if they show any signs of cracks.
Method C: Ultrasonic cleaning in nitric acid, weekly or monthly, depending on the application.
Soak the Cone overnight in a 25 % solution (4x dilution) of Fluka RBS-25. 2. Rinse with deionised water. 3. Be very careful to avoid damaging the tip of the Cone. The Cone must not be placed in the ultrasonic bath without being supported or enclosed. One way to prevent damage is to place the Cone in a sealable plastic bag half filled with 5% nitric acid and allow the bag to float in the ultrasonic bath. Make sure the bag floats so the Cone doesn’t rest on the bottom or touch the walls of the pool. This also minimizes the volume of nitric acid used, as the bath can be filled with water. 4. Place in ultrasonic bath for 5 minutes. 5. Wipe with a soft cloth. 6. Wash thoroughly with deionised water. 7. Replace the nitric acid with deionised water and sonicate for 2 minutes to remove any residual nitric acid. 8. Replace the deionised water and repeat step 6 at least twice (the Cones must be washed in the ultrasonic bath at least three times), using fresh deionised water each time. 9. Rinse with deionised water and leave to dry or blow-dry with clean argon or nitrogen. Ensure that the Cones are completely dry. It may help to heat them in a laboratory oven at about 60 °C. After cleaning your Sampler and Skimmer Cone, it is also important to check the condition of the Cone’s consumables. Many Sampler and Skimmer Cones depend on a gasket or O-ring for a good seal. Installing a new or recently cleaned Cone with a worn gasket or O-ring can prevent a good vacuum and result in rapid overheating of the Cone. Some Cones require additional screws for installation within the interface. Heavily corroded screws can lead to the same problems and in some cases result in an elevated iron background as many of the screws are made of steel. You do not want to ruin a Cone for an O-ring or gasket. We therefore recommend replacing the gasket on the Sampler every time you replace the Sampler Cone to ensure a good seal. Check the condition of the O-rings regularly and replace them if they show any signs of cracks.
Platinum tipped Cones
When treating a high TDS matrix analyzed by ICP-MS, Pt-Cones are often preferred over Ni. The Pt insert becomes warmer than Ni, which slows down the build-up of salts at the opening. This allows the ICP-MS analyst to work longer before maintenance is required on the Cones. Pt tipped Cones are also recommended for the analysis of sample matrices containing aggressive acids such as hydrofluoric acid (HF), sulfuric acid (H2SO4 ) and phosphoric acid (H3PO4 ). For the lowest detection limits, Pt-tipped Cones are often used in the semiconductor industry. For more aggressive samples, e.g. a combination of high TDS and high acid concentration, a Sampler Cone with a larger diameter Pt insert can be used. For some ICP-MS models a Sampler is available with a 10, 15 or 18 mm Pt insert. The larger insert ensures a much longer life due to the larger surface area. A Glass Expansion customer found that the 15mm and 18mm inserts last 18-24 months compared to 6-8 months with the 10mm inserts, or as long as the Orifice was good.
Options for Agilent ICP-MS instruments
For Agilent ICP-MS instruments a variety of different Cones- and Skimmer Insert combinations are available from Glass Expansion to choose the best option for your laboratory. As an example, Glass Expansion’s Sampler and Skimmer Cone options for the Agilent 7900 ICP-MS are listed in Table 1 and Table 2 respectively. It is recommended to use Pt Skimmer Cones with a brass Skimmer base and Ni Skimmer Cones with a stainless steel Skimmer base. Choosing the right Skimmer base will help prevent overheating and prolong the life of the Skimmer Cone.
| Description | P/N | OEM P/N | Recommendation |
|---|---|---|---|
| Nickel sampler cone | AT7701-Ni | G3280-67040 | Standard with x-lens, suitable for most applications |
| Nickel plated Nickel sampler cone | AT7701-Ni/Ni | G3280-67061 | For samples with > 0.5% HCl or for routine operation with UHMI |
| Aluminum sampler cone | AT7701-Al | For lowest nickel background and laser ablation applications | |
| Platinum sampler cone | AT7706-Pt | G3280-67036 | Standard with s-lens, for lowest detection limits and for higher matrix samples with x-lens |
| Platinum sampler cone (18 mm insert) | AT7706A-Pt | G3280-67056 | For use with high viscosity, high boiling point acids |
| Platinum sampler cone Boron Free | AT7706-Pt-BF | For lowest boron background | |
| Nickel plated Platinum sample cone | AT7706-Pt/NiP | Increased durability for samples with > 0.5% HCl | |
| Platinum sampler cone with Nickel base | AT7706-Pt/Ni | Used when cone deposition is rapid due to high TDS | |
| Platinum sampler cone (15 mm insert) with Nickel base | AT7706B-Pt/Ni | For use when cone deposition is rapid due to high TDS and increased durability requied |
| Description | P/N | OEM P/N | Recommendation |
|---|---|---|---|
| Nickel skimmer cone for x-lens | AT7902X-Ni | G8400-67200 | Standard with x-lens, suitable for most applications |
| Aluminum skimmer cone for x-lens | AT7902X-Al | For lowest nickel background and laser ablation applications | |
| Platinum skimmer cone Copper base for x-lens | AT7908X-Pt | G8400-67201 | Lowest detection limits and high matrix samples |
| Platinum skimmer cone Nickel base for x-lens | AT7908X-Pt/Ni | G8400-67202 | Organic analysis with x-lens |
| Nickel skimmer cone for s-lens | AT7702S-Ni | G3280-67066 | Economical option for the s-lens |
| Copper skimmer cone for s-lens | AT7702S-Cu | G3280-67067 | Economical option for the s-lens |
| Platinum skimmer cone Copper base for s-lens | AT7708S-Pt | G3280-67064 | Standard with s-lens, aggressive acids and lowest detection limits |
| Platinum skimmer cone Nickel base for s-lens | AT7708S-Pt/Ni | G3280-67065 | Organic analysis with s-lens |
| ICP-MS Manufacturer | Ni | Al | Pt | Pt -Boron Free | Cu |
|---|---|---|---|---|---|
| Agilent | X | X | X | X | X |
| Fluidigm (TOF-ICP-MS) | X | ||||
| Nu Instruments | X | X | |||
| PerkinElmer | X | X | X | X | |
| Shimadzu | X | X | X | ||
| Thermo | X | X | X | X |
Text: Ryan Brennan en Justin Masone van Glass Expansion, USA