The sampler cone, being exposed to the plasma, will usually need cleaning more often than the skimmer cone. If the performance of the instrument does not recover when the cones are cleaned, then you may need to replace them.
The method of cleaning will also depend on the application. If the samples are relatively clean, a gentle cleaning process will be sufficient. But if the samples contain high levels of dissolved solids or are highly corrosive, a more aggressive cleaning procedure will be required. A Citranox solution is a gentle and effective cleaning agent, and we recommend that it be tried first. If Citranox is not effective, it may be necessary to use a more aggressive cleaning agent such as nitric acid. However, we recommend that nitric acid not be used unless it is necessary. Nitric acid is more corrosive than Citranox, and prolonged use will reduce the lifetime of the cones. Note that even Citranox will attack copper cones, so the cones should not be exposed to high concentrations of Citranox or exposed for long periods. When cleaning cones which have a screw thread, be particularly careful that the thread is not contacted by nitric acid. Pre-soaking the cones in a detergent such as Fluka RBS-25 before cleaning with Citranox or nitric acid will help the cleaning process. Citranox is manufactured by Alconox Inc. (www.alconox.com), and Fluka RBS-25 by Sigma-Aldrich. Both are available from most suppliers of laboratory chemicals.
The cleaning process does not necessarily need to reproduce the original, as-new, polished appearance. Sample deposits need to be removed, but it is not usually a problem if the cone is discoloured. This may result in a more stable signal.
There are three common methods of cleaning cones. From the simplest and gentlest to the most thorough and aggressive, these are:
Soak in Citranox - daily or weekly, depending on the application:
- Soak the cone overnight in a 25% solution (4x dilution) of Fluka RBS-25.
- Rinse with deionized water.
- Place the cone in a 2% Citranox solution and soak for about 10 minutes.
- Wipe with a soft cloth or Kimwipe dipped in the Citranox solution.
- Wash thoroughly with deionized water.
- Place the cones in deionized water and soak for 2 minutes to remove any residual Citranox.
- Replace the deionized water and repeat the last step at least twice, ie, the cones should be washed in the ultrasonic bath at least 3 times, using fresh deionized water each time.
- Rinse with deionized water and allow 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.
Sonicate in Citranox - daily or weekly, depending on the application:
- Soak the cone overnight in a 25% solution (4x dilution) of Fluka RBS-25.
- Rinse with deionized water.
- Be very careful to avoid damaging the cone tip. The cone should not be placed in the ultrasonic bath without being supported or contained. One way to avoid damage is to place the cone in a ziplock plastic bag half filled with a 2% Citranox solution and float the bag in the ultrasonic bath. Ensure that the bag is floating so that the cone is not resting on the bottom or touching the walls of the bath. This also minimizes the volume of Citranox used since the bath can be filled with water.
- Sonicate for 5 minutes.
- Wipe with a soft cloth or Kimwipe dipped in the Citranox solution.
- Wash thoroughly with deionized water.
- Replace the Citranox with deionized water and sonicate for 2 minutes to remove any residual Citranox.
- Replace the deionized water and repeat last step at least twice, ie. the cones should be washed in the ultrasonic bath at least 3 times, using fresh deionized water each time.
- Rinse with deionized water and allow 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.
Sonicate in nitric acid - weekly or monthly, depending on the application:
- Soak the cone overnight in a 25% solution (4x dilution) of Fluka RBS-25.
- Rinse with deionized water.
- Be very careful to avoid damaging the cone tip. The cone should not be placed in the ultrasonic bath without being supported or contained. One way to avoid damage is to place the cone in a ziplock plastic bag half filled with 5% nitric acid and float the bag in the ultrasonic bath. Ensure that the bag is floating so that the cone is not resting on the bottom or touching the walls of the bath. This also minimizes the volume of nitric acid used since the bath can be filled with water.
- Sonicate for 5 minutes.
- Wipe with a soft cloth.
- Wash thoroughly with deionized water.
- Replace the nitric acid with deionized water and sonicate for 2 minutes to remove any residual nitric acid.
- Replace the deionized water and repeat last step at least twice, ie. the cones should be washed in the ultrasonic bath at least 3 times, using fresh deionized water each time.
- Rinse with deionized water and allow 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.
The recommended concentrations of Citranox and nitric acid, and the wash times, should be used as a guide only. Given the wide range of ICP-MS applications, you may need to experiment a little to find the best cleaning procedure for your application. We recommend that you do not use nitric acid any more than is necessary, since it will attack the cone materials. If nitric acid is used excessively, the size of the cone orifice may be increased. If this happens, or if the tip is damaged or deformed, then the cone needs to be replaced.
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