Sometimes in the course of human events a nebulizer will become clogged. Clogging can be diagnosed by a steady decrease in the Ar flow rate with a corresponding rise in the Ar backpressure. Additionally, the stability of the instrument will greatly decrease. Because of the importance of the nebulizer to the analytical process, great care must be taken to be prevent clogging.
The best way to unclog a nebulizer is to never let it clog in the first place. This can be accomplished by filtering all samples, standards, drifts, and any other solution that is aspirated. Keep the wash bottle, rinse bottle, and other solutions covered whenever possible. If a wide-mouth bottle is used for the rinse bottle, boring a small hole in the cap will minimize the input of dust into the solution.
Never use an ultrasonic bath to unclog a nebulizer. The vibrations in such a bath will harm the delicate glass channel of the nebulizer. Because the channel of a concentric nebulizer gets successively more narrow towards the tip, never try to clean a nebulizer by forcing gas or water in the forward direction.
Soaking the nebulizer in 20% (or greater) HNO3 or in aqua regia solution (1 part HNO3:3 parts HCl) greatly assists the unclogging process. Inject the acid solution (wearing gloves) into the front of the nebulizer, and also gently inject some acid up from the Ar channel. This will ensure that the clogged tip will be inundated from all directions. Such injection can be achieved by outfitting a syringe with the appropriate sized Tygon tubing. Let the nebulizer soak overnight, in a heated bath if possible. Additionally, provided the nebulizer has been thoroughly rinsed with deionized water (and thus there is no remaining acid present), the nebulizer can be sometimes unclogged by unhooking one of the Ar gas flow lines from the ICP torch assembly, placing the end of the tube over the tip of the nebulizer, and using the high Ar pressure to blow back through the nebulizer. Be sure to hold the nebulizer tightly to prevent it from launching across the room.
The fully demountable torch assembly from JY lends itself to easy cleaning. Precipitate will build up on the surfaces of the outer tube, inner tube, and alumina injector. This is detrimental to the analysis because it affects plasma shape and stability and inhibits analyte ionization. Depending on the concentration of acid and the dilution factor of the LiBO2 fusions, the quartz tube surfaces will chip and abrade. For the fused rock and sediment samples, it is recommended to clean the glassware frequently (after 2-4 analytical runs) to help maintain instrument stability and minimize glassware corrosion.
There is a difference between precipitate buildup and staining. Staining is inevitable and can be tolerated. Precipitate on the surfaces of the glassware, however, is more serious and must be monitored. The key issue is that the glassware must be smooth, with the unchipped and high-quality edges. The outer quartz tube must be very clean with minimal stains.
Soaking all glassware in 20% (or stronger) HNO3 or aqua regia solution helps the cleaning process. As with the nebulizer, let the glassware soak overnight, in a heated bath if possible. Avoid the use of an ultrasonic bath. Use KimWipes or other clean lint-free cloths to polish the outside of the tube, and pass the KimWipe through the inside of the cylinder and pass back and forth.
The inner quartz tube can be inverted (reversed) so the stained end is at the bottom of the torch assembly, but if this is done be sure that the edges of the tube are smooth and sharp so that the bottom of the tube is seated properly. Soaking the upper end of the alumina tip, even in relatively weak HNO3, helps clean away precipitate easily.