The total amount of material (including major species) in solution in your samples. In general this should be between 0.2% and 0.5%. The general rule for maximum dissolved solids is to consider the boiling point of the matrix oxide; if the matrix oxide is refractory the material is more liable to build up on the cones and the maximum TDS should be kept to 0.2%. If the matrix oxide does not form a refractory oxide, then material is less likely to build up on the cones, and the maximum TDS can be 0.5%. If the matrix forms a gaseous oxide such as with high levels of organic material (ammonium acetate, digested biological material etc.), then the level can go as high as 10%. As long as the TDS remains within sensible limits the lenses require cleaning routinely for normal sample loads every 6 - 12 months which is the normal preventative maintainance secheduling, outside of this the user should not need to attend to the lens components of the X Series ICP mass spectrometer.