Measurement and Results - Aluminum results fluctuate in ICP MS

Hi, Our analysis is by microwave digestion with 0.25g product(pectin, carrageenan, fiber etc.) in 5 mL HNO3 and 1 mL HCl. We have two calibration curves as we for some light metal have very high content but also low content. We normally see the same results with both calibrations but uses the results there is within one of the calibration curves. We have then observed for some matrixes that aluminum results fluctates alot between our directly analysed sample and when it has been diluted 10 times. e.g. when measure directly after digesten gives 8.58ppm and after a dilution factor of 10, gives 13.5ppm. A colleague sugested that Aluminum need Cl to solubolize and wee tried adding more HCl after digestion but also in the digestion. But we do not get consisten results. Can you help? or what is the best way to get aluminum solubilized? the source of aluminum can be many as it is a natural product but also get som from the production equipment.