Low sensitivity

Hi, we have an ICP-MS-QQQ Agilent 8900. Some days ago, we noted the counts for mass 91 on traditional UP dating on zircons were low. So, we did the PA factor and had a low signal on mass 47. We cleaned the sampling cone and skimmer and did the PA factor again, but the results are the same, look at the following picture and the excel attached: 


What should I test now?

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