Running ICP-MS 7500ce in nogas & Helium reaction mode obtains different results?

Using blank as benchmark for testing Arsenic, cadmium, mercury, and lead.  Tests with zeros on the blank in helium mode hardly ever yielded zeros, but, positive numbers were recorded during testing.  While nogas mode had concentrations that matched up with the blank with zeros.  How can these results better match up with each other?

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