Atomic Absorbance problem in Spectrophotomerer  280Z AA

Atomic Absorbance Spectrophotomerer (Agilent Company, USA) with the Model of 280Z AA., some problems as I told before. We cleaned the furnace, Graphite and Optical lenses. When we run the Arsenic heavy metals, for blank         (De-ionized water), we heat red heat flame/emission in the furnace. But during standard, we are not getting those red flame/emission. So we get less value of absorbance (0.03) than the value we got 15 days before (0.1) for 20ul of 1ppm standard solution. so when we run the sample blank and sample, we get over value like that. We need your valuable idea to solve this problem. With best regards, 

thank you.

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