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Measurement and Results - Low molybdenum (Mo) recoveries for powdered metals

 
We've been having issues with Mo measurements in powdered metal mixes using an ICP-OES. About a month ago, the Mo started dropping in our test results. It typically would come in at 0.53-0.55% on our in house check standard, made from the base powder we use in most powdered metal mixes. It now comes in at 0.46-0.50% , and every part sample I have dissolved has come in low or under spec. I tried all 4 Mo lines, both radial and axial views…no luck. I run a blank, the Mo standard we purchase from you (Mo 100PPM), then I run the standard as a sample….it comes in right on the money. But when I run the base powder sample…(the Cert sheet from the powder supplier has it at 0.55%)…I only get 0.46-0.48% most times??? It is the same base powder we were using previously and getting good results. Do you have any insights as to what the issue could be?
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admin Total posts: 529

From your description of the problem it sounds like a matrix effect. Take a base powder preparation sample solution and split it exactly in half. To one half spike in a known amount of Mo and to the other sample spike in enough water to equal to the volume of the Mo spike. Get net intensities for these two sample solutions plus a blank. Calculate the Mo in the base powder from these data using the net signal from the spike solution as the calibration/standard. If the Mo comes out correct using this approach then the problem is due to a matrix effect.

Posted: 09/05/18 20:24:50

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