Chromatography Forum

I recently had a physical that included heavy metals screening done. I got results for Total As, MMA, and DMA: but for "inorganic" and "total toxic" there was a code 'SPRCS.' I got a copy of the lab report, and it said "Unable to complete test due to unknown interference."

The test is their own method, using HPLC-ICP-MS. I'm curious if anyone has thoughts about what might have been the problem.

I'm only familar with ICP-OES and GC/MS. But the thought that the matrix is too difficult strikes me as pretty weird. It can't be that different from anybody else's, and I would assume it's what their test was designed for. Is there something else that's 74.9 AMU and has similar retention times to what they are looking for? Or is it not that simple? Maybe there's some other issue?

Or.... they couldn't get a tune to pass that day so they just didn't do the test?

I recently had a physical that included heavy metals screening done. I got results for Total As, MMA, and DMA: but for "inorganic" and "total toxic" there was a code 'SPRCS.' I got a copy of the lab report, and it said "Unable to complete test due to unknown interference."

The test is their own method, using HPLC-ICP-MS. I'm curious if anyone has thoughts about what might have been the problem.

I'm only familar with ICP-OES and GC/MS. But the thought that the matrix is too difficult strikes me as pretty weird. It can't be that different from anybody else's, and I would assume it's what their test was designed for. Is there something else that's 74.9 AMU and has similar retention times to what they are looking for? Or is it not that simple? Maybe there's some other issue?

Or.... they couldn't get a tune to pass that day so they just didn't do the test?

ICP/MS has a problem with forming combinations not normally found that will interfere with other elements. Just looking at a quick chart for As(75) there are interferences from ArCL+, CaCl+, CaO2+, NaCAr+, CPO2+ and ArK+ which are isobaric having the same mass and with Sm and Nd rare earths the 150 mass that can be doubly charged and appear as 75.

We think of Argon as being a non reactive noble gas, but in the plasma it reacts with a lot of things to form species that will be detected. When tuning we try to minimize formation of oxides and doubly charged by adjustments to lenses and the plasma but there are always some present. The best thing for analysis of As is using an instrument with a collision or reaction cell to help remove these problem species. If the lab is using an older non collision cell instrument or just doesn't have it setup right I guess that could be part of the interference.