Hi there. I recently started using an ICP-OES and after replacing the less concentrated reference for a new one, the values for Tin and Antimony are higher than they should be. E.g. now reading 0.0045% for a sample that have no more than 0.0005%. Why?

This is a difficult question to answer because I cannot see the data. Have you verified your results by using more than one wavelength for Tin and Antimony? What do you mean by "replaced the less concentrated reference for a new one"? Is this a certified reference material? How many calibrations points are you using? Are you using weighted fit?

Hello, Tina.

Thanks for your reply. I have no experience with this spectrometer, as I have used an AES for liquids (oils) but not an OES for solid (metal) samples.

- The reference or standard that was changed is NOT a certified reference material, for what I understand. Its composition is not exact, eg. the concentrations are reported as: Sn <0.0005%, Sb<0.0001, As<0.0003, and so on. The only exact concentrations reported are for Bismuth  and Copper, as these two are very consistent when tested. This reference slab contains the lowest concentrations of metals/impurities. We bought it from the company who makes the spectrophotometer and it is identified as RPb11/(Serial number), if that gives you any information. The reason why it was changed it's because I ran out of the previous one.

- I haven't verified with other wavelength cause I don't know how to use that option. Is that from the software?

- I am not sure whether you use calibration and standardisation interchangeably but every time I standardise the equipment (after every optical cell cleaning) I use five different slabs with different concentrations of "contaminants" / metals.

-In regards to weighted fit, I am reading the weight percentages for each metal if that's what you mean.

If my reply is still vague it's because I have no previous experience with OES. Is there any text, website or document where I can find related info? I know the foundations of the technique but I don't know if my questions are too specific for the software or can be general to any OES device. 

ICP wavelengths are both atomic and ionic in nature, hence the term optical emission spectrometer (ICP-OES) applies, rather than just atomic emission spectrometer (AES). I am a bit confused, because it sounds like you are analyzing solid samples. Are you digesting the samples and presenting them to the ICP-OES in liquid form?  What kind of Agilent ICP-OES do you have?

I would refer you to the manufacturer of your instrument for questions like this.