Dear Sergio Gomez-Salazar you must again check the methodology for the preparation of ppm solution. Confirm the purity of compound you used for preparation of standard solution. Assure the calibration of used instruments and also check the purity of solvent . Four M tels us to find the problems 4M means the mistake always executed by 1.Man, 2.Material,3.Machine 4. Methodology

Dear muhammad.

Thank you for your answer. We already checked the 4M you mention. We have repeated two times the measurement with the same result. Always obtained these results. I checked personally the methodology and it was correct. The material purity. The only thing left to check was the instrument. But it was recently maintained. I do not know what to do. Do you have another advise??

In my view there is two things that can be wrong:

1) the calibration solution that has been used to calibrate the machine (always assuming You calibrate frequently, i.e., on a daily basis.

2) a systematic error when making the solutions such as doing the calculations with what was on the balance in the beginning and forgetting to take the counter ions and the cristal water etc. into account.

Thank you again for your response. I rechecked all calibration procedures and solutions and they were all correct. Also, I checked all calculations to prepare the three solutions and they included the hydration water in the crystals. So, I do not know what can be the problem. Any other suggestion as to the source of this problem? Appreciate your comments.

That is a very high concentration of mercury for ICPMS measurement. Does your calibration range even approach that sort of concentration? Modern ICP-MS instruments are capable of measuring a wide range of concentrations (sub-ng/L to mg/L) but that doesn't mean you observe a linear response across the entire range.

I suggest you dilute the sample down by several orders of magnitude (1 in 10000 at least). You won't hurt the instrument by measuring a low concentration, but can create all sorts of problems by adding too much.

I would also examine what sort of acid you are using for dilution and calibration. If you dilute in 1% hydrochloric acid, calibrate with 1% hydrochloric acid.

Check the link to mercury at https://www.inorganicventures.com/periodic-table for some further details.

Also search their forum: https://www.inorganicventures.com/forum.

Do you have anyone at your facility that can help you with this? Consulting them may save you considerable amounts of time, money and sample.

I would like to add that it could be also a matter of Hg chemistry. Hg is not stable, it evaporates, it likes to accumulate in the sample introduction system (memory effect). First of all, 1000 ppm is indeed very, very high concentration, and there is no need to overload the instrument. I'm not sure which calibration range you need for your samples, but up to 10 ppb should be enough. You can always dilute your samples and recalculate the result.

Also, literature says, you could add Au in an internal standard solution or in a rinse solution (it stabilizes Hg). You can also add HCl (1-2%) in rinse solution and prolong wash time a bit, but then you eventually could have some interferences with other elements.

As Mathew Wheal already mentioned, the concentration you are trying to measure (1000 ppm Hg) is waaay too high for an ICPMS, or any common instrumental technique. If you wish to measure high concentrations, dilute them gravimetrically, e.g. two 100X dilutions in series which will give you 100 ppb with ample sensitivity. You may go even down to 10 ppb levels which is even safer. Hg is a very notorious element to cause memory effect (carry over) in ICPMS instruments due to slow washout. You may have already contaminated the system which may take a long time to get the blanks down to sub ppb levels by rinsing. I would start with a thorough clean-up of the system (sample intro, torch, cones, etc.). 1-2% HCl would be better than HNO3 for rinsing out Hg.

As a good practice, if you already know the approximate concentration, try not to introduce more than 100 ppb of the analyte that you try to measure.

Thank you all for your kind responses. I woul like to mention that the concentration I measures in the ICP-MS was diluted, of course I know I cannot measur 1000 ppm directly into the instrument and it has to be diluted. But still when I make my conversions it gives me that reading. I also took into account the memory effect of Hg. I used a 5 ppm gold solution into all my samples, stds and washing solutions. But still the problem persists.

Sergio, a problem in the matching of the matrixes can also be a possibility, assuring that both solutions were diluted in the same acid concentration ( e.g., 2%HNO3) the big difference might be due to a problem in one of the solutions. I explain myself, sometimes I have also experienced that problem when the standard solution I am using is too old, I have prepared it a long time ago, it has not been stored properly or it has pollution or any other problem, so there will be a difference. So you might check if either one of the standard solutions you are using has a problem, especially since Hg stability is an important factor because of the methylated forms. I might advise checking with any other available Hg standard solutions or spiked samples and see if still the problem persists. Also if the tunning values of the instrument are right and the recovery of the internal standard. These might be some of the causes, good luck ~

Sergio,

I also suggest diluting the concentration first and then you can calculate the concentration by multiplying the dilution factor later. I think due to high exposure of Hg in the instrument left the contaminant behind. So the sensitivity of the instrument will be affected. You should keep the cones/extraction lens in 1 - 2 % nitric acid for 5 min. The torch should also wash with HCL. Change the sample and drain tubes. 1% nitric acid solution can be used for rinsing the solution. After the igniting of the plasma let him stabilize for 15-20 min before starting the performance report.

Calibration is also responsible for this type of problem pls check your concentration of calibration points.

Also, check in the sample list if any wrong dilution factor is given

As you may know concentration depends on your calibration.

You Should check your calibration point value in the batch.

You should also use pure blank (1% HNO3 in type-1 water)

1000ppm concentration of any analyte is not good for the instrument. You can dilute the analyte with type-1 water and than multiply instrument reading with the dilute factor .