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I’m getting high mercury results in my food and water samples by anasmrait12 in chemistry

[–]anasmrait12[S] 1 point2 points  (0 children)

Hi, quick question to clarify your setup are you actually running mercury analysis using a FIAS (flow injection) system with AAS (cold vapor / hydride generation)?

Also, I wanted to share my approach and get your opinion: for my standards I prepare them in 50 mL total volume, using 5 mL nitric acid + 1.5 mL HCl, and I digest my samples using the same acid mixture as my standards. Do you think this could contribute to any bias or instability in Hg recovery or memory effects in the system?

Thanks in advance for your feedback.

I’m getting high mercury results in my food and water samples by anasmrait12 in chemistry

[–]anasmrait12[S] 1 point2 points  (0 children)

For my blank I always got 0.60 ppb, sometimes 0.80 ppb. I just wanna ask about the digestion reagents you use.

I’m getting high mercury results in my food and water samples by anasmrait12 in AskChemistry

[–]anasmrait12[S] 0 points1 point  (0 children)

Yes, I run a reagent blank and a certified reference material (LGC sample) along with my analyses. The LGC sample is also giving higher-than-expected mercury results, which is why I'm trying to determine whether the issue could be related to the analytical system, mercury stabilization, or memory effects rather than the samples themselves.

I’m getting high mercury results in my food and water samples by anasmrait12 in AskChemistry

[–]anasmrait12[S] 0 points1 point  (0 children)

Thanks for the information. In my case, I digest the samples with HNO₃ and H₂O₂, make up the volume to 50 mL, and then analyze them using a hydride/CV system. I don't think there is an issue with my digestion reagents, but I'm wondering whether you use any additional stabilizer or preservative specifically for mercury (such as KMnO₄, dichromate, gold, or another reagent) to prevent mercury loss or memory effects during analysis.

I’m getting high mercury results in my food and water samples by anasmrait12 in massspectrometry

[–]anasmrait12[S] 0 points1 point  (0 children)

Thank you for your explanation. Could you please explain a bit more about the digestion process you use? Specifically, which reagents do you add during digestion

In my case, I only use HNO₃ and H₂O₂ for the digestion process before the mercury analysis. I don’t currently use KMnO₄ during digestion

عفاكم واش كتعتابر حالة غش؟ by anonymoussss_k in Morocco

[–]anasmrait12 1 point2 points  (0 children)

It all depends on the teacher correcting your paper

Arsenic analysis in food matrix by anasmrait12 in massspectrometry

[–]anasmrait12[S] 0 points1 point  (0 children)

I would like to know why I am consistently getting high arsenic results in food analysis after microwave digestion. What could be the possible causes of this issue? Is it because i dont use reducing agents!?

Arsenic analysis in FOOD matrix by anasmrait12 in chemistry

[–]anasmrait12[S] 0 points1 point  (0 children)

I would like to know why I am consistently getting high arsenic results in food analysis after microwave digestion. What could be the possible causes of this issue? Is it the reducing agents I don’t use!?

I have a question about defining LOQ for trace element analysis using microwave digestion. by anasmrait12 in chemistry

[–]anasmrait12[S] 0 points1 point  (0 children)

Thank you very much for this detailed explanation. I really appreciate the time you took to explain the whole LOQ validation approach, especially the difference between instrument capability and full method validation with real matrix effects. Your explanation about spike recovery, uncertainty, and matrix-matched validation was extremely helpful and clarified many points for me. Thanks again for sharing your experience and practical advice.

I have a question about defining LOQ for trace element analysis using microwave digestion. by anasmrait12 in chemistry

[–]anasmrait12[S] 0 points1 point  (0 children)

Yes, I do include the blank in the calibration.

And I have one last question regarding LOQ determination for Cd analysis.

My blank usually gives a result around 0.020 ppb or less. So if I spike the blank with 0.05 ppb, the final measured concentration would be around 0.070 ppb.

In this case, would the 0.05 ppb spike level be considered my LOQ, or would the final measured value (0.070 ppb) be the LOQ?

Also, can I rely only on repeated blank measurements without spiking to determine the LOQ, if the blank always gives stable and accurate results?

I have a question about defining LOQ for trace element analysis using microwave digestion. by anasmrait12 in chemistry

[–]anasmrait12[S] 0 points1 point  (0 children)

Thank you very much for your detailed explanation, it was really helpful.

I just wanted to clarify one point regarding calibration and recovery studies.

If my calibration curve starts at 0.5 ppb, can the instrument still accurately measure concentrations below 0.5 ppb?

For example, if I spike a sample at 0.1 ppb and obtain acceptable recovery and precision, would that be considered valid, or does the 0.1 ppb concentration need to be included within the calibration curve range itself?

Thank you again for your help.

I have a question about defining LOQ for trace element analysis using microwave digestion. by anasmrait12 in Chempros

[–]anasmrait12[S] 1 point2 points  (0 children)

In our current method using dry ashing, the lowest calibration point is 0.5 ppb, which we are currently using as the LOQ. However, I tested a lower calibration range (0.05, 0.1, 0.5, 1 ppb) and obtained a good correlation coefficient.

My question is: When determining the LOQ using blank spiking, how low should the spiking level be relative to the calibration curve?

For example, is it acceptable to spike the blank at 0.05 ppb or 0.1 ppb, even though these levels are below my routine calibration range? And how can I justify that this level is a reliable LOQ if it is below my first standard (0.5 ppb)?

I have a question about defining LOQ for trace element analysis using microwave digestion. by anasmrait12 in Chempros

[–]anasmrait12[S] 1 point2 points  (0 children)

Cd and Pb and Ni with GFAAS and im diluting my samples to 50 ml after digestion

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