ICP-OES helps to quantify the various environmental contaminants and is used as the Environmental safety assessment. However, ICP MS is especially used for analyzing samples with low regulatory limits. So, I was kind of interested to know why ICP-OES has higher tolerance towards Total dissolved solids in any samples compared to that of ICP-MS?
Briefly, and rather unscientifically:
ICP-MS is somewhat more sensitive (10-1000 times) than ICP-OES for many of the "contaminant" elements (As, Cd, Pb etc) relevant to toxicology studies. However, being more sensitive can make it more prone to matrix errors that affect those low-concentration elements (bias and drift etc).
ICP-OES on the other hand, is less able to detect those elements at the low concentrations likely to be toxic to environment/plants/animals etc. in the first place. A higher TDS has less impact on elements that won't be detected by that instrument anyway.
Both techniques are much better if you simplify the matrix (salt removal, digest organics, uniform sample composition).
Imagine a 1 part-per-billion solution of lead in a high salt (1%) background. Depending on your instrument model, an ICP-OES might just detect this, but the high salt needs to be diluted at least 1in5 to get to 0.2% TDS. This is most likely under the detection limit of ICP-OES.
For the ICP-MS, 200 parts per trillion of Pb is well within range although there might still be matrix issues from the 0.2% salt.
ICP-OES quantitation is based on measurement of excited atoms and ions at the wavelength characteristics for the specific elements being measured. ICP-MS, however, measures an atom’s mass by mass spectrometry (MS). Due to the difference in metal element detection, the lower detection limit for ICP-MS can extend to parts per trillion (ppt), where the lower limit for ICP-OES is parts per billion (ppb). Obviously, if the elements for detection have regulatory limits that are below or near the lower detection limit of ICP-OES, ICP-MS is the instrument of choice.
Matthew Wheal, thank you so much for your response! Now, I have a brief idea of what really is the significant difference between these two distinct techniques. In my understanding, what you are saying is that ICP-MS being more sensitive, can be more vulnerable and thus can have more errors during the experimentation compared to that of ICP-OES. I have been trying to learn more about this machine and its applications in various water-related research and other toxicological studies. So, these machines are a little sophisticated and it is sometimes really challenging to find out the protocols for it. As I am a starter, in this field would you recommend any sites, materials where I can have access to more information as I will be very soon using this machine for my setup? Thank you again for your help!
Muhammad Amjad, thank you for your clarification and for explaining the chemistry behind why ICP-MS is more sensitive, and why it is considered as the best tool for the evaluation and detection of the concentration of the element at very low regulatory limits up to the range of parts per trillion (ppt).
ICP-OES is mainly used for samples with high total dissolved solids (TDS) or suspended solids and is, therefore, more robust for analyzing ground water, wastewater, soil, and solid waste. ... ICP-MS, on the other hand, is especially useful for analyzing samples with low regulatory limits.
Modern ICP-MS instruments range in sensitivity in this mass region from around 10 Mcps/(mg/L) up to 1000 Mcps/(mg/L) (7). The difference in sensitivity of these two isotopes is due primarily to difference in natural abundance and ionization in the plasma.
Samir Budhathoki Most of the instrument manufacturers have basic "introduction to ICP" literature on their websites. My main sources are Agilent and Perkin-Elmer, but Thermo, Shimadzu, Spectro, AnalytikJena and some smaller manufacturers will all have some brochures and literature that will help. Plasmachem-L https://listserv.syr.edu/scripts/wa.exe?A0=PLASMACHEM-L is a good user resource as well.
Totally agree with Matthew Wheal s answer, Both ICP-OES and the ICP-MS have unique characteristics with interference.
For example, ICP-OES high salt matrix carrying a lot of organics will interfere with some elements at trace levels, therefore need to process, digest, and dilute the samples.
For ICP-MS, known polyatomic interferences can be associated with salt-affected matrices (Ex: As).
Therefore, with the scope of the analysis, required analytes, need to prepare the samples.
Meanwhile, for quality assurance of the salt matrics samples, you can have some Certified Reference Material.
I have experience in (SLEW-3) CRM analysis. For this, additional ICP-MS spectrometer optimization, sample processing are required to achieve these specific samples. That will help to assure the accuracy and precision of the salt matrix sample results.
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