Peak hight

[Peter Apps]

I always thought that "TIC" stands for Total Ion Chromatogram. It is a basic principal of measurement that a number without a unit is not a measurement. The SI unit for counting entities such as ions is the Mole.

Peter

[dblux_]

I always thought that "TIC" stands for Total Ion Chromatogram. It is a basic principal of measurement that a number without a unit is not a measurement. The SI unit for counting entities such as ions is the Mole.

Peter

From the beginings I thought TIC = total ion current http://tinyurl.com/bmm7fkp

and on Y-axis is relative abundance, thus has no dimension

[Peter Apps]

Hi dblux

If TIC = Total Ion Current then the unit is Amperes.

The MS software that I have (Bruker) shows signal strength in "counts" not relative abundance (which prompts the question; relative to what ?).

Since in ordinary GC-MS all the ions are singly charged, the Coulomb would be an alternative to the Mole in the SI.

Peter

[dblux_]

Hi dblux

If TIC = Total Ion Current then the unit is Amperes.

The MS software that I have (Bruker) shows signal strength in "counts" not relative abundance (which prompts the question; relative to what ?).

Since in ordinary GC-MS all the ions are singly charged, the Coulomb would be an alternative to the Mole in the SI.

Peter

Hi Peter. Can't be Mole. How can you imagine 2 000 000 or 3 000 000 moles of any ion in MS chamber ?

ChemStation shows signal intensity in "counts" as well. And counts is related to number of ions hiting MSD detector (horn). However that number is multiplied by electron multiplier.

PS - relative to constant (factor or how it is called in English) of the detector

PS 2 - if FDA is reliable source of information see 1st chromatogram in an article:
http://www.fda.gov/Food/ScienceResearch ... 113209.htm

Y-axis is abundance !

[Peter Apps]

Hi dblux

If TIC = Total Ion Current then the unit is Amperes.

The MS software that I have (Bruker) shows signal strength in "counts" not relative abundance (which prompts the question; relative to what ?).

Since in ordinary GC-MS all the ions are singly charged, the Coulomb would be an alternative to the Mole in the SI.

Peter

Hi Peter. Can't be Mole. How can you imagine 2 000 000 or 3 000 000 moles of any ion in MS chamber ? I can't imagine that, but what I can omagine does not alter the fact that the SI unit for defined entities such as the ion fragments in an MS is the Mole, with the entities to be specified. If the entities are not specified, since we have a charged particle the Coulomb might be appropriate. That the vertical scale on the chromatogram of MS software has huge numbers on it simply means that the units on the screen are not SI units

ChemStation shows signal intensity in "counts" as well. And counts is related to number of ions hiting MSD detector (horn). However that number is multiplied by electron multiplier.and then converted and digitized before any of us get to see it. In terms of quantity of analyte present, the signal intensities are arbitrary until they have been converted to masses or Moles via a calibration of signal (usually in terms of peak area) vs known analyte quantity

PS - relative to constant (factor or how it is called in English) of the detector a drawback of MS (compared to e.g. an FID) is that the response per unit analyte is not constant

PS 2 - if FDA is reliable source of information see 1st chromatogram in an article:
http://www.fda.gov/Food/ScienceResearch ... 113209.htm

Y-axis is abundance !

Yes it is, but abundance of what ?, and what are the units ?. The heading has Total Ion Chromatogram, not Total Ion Current by the way

Peter

[dblux_]

Abundance of ions; counts is the measure of abundance, it is dimensionless (or cps=Hz) really doesn't matter.
Above statement is only according to my humble opinion. If there is a reliable source of knowledge published as eg. manual or help file to MS CDS which may indicate I'm wrong I would change my opinion.


Yes, Total Ion Chromatogram. It's a short form of Total Ion Current Chromatogram. It's only naming convention.

PS - you are encouraging me to read the book from my 1st link, well maybe in the future

[JI2002]

In my opinion, the abundance is directly related to the number of electons generated in the electon multiplier. This number is relative and arbitrary because the parameters in the MS, especially electon multiplier voltage, have huge impact on the abundance.

[Peter Apps]

Abundance of ions; counts is the measure of abundance and so the unit is ion, but this is not an SI unit, which is what Jaap was asking for, it is dimensionless (or cps=Hz)the c in cps is cycles per second, not counts really doesn't matter.
Above statement is only according to my humble opinion. If there is a reliable source of knowledge published as eg. manual or help file to MS CDS which may indicate I'm wrong I would change my opinion.


Yes, Total Ion Chromatogram. It's a short form of Total Ion Current Chromatogram. It's only naming convention.

PS - you are encouraging me to read the book from my 1st link, well maybe in the future

[dblux_]

and so the unit is ion, but this is not an SI unit, which is what Jaap was asking for

Peter, ion is not an unit !, it's a particle bearing electric charge. Count is unit and it has no SI dimension like number of digits at your hand. That's like counters measure numbers of charged particles.

,...(or cps=Hz)the c in cps is cycles per second, not counts...

Noooo, the c in cps is not cycles per second, it's simply cycles, combined with "ps" gives Hz. But dimension of abundance expressed as counts really doesn't matter and no one needs it neither for quality nor quantity analyses.

[Peter Apps]

and so the unit is ion, but this is not an SI unit, which is what Jaap was asking for

Peter, ion is not an unit !, it's a particle bearing electric charge. Count is unit and it has no SI dimension like number of digits at your hand. That's like counters measure numbers of charged particles.

,...(or cps=Hz)the c in cps is cycles per second, not counts...

Noooo, the c in cps is not cycles per second, it's simply cycles, combined with "ps" gives Hz.you are right, my bad, but what has cycles per second got to do with counting ions ? But dimension of abundance expressed as counts really doesn't matter and no one needs it neither for quality nor quantity analyses.

These people are much better at explaining the SI than I am http://www.bipm.org/ - the plans to reform the whole system, and discussions on what the units should be for counting are particularly relevant to this discussion.

Peter

[MaryCarson]

Hi,
I guess the "counts" is a part of term "Total Ion Counts (TIC)". If yes, there is no unit for "counts" then. It is just a natual number. However, the y axis units, ABUNDANCE, for either TIC, (time vs. abundance) or mas spectra (m/z vs. abundance) uses unit of percentage or ppm (1% = 10,000ppm).

Actually, "TIC" is a little ambiguous. Over the the years, I've seen it called "total ion current" and "total ion chromatogram" more often than "total ion count."

What your axis is labelled sometimes depends on your software and how it is set up--I have never used it where the y-axis is a percent as that is not useful for me.

[wulisheng2]

"abundance expressed as counts"

We may find the best fit definitions of "Abundance" from the website below:

http://en.wikipedia.org/wiki/Abundance.