Chromatography Forum

Showing any chromatograms, we know the unit for peak area is "mV/sec". However, what is the unit for peak HIGHT please?

Guessing you mean peak height...Its pA--picoamps.

Guessing you mean peak height...Its pA--picoamps.

Ops, you are exactly right that is Peak Hight.

Thank you so much!

Guessing you mean peak height...Its pA--picoamps.

So if area is in mv.s, how do you get from a height in pA and width in seconds to the area ?

Peter

Guessing you mean peak height...Its pA--picoamps.

So if area is in mv.s, how do you get from a height in pA and width in seconds to the area ?

Peter

In my practise, I use the mV/sec as the unit of Peak Area versus concetrations for establishing a regression coordinate. The peak areas are obtained from the integration of a peak on chromotogram where the y axis is absorbance unit and x is time. So to perform an integration for peak area needs a range, the time points from peak initial to end. A peak integration result is a measure of area that consists of unlimited numbers of line measures between the two time points. However, Peak Hight does not, as it is a length measuement that is a verdical line from peak top point to baseline. That means no integration needed for Peak Hight.

Guessing you mean peak height...Its pA--picoamps.

So if area is in mv.s, how do you get from a height in pA and width in seconds to the area ?

Peter

In my practise, I use the mV/sec as the unit of Peak Area versus concetrations for establishing a regression coordinate. The peak areas are obtained from the integration of a peak on chromotogram where the y axis is absorbance unit and x is time. So to perform an integration for peak area needs a range, the time points from peak initial to end. A peak integration result is a measure of area that consists of unlimited numbers of line measures between the two time points. However, Peak Hight does not, as it is a length measuement that is a verdical line from peak top point to baseline. That means no integration needed for Peak Hight.

OK, let me put it another way; to measure an area in mV.s you need linear measurements in mV, not in pA. How do you get from pA to mV ?

Peter

Current and voltage can be converted to each other if a series resitor is used.
Remember ohm's law : V= I x R

The question on how one can convert pA to mv is the electronic equivalent of asking on how one can convert flow to pressure. You can not convert flow to pressure without knowing other factors. For a capillary column you need to know the length, internal diameter, temperature and the viscosity of the gas. With this information you could then convert flow to pressure. For a packed column this would not be possible.

As uzman points out, you can convert pA to mv if you know the resistance of the circuit. If you are talking about an amplifier, there is no easy answer, without knowing the circuitry in detail. This means that pA to mv can vary from manufacturer to manufacturer. For the same manufacturer it could change from GC model to GC model, and on the same instrument of a manufacturer it can vary from the digital sigal output and the analogue output.

In summary, there is no general rule to convert pA to mv, other than Ohm's law as already pointed out, which only applies to a simple resistor.

Gasman

I am apt to accept Gasman's points, we may not get adequate factors to convert PA to mV and I think it requires more complicated math machanisms.

We may pay attention to another observation that is the coordinate of the Voltage/time (uV/min) while a GC is running. The y axis unit is uV. So could we say the unit for Peak Hight is pico or micro Volt(V), rather than Ampere(A)?

Thanks

We may pay attention to another observation that is the coordinate of the Voltage/time (uV/min) while a GC is running. The y axis unit is uV. So could we say the unit for Peak Hight is pico or micro Volt(V), rather than Ampere(A)?

Thanks

That's the point Peter was trying to make.

We may pay attention to another observation that is the coordinate of the Voltage/time (uV/min) while a GC is running. The y axis unit is uV. So could we say the unit for Peak Hight is pico or micro Volt(V), rather than Ampere(A)?

Thanks

That's the point Peter was trying to make.

Indeed it was !

Peter

Now we're on this signal discussion:

why is the Y-signal in MS always listed as "counts"? Whats SI dimension of [counts]?. I wanted to ask that for quite some time being a non-MS specialist.

jaap

Now we're on this signal discussion:

why is the Y-signal in MS always listed as "counts"? Whats SI dimension of [counts]?. I wanted to ask that for quite some time being a non-MS specialist.

jaap

"Counts" as abundance unit is dimensionless.

Hi Jaap

"counts" is how many ions hit the detector. The only applicable SI unit is the Mole.

Peter

Hi Jaap

"counts" is how many ions hit the detector. The only applicable SI unit is the Mole.

Peter

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).