analysis of water

[offroad]

Dear friends,

what detector is more suitable for measuring water content?

Thanks

[JGK]

Like many forms of analysis it will depend on what type of sample you want to analyze

Solid, Liquid, Gas ?

In short we need a bit more information.

[offroad]

Thank you for answering.

My sample is: water and phenols.
They are all dissolved/diluted in water. I would like to know how to quantify water, once I have the following detectors:

Attached to an HPLC:
Refractive index detector - RID
Photovoltaic Diode Array - PDA

Attached to a GC:
Mass Spectometer - MS
Flame Ionization Detector - FID
Thermal Conductivity Detector - TCD

Thank you in advance.

Marcio

[JGK]

Are the phenols at trace levels only? i.e. water is the majority of the matrix.

or is it a phenolic solution with trace amounts of water?


I don't think I've ever heard of quantifying "Water" by HPLC or by GC (but I've only been in Chromatography 20+ years).

Moisture Analysis, check out the techniques listed here http://en.wikipedia.org/wiki/Moisture_analysis

[offroad]

Are the phenols at trace levels only? i.e. water is the majority of the matrix.

Yes, water is the majority of the matrix.

I am really new to this subject, so why I can't understand why water may not be properly quantified by a GC (for example).

Thank you for your thoughts.

Marcio

[chromatographer1]

I have done water at percent levels and ppm levels.

I suggest the R porous polymer or one of the polar Chromosorb 100 Century series polymers.

TCD is preferred.

Use columns that are not bare metal, but glass or fused silica coated.

Keep oven temperatures above 90°C and inject a minimal amount consistently with a syringe (Chaney adapter) or use a liquid valve injector.

best wishes,

Rodney George
consultant

[offroad]

Wow...Thank you.

[JGK]

Are the phenols at trace levels only? i.e. water is the majority of the matrix.

Yes, water is the majority of the matrix.

I am really new to this subject, so why I can't understand why water may not be properly quantified by a GC (for example).

Thank you for your thoughts.

Marcio

To be honest this is the first time I've ever heard of anyone wanting to quantify water. Especially when from your answers it would appear you have a water sample with small/trace levels of phenols in it (i.e. it is virtually 100% water).

With this type of sample, I would expect quantitation of the impurities rather than the concentration of water present.

[offroad]

To be honest this is the first time I've ever heard of anyone wanting to quantify water. Especially when from your answers it would appear you have a water sample with small/trace levels of phenols in it (i.e. it is virtually 100% water).

With this type of sample, I would expect quantitation of the impurities rather than the concentration of water present.

Well, actually, it's not traces, I believe it's more or less 2-5 % phenols. And there's a few of them that goes from 8 to 15 % phenols, catechol, hydroquinone and water, water is expected to be 70% of the mix.

[chromatographer1]

Sometimes it is easier to measure water content than to measure each and every impurity to measure water by difference.

Karl Fisher would be preferred but sometimes you are limited by your equipment and personnel.

I have done 2500 ppm water in acetone ACCURATELY +/- 50 ppm and 0-100 ppm water in alkanes +/- 2ppm.

The most difficult part is injecting reproducibly, but I started in 1971 when autosamplers were rare and chemists were plentiful and cheap, as was their time.

Rodney George
consultant

[offroad]

Thank you all, very much.

[smith2287]

hi.
I want to know that chromatography may also depends on the mass of the substances ?

[gstaepels]

No, not exactly. In GC the response of the dector to an analyte is the key factor. Therefore, in order to quantify one should use a standard with known weights of the sustances to measure the response of an analyte to the detector.
Many people will use area % and thus neglect the response of the detector. this fine as long as you stay with the same type of samples and use the results relative to eachother. But be aware that these results are not weight %.

[HW Mueller]

Gilbert, what is
"the same type of samples" . . . . , and how do you "use the results relative to each other" . . . ?

[gstaepels]

With "the same type of samples" I mean a set of samples with the same matrix, in which the components may differ in concentration: e.g. samples from a chemical process, taken at various times.