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November 01, 2025, 12:00:47 pm
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Author Topic: Reasoning HPLC, GLC, GSC  (Read 1145 times)  Share 

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kenhung123

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Reasoning HPLC, GLC, GSC
« on: April 27, 2010, 04:25:06 pm »
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Why is it that HPLC is used for non volatile yet decomposable substances when heated? I don't get that so it must not turn to a gas but must break down?

Same to GLC and GSC, they are used for volatile yet non decomposable substances. So they must turn into a gas but not break down.

Firstly, how does that work and why is the instrument selective in such a way?


Thanks in advance
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kyzoo

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Re: Reasoning HPLC, GLC, GSC
« Reply #1 on: April 27, 2010, 07:50:09 pm »
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For GLC and GSC, the analyte must be able to flow through the chromatography column (a long 50m glass column that is winded up) by being carried by the carrier gas. The analyte cannot do so unless it is a gas. And it cannot break down otherwise you don't get the actual component substances of the analyte.

For HPLC the analyte is carried through the chromatography column via the solvent which is pumped through it at a high pressure. Only a liquid analyte can be carried by a liquid solvent at high pressure, hence the analyte cannot be volatile. And substances that are decomposable while heated are analysed in HPLC because HPLC DOES NOT INVOLVE HEATING. So HPLC is used for decomposable substance because there is no risk of the substance becoming decomposed in HPLC. It never says that decomposable substances HAVE TO BE used for HPLC.
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kenhung123

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Re: Reasoning HPLC, GLC, GSC
« Reply #2 on: April 27, 2010, 08:00:21 pm »
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Oh silly me. I get what it means now. So it is saying since it does not involve heating, it would not decompose anything therefore it is suited to substances that would decompose (but in fact it won't decompose in the process). Thanks kyzoo!
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Martoman

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Re: Reasoning HPLC, GLC, GSC
« Reply #3 on: May 02, 2010, 05:56:36 pm »
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Also, lower molar mass ie: <300, used for GC as these substances will decompose easily. For higher, use HPLC as it is only required in liquid form.
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superflya

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Re: Reasoning HPLC, GLC, GSC
« Reply #4 on: May 02, 2010, 06:00:45 pm »
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Quote from: Martoman on May 02, 2010, 05:56:36 pm
Also, lower molar mass ie: <300, used for GC as these substances will decompose easily. For higher, use HPLC as it is only required in liquid form.

u mean substances that decompose easily when vapourised shouldnt be used in GC..
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macca69831

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Re: Reasoning HPLC, GLC, GSC
« Reply #5 on: May 04, 2010, 10:16:59 pm »
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Decomposition will cause the substance to block the column
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Martoman

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Re: Reasoning HPLC, GLC, GSC
« Reply #6 on: May 08, 2010, 04:47:36 pm »
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Quote from: superflya on May 02, 2010, 06:00:45 pm
Quote from: Martoman on May 02, 2010, 05:56:36 pm
Also, lower molar mass ie: <300, used for GC as these substances will decompose easily. For higher, use HPLC as it is only required in liquid form.

u mean substances that decompose easily when vapourised shouldnt be used in GC..

 Yes, that. ::)
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