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By Anonymous on Wednesday, November 19, 2003 - 03:20 am:
Hi, we are developing a method for the determination of an ACE drug and its metabolite by LC electrospray ionization mass sspectrometry. We are currently working with an aqueous/methanol mobile phase containing 0.05% formic acid and we cannot explain the serious instability of the ms signal of the metabolite. Do you believe that a small quantity of sodium hydroxide less than 0.01% could affect the ms signal? Notice that a less than 5% adduct with sodium was observed in the mass spectrum of the metabolite.
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By Anonymous on Wednesday, November 19, 2003 - 03:25 pm:
To anomymous above: why should there be any sodium adduct if your mobile phase does not contain any sodium?
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By Basil on Thursday, November 20, 2003 - 01:23 am:
To anonymous: the sodium adduct comes from the sodium extracted from glass bottle or any other glass component.
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By Anonymous on Thursday, November 20, 2003 - 02:14 pm:
to Anon ACE drug:
do you see a 2M+Na signal? You may only get 5% on the M+Na adduct, but the dimer (from pi - cation-pi interaction) may be a significant. Also, check the 2M+H response.
I usually avoid ESI for quantitation since it is infamous for nonlinear response. Often, I use uv detector and MSD in tandem. MSD for identification, and uv for quant.
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By Anonymous on Thursday, November 20, 2003 - 10:52 pm:
To Anon of November 20, 2003 - 02:14 pm.
If you make a survey of the literature, ESI is the most used technique in LC/MS.
IT IS MOSTLY USED FOR QUANTITATION, AND GIVES LINEAR RESPONSE (you have to use the right concentration range, however, because saturation occurs as with any type of detector including UV).
Using a combination of MSD for identification and UV for quantitation reminds me of the people who used a chart-strip recorder in combination with the integrator, when the first computer-based data systems were introduced (just in case...)
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By Anonymous on Friday, November 21, 2003 - 11:28 pm:
A quick survey of the literature shows me that ESI is mostly used for proteomics. It can be used for quantitiation but that typically requires purchasing or synthesizing stable isotope standards to normalize the signal response.
I have found the uv detector to be inheritently more robust, reproducible, and trouble free than the MSD response. ie. the above Na interference would have no effect in delaying my project's completion.
Hi, we are developing a method for the determination of an ACE drug and its metabolite by LC electrospray ionization mass sspectrometry. We are currently working with an aqueous/methanol mobile phase containing 0.05% formic acid and we cannot explain the serious instability of the ms signal of the metabolite. Do you believe that a small quantity of sodium hydroxide less than 0.01% could affect the ms signal? Notice that a less than 5% adduct with sodium was observed in the mass spectrum of the metabolite.
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By Anonymous on Wednesday, November 19, 2003 - 03:25 pm:
To anomymous above: why should there be any sodium adduct if your mobile phase does not contain any sodium?
-------------------------------------------------------------------------------------------------------
By Basil on Thursday, November 20, 2003 - 01:23 am:
To anonymous: the sodium adduct comes from the sodium extracted from glass bottle or any other glass component.
-------------------------------------------------------------------------------------------------------
By Anonymous on Thursday, November 20, 2003 - 02:14 pm:
to Anon ACE drug:
do you see a 2M+Na signal? You may only get 5% on the M+Na adduct, but the dimer (from pi - cation-pi interaction) may be a significant. Also, check the 2M+H response.
I usually avoid ESI for quantitation since it is infamous for nonlinear response. Often, I use uv detector and MSD in tandem. MSD for identification, and uv for quant.
-------------------------------------------------------------------------------------------------------
By Anonymous on Thursday, November 20, 2003 - 10:52 pm:
To Anon of November 20, 2003 - 02:14 pm.
If you make a survey of the literature, ESI is the most used technique in LC/MS.
IT IS MOSTLY USED FOR QUANTITATION, AND GIVES LINEAR RESPONSE (you have to use the right concentration range, however, because saturation occurs as with any type of detector including UV).
Using a combination of MSD for identification and UV for quantitation reminds me of the people who used a chart-strip recorder in combination with the integrator, when the first computer-based data systems were introduced (just in case...)
-------------------------------------------------------------------------------------------------------
By Anonymous on Friday, November 21, 2003 - 11:28 pm:
A quick survey of the literature shows me that ESI is mostly used for proteomics. It can be used for quantitiation but that typically requires purchasing or synthesizing stable isotope standards to normalize the signal response.
I have found the uv detector to be inheritently more robust, reproducible, and trouble free than the MSD response. ie. the above Na interference would have no effect in delaying my project's completion.
