Chromatography Forum

hello
what are the bufers used in mass with some detail
thank you

Use volatile buffers like Acidic , fromic , TFA ammoniumacetate , Ammonium formate, TEA etc

Use volatile buffer such as Ammonium Formate or Ammonium Acetate and Formic acid or Acetic acid.
For example,

Mobile Phase A : 3 mM Ammonium Formate/0.1% Formic acid in Water
Mobile Phase B : Acetonitrile or 0.1% Formic acid/Acetonitrile (some application use Methanol)

All solvent minimum as HPLC grade or use LC-MS grade is reccommended.

Jetjamnong

thank you for your reponses
can you explain me the difference bettween formate and acetate

are acetate/formate of TEA, DEA and TMA volatils
what about nitrate
...

Here are detailed of LC-MS user manual about solvents and Buffers
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Solvents :
ESI requires polar solvents. Non-polar solvents, however, can often be used successfully if a polar modifier is added. For example, toluene, a non-polar solvent, modified with 15% isopropyl alcohol can be used as a solvent for the ESI analysis of fullerenes in negative ion mode. The following table includes examples of other solvents that can be used for normal-phase chromatography when modifiers are added. For positive ionization, mixtures of acetonitrile/water, methanol/water, and isopropyl alcohol/water are most common but other mixtures can be used with success. Acetonitrile/water, isopropyl alcohol/water and n-propyl alcohol/water are good starting mixtures for negative ionization. API-electrospray sensitivity is best with either acetonitrile or methanol and water. Typically, the pH of the mobile phase is adjusted in order to cause the highest yield of ionization in the solution phase.

Partial list of solvents and their suitability for ESI
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Commonly used Special cases
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Water (<80%)Benzene,1
MethanolCarbon disulfide,1
EthanolCarbon tetrachloride
n-Propyl alcoholCyclohexane,1,2
Isopropyl alcoholHexane,1
t-Butyl alcoholLigroin,1
AcetonitrileMethylene chloride,1,2
AcetoneToluene,1,2
Tetrahydrofuran
Acetic acid
Formic acid
Chloroform
Formamide
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1,Requires modifier
2,Normal-phase chromatography
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Buffers :
Buffers are used for many reasons including:
Adjusting solution pH to support ion formation in solution (generally, positive analyte ions are formed more readily in acidic solutions and negative analyte ions are formed more readily in basic solutions). Ensure formation of specific desired adduct ions or prevent the formation of undesirable adducts Assist or optimize chromatography a buffer is added. Buffers that assist or optimize chromatography and those that do not hinder the electrospray process can be added before the separation. Buffers that interfere with the separation must be added post column. For most positive ion analysis of polar materials such as amino acids, peptides and proteins, the pH of the solution should be adjusted to a pH of 2 – 5. The addition of acetic acid at 0.1% to 0.2% is a good starting point. For positive ion analysis of pharmaceuticals, a solution of 0.015 % formic acid serves the same purpose and may have less chemical noise and smell than acetic acid. Some pharmaceutical compounds can be analyzed successfully in a neutral mobile phase. For example, benzodiazepines and opiates can be analyzed with a traditional mobile phase of acetonitrile and water. Buffers such as sodium acetate or potassium acetate (alkali metals) can be used to form adducts with the analytes that would otherwise not ionize in solution. Sugars and urea are two examples of chemicals that form sodium adducts that can be analyzed in positive ion mode. Other buffers, such as ammonium acetate and ammonium formate, are sometimes added to prevent undesired adduction of the analyte with sodium or potassium ions from endogenous sources. Buffers can be used to optimize chromatography. The addition of 50 micromolar ammonium acetate or ammonium formate is often used to increase chromatographic resolution of basic nitrogen containing compounds on reversed-phase silica columns. This improves the peak shape, thereby enhancing signal and improving sensitivity. The final solution (solvent + analyte) should be neutral to acidic for good positive ionization.
Buffers or other additives used to optimize chromatography can sometimes interfere with the ionization process. For example, TFA is almost always used for the chromatography of peptides and proteins. TFA enhances the chromatographic
resolution but may actually suppress ion formation. Post-separation addition of a weaker acid such as propionic acid can effectively counteract the TFA ion suppression problem.
When performing ESI standard buffers such as phosphate, borate, and sulfate buffers are non-volatile and form ion pairs in solution. To maximize ESI sensitivity, use buffers that are volatile and do not form ion pairs. Adjust the pH with buffers, formic acid, acetic acid, and ammonium hydroxide or triethylamine. Typical pH for positive ion is neutral to pH 2 and for negative mode typical pH is neutral to pH 10. For ion pair separations, use additives such as heptafluoro butyric acid or tetraethylammonium hydroxide or tetrabutylammonium hydroxide.

Jetjamnong

thank you Jetjamnong for your detailed answer
but I have other questions
what we prefer buffer or acidic additif (formic...)
is it true that TFA enhanse the sensitivity in mass
what is the highest concentration of a salt in LC/MS
is 200mM caused problem

Normally, Formic acid is better than Acetic acid in term of volatility and backgroud noises.
200 mM TFA is very high concentration when using with LC/MS. I think TFA is the buffer that can reduces the LC/MS signal, it's not to enhance the sensitivity in LC/MS. TFA has serious disadvantages for LC/MS, while TFA has little effect on UV detection.

200mM of buffer not of TFA (this concentration is very acidic)
an other question
what is the lower LOD of UV-Vis detector (

For positive ion analysis of pharmaceuticals, a solution of 0.015 % formic acid serves the same purpose and may have less chemical noise and smell than acetic acid.

Thing more important to keep in mind than smell is that formate and acetate have differend pKa and therefore differen buffering ranges. Going outside range you end up with solution of particular but not necssarily stable pH.

Suggestions given by others are good. Only thing i want to add is that avoid TEA as the background will be contaminated for a long time.

200 mM of any buffer is extremely high for LC-ESI-MS and you may experience strong ion suppression at this concentration. Generic conditions range from 5-50 mM. Some applications (e.g. HILIC-ESI-MS) require higher buffer concentration for chromatographic reasons, which may be detrimental to MS sensitivity.

hello
I continue in the same subject
when we ajust the pH of a mobile phase, we use the same acid then used
can I ajuste the pH with anothet acid like HCl, HNO3 ...
are they volatils (HCl and HNO3)
is it better to ajust the pH of the aquous phase or the mobile phase
thank you

Personally, I avoid inorganic acids, and prefer to keep buffers as defined as possible. For example, if I want to make a 20mM ammonium acetate buffer pH 7.5, I prepare 20mM ammonium hydroxide and 20mM ammonium acetate, and mix to pH. That way I know that the overall concentration of ammonium is 20mM and assuming my pH meter is calibrated and temperature isn't too variable, I have a defined pH. Others will probably disagree, and life is far from perfect: it's hard to make a defined 20mM solution of something as volatile as ammonium hydroxide.

I adjust the pH of aqueous buffers, but not of organic solvents. In an aprotic solvent such as acetonitrile, which has no acid hydrogens, pH is a concept I don't properly understand! Most of my methods involve gradients, and rarely reach 100% organic. To me, it doesn't matter what the pH actually is in the column, and how it is affected by addition of organic solvent, provided the pH is the same every time I run the method, and peak shapes/retention times remain reasonably constant.

thank you
In my case, I have adjusted the pH of the aquous phase, but the apparent pH of the mobile phse ( I use the HILIC mode) increase.
however, I will be near the pKa of my analyte or in a form different that I like
when I adjust the pH (mobile phase) with the organic acid, I must use a high amount