What is the most preferred solvent for dissolving a sample prior to injection on GC/MSD especially for pesticide analysis?
It depends on the pesticides you are analysing and also on the matrix from where the pesticides are being extracted. Ethyl acetate or acetonitrile are good solvents for this purpose. Generally modified QuEChERS methods prefer to use EA or ACN. These solvents can extract most of the pesticides present in a matrix, but still some matrices need different approaches. Selection of solvent depends on many factors like solubility, polarity; and as GCMS operates at high temperature, vapour generated from solvent after injecting sample plays important role. You can find good papers on this aspects.
It depends on the pesticides you are analysing and also on the matrix from where the pesticides are being extracted. Ethyl acetate or acetonitrile are good solvents for this purpose. Generally modified QuEChERS methods prefer to use EA or ACN. These solvents can extract most of the pesticides present in a matrix, but still some matrices need different approaches. Selection of solvent depends on many factors like solubility, polarity; and as GCMS operates at high temperature, vapour generated from solvent after injecting sample plays important role. You can find good papers on this aspects.
Ethyl acetate and acetonitrile are undoubtly good solvents. In the past, when I was dealing with pesticide analysis on vegetables I used Dichloromethane that has a wide extraction spectrum over a lot of different active substances. But it is quite harmful for the operator. In rotavapor you can concentrate your extract at 35°C without grat losses of more volatile substances (i.e. Dichlorvos..) whereas with ethyl acetate e.g. you have to set temperature of rotavapor bath at least at 55°C (if you concentyrate in nitrogen of air flow, this problem could be overcome: to avoid loss of more volatile compound you can add some 100-500 ul of toluene to avoid complete evaporation of the solvent and consequent complete loss of more volatile active substances). Dichloromethane but also ethyl acetate have good extraction power but they are not soluble in water: if you dry your homogenized vegetable with extralut or diatomaceous earth you can extract your pesticides without many interfering co-extracts; if the dried vegetable has too residue moisture your recoveries will be poor. Acetone has also good extraction power and in also soluble in water, so it is good for interacting with acqueous phase of the vegetable and for extracting pesticides, but also extracts many and interfering matrix substances. You can find exhaustive paper where acetonitrile is used as extraction solvent in 100-200 substances multiresidue methods.
Just in general, methanol is a very good solvent since it has a very low molecular weight (32) and will not show up in your background. For example, you could analyze ethanol using MEOH as a solvent scanning 35 to 100. For pesticides, we would usually screen on a GC/ECD or GC/NPD and confirm on GC/MS, usually in SIM mode. Solvent was usually hexane or dichloromethane.
It completely depends upon your sample and the pesticides you're looking for. As a general screening method QuEChERS is an outstanding method; we directly inject the acetonitrile without any major problems using large volume/low split ratio injections. Acetonitrile/QuEChERS is not good for some compounds. In those cases you're better off using a polar solvent with solvent exchange into MeCl2 or hexane.
As long as you're careful with your injection technique any solvent lighter than toluene will perform adequately.
There is one rule: Similar dissolved in a similar. If You analyze water samples You have to use polar solvent, for example: methanol or acetonitirile. If You use standards dissolved in hexane or isooctan, then water sample does not mix with the standards. You will have a similar situation when you mix water with oil. If You analyze fruits or vegetables I recommend QuEChERS method.
thanks all but i need to know if i inject directly in acetonitrile is that has any bad effect on GCMS system like shortten filament life time
After proper clean-up of your sample you can directly inject ACN or EA to your system. Use low sample volume.
absolutely not. If You use a GC grade pure acetonitirle will be fine. Of course after long work and many samples You will have to clean ion source, but it is not so complicated process. When You calibrate equipment and optimize separations of compounds You have to use standards in pure solvent. I never have problems with acetonitirle on GCMS.
Hexane and Acetonitrile als well as a mixture of both give good results on non polar and medium polar GC columns.
You have to be aware of a vapour volume of Acetonitrile to be as twice as n-Hexane. From my experience, Methanol is not a very good choice on non polar colums and has the largest vapour volume (three times than n-Hexane).
for detection of aromatic compounds in a sample what solvent we should use
Hexane is good injection solvent because the vapor volume is low and would not over-flow the injector liner. However, it may not dissolve polar pesticide such as OP and NSO. I would use ethyl acetate or acetonirile.
I have similar problem now.....please solvent can be used for GCMS analysis of aqueous extract in order to detect aromatic plant components.
Acetonitrile is the most suitable solvent for extraction of a wide polarity range of pesticide residues. Very low volatility of toluene make this solvent also highly suitable. See the article “K. Maštovsk´a, S.J. Lehotay / J. Chromatogr. A 1040 (2004) 259–272”.
n-Hexane is the most famous and suitable solvent and in some cases we used Dichloromethane.
From the injection volume, point of view
Hexane and isooctane are the best..but analyte solubility/compatibility still a concern
http://www.agilent.com/cs/library/Support/Documents/F03050.pdf
In case of the solvents direct injection is not expected to make problem in your GC, but it is preferred to use split mode for direct injection more owing to protection of the column.
Several aspects have to be considered...analyte solubility and injection conditions are most critical.
check the sites
http://www.restek.com/images/calcs/calc_backflash.htm
https://www.fda.gov/Food/FoodScienceResearch/LaboratoryMethods/ucm2006955.htm
https://www.intechopen.com/search?term=gc
which solvent is better for direct injection of 10 mg/L Dichlorovos in GC Mass ?can we use Deionized water as a solvent?is that water problem for GC?
I am new to pesticide analysis using GC/MS ...so this might sound stupid question...can we use standards in Toulene or they have to be in ACN?.
What is the most preferred solvent for dissolving leave sample prior to injection on GC-MS.
Well let me tell you at the onset that several factors needs to be taken into consideration before deciding on the solvent and these are as follows:
1. the choice of the operator (if the instrument is taking jobs for outsiders. Ultimately they can not afford a breakdown frequently.
2. Solubility of the compound (to be more precise, partition coefficient between different solvents). The solution should be very clear and not turbid or colloidal etc.
3. Certain solvents are forbidden like DMSO, cyclohexane, benzene, toluene, DMF, etc. It can kill the columns of GC and MS as well.
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