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- Posts: 292
- Joined: Wed Jan 19, 2005 2:20 pm
Working in the pharma. industry the majority of our analytes are basic, and thus we tend to work in the +ve ESI mode when using LC-MS quadropole instruments.
Recently we have been having trouble with obtaining suitable S/N sensitivity to identify unknown peaks in our total ion chromatograms (TIC). We have only been observing the main peak. Our analytical flow rate is 1.0 ml/min and we run with water/AcN/MeOH gradients that contain 0.05% TFA. The split post column from the DAD is approximately set so that a flow of 500µL/min enters the LC-MS. Recently some colleagues, looking to optimise the LC-MS TIC response, reduced the effluent flow to the LC-MS to ca. 200µL/min. They observed a dramatic increase in the S/N ratio and were able to decipher more peaks than just the main peak!
My question then is: what is the optimum flow rate setting for the LC-MS in ESI +ve mode (quadrople) to obtain good S/N of small impurity peaks in the TIC trace? Is 200µL/min still too large? Also what flow splitter device would users recommend? Currently we are using a simple tee-piece but may not be most user friendly device out there. We are considering either a metered valve (http://www.upchurch.com/Products/specsh ... 70&vFrom=L) or a set flow splitter (http://www1.dionex.com/en-us/webdocs/43 ... ro_V12.pdf - p.6). Any opinions on such devices? It appears that the flow splitting box may have a set split flow ratio that may not be ideal if we ever wanted to chnage this.
Recently we have been having trouble with obtaining suitable S/N sensitivity to identify unknown peaks in our total ion chromatograms (TIC). We have only been observing the main peak. Our analytical flow rate is 1.0 ml/min and we run with water/AcN/MeOH gradients that contain 0.05% TFA. The split post column from the DAD is approximately set so that a flow of 500µL/min enters the LC-MS. Recently some colleagues, looking to optimise the LC-MS TIC response, reduced the effluent flow to the LC-MS to ca. 200µL/min. They observed a dramatic increase in the S/N ratio and were able to decipher more peaks than just the main peak!
My question then is: what is the optimum flow rate setting for the LC-MS in ESI +ve mode (quadrople) to obtain good S/N of small impurity peaks in the TIC trace? Is 200µL/min still too large? Also what flow splitter device would users recommend? Currently we are using a simple tee-piece but may not be most user friendly device out there. We are considering either a metered valve (http://www.upchurch.com/Products/specsh ... 70&vFrom=L) or a set flow splitter (http://www1.dionex.com/en-us/webdocs/43 ... ro_V12.pdf - p.6). Any opinions on such devices? It appears that the flow splitting box may have a set split flow ratio that may not be ideal if we ever wanted to chnage this.
