by
Kenn » Fri Apr 13, 2018 10:41 pm
Lijun-Zhang wrote:
Hi All,
I want to develop an LCMSMS method for pesticide of Naled analysis.
The settings of precursor and product ions are 398>127 and 398>109.
I don't see the peak even at 200 ppb.
The mobile phase is 0.1% formic acid, 5mM ammonium acetate in water and pure methanol.
Could anyone help me figure out what caused the problem?
You are looking at the wrong mass. I developed and validated a method for Naled about 5 yrs ago for a chronic tox study. Was then analyzing samples over the course of about 6 months twice a week. I was going to scribble down some of the parameters today because I read this post this morning and glanced at some of the data today while at work. I do remember the mobile phases were 0.1% formic in water and 0.1% formic in CH3CN. Gradient started at 10% CH3CN and ran to 90% over the course of 4 min with a 4 min re-equib at 10%. Retention was about 4 min. Column was a Thermo Betasil c18, 50x2.1, 5um. I would suggest you infuse on your own inst to get the rest of the optimized parameters, I would bet I infused in 50:50:0.1 MeOH:H2O:formic. When you start to infuse set the DP to about 60 because that is where it will end up when you optimize. The parent mass is like 381 and for some reason I remember there was some trouble initially seeing it. Give it some time when infusing, it may have been one of those that for some reason doesn't jump out at you the instant you hit start. If you don't see it, force it, tell the inst the mass is 380 w/1 charge and optimize, I bet it finds it even if you don't don't see it when scanning. Positive mode.