Variable peak area - elaidic acid

[Robotjock]

Virtual Colleagues,

I have been requested to assist a colleague who is experiencing variable peak areas for replicate injections of a standard elaidc acid soln. [Elaidic acid is an impurity in a client's drug substance we manufacture.]
The HPLC conditions....

Agilent 1100 system
Alltech alltima C18, 150 mm x 4.6 mm 5u column
MP A - Water (0.1 % TFA)
MP B - THF (0.1 % TFA)
Gradient - (time/%B): 0/50%, 10/80%, 15/80%, 5 min post time
50 uL injection
Column @ 25C
Flow rate @ 1 mL/min
Detection - ELSD (Alltech 2000) Drift tube temp @ 78C, gas flow @ 2.4 L/min, Impactor is off
Sample diluent - 60% THF/40% MeOH
Sample conc. - 0.1 mg/mL to 1 mg/mL

My colleague has observed ~ 15% RSD for multiple injections from same vial or different vials.

Helpful insights/comments would be appreciated... so would humorous ones! (I can use a good laugh now and then.)

Thanks in advance,

[SIELC_Tech]

try to lower ELSD temperature to 40*C. Elaidic acid might be still volitile at 78*C (sublimation??). We observed lower response for fatty acids C16-C20 until we dropeed temperature from 60*C to 35.

Vlad