Gestagens, a class
of veterinary drugs also called progestogens,
are synthetic hormones used to increase feed efficiency and rate of
gain in heifers. The Canadian Food Inspection Agency analyzes progestogens
melengestrol acetate (MGA), megestrol acetate, and chlormadinone acetate
using liquid chromatography–mass spectrometry (LC–MS).
Our conventional gestagen method for kidney fat has many time-consuming
steps, including solid-phase extraction. A sample preparation procedure
having fewer clean-up steps was developed for routine diagnostic analysis
of kidney fat and provided similar results faster, and at lower cost.
A confirmatory liver method for gestagens, developed using salt-assisted
extraction, employed minimal clean-up steps that resulted in high
chemical background at the desired lower limit of quantification (LLOQ).
Differential ion mobility spectrometry, specifically high-field asymmetric
waveform ion mobility spectrometry (FAIMS), was used to filter chemical
background in the gas phase. The effect of the ionization probe position
on FAIMS parameters, including sensitivity, is described. With LC-FAIMS-MS,
chemical background for each gestagen was virtually eliminated, resulting
in a quantitative liver method having the desired 0.6 ng/g LLOQ and
estimated limits of detection (LODs) up to 140 times lower than LC-MS.
Incurred MGA samples, analyzed using kidney fat and liver methods
from the same animal, show levels within the quantitative ranges of
both methods.