Published:Journal of Chromatographic Science,
ISSN 0021-9665Volume
40, Number 6, July 2002, pp. 331-336
Comparison of Ion-Pairing and Ion-Suppressing Liquid Chromatographic
Methods for the Determination of Pyrimethamine and Ormetoprim in Chicken Feed
Shih Yuh Lin and Shiow Lian
Jeng National Institute for Animal Health, Council of Agriculture,
Tansui, Taipei 251, Taiwan
A high-performance liquid chromatographic (HPLC) method is developed
to simultaneously determine pyrimethamine (PYR) and ormetoprim (OMT) in chicken
feed. In the ion-pairing HPLC determination of PYR and OMT, the relation between
the retention factor (k') and the concentration of the organic phase (acetonitrile)
shows a characteristic curve. The k' value first decreases and then increases
slowly with increasing concentrations of acetonitrile, but then increases rapidly
when the acetonitrile concentration increases to 90%. Resolutions (Rs) of PYR
and OMT decrease gradually when the concentration of organic phase increases.
Increasing the concentration of the pairing ion sodium 1-octanesulfonate (PIC
B-8) can decrease the k' and Rs values. Optimum values of k' and Rs are obtained
using 82% acetonitrile in 0.005M PIC B-8. In ion-suppressing HPLC, varying the
concentration of Na2HPO4 has little effect on either the k' or Rs values of
PYR or OMT at pH 7.5. However, at pH 4.0, k' and Rs decline when the concentration
of Na2HPO4 increases. In general, ion-pairing HPLC generates more satisfactory
results than ion-suppressing HPLC. Using 82% acetonitrile in water containing
0.001M PIC B-8 as the mobile phase, linear calibration curves are obtained in
the range from 1 to 5 mg/L of PYR and OMT. Sulfamonomethoxine, sulfadimethoxine,
sulfaquinoxaline, trimethoprim, amprolium, clopidol, and nicarbazin do not interfere
with the detection of PYR or OMT. The recoveries of PYR from spiked feed at
1 and 5 mg/Kg are 73.0% and 72.0%, respectively, and those of OMT from spiked
feed at 3 and 7 mg/Kg are 50.3% and 53.6%, respectively.
Reproduction
of editorial content of this journal is prohibited without publisher’s
permission.
This
article is available in its entirety by fax for $4.00 per
page.
Visa or MasterCard accepted.
To
order electronicallyclick here or call: 847-647-2900 ext. 1323 or fax request to: 847-647-1155.
Please
indicate JCS volume and issue along with
page numbers.
