Abstract:
Several automated reversed-phase HPLC methods have been
developed to determine trace concentrations of carbamate
pesticides (which are of concern in Ontario environmental samples)
in water by utilizing two solid sorbent extraction techniques.
One of the methods is known as on-line pre-concentration'.
This technique involves passing 100 milliliters of sample water
through a 3 cm pre-column, packed with 5 micron ODS sorbent, at
flow rates varying from 5-10 mUmin. By the use of a valve
apparatus, the HPLC system is then switched to a gradient mobile
phase program consisting of acetonitrile and water. The analytes,
Propoxur, Carbofuran, Carbaryl, Propham, Captan, Chloropropham,
Barban, and Butylate, which are pre-concentrated on the pre-column,
are eluted and separated on a 25 cm C-8 analytical column and
determined by UV absorption at 220 nm. The total analytical time is
60 minutes, and the pre-column can be used repeatedly for the
analysis of as many as thirty samples. The method is highly
sensitive as 100 percent of the analytes present in the sample can
be injected into the HPLC. No breakthrough of any of the analytes
was observed and the minimum detectable concentrations range
from 10 to 480 ng/L. The developed method is totally automated for
the analysis of one sample.
When the above mobile phase is modified with a buffer
solution, Aminocarb, Benomyl, and its degradation product, MBC, can
also be detected along with the above pesticides with baseline
resolution for all of the analytes. The method can also be easily modified to determine Benomyl and MBC both as solute and as
particulate matter.
By using a commercially available solid phase extraction
cartridge, in lieu of a pre-column, for the extraction and
concentration of analytes, a completely automated method has been
developed with the aid of the Waters Millilab Workstation. Sample
water is loaded at 10 mL/min through a cartridge and the
concentrated analytes are eluted from the sorbent with acetonitrile.
The resulting eluate is blown-down under nitrogen, made up to
volume with water, and injected into the HPLC. The total analytical
time is 90 minutes. Fifty percent of the analytes present in the
sample can be injected into the HPLC, and recoveries for the above
eight pesticides ranged from 84 to 93 percent. The minimum
detectable concentrations range from 20 to 960 ng/L. The developed
method is totally automated for the analysis of up to thirty
consecutive samples. The method has proven to be applicable to both
purer water samples as well as untreated lake water samples.
