Analysis of Carbaryl and Carbofuran in Drinking ... - BGB Analytik AG

Results and Discussion
Separation
The standard solutions were analyzed by injecting 10 µL of
each of the standard solutions onto the Agilent TC-C18(2)
column. The chromatograms from the standard injections
(Figure 3) show high performance, high resolution, and symmetrical
peaks. We have also run this on an HC-C18(2) column.
A little longer retention was achieved with almost the
same performance as with the TC-C18(2) column. These
columns have a different carbon load: 17 percent for the
HC-C18(2) column and 12 percent for the TC-C18(2) column.
These differences impact retention, with the HC-C18(2) column
typically retaining nonpolar and moderately polar compounds
more when compared with the TC-C18(2) column. We
prefer the column providing a shorter analysis time but resolving
all the peaks. Although both columns are suitable for this
method, we chose the TC-C18(2) because it provided a slightly
shorter analysis time.
LU
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
Carbofuran
4.88 ng
Carbaryl
6.0 ng
0 2 4 6 8 10 12
Figure 3. Chromatogram of carbofuran and carbaryl standards on Agilent TC-C18(2),
4.6 × 150 mm, 5 µm columns.
Linearity, Reproducibility, and Limit of Detection
The calibration curves resulting from these standard injections
on the TC-C18(2) column are shown in Figure 4. The
method shows excellent linearity, being very close to 1.0
(0.9997). To evaluate the reproducibility of this method on the
TC-C18(2) column, two concentrations of carbofuran and carbaryl
were each injected 10 times. The reproducibility of the
peak areas is shown in Table 2; the absolute peak area reproducibility
is superior. The average relative standard deviation
(RSD) is below 3 percent. We calculate the LOD from the
level 1 standard with a signal-to-noise ratio of 3. The LOD is
0.066 ng for carbofuran and 0.080 ng for carbaryl, which is
three to four times better than the 0.25 ng that is regulated by
China's drinking water standard.
min
4
Area
80
60
40
20
0
Area
70
60
50
40
30
20
10
0
0
0
1 2
1 2
Carbofuran, FLD1 A
Area = 7.38558201*Amt + 0
Rel. Res%(4): 3.286
3
5
Amount[ng]
Carbaryl, FLD1 A
Area = 6.73870683*Amt + 0
Rel. Res%(1): _ 3.824
3
Table 2. Reproducibility of Standards Injections
4
4
10
5
Correlation: 0.99975
5 10
Amount[ng]
5
Correlation: 0.99974
Figure 4. Calibration curves of carbofuran and carbaryl [Agilent TC-C18(2),
4.6 × 150 mm, 5 µm columns].
RSD (%) n = 10 RSD (%) n = 10
Carbofuran 48.8 ppb Carbofuran 488 ppb
Analyte Carbaryl 60.0 ppb Carbaryl 600 ppb
Carbofuran 2.3 1.6
Carbaryl 1.8 1.5
Recovery
Two different levels were spiked in reagent water and tap
water, respectively, and then followed the sample preparation
procedure. The recovery data are good, with a typical recovery
in the range of 80 to 110 percent (Table 3).
To better match the China drinking water method, in which
dichloromethane is used for liquid-liquid extraction, we chose
dichloromethane as the SPE cartridge eluent. That provided us
clean chromatograms.