Environmental Engineering Reference
In-Depth Information
was used. In another study, using hexane and dichloromethane as extraction solvents was found to
interfere with quantitation of 1,4-dioxane in the mass spectrometer. Use of a lower molecular weight
solvent, acetonitrile, was found to avert the interference (Song and Zhang, 1997).
SPE media must be completely air-dried prior to solvent extraction, or the eluted solvent must
be dehydrated by using anhydrous sodium sulfate crystals. When water is present in the eluate
from the SPE media, the resulting chromatographic peaks for 1,4-dioxane and 1,4-dioxane-d
8
become signii cantly less sharp. With increasing water content, a shoulder develops on the left side
of the peak between 13.3 and 13.5 min at 7.6% water content. At 14% water content, the peak
broadens dramatically between 13 and 13.5 min (Kawata et al., 2001). To eliminate water from the
SPE cartridge, researchers recommend drying with clean laboratory air for 2 min using an aspira-
tor, followed by centrifuging at 1700
g
(3000 RPM) for 10 min (Kawata et al., 2001). Figure 4.5
displays the deterioration of the 1,4-dioxane peak with increasing water content.
The temperature at which SPE desorption of target analytes occurs also affects the size of the peak
area, that is, the recovery efi ciency of the extraction. A German study of SPDE effectiveness deter-
mined that increasing the desorption temperature between 30°C and 70°C increased the efi ciency of
extraction at higher temperatures. A plot of chromatographic peak area versus extraction temperature
creates a series of exponential curves. The curve determined for 1.4-dioxane is described by
y
= (1.73 × 10
5
)e
0.0376
X
,
(4.2)
where
y
is the peak area and
X
is the extraction temperature in Celsius. The correlation coefi cient
was 0.999. For 1,4-dioxane, extraction recovery at 70°C is 4.5 times greater than at 30°C (Jochmann
100
Confirmation ion,
m
/
z
= 88
0
100
Water content = 0%
Quantitation ion,
m
/
z
= 58
0
12.5
13.0
13.5
14.0
100
88
100
0
Water content = 1.6%
58
0
12.5
13.0
13.5
14.0
100
88
0
100
Water content = 7.6%
58
0
12.5
13.0
13.5
14.0
100
88
0
100
Water content = 14%
58
0
12.5
13.0
Retention time (min)
13.5
14.0
FIGURE 4.5
Deterioration of 1,4-dioxane peak with increasing water content. (After Kawata, K. et al., 2001,
Journal of Chromatography
A
911: 75-83. With permission.)
Search WWH ::
Custom Search