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2
However, applications of Corexit EC9527A in an oil spill
response could potentially yield localized high concentrations
of 2-butoxyethanol in surface waters. Therefore, an
LC-MS/MS method capable of simultaneously detecting
and quantifying the two main components of Corexit
EC9527A could be useful to assess if this formulation
was used.
Experimental
Reagents and Solvents
2-butoxyethanol was from the Acros Organics brand, part
of Thermo Fisher Scientific. The surrogate standards
sodium dodecyl-
d
25
sulfate (DDS-
2
H
25
) and
2-butoxyethanol-
2
H
4
were purchased from CDN Isotope
Laboratories (Quebec, Canada). Certified DOSS and
DOSS-
13
C
4
standards were purchased from Cambridge
Isotopes Laboratories (Andover, MA). Stock and working
solutions of all compounds were prepared in acetonitrile.
The concentrations of the stock solutions were as follows:
DOSS and DOSS-
13
C
4
were 100 mg/L (certified standards);
2-butoxyethanol was 8000 mg/L; 2-butoxyethanol-
2
H
4
was 20000 mg/L; and DDS-
2
H
25
was 72 mg/L. Working
solutions concentrations are presented in the Sample
Preparation section. Artificial seawater was prepared to
3.5% w/v using the commercially available Instant Ocean
®
sea salt. Chromatographic studies were performed using
Fisher Chemical
™
Optima
™
LC/MS-grade formic acid,
acetonitrile, and water.
Sample Preparation
Seawater
Seawater samples were collected from Biscayne Bay in
Florida and filtered through 0.45 µm fiberglass filters.
A 5 mL seawater subsample was placed in a glass vial
containing 2.5 mL of Optima-grade acetonitrile and
stored until analysis. Then, 1200 µL of the acetonitrile-
diluted seawater was transferred to a 2 mL amber LC vial
already containing 47 µL of acetonitrile and 200 µL of
artificial seawater. To that was added 18.9 µL of DDS-
2
H
25
surrogate (7.9 mg/L in acetonitrile), 18.8 µL of
2-butoxyethanol-2H4 surrogate (8.0 mg/L in acetonitrile),
and 15.8 µL of DOSS-
13
C
4
surrogate (1.9 mg/L in
acetonitrile) for a final volume of 1500 µL that maintained
the 33.3% v/v of acetonitrile. The samples were thoroughly
mixed using a vortex and analyzed directly by LC-MS/MS.
Crude oil
A sample of sweet-light crude oil from the MC-252 riser,
known to contain DOSS, and a sweet-light crude oil from
the Wilcox formation in Texas, were used to test the
method. The crude oil samples (5.0 µL) were added to 2 mL
amber LC vials and spiked with 37.5 µL of
2-butoxyethanol-
2
H
4
surrogate and 40.0 µL of DOSS-
13
C
4
surrogate. The surrogate-fortified oil was suspended in
1260 µL of acetonitrile, capped, and mixed using a vortex
for 2 min. This resulted in a two-phase system with
undissolved oil on the vial walls. For instrumental analysis,
an aliquot from the acetonitrile phase of each sample was
added to a new 2 mL amber LC vial containing 1000 µL
of artificial seawater and 18.9 µL DDS-
2
H
25
surrogate.
Acetonitrile was added to make a final volume of 1500 µL.
To minimize analysis time and ensure method uniformity,
the injected sample was prepared to match the 66%
seawater and 33% acetonitrile matrix of the calibration
solutions and seawater samples.
Calibration solutions
Calibration solutions were prepared in artificial seawater
with the same salt and acetonitrile ratio of the analysis-
ready seawater and oil samples. Then, 1000 µL of
artificial seawater was transferred to a 2 mL LC amber
vial, and 18.9 µL of DDS-
2
H
25
surrogate, 18.8 µL of
2-butoxyethanol-
2
H
4
surrogate, and 15.8 µL of DOSS-
13
C
4
surrogate were added. Increasing amounts of DOSS
and 2-butoxyethanol were added to the solutions, and
acetonitrile was added to make a final volume of 1500 µL.
A seven-point calibration set was freshly prepared for
each analysis day.
Liquid Chromatography
HPLC analysis was performed using a Thermo Scientific
™
Accela
™
quaternary pump equipped with an HTC-PAL
™
autosampler system (CTC Analytics, Zwingen, Switzerland).
LC Parameters
Column:
Thermo Scientific
™
Hypersil GOLD
™
aQ column
(50 mm × 2.1 mm, 3 µm particle size)
Pre-column
Hypersil GOLD aQ (10 mm x 2.1 mm, 3 µm
particle size)
Injection volume 20 µL
Run time
10 min
Flow rate
325 µL/min
Mobile phase A 0.1% formic acid and 1% water in acetonitrile
Mobile phase B 0.1% formic acid in water
Gradient
Time
%A
%B
0.0
2
98
0.9
2
98
3.7
98
2
5.6
98
2
5.9
2
98
10.0
2
98
Instrument control and data acquisition was performed
using Thermo Scientific
™
Xcalibur
™
software version 2.1.