On-fiber derivatization for determination of ethylene glycol concentration in lubricant oil by SPME-GC/MS

Full text of DOI:10.1002/bkcs.10769

Note
DOI: 10.1002/bkcs.10769
BULLETIN OF THE
J.-B. Lee et al.
KOREAN CHEMICAL SOCIETY
On-fiber Derivatization for Determination of Ethylene Glycol
Concentration in Lubricant oil By SPME-GC/MS
†
‡
†
§
Joon-Bae Lee, Shungkun Shon, O-Seong Kwon, Ji Sook Min,
†
¶,
*
Nam Yee Kim, and Ki-Jung Paeng
†Chemical Analysis Division, National Forensic Service, Wonju 26460, South Korea
‡
Department of Forensic Science, Daejeon Health Institute of Technology, Daejeon 34504, South Korea
§
Daegu District Office, National Forensic Service, Chilgok 39872, South Korea
¶
Department of Chemistry, Yonsei University, Wonju 26493, South Korea. *E-mail: paengk@yonsei.ac.kr
Received January 21, 2016, Accepted February 20, 2016, Published online May 19, 2016
Keywords: Ethylene glycol, Lubricant oil, Solid-phase microextraction, Derivatization, Cyclohexanone,
Gas chromatography/mass spectrometry
5
Lubrication of the moving parts in machinery is required
for their proper function, because it reduces friction and
aids in cooling, while cleaning and sealing the mechanical
contacts. In particular, internal combustion engines cannot
be operated properly without lubricant oil, because the ther-
mal load is too high. However, lubricant oil is deteriorated
by high temperature, combustion products, and extraneous
impurities. Oil can also be contaminated by ethylene glycol
the trimethylsilyloxy (−OSi(CH ) ) group. In this study,
3
3
we employed the ketalization of EG with cyclohexanone
(CH-one) for polluted lubricant oil, because it is less vul-
nerable to ambient moisture than that of trimethylsilylation.
The ketalization or acetalization reaction is usually used in
organic synthesis for protecting the aldehyde and ketone
carbonyl groups, because dioxolane is stable against chemi-
6,7
cally active reagents.
(
EG) leaking from the cooling systems of the equipments.
We adopted CH-one among the C4–C7 cycloalkanone
reagents, following our previous report.8 EG reacts with
CH-one to form a spiro-dioxolane, 1,4-dioxaspiro [4.5]dec-
ane (CAS no.: 177-10-6; MW, 142 g/mol). The dioxolane
is so stable that it is traded commercially for use in interme-
diate organic synthesis. The intensity of the base ion in the
product is higher than that of the base ion in
trimethylsilylized EG.
The EG and internal standard (IS) derivatization reaction
scheme with CH-one is described in Figure 1.
The mass spectra of the derivatized products are
described in Figure 2(a) and (b). The base ions for each
case were the m/z 99 and 103 ions.
Ethylene glycol (CH OHCH OH, EG) is the main compo-
2
2
nent of coolant used in internal combustion engines. In
many cases, coolant from the cooling system could leak
into the lubricating system, particularly in machinery under
harsh and overloaded conditions. Contamination of oil with
EG reduces its tribological properties, which lead to engine
cylinder fusion. Thus, the periodic examination of lubricant
oil is necessary to prevent this phenomenon. To this end,
ASTM Method D 2982 is a commonly used local test
1
method to inspect oil. However, this method applies color-
imetric measurement using a Schiff’s reagent, which may
lead to inexact determination of the state of the oil. Incor-
rect results may be generated because the color developing
reaction may occur for inherent aldehydes in the oil as well
Moreover, combining derivatization and extraction using
solid-phase microextraction (SPME) makes it possible to
conduct the pretreatment process with easier and faster
way. In addition, this method needs no solvent, so it is an
environment friendly analysis.
2
,3
as oxidized combustion products.
4
Therefore, methods using gas chromatography (GC) or
gas chromatography/mass spectrometry (GC/MS) are
recommended to overcome this flaw. However, GC/MS
analysis requires a cumbersome pretreatment step including
solvent extraction from the complex matrix of contaminated
lubricant oil. For enhanced GC performance, an extra-
pretreatment process in addition to extraction, purification,
and concentration is often required. The highly polar target
compounds must be converted into less polar, more vola-
tile, and stable compounds to increase their analytical per-
formance, which is accomplished by derivatization.
Trimethysilylation (TMS) is generally used for alcohol
samples to protect hydroxyl group (−OH) by converting to
SPME fiber is composed of silica rods coated with
adsorbent. It looks like the syringe needle, so it can be eas-
ily injected into a GC. The SPME principle is the extraction
on the fiber as the respective partition ratio between the
fiber polymers and the target compound in the sample.
Polymers on commercial SPME fibers are polydimethylsi-
loxane (PDMS), polyacrylate (PA), and copolymers of divi-
nylbenzene (DVB), polyethylene glycol (PEG), or
9–11
carboxen (CAR).
These compounds have different pola-
rities, which is distinguished by the hub color in SPME
fibers, as shown in Table 1.
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The extraction by SPME and derivatization has been
widely applied to complex matrix samples as urine, algae,
and wine.
the best performance for spiro-dioxolane and ketalized EG
among the five kinds of fibers, which may have been due
to the excellent adsorption properties of carboxen with vari-
ous pore sizes.
This result could be compared to the calculated area
response value of EG and CH-one by multiplying the area
response of m/z 31 for EG and are a response of m/z 55 for
CH-one and the calculated results are shown in Figure 4.
The spiro-dioxolane area response measured by GC/MS
was similar to that of the multiplied area response of m/z
31 for EG and m/z 55 for CH-one in its tendency to be
absorbed through the SPME fibers.
12–14
The mass spectra for EG and CH-one are obtained. The
average area response of each fiber for the EG (m/z 31),
CH-one (m/z 55), and derivatized EG (m/z 99) base ions is
shown in Figure 3. Based on these results, we adopted
CAR/PDMS fiber to measure EG in the lubricant oil.
The area response of EG was smaller in all fibers com-
pared to that of CH-one and spiro-dioxolane. This was
probably due to the ionic stability of EG in the MS and its
extraction ability on SPME fiber. CAR/PDMS fiber showed
Therefore, the adsorption abilities of the analyte and the
derivatizing reagent on the fiber should be similar in capac-
ity to obtain the best performance when combining adsorp-
tion and derivatization on SPME fibers using GC/MS
analysis.
The area response for the m/z 99 and 103 ions is depicted
in Figure 5 for the standard oil sample containing
0.01–20 mg/g of EG. The IS concentration added was the
same for all samples.
As the concentration of EG increased, the area response
for the derivatized IS showed a decreasing trend in contrast
to that for derivatized EG. This was probably due to mass
detector saturation and competition of EG and IS for the
H
H
O
HO
H
OH
O
H
D
O
O
D
D
HO
D
O
OH
D
D
D
D
Figure 1. Reaction scheme of EG and the IS with CH-one.
Figure 2. Mass spectra of (a) derivatized EG and (b) derivatized IS obtained from SPME-GC/MS.
Table 1. SPME fibers used.
ꢀ
Fiber coating type
Polarity
Hub color
Maximum temperature ( C)
Fiber conditioning
ꢀ
PEG, 60 μm
Polar
Purple
Black
Red
White
Gray
250
310
280
300
270
240 C (0.5 h)
ꢀ
CAR/PDMS, 75 μm
PDMS, 100 μm
PA, 85 μm
Bipolar
Nonpolar
Polar
300 C (1 h)
ꢀ
250 C (0.5 h)
ꢀ
280 C (1 h)
ꢀ
DVB/CAR/PDMS, 50 μm
Bipolar
270 C (1 h)
Bull. Korean Chem. Soc. 2016, Vol. 37, 938–941
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KOREAN CHEMICAL SOCIETY
30
25
20
15
10
5
0
limited number of adsorption sites; thus, increasing the
spiro-dioxolane concentration resulted in a plateau at higher
concentration.
The EG calibration curve in the standard lubricating oil
samples is shown in Figure 6. The ratio of the area for the
m/z 99 ions of 1,4-dioxaspiro[4.5]decane from EG at
Area Response for SPME fibers
EG CH-one Spiro-Dioxolane
7.96 min and the area for the m/z 103 ions in d -1,4-dioxas-
4
piro[4.5]decane from the IS at 7.93 min was plotted against
EG concentration. The EG calibration curve with CH-one
2
exhibited a 0.9926 r value and showed good linearity. The
detection limit for the analysis was < 0.1 μg/g in the oil.
1
1
200
000
Area responses of m/z 99 for EG and m/z 103 for IS
8
6
4
2
00
00
00
00
0
SPME Fiber
Figure 3. Area response for the base ions of ethylene glycol (EG),
cyclohexanone (CH-one), and ketalized EG in the oil sample
m/z 99 for EG
m/z 103 for IS
(1000 μg/g).
0
5
10
15
20
Concentration of EG (mg/g)
30
25
20
15
10
5
0
Comparison of area response
Figure 5. The area response of derivatized ethylene glycol (EG)
m/z 99) and derivatized internal standard (IS) (m/z 103) with
CAR/PDMS fibers at 250 μg/g IS in the oil sample.
(
Multiplied
Measured
60
Calibration curve for derivatized EG
with CAR/PDMS fiber
5
4
0
0
y = 2.4713[EG] - 0.0049
r2 = 0.9926
30
20
10
0
SPME fiber
0
5
10
15
20
25
Concentration of EG (mg/g)
Figure 4. Comparison of the area response between the m/z
9 ions of ketalized EG and the multiplied area response with the
m/z 31 ions of EG and the m/z 55 ions of CH-one.
9
Figure 6. Ethylene glycol (EG) and CH-one calibration curve
with CAR/PDMS fibers.
Bull. Korean Chem. Soc. 2016, Vol. 37, 938–941
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Table 2. Gerstel MPS2 A/S conditions.
Table 3. GC/MS condition.
Autosampler (A/S)
Condition
Instrument Condition
ꢀ
ꢀ
Agitator
Fiber
Incubation temperature
Incubation time
Speed
Pre-bakeout time
Derivatization mode
Derivatization time
Extraction time
Desorption time
40 C
GC/MS
Injector
temperature
250 C
10.00 min
250 rpm
10.00 min
Post-extraction
0.20 min
Split ratio
Transfer line
temperature
Carrier gas
Oven
40:1
ꢀ
280 C
He 1.0 mL/min
ꢀ
ꢀ
60 C (3 min) ! (10 C/
Sample
5.00 min
3.00 min
ꢀ
ꢀ
ꢀ
temperature
min) ! 130 C ! (25 C/
min) ! 250 C (10.2 min)
Column
DB-5MS (0.25 mm × 0.25
μm × 30 m)
And, this method is successfully applied to real samples
with good accuracy and precision.
In this study, we examined EG in polluted oil using
GC/MS analysis and a combined SPME fiber extraction
and derivatization with CH-one. This method proved to be
solvent free, easy, and fast.
Among the five kinds of SPME fibers, CAR/PDMS fiber
showed better performance than that of the others. A satura-
tion effect was observed at higher concentrations. The
ꢀ
Ion source
temperature
230 C
in a post-extraction mode by exposing the extracted EG on
the SPME fiber to CH-one vapor containing 10% TMCS
for 12 s.
2
References
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bration curve was 0.9926.
1
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4
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1
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2
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Bull. Korean Chem. Soc. 2016, Vol. 37, 938–941
© 2016 Korean Chemical Society, Seoul & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.bkcs.wiley-vch.de
941