Tłumaczenie tekstu naukowego - Tłumaczenia

Poproszę bardzo o przetłumaczenie tekstu naukowego, a dokładnie działów
1. Wprowadzenie
2.Materiały i metody
2.1
2.2
2.3
3. Wyniki i dyskusja :)

1. Introduction
Persistent organic pollutants (POPs) are toxic chemical compounds
that stay stable in the environment over extended periods
of time and biomagnify as they move up through the food chain.
The use of these compounds was banned [1] or restricted [2] in
the European Union in the 1970s due to their low biodegradability,
high persistence and toxicity characteristics that include cancerinducing
and endocrine-disrupting properties. Within this group,
some organochlorine pesticides (OCPs) and polichlorobiphenyls
(PCBs) are of special concern since the Stockholm Convention,in 2001, when they were included in the so-called “dirty-dozen”
[3].
Fish oil is a by-product of the fish meal manufacturing industry.
Concentrated omega-3 fatty acids can be found in fish oil, whose
daily ingestion slows down the progression of coronary artery disease
[4]. Since POPs are lipophilic and tend to accumulate through
the aquatic food chain [5], they can be found in the lipid compartments
of fish and also in the products extracted thereby. Thus, it has
been reported that fish oils contain relatively high levels of OCPs,
PCBs and other POPs [6–11].
The preferred technique for the determination of volatile pesticides
in oils is capillary gas chromatography (GC) due to its high
separation efficiency and the variety of selective detection methods
that can be used. For the particular case of organochlorine compounds,
electron-capture detection (ECD) has been widely used due to its high sensitivity and selectivity [12–14]. Nevertheless, analytical
problems associated with the analysis of pesticides in fatty
matrices are well known and thus the unequivocal confirmation
of identity is often compromised. Mass spectrometry (MS), usually
in the selected ion monitoring (SIM) mode, is the preferred
method of choice [14–17] although confidence in the confirmation
of identity may be reduced if one or more of the selected
ions are affected by matrix interferences, giving poor spectral
information. Alternatively, MS/MS with ion trap [18,19] or triple
quadrupole [14,20] can be employed to achieve a high level of
selectivity and low detection limits in dirty extracts [21]. Other
authors have used high resolution mass spectrometry (HRMS) [17]
and reverse-phase liquid chromatography coupled to GC with ECD
and nitrogen-phosphorus detection for this purpose [22]. More
recently, Hoh et al. have used the comprehensive two-dimensional
GC coupled to time-of-flight mass spectrometry (TOF-MS) after
direct sample injection for the analysis of fish oils [23,24]. In these
papers, not only the authors have determined target analytes, but
they also have managed to identify unknown peaks in the traditional
one-dimensional GC–MS analysis, thanks to the increase
of the power separation and to the mass spectra provided by
the TOF-MS. It is evident that all these techniques allow reducing
significantly the sample preparation step, but they are either
too expensive or too sophisticated to be implemented for routine
analysis.
Due to the large variety of POPs to be determined and also to
the complex nature of the matrix, the trace analysis of these compounds
requires the development of multiresidue methodologies
including sample preparation prior to analytical determination.
In general, the sample preparation consists of two separate steps
[7,25]. First, the lipids are destroyed by adding concentrated
sulphuric acid, and second, a clean-up step by gel permeation chromatography
(GPC) and/or mixed silica, alumina or florisil columns
is carried out. More recently, other techniques have been used,
such as dialysis instead of sulphuric acid followed by a cleanup
was carried out with neutral and acid silica gel multilayer
column [26] or ultrasonication followed by single drop microextraction
[27] but these are still two-step strategies for sample
preparation.
These approaches lead to extremely time consuming sample
preparations and also large amounts of reagents to be used,
which generates considerable liquid and solid wastes. For this
reason a single-step strategy with minimal reagent consumption
for sample preparation is preferable. In this way, a previous
work using this strategy and GC-ECD as analytical technique
for the determination of DDTs was carried out with satisfactory
results [28]. However, more efforts had to be made to go
on decreasing the reagents consumed and the analysis time,
and also other analytes of environmental concern had to be
studied to widen the applications and mass spectrometry had
to be used as detector so as to get a more unambiguous
determination.
The aim of this work is to improve the sample preparation
in terms of economy, time of analysis and respect for the
environment without sacrificing sensitivity, accuracy and precision
in fish oil samples, for the determination of -, -, - and
-HCH, p,p-DDT, p,p-DDD and p,p-DDE, PCBs congeners #28,
#52, #101, #153, #138 and #180 and Hexachlorobenzene in
fish oil. To do so, our approach has been to use a single-step
sample preparation strategy for both fat removal and clean-up/
fractionation.
Moreover, a GC–MS method was validated for the analysis of
all these organochlorine compounds (OCs). The methodology was
applied to certified reference materials and fish oil samples. The
results were compared with those obtained previously by GC-ECD
when possible. 2. Materials and methods
2.1. Standards, chemicals and samples
A solid mixture of -, -, - and -HCH isomers (PestanalTM)
and a standard solution of DDT at 100gmL−1 were purchased
from Sigma–Aldrich (Seelze, Germany).
Standard solutions of DDE and DDD at 200 and 5000gmL−1,
respectively, and a solid standard of HCB were obtained from
Supelco (Bellefonte, PA, USA).
A standard solution of PCB congeners #28, #52, #101, #153,
#138 and #180 at 10gmL−1 was purchased from Dr. Ehrenstorfer,
GmbH (Augsburg, Germany) and kept refrigerated until used.
A stock solution of 1,2,3,4-tetrachloronaphtalene (TCN) (Dr.
Ehrenstorfer, GmbH) at 200 ngmL−1 was prepared in hexane and
kept refrigerated until used as internal standard.
Anhydrous sodium sulphate, silica gel 60 and n-hexane were
purchased from Panreac Química S.A. (Barcelone, Spain) and Sulphuric
acid was from Scharlau Chemie S.A. (Sentmenat, Spain). All
these reagents were analytical grade or better.
Helium (Carburos Metálicos S.A., Barcelona, Spain) was Premier
X50S quality.
A set of HamiltonTM mycro-syringes of volumes ranging from
10 to 250L was used throughout the work.
The certified reference materials of cod liver oil used were BCR
598 and BCR 349, from the Institute for Reference Materials and
Measurements (Geel, Belgium).
Cod liver oil pills, “Kromenat” (Kromenat, Spain), and salmon
oil pills, “Verdalia” (Naturland I.C.C., Carros, France) and “Arkocaps”
(Arkopharma, Carros, France) were purchased in a supermarket as
samples. They were codified as CL-1, S-1, and S-2, respectively. The
content of three pills of each sample was mixed in a glass vial and
then 0.2 g were taken for sample pretreatment.
Glass hypodermic syringes of 5mL were used as columns for
sample preparation (Normax, Lda., Marinha Grande, Portugal).
2.2. Instrumentation
The analyses were carried out in an Agilent 6850 gas chromatograph
(Agilent Technologies, Tokyo, Japan) coupled to an
Agilent 5975B mass spectrometer. A 30m HP-5MS (J&W Scientific,
Folsom, CA, USA) fused silica capillary column (0.25mm I.D.,
0.25m film thickness) was used for separation. The following
temperature program was applied: 100 ◦C (2min) – 10 ◦C min−1
– 180 ◦C (2min) – 1.5 ◦Cmin−1 – 200 ◦C – 20◦Cmin−1 – 250 ◦C –
30 ◦Cmin−1 – 280 ◦C (4min). Helium was employed as carrier gas
at 1mLmin−1. The injector, ion source and quadrupole were set
at 250, 230 and 280 ◦C, respectively. 1L of sample was injected
in splitless mode. The ionisation was made by electronic impact
at 70 eV.
A Reacti-Therm heating module (Pierce, Rockford, IL, USA) with
an evaporating unitwasused for preconcentration. The evaporating
unit uses nitrogen and can concentrate nine samples simultaneously.
A Visiprep solid phase extraction vacuum manifold system
(Supelco, Bellefonte, PA, USA) coupled with a Laboport vacuum
pump (KNF Neuberger Inc., Trenton, NJ, USA) was used to facilitate
the passage of solvent through the column and expedite the
sample preparation.
2.3. Sample preparation
The sample preparation was carried out in glass columns. Glass
was preferred to plastic because preliminary experiences showed
that recoveries of some analytes when using plastic columns were
lower than recoveries obtained when using glass columns. This is probably due tosomekind of adsorption processes of these analytes
in plastic. The columns were 7.6cmlong×1.3cmof inner diameter.
The columns were filled, from bottom to top, with 0.4cm of anhydrous
Na2SO4, 0.8cm of neuter activated silica, 1.1cm of sulphuric
acid modified activated silica at 22% (w:w), 2.3cm of sulphuric
acid modified activated silica at 44% (w:w), and 0.4cm of anhydrous
Na2SO4. This multilayer silica column was bottomed with a
polyethylene fritted disk and was washed with 20mL of hexane
prior to use.
Each sample of oil, typically 0.2 g, was accurately weighed in a
5mL glass vial, dissolved in 1mL of hexane and added 2.5L of TCN
at 200 ngmL−1. The sample was loaded into a mixed silica column
prepared and activated as explained above and allowed to equilibrate
for 5min. The samples were then eluted with 15mLof hexane
by vacuum, collecting the eluent in test tubes. Later on, this eluent
was evaporated, transferred to conical bottom injection vials
and evaporated to dryness under a gentle nitrogen stream. Finally,
samples were reconstituted with 50L of hexane and analysed by
GC–MS by triplicate.
3. Results and discussion
Once the column was set up as described in Section 2, placed in
the vacuum manifold, and washed, the volume of solvent necessary
for the elution of the analytes from the column had to be studied.
For this purpose, a stock solution (10 ngmL−1) of the analytes and
internal standard was loaded into a mixed silica column prepared and activated as explained above. Hexane was used for the elution
of the analytes.
In order to reduce the consumption of both sorbents and eluent
and, consequently, the wastes, a downsizing of the columns,
in comparison with previous works [28–30], was accomplished.
Likewise, in order to reduce the analysis time, the activation of
the column and the elution of the analytes were made by vacuum,
instead of doing so by gravity.
The elution was carried out with 20 fractions of 1mL each
of hexane. These fractions were collected, evaporated to dryness,
reconstituted with 50L of hexane and injected in the chromatographic
system. The results showed that the compounds were
present in the fractions #1 to #15. As a consequence, the elution
volume selected was 15 mL.
Owing to the reduction in the sorbents used in the columns, the
amount of sample that can be purified should be evaluated too. In
order to find out this, different amounts of fish oil, from 0.1 up to
0.5 g, were weighed, dissolved in hexane as explained in the sample
preparation section, and loaded into the multilayer columns. The
columns showed total fat removal efficiency up to 0.2 g of fish oil,
whereas remnants of oil were noted in the eluate corresponding
to the rest of the samples. Consequently, a maximum of 0.2 g of oil
could be purified with these columns. This amount proved to be
adequate for the levels of the analytes.
The column washing volume, the total amount of sorbents used
and the volume of eluent resulted to be up to 6 times smaller than
in our previous work reporting the analysis of fish oils for DDTs
[29]. The amount of oil analysed in that work was from 0.2 to 0.4 g,
which means that the amount of sorbents and solvents by using
the presented methodology would be reduced by one-sixth to onethird,
respectively.
The use of vaccum for the conditioning of the column and also
for the elution of the analytes allowed these steps go faster than if
they had been carried out only by gravity. Thus, the time required
from the column conditioning to the reconstitution with hexane
was about 60 min. Unfortunately, no data reporting this time was
found in the papers mentioned above, but the procedures described
in them are likely to take much longer because the elution of the
analytes was carried out by gravity and also because the volume
of eluate to evaporate was about 10-fold the volume we get in this work.