Oceanological and Hydrobiological Studies
International Journal of Oceanography and Hydrobiology
Vol. XXXIX, Supplement 1
Institute of Oceanography
ISSN 1730-413X
(65-78)
2010
Original research paper
University of Gdańsk
eISSN 1897-3191
Received:
Accepted:
June 01, 2009
September 08, 2010
Determination of methylmercury by Gas Chromatography –
Cold Vapour Atomic Fluorescence Spectrometry
Jerzy Górecki1, Agnieszka Iwanicha, Mariusz Macherzyński,
Katarzyna Styszko, Janusz Gołaś
Department of Environmental Sciences in Energy Research
University of Science and Technology
Al. Mickiewicza 30, 30-059 Kraków, Poland
Key words: methylethylmercury, SPME, Tenax, NaBEt4
Abstract
In this study two popular methylmercury accumulation techniques (Solid Phase Micro
Extraction fibre and Tenax trap) prior to methylmercury determination by Atomic Fluorescence
Spectrometry were compared. Mercury compounds present in the sample were concerted into
their volatile derivatives by ethylation.. In a reaction with derivatisation agent methylmercury was
converted to methylethylmercury and inorganic mercury was converted to dimethylmercury.
After the ethylation step, volatile mercury species were extracted from the sample, separated by
Gas Chromatograph and determined by Tekran detector. Both methods are characterized by
similar repeatability. Simplification of the method with Tenax trap was proposed.
1
Corresponding author: [email protected]
Copyright© by Institute of Oceanography, University of Gdańsk, Poland
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66
J. Górecki, A. Iwanicha, M. Macherzyński, K. Styszko, J. Gołaś
INTRODUCTION
Mercury can be found in the environment in many different forms: from
elemental (metallic) mercury to various inorganic and organic mercury
compounds. Mercury does not have any known biological role in the
environment; at the same time it is toxic to all living organisms (Seixas et al.
2005). Organic mercury compounds, inclusive of the most widely present in the
environment methylmercury (MeHg), are most toxic. In particular, the nervous
system of a developing foetus is very sensitive and can be damaged by even low
concentrations of organic mercury compounds. Methylmercury is mainly
formed in the aquatic environment where it then accumulates in biota,
especially fish (Campbell et al. 2003, Downs et al. 1998). Bioaccumulation and
biomagnification of organic mercury compounds in aquatic food chains had not
been known prior to the Minamata (Japan) ecological catastrophe.
Toxicity of the mercury compounds differs significantly and is dependant of
the physical and chemical form of the mercury compound. Thus mercury
speciation, as opposite to total mercury determination, became necessary.
Mercury speciation is very difficult and many speciation methods are dedicated
to specific samples. Mercury speciation is also expensive, time-consuming and
requires specialist equipment and a highly skilled and experienced team of
analysts. Still, many Polish research centres specialise in mercury determination
and speciation i.e. in air samples (Hławiczka et al. 2003), water samples
(Kowalski et al. 2007), soil and sediment samples (Boszke et al. 2006,
Konieczka et al. 2001) and biological samples (Bełdowska et al. 2007,
Ciesielski et al. 2006, Falandysz et al. 1993, Górecki et al. 2007).
Several sensitive and selective methods of mercury determination and
speciation in the environmental samples are described in the literature. One can
name spectrophotometry (colorimetry and fluorometry), Atomic Absorption
Spectrometry (Cold Vapour Atomic Absorption Spectrometry CV-AFS,
Electrothermal Atomisation Atomic Absorption Spectrometry ETA-AAS),
Atomic Fluorescence Spectrometry (AFS), Atomic Emission Spectrometry
(Inductively Coupled Plasma Atomic Emission Spectrometry ICP-AES,
Microwave-Induced Plasma Atomic Emission Spectrometry MIP-AES,
spectrography), Mass Spectrometry (MS), X-ray Fluorescence Spectroscopy
(XRF), neutron activation analysis (NAA), electrochemistry (polarography,
amperometry, voltamperometry) and many hyphenated techniques.
The most widely used separation technique in methylmercury determination
in the biological and environmental samples is Gas Chromatography (GC)
coupled with Electron Capture Detection (ECD), Atomic Emission
Spectrometry (AAS) or Atomic Fluorescence Spectrometry (AFS). Atomic
Fluorescence Spectrometry is a very sensitive detection technique, enabling the
Copyright© by Institute of Oceanography, University of Gdańsk, Poland
Determination of methylmercury by Gas Chromatography…
67
determination of picograms of mercury in the environmental samples after
reduction, gold amalgamation and thermal decomposition (700ºC–1000ºC).
With the expansion of capillary Gas Chromatography certain sample
preparation techniques became more popular. Conversion of mercury
compounds to volatile and non-polar alkyl derivatives is currently one of the
most popular sample preparation techniques. Volatile mercury derivatives are
easily separable by Gas Chromatography (Baeyens et. al. 1999, Garcia
Fernandez et. al. 2000, Rodil et. al. 2002). Determination of volatile alkyl
mercury derivatives usually requires Atomic Spectrometry detection.
Best separation results on capillary columns are achieved for divalent
mercury compounds. One of the derivatisation methods resulting in creating
divalent volatile mercury compounds is the ethylation of mercury compounds in
the water phase by sodium tetraethylborate (NaBEt4). The derivatisation step is
followed by extraction (i.e. Solid Phase Microextraction SPME) or Tenax trap
pre-concentration, pirolysis (P) and Atomic Fluorescence Spectrometry
determination (Cai et al. 2000, De Wild et al. 2002, Krystek et al. 2004, Lynam
et al. 2002).
In this study methylmercury determination was conducted by using the
SPME/Tenax-GC-P-CV-AFS method. Procedure was adopted from procedures
described elsewhere (Bravo-Sanchez et al. 2004; Centineo et al. 2004, 2006,
Criteria… 2008; De Smaele et al. 1999; Grinberg et al. 2003; Leermakers et al.
2003). Using this procedure enables simultaneous determination of
methylmercury (MeHg) and inorganic mercury compounds (Hg2+). Mercury
compounds present in the sample were concerted into their volatile derivatives
by ethylation with NaBEt4. In a reaction with NaBEt4 methylmercury was
converted to methylethylmercury (MeHgEt) and inorganic mercury was
converted to dimethylmercury (Et2Hg). After the ethylation step, volatile
mercury species were extracted from the sample by SPME fibre or Tenax trap,
separated by GC and determined by AFS.
This paper compares methylmercury determination results, analytical signal
strengths and the quality of results obtained.
MATERIALS AND METHODS
Apparatus
Methylmercury determination was conducted by using Atomic
Fluorescence Spectrometer Tekran 2500. Argon 5.0 was used as a carrier gas
(30 ml min-1). For Tenax traps analysis carrier gas was re-directed and flew
through the injection port of the Gas Chromatograph.
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J. Górecki, A. Iwanicha, M. Macherzyński, K. Styszko, J. Gołaś
Desorption of organic mercury compounds from Tenax traps was carried
out by using Hot Air Soldering Station PT-852. A modified air vent of The Hot
Air Soldering Station enabled even heating of the trap up to 200ºC. This nontypical and inexpensive construction solution proved to be very effective,
especially for Tenax traps cleaning purposes. Tenax traps cleaning time has
been significantly reduced (from several hours to several minutes) in
comparison with using specialist amalgamation module (BrooksRand) for the
same purpose.
Prior to determination, mercury compounds were thermally decomposed by
using a pyrolyser made in-house. A non-treated chromatographic column
(0.53 mm) has been fitted inside a quartz tube (ø 5 mm). This construction was
heated up to 900ºC by using a 20 cm long electric tube oven (1000 W).
Mercury concentration in standard and working solutions was determined
by Automated Mercury Analyser MA-2 (Nippon).
Reagents and Standards
All reagents and standard used were of an analytical grade or higher.
Deionised water was purified by using HLP5 (Hydrolab) system. Derivatisation
agent, sodium tetraethylborate NaBEt4, (97%, 1 g) was purchased from Aldich.
Air-tight microsyringes (250 μl, Hamilton) were used to measure out 1%
derivatisation agent. Working methylmercury solutions were prepared by
diluting certified methylmercury standard (1000 mg ml-1, Alfa Aesar). Tenax
trap (ø5 mm) have been filled with 0.3 ml of Tenax material (TA 60/80,
Supelco). Tenax material was kept in place by glass wool plugs (BrooksRand).
Solid Phase Microextraction fibres were purchased from Supelco. Fibres with
polidimethylosiloxane (PDMS) coating were used (100 μm) during
experiments. Argon 5.0 has been used as a carrier gas.
Preparation of 1% solution of NaBEt4
Sodium tetraethylborate is highly sensitive to water and oxygen so strict
storage and preparation procedures need to be established and followed.
According to literature, 1% NaBEt4 solution can be stored for a maximum of
24 h after preparation. Daily preparation of derivatisation agent is onerous so an
alternative method of the solution preparation was proposed.
6-7 (20 ml) glass vials with rubber septa were carefully weighted on
analytical balance (m1) and placed in a glove box filled with argon. Small
quantities (0.03-0.05 g) of NaBEt4 powder were added to vials and caps with
septa were secured. Vials were weighted again (m2) and the exact amount of
NaBEt4 in each vial was calculated as a difference between m2 and m1. Vials
were stored in the dark at low temperature (4-6ºC) and in argon atmosphere
Copyright© by Institute of Oceanography, University of Gdańsk, Poland
Determination of methylmercury by Gas Chromatography…
69
until needed. To prepare 1% NaBEt4 solution an appropriate volume of
deionised and deoxygenated water was introduced into the vial through septum
by using a microsyringe. Deoxygenation time was 10 min. The contents of each
vial was shaken well before use. Before the 1% NaBEt4 solution was taken out
of the vial, an appropriate volume of argon was introduced to prevent under
pressure and air suck-in.
NaBEt4 solution was stored at low temperatures (4-6ºC) between uses. Once
prepared the solution could be used for up to 48 h.
RESULTS AND DISCUSSION
Methylmercury determination procedure consists of several steps:
− derivatisation of organic mercury compounds by using sodium
tetraethylborate as a derivatisation agent,
− pre-concentration of mercury derivatives by using microextraction fibre
of Tenax trap,
− thermal decomposition of mercury compounds (pyrolysis),
− mercury detection by Atomic Fluorescence Spectrometry.
After the derivatisation step, organic mercury species were
chromatographically separated on an RTX-1 (Restek) column (15 m × 0.53
mm). The column was kept in 30ºC for 2 min, then heated to 80ºC (25ºC min-1 )
and kept in 80ºC for 5 min. Mercury compounds were desorbed from SPME in
the injection port of the Gas Chromatograph (splitless mode). Desorption
temperature was 170ºC and desorption time was 1 min. Carrier gas flow was
30 ml min.-1.
For desorption on mercury compounds from Tenax traps, carrier gas was
supplied to the Gas Chromatograph through the injection port.
Typical chromatogram for methylmercury determination in standard
solution (with Tenax trap pre-concentration) is shown on Figure 1. Three peaks
are visible. The first one represents elemental mercury Hgº, the second –
methylethylmercury MeHgEt and the third – diethylmercury Et2Hg. Elemental
mercury’s presence is a result of the thermal decomposition of organic mercury
compounds in the injection port. Chromatograms for methylmercury
determination (with SPME fibre extraction) are similar, with the main
difference being peak areas.
Organic mercury
Microextraction
compounds
pre-concentration
by
Solid
Phase
Pre-concentration procedure of the organic mercury compounds by Solid
Phase Microextraction was as follows: 3 ml of pH 5.0 acetate buffer was
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70
J. Górecki, A. Iwanicha, M. Macherzyński, K. Styszko, J. Gołaś
Fig. 1. Typical chromatogram for methylmercury determination (with Tenax trap
pre-concentration).
introduced to a glass reaction vial. Methylmercury standard solution and
Teflon-coated stir bar were added and the vial’s cap (with septum) was tightly
screwed. 100-200 μl of 1% NaBEt4 solution was added through the septum. The
vial was placed on a magnetic stirrer and the content of the vial was stirred for
10 min. Once the equilibrium between the sample and the sample head-space
was reached, SPME fibre was introduced into the sample head-space. After 5
min the fibre was withdrawn from the sample head-space and immediately
placed in the injection post of the Gas Chromatograph. Organic mercury
compounds were thermally desorbed from the fibre at 170ºC for 1 min.
Organic mercury compounds pre-concentration by Tenax trap
The procedure of organic mercury compounds pre-concentration was
established. The procedure minimises the amount on water retained in the trap
and then subsequently released and introduced to the Atomic Fluorescence
Spectrometer. The procedure eliminates the use of a scrubber (which is
normally used for organic mercury compounds pre-concentration on Tenax
traps). Instead, methylethylmercury from the head-space was purged from the
reaction vial, directed into Tenax trap and adsorbed on Tenax material. The
Copyright© by Institute of Oceanography, University of Gdańsk, Poland
Determination of methylmercury by Gas Chromatography…
71
main advantage of this approach is significant reduction of the amount of water
that is retained in the trap. The trap and detector’s cell drying times are thus
significantly reduced.
The system for organic mercury compounds pre-concentration by Tenax
trap consisted of the following elements:
- 20 ml reaction vial with modified cap. Cap with septum was modified
in a way that enabled repetitive purging of sample head-space with the
carrier gas. Air-tightness of the modified cap was checked regularly.
- trap filled with 0.3 cm3 of Tenax material.
- valve enabling the carrier gas routing from the trap to either the Gas
Chromatograph or outside the system (trap drying step).
The procedure of pre-concentration of organic mercury compounds by
Tenax trap was as follows: 3 ml of pH 5.0 acetate buffer was introduced to a
glass reaction vial. Methylmercury standard solution and Teflon-coated stir bar
were added and the vial’s cap (modified) was tightly screwed. 100 μl of 1%
NaBEt4 solution was added through the septum. The vial was placed on a
magnetic stirrer and the content of the vial was stirred for 5 min. Alternatively,
the content of the vial was shaken for 5 min (600 rpm). Sample head-space was
purged by argon gas (60-200 ml min-1). Gas flow was directed to the Tenax
trap. Once the organic mercury compounds were adsorbed the valve was
switched and argon gas was re-directed to flow outside the system. Trap drying
time was 5 min with argon gas flow of 750 ml min-1.
Once the drying time elapsed, gas flow was re-directed again to flow
directly to the injection port of the Gas Chromatograph (through the non-treated
capillary column). This was the only supply route for the carrier gas. Pressure in
the injection port was 100 kPa. Flow stabilisation time was 3 min. Then the
Tenax trap was heated to 200ºC and kept in this temperature for 2 min. Organic
mercury compounds were thermally desorbed from the Tenax trap and
introduced to the Gas Chromatograph for separation and subsequent thermal
decomposition and detection.
Repeatability and analytical signal strength in methods with SPME and
Tenax trap
Derivatisation reaction is characterised by low repeatability. To eliminate
the influence of derivatisation on the quality of results, a procedure of multiple
extractions from the same sample was developed. Organic mercury compounds
were first extracted by SPME and then by Tenax trap. The procedure consisted
of the following steps:
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J. Górecki, A. Iwanicha, M. Macherzyński, K. Styszko, J. Gołaś
72
-
sample derivatisation (after the derivatisation agent addition the sample
was stirred by 10 min until the equilibrium between the sample and the
headspace was reached),
- volatile organic mercury compound absorption on SPME fibre material
(5 min),
- thermal desorption of volatile organic mercury compounds from the
fibre in the injection post of the GC at 170ºC (1 min),
- pre-concentration of volatile organic mercury compounds from the head
space on the Tenax trap,
- Tenax trap drying (3 min, 750 ml min -1),
- thermal desorption of volatile organic mercury compounds from the
Tenax trap at 190ºC (1 min),
- detector cell drying (8 min, 750 ml min-1).
Three sets of experiments were conducted according to the procedure
described above. Different Tenax trap pre-concentration times, carrier gas flows
and MeHg concentrations were applied. The parameters of each set of
experiments are listed in the Table 1. Thermal desorption of volatile organic
mercury compounds was conducted at 190ºC for 1 min.
Relative Standard Deviation (RSD) and the strength of analytical signals
from MeHgEt obtained after thermal desorption from SPME fibre and Tenax
trap for all three sets of experiments were compared. Results are shown
in Table 2.
Table 1
Parameters of Tenax trap pre-concentration step for three sets of experiments.
Pre-concentration time
Carrier gas flow
MeHg concentration
Experiment 1
1 min
-1
90 ml min
-1
0.65 μg l
Experiment 2
9 min
-1
60 ml min
-1
0.3 μg l
Experiment 3
9 min
-1
200 ml min
-1
0.1μg l
Table 2
Comparison of analytical signals ratios and Relative Standard Deviations for
SPME fibre and Tenax trap for three sets of experiments.
RSD [%]
Tenax/SPME signals ratio
Number of measurements [n]
Experiment 1
TENAX
SPME
4.3
5.4
17
5
Copyright© by Institute of Oceanography, University of Gdańsk, Poland
Experiment 2
TENAX
SPME
9.6
4.6
20
6
Experiment 3
TENAX
SPME
4.3
7.8
13
3
Determination of methylmercury by Gas Chromatography…
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Comparison of the length and the difficulty of the procedures of
methylmercury determination by SPME and Tenax trap
The length and the difficulty of the procedures of methylmercury
determination by SPME and Tenax trap were compared.
Extraction of MeHgEt by SPME fibre consisted of the following steps:
- derivatisation (10 min, required steps: placement of the vial on the
magnetic stirrer),
- absorption of MeHgEt on SPME fibre (5 min, required steps: fibre
placement in the reaction vial),
- thermal desorption of MeHgEt in the injection port (1 min, required
steps: fibre withdrawal from the vial, fibre transfer to the injection port,
fibre withdrawal from the injection port),
- detector cell drying (3 min, required steps: carrier gas connection).
- Total length of the procedure of extraction of organic mercury
compounds by SPME fibre was 19 min.
- Pre-concentration of MeHgEt on Tenax trap consisted of the following
steps:
- derivatisation (5 min, required steps: placement of the vial on the
shaker),
- adsorption of MeHgEt on Tenax material (3 min, required steps:
modified cap connection to the trap, valve position change),
- trap dying (3 min, required steps: trap de-connection from the vial,
carrier gas connection to the trap),
- stabilisation of the pressure in the system (3 min, required steps: valve
position change, carrier gas flow adjustment),
- thermal desorption of MeHgEt from the Tenax trap (2 min, required
steps: Hot Air Soldering Station switching on and off),
- detector cell drying (5 min, required steps: connection of the carrier
gas).
Total duration of the procedure of pre-concentration of MeHgEt on Tenax
trap was 21 min.
The main difference between the method with SPME fibre and the method
with Tenax trap is the strength of the analytical signals. Extraction with SPME
fibre uses the equilibrium between the organic mercury compounds absorbed by
the polidimethylosiloxane (PDMS) coating of the fibre and the organic mercury
compounds in the head-space. The amount of analyte absorbed and therefore
analysed varies from 3.5 to 5% of the total MeHg present in the sample. In case
of Tenax traps the total amount of analyte adsorbed on the Tenax material is ca.
60% of the total MeHg present in the sample. Analytical signal strength
obtained after the thermal desorption from the Tenax trap depends on the preconcentration time and the carrier gas flow. In the first set of experiments
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J. Górecki, A. Iwanicha, M. Macherzyński, K. Styszko, J. Gołaś
described in paragraph 4.4 (1 min pre-concentration time, 90 ml min-1 carrier
gas flow) the analytical signals ratio from MeHgEt between Tenax and SPME
was 17. In the second set of experiments, where the pre-concentration time was
lengthened 6-fold, the analytical signals obtained were only slightly higher
(analytical signals ratio in the second set of experiments was 15% higher than
the analytical signals ratio in the first set of experiments); however, single
measurement time was significantly longer. Increase of the carrier gas flow to
200 ml min-1 resulted in the analytical signals ratio decrease (from 17 to 13).
The decrease was a result of shortening the time of contact of MeHgEt with
Tenax material.
Relative Standard Deviation (RSD) for SPME analysis ranged from 4.6% to
7.8% and for Tenax trap analysis ranged from 4.3% to 9.6%.
For long series of measurements of methylmercury concentration with
Tenax trap pre-concentration and Tekran detection, a decrease of analytical
signal is observed. Literature explains the decrease is a result of water
accumulation in the detector cell. Water is released from Tenax trap during
thermal desorption of organic mercury compounds. Authors of this study
observed the analytical signal decrease for long series of measurements with
SPME fibre; however, the decrease was significantly smaller than that observed
for Tenax trap. Preliminary studies of subsequent methylmercury determination
after SPME extraction and Tenax trap pre-concentration showed that the
decrease of analytical signal on Tekran detector cannot be explained solely by
the presence of water in the detector cell. In the third set of experiments, an
increase of carrier gas flow to 200 ml min-1 resulted in an increase of the
amount of water absorbed by Tenax material and, as a consequence, released
and transferred to the detector cell. In the second part of the third set of
experiments carrier gas flow during pre-concentration was reduced to
60 ml min-1 and trap drying time was increased to 15 min (detector cell hasn’t
been dried). Despite that, the analytical signal decreased. After 5 measurements
the analytical signal from methylethylmercury was 47% lower in comparison to
the first measurement in the series. According to the literature, the decrease of
the analytical signal was a result of water condensation in the detector cell. A
series of measurements was carried out where the methylmercury was
determined alternately after the procedure with SPME fibre extraction and
Tenax trap pre-concentration. In the series, the decrease of the signal observed
after the procedure with SPME fibre was significantly smaller than the decrease
after the procedure with Tenax trap pre-concentration (6% of the latter) despite
alternate measurements conducted by the same detector. In the series, the RSD
for the method with SPME fibre extraction was 3.5% while the RSD for the
method with Tenax trap pre-concentration was 30.7%. The above confirms that
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Determination of methylmercury by Gas Chromatography…
75
the decrease of the signal cannot be solely explained by water condensation in
the detector cell.
The problem of the decrease of the analytical signal during one series of
measurements is extremely important from point of view of the quality of
results. At this preliminary research stage satisfactory explanation of the signal
decrease is not possible and further studies are needed.
In case of Tenax trap the ‘history’ of the trap is very important. Single
measurement with the method with Tenax trap pre-concentration should be
characterised by i.e. the time between two measurements, methylmercury
concentration during previous measurement, thermal ‘cleaning’ of the trap
between measurements, etc. Poor repeatability which can be attributed to the
trap history is a result of analyte diffusion into the Tenax material. Strict control
of the time between two measurements and between all steps in the single
analysis resulted in the decrease of the results variation i.e. in a series of
measurements where time was strictly controlled RDS was as small as 1.9%
(n=6, c=0.3 µg L-1). Unfortunately, as a result of the level of complexity of the
method with Tenax trap pre-concentration the strict time control is not always
possible.
In the case of SPME fibre, apart from the extraction time, the time between
withdrawal of the fibre from the sample head-space and introduction of the fibre
to the injection port is also important. The longer the time, the weaker the signal
recorded on the detector. Analyte loss can be associated with its evaporation.
Strict control of the time between the withdrawal of the fibre from the sample
head-space and introduction of the fibre to the injection port is necessary. Time
control is easier than in case of the method with Tenax trap.
Tenax trap cleaning, if not a part of the standard procedure; can contribute
to the significant decrease of the analytical signal. In an experiment where the
trap was thermally cleaned between measurements for 6 min the analytical
signal decrease of 40% was observed (RSD for the series was 3.4%, exclusive
of the result obtained after the cleaning, c=0.4 µg l- 1).
Total time required to conduct a single measurement of methylmercury
concentration by both methods (with SPME fibre and Tenax trap) was
comparable. Combined time for all the steps required on the analyte
accumulation stage was 21 min; however, the method with Tenax trap was
much more complicated which can result in errors. The method with Tenax trap
has some advantages though i.e. a shaker can be used instead of a stirrer so the
equilibrium is reached in a shorter time; Teflon-coated stirring bar can be
excluded so the risk of carry-over effect is reduced; glass cleaning is simpler
and requires less time and resources as the scrubber is eliminated.
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J. Górecki, A. Iwanicha, M. Macherzyński, K. Styszko, J. Gołaś
CONCLUSION
Two popular methylmercury accumulation techniques prior to
methylmercury determination by Atomic Fluorescence Spectrometry were
compared. Both methods, with SPME fibre extraction and Tenax trap preconcentration are characterised by similar repeatability. Simplification of the
method with Tenax trap was proposed. In the simplified method the
methylethylmercury from the sample head-space is purged into the Tenax trap
and where it is adsorbed on the Tenax material. In this method ca. 60% of the
methylmercury originally present in the sample is adsorbed on the Tenax
material. The analytical signal from methylmercury obtained after thermal
desorption on organic mercury species from Tenax trap is ca. 19 times stronger
than the analytical signal obtained after thermal desorption from the SPME
fibre. The proposed method results in the reduction of water introduced to the
Tenax trap which is subsequently thermally released from the trap and
condensed in the detector cell. The proposed method enables the reduction of
time necessary for trap and detector cell drying.
Combined times for all the steps required on the analyte accumulation stage
for both methods were equal (21 min). When the accumulation method is
chosen the complexity of the method should be considered. The method with
Tenax trap pre-concentration is much more complicated; however, the carryover effect is reduced and the analytical signal is stronger. These two factors are
very important when trace analysis is conducted.
Thermal desorption of organic mercury compounds from Tenax trap was
conducted by using a simple and inexpensive device (Hot Air Soldering
Station). Use of the HASS device proved to be as effective as the use of a
specialist amalgamation module which is more than 10 times more expensive
than the HASS device.
The authors of this study recommend the use of the method with SPME
fibre extraction for samples with higher methylmercury contents (as the
procedure is much simpler). For low concentrations of methylmercury the
method with Tenax trap pre-concentration is recommended.
ACKNOWLEDGEMENTS
The study was financed by AGH University of Science and Technology
project nº 11.11.210.199.
Copyright© by Institute of Oceanography, University of Gdańsk, Poland
Determination of methylmercury by Gas Chromatography…
77
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