2. ENVIRONMENTAL ChEMISTRy & TEChNOLOGy 2.1. Lectures

Chem. Listy, 102, s265–s1311 (2008) Environmental Chemistry & Technology
P51 SIMuLTANEOuS SPECIATION OF SELENIuM
AND MERCuRy IN ENVIRONMENTAL
SAMPLES by uSING A COLuMN SwITChING
SySTEM wITh LIQuID ChROMATOGRAPhy
COuPLED TO ICP-MS
F. MOREnO, T. GARCíA-BARRERA and J. L. GóMEZ-
ARIZA
Departamento de Química y Ciencia de los Materiales “Prof.
J. C. Vílchez Martín”. Facultad de Ciencias Experimentales.
Universidad de Huelva, Campus de El Carmen. 21007
Huelva (Spain),
fernando.moreno@dqcm.uhu.es
Introduction
Mercury is a very toxic element which damages the central
nervous system, endocrine system, kidneys, and other
organs. Exposure over long periods of time or heavy exposure
to mercury vapour can result in brain damage and ultimately
death. Mercury and its compounds can produce serious birth
defects.Compounds of mercury tend to be much more toxic
than the element itself. 1–3
On the other hand selenium is an essential micronutrient
for animals with biological functions as cofactor. However
it is toxic in large doses. Selenium deficiency can lead to
Keshan and Kashin-Beck diseases. If it is taken in excess it
can lead to seleniosis. In addition, several studies have suggested
a link between cancer and selenium deficiency 4 .
It has been issued that Se-methionine inhibits some neurotoxic
effects of methylmercury. 5–7
For this reason, the development of new analytical strategies
for multielemental speciation is a primordial issue.
In the present study, a new method for the detection
of Se- and Hg- species has been developed, including chiral
species.
Experimental
I n s t r u m e n t a t i o n
The HPLC system is an Agilent 1100 series. The
columns used were a Phenomenex Bondclone C18,
300 mm × 3.90 mm, 10 μm; and an Astec Chirobiotic T
column, 250 mm × 4.6 mm.
An inductively coupled plasma mass spectrometer
Model HP 4500 (Hewlett Packard, Yokogawa, Analytical
System, Tokyo, Japan) equipped with a Babington nebuliser
was used in this study.
R e a g e n t s a n d S t a n d a r d s
All reagents were of analytical reagent grade. Deionized
water (18 MΩ cm –1 ) was obtained from a Milli-Q water
purification system (Millipore, UK). 2-mercaptoethanol 98%
was purchased from Sigma–Aldrich (Steinheim, Germany)
and tetraethylammonium chloride from Fluka (Switzerland).
Ammonium acetate and nitric acid were obtained from Merck
(Darmstadt, Germany).
s435
Stock standard solutions of 1,000 mg Se dm –3 were
prepared in deionized water from selenocystine (SeCys 2 ,
Sigma), seleno-DL-methionine (Se-DL-Met, Sigma), seleno-
L-methionine (Se-L-Met, Sigma), selenomethylselenocysteine
(SeMeSeCys, Sigma), selenocystamine (SeCA, Sigma),
sodium selenate (na 2 SeO 4 ) and sodium selenite (na 2 SeO 3 ).
Methylmercury chloride stock standard solution was
prepared at 1,000 mg Hg dm –3 by dissolving methylmercury
chloride (Merck (Darmstadt, Germany) into 2% HnO 3 .
Mercury chloride stock standard solution was prepared as
1,000 mg Hg dm –3 solution by dissolving mercury chloride
(Merck (Darmstadt, Germany) into 10% HnO 3 .
P r o c e d u r e
A 0.075% tetraethylammonium chloride water solution
at pH 4.5 (mobile phase A) and a 5% (v/v) methanol-water
solution containing 0.06 mol dm –3 ammonium acetate and
0.1% (v/v) 2-mercaptoethanol (mobile phase B) were used as
the mobile phases for HPLC. The flow rate was 1 ml min –1 and
the sample injection volume was 100 μl. The columns were
connected using three valves to build a column swithching
system and species were on-line detected by ICP-MS. The
columns outlets were connected directily to the nebulizer of
the ICP-MS system.
Elemental detection was performed using a model 4500
ICP-MS system. The plasma and auxiliary argon flow rates
were 15 and 1 dm 3 min -1 , respectively. The nebulizer gas flow
rate was 1.28 dm 3 min -1 . The forward RF power was fixed at
1,266 W. The dwell time was 3 seconds per isotope and 77 Se,
82 Se and 202 Hg were monitored.
Table I
HPLC conditions
Time Mobile phase Columns
0–5.1 A RP
5.1–6.15 A RP + Chiral
6.15–8.3 A RP
8.3–13.3 A RP + Chiral
13.3–25 B RP
RP = Phenomenex Bondclone C18 column,
300 mm × 3.90 mm, 10 μm
Chiral = Astec Chirobiotic T column, 250 mm × 4.6 mm,
In our study of selenium and mercury speciation have
been successfully separated six selenium compounds and
two major mercury compounds in biological samples using
a reversed-phase column. The chiral species of selenium was
later separated with the second column.
After the injection in the loop, all species go into the
reversed phase column and later directly to the ICP-MS,
using the mobile phase A. With this program, SeCM, SeCys,
SeMeSeCys and Se (IV) elute before 5.1 minutes. At 5.1
minutes we active the second column, and D-selenomethionine
and L-selenomethionine go throught the chiral column.
After that, at 6.15 minutes we switch off the chiral column,