Synthesis, identification and chemical features of high-purity trimethylselenonium iodide

Article abstract of DOI:10.1080/17415993.2010.516435

High-purity (99.8%1.1) trimethylselenonium iodide (TMSeI) was synthesized from dimethyl selenide and methyl iodide. Its chemical structure was confirmed using the spectroscopic methods of nuclear magnetic resonance, Fourier transform infrared and electrospray ionization-mass spectrometry. Some thermodynamic properties of the pure TMSeI were studied with differential scanning calorimetry, and its decomposition point and entropy were determined to be 157.7C and 100.7kJ mol-1, respectively. The chromatographic and UV absorption behavior of the trimethylselenonium cation was also studied and the photochemical and chemical stability of TMSe+ and its decomposition products under varying microwave digestion conditions were examined. Some peculiar, yet interesting chemical properties on the stability of the compound were revealed. This is the first time that the chemical properties of this compound are comprehensively studied by various techniques and from different angles. The high purity of the synthesized compound allows it to be used as a primary standard compound in analytical method development and in basic and environmentally related studies.

Full text of DOI:10.1080/17415993.2010.516435

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Synthesis, identification and
chemical features of high-purity
trimethylselenonium iodide
Qiu-Xiang Zhao a b d , Yu-Wei Chen b , Sabine Montaut b , Helen A.
Joly b , Mohui Wang a & Nelson Belzile b c
a Department of Applied Chemistry and Bioengineering , Chengdu
University of Technology , Chengdu, 610059, People's Republic of
China
b Department of Chemistry and Biochemistry , Laurentian
University , Ramsey Lake Road, Sudbury, ON, Canada , P3E 2C6
c Cooperative Freshwater Ecology Unit, Laurentian University ,
Ramsey Lake Road, Sudbury, ON, Canada , P3E 2C6
d Guangdong Province Material Testing Center , 751 Dongfeng
Dong Road, Guangzhou, 510080, People's Republic of China
Published online: 28 Sep 2010.
To cite this article: Qiu-Xiang Zhao , Yu-Wei Chen , Sabine Montaut , Helen A. Joly ,
Mohui Wang & Nelson Belzile (2010) Synthesis, identification and chemical features of
high-purity trimethylselenonium iodide, Journal of Sulfur Chemistry, 31:5, 373-385, DOI:
10.1080/17415993.2010.516435
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Journal of Sulfur Chemistry
Vol. 31, No. 5, October 2010, 373–385
Synthesis, identification and chemical features of high-purity
trimethylselenonium iodide
Qiu-Xiang Zhaoa,b,d, Yu-Wei Chenb, Sabine Montautb, Helen A. Jolyb, Mohui Wanga
and Nelson Belzileb,c
*
aDepartment of Applied Chemistry and Bioengineering, Chengdu University of Technology, Chengdu
610059, People’s Republic of China; bDepartment of Chemistry and Biochemistry, Laurentian University,
c
Ramsey Lake Road, Sudbury, ON, Canada P3E 2C6; Cooperative Freshwater Ecology Unit, Laurentian
University, Ramsey Lake Road, Sudbury, ON, Canada P3E 2C6; dGuangdong Province Material Testing
Center, 751 Dongfeng Dong Road, Guangzhou 510080, People’s Republic of China
(Received 31 May 2010; final version received 15 August 2010)
High-purity (99.8% 1.1) trimethylselenonium iodide (TMSeI) was synthesized from dimethyl selenide
and methyl iodide. Its chemical structure was confirmed using the spectroscopic methods of nuclear
magnetic resonance, Fourier transform infrared and electrospray ionization-mass spectrometry. Some
thermodynamic properties of the pure TMSeI were studied with differential scanning calorimetry, and
its decomposition point and entropy were determined to be 157.7 ◦C and 100.7 kJ mol−1, respectively. The
chromatographic and UV absorption behavior of the trimethylselenonium cation was also studied and the
photochemical and chemical stability of TMSe+ and its decomposition products under varying microwave
digestion conditions were examined. Some peculiar, yet interesting chemical properties on the stability of
the compound were revealed. This is the first time that the chemical properties of this compound are com-
prehensively studied by various techniques and from different angles. The high purity of the synthesized
compound allows it to be used as a primary standard compound in analytical method development and in
basic and environmentally related studies.
Keywords: trimethylselenonium iodide synthesis; NMR; FTIR; ESI-MS; DSC; microwave digestion
1. Introduction
More than 50 years ago, Schwarz and Foltz (1) reported that Se was an essential trace element in
biological systems. Later, many more studies confirmed that the deficiency of Se can cause several
serious epidemic diseases to human and animals, such as the Keshan (2) and white muscle diseases.
Other health-related problems, such as an impaired immune system, could also be induced by an
insufficient intake of Se (3, 4). However, diets high in Se concentration can provoke Se intoxication
(5–7), and yet the Se concentrations range between safe and toxic is very narrow. Interestingly, it
*Corresponding author. Email: nbelzile@laurentian.ca
ISSN 1741-5993 print/ISSN 1741-6000 online
© 2010 Taylor & Francis
DOI: 10.1080/17415993.2010.516435
http://www.informaworld.com

374 Q.-X. Zhao et al.
has also been observed that the presence of Se in aquatic systems can significantly reduce mercury
methylation and bioaccumulation in the aquatic food web (8–10).
Like sulfur, Se presents in glutathione peroxidase, thioredoxin reductase and thyroid hormone
deiodinase. It is actively involved in redox and metabolic reactions (11, 12). The trimethylse-
lenonium (TMSe+) ion, an analog of trimethylsulfonium (TMS+), has been reported as an
important metabolite and it has been found in the urine of rats fed with sodium selen-
ite dissolved in water (13–17). Its existence was also analytically confirmed in some recent
studies (18–20). The excreted TMSe+ has been considered as a metabolite of Se detoxifica-
tion and a metabolic pathway of Se compounds has been proposed based on these findings
(12, 21). However, there is a controversy on the validity of some of the published data. In
a recent review, Francesconi and Pannier (22) criticized the historic lack of necessary pre-
cautions and precision in the characterization of isolated TMSe+ and in the quantization of
synthesized compound in past reports. They questioned the very existence of TMSe+ as a
biological metabolite and proposed that selenosugars would be more likely urinary metabo-
lites. In fact, until now, we still know little about the chemical and physical properties of this
compound.
One of the important reasons for this problem originates from the unavailability of a commercial
source of a high-purity TMSe+ compound. The majority of the research studies that have used
TMSe+ relied either on a product synthesized in house or on a donation from other laboratories.
In both situations, there is a serious lack of detailed synthetic protocol and comprehensive identi-
fication of this compound. The across citation is a common practice. For instance, several groups
(16, 23, 24) synthesized their sample using the protocol of Palmer et al. (14) who in turn applied
the Bird and Challenger protocol in their TMSe+ synthesis (25). In one study, Gammelgaard
et al. (19) synthesized TMSe+ using the Foster and Ganther procedure (26), which was based
on Hashimoto et al.’s work (27). In the Foster and Ganther procedure (26), labeled TMSe+ was
synthesized from 75Se-methyl-selenocystine and methyl iodide in formic acid for 7 days without
special precaution taken to exclude atmospheric oxygen. Considering the reactive nature of CH3I,
one can seriously question the purity of the synthesized compound. In a subsequent study by the
same group (17), sodium borohydride was used to react with sodium selenite and the authors
produced the TMSe+ ionic compound without detailed explanation.
Bird and Challenger (25) were among the first researchers to synthesize alkyl derivatives of
Se. This work has been cited by several researchers (14, 27, 28) in their individual TMSe+ syn-
thesis work. However, in this early study (25), there is no information directly related to the
synthetic procedure of TMSe+, but only a brief mention which states that in the preparation of
dimethyl/ethyl selenides from powdered Se and in order to avoid the formation of trialkyl seleno-
nium iodide, methyl or ethyl iodide should be added slowly to a mixture of sodium formaldehyde
sulfoxylate, sodium hydroxide and water. The methods used in (14, 27) were based on the reaction
between dimethyl selenide and an excess of methyl iodide. Unfortunately, both of them failed to
provide a detailed protocol, product identification and quantitative measurement on the purity of
the compound.
As concerning to the chemical stability of TMSe+, several authors in earlier studies (29, 30)
had expressed concerns on the difficulty of breaking down TMSe+ in biological samples during
digestion, despite the fact that there was not much experimental evidence. D’Ulivo et al. (31, 32)
are the only few researchers who have presented some analytical data to demonstrate that the
presenceofBr− canfacilitatethebreakdownoftrimethylselenide.Achemicalreactionmechanism
of nucleophilic attack was proposed (32).
In this paper, we propose a well-defined and simple protocol for the synthesis of high-purity
trimethylselenonium iodide (TMSeI). Much of the careful investigation has been done in order to
provide researchers with new information on the physical, chemical and photochemical properties
of this interesting compound.

Journal of Sulfur Chemistry 375
2. Results and discussion
2.1. Purity of the synthesized TMSeI
The purity of the synthesized product was determined by measuring Se in a solution containing an
exactly known mass of TMSeI. The Se in the solution was measured by three different analytical
methods without any prior treatment (Section 4.5). Triplicate analysis was carried out with each
technique and the average purity and analytical precision obtained from three analytical methods
techniques was 99.8 1.1% (n = 9). The high purity of the synthesized (CH3)3SeI allows it to
be used as a primary standard material in any analytical method development, basic chemistry
and environmentally related research.
2.2. Characterization of TMSeI by IR, NMR and HPLC–ESI-MS
Several techniques were used to characterize the synthesized compound. The Fourier transform
infrared (FTIR) spectrum of the product (Figure 1) demonstrates very strong bands at 2988 and
3005 cm−1, characteristic bands of the C3sp–H stretching vibration of the –CH3 groups. The bands
at 1412, 1300 and 1265 cm−1 are consistent with C–H bending vibrations, which are also observed
in the spectra for both dimethyl diselenide (1258.4 cm−1, our own standard) and dimethyl selenide
(1423.9, 1263.9 cm−1) (13, 14). The large band found at 988 cm−1 is possibly assigned to the C–
Se rocking mode, which has been earlier identified (33). Similar IR absorption bands have been
observed at 957 and 912.3 cm−1 for dimethyl selenide (13, 14) and at 892 cm−1 for dimethyl
diselenide (our own standard). The nuclear magnetic resonance (NMR) spectrum of the product
is characterized by a singlet at a chemical shift of 2.76 ppm, indicating that all protons situated
in three methyl groups of TMSe+ in the compound are chemically equivalent. This is consistent
with the NMR data reported for TMSeI (34).
The high-performance liquid chromatography (HPLC)-UV-electrospray ionization-mass spec-
trometry (ESI-MS) spectra of the synthesized product are presented in Figure 2. A species with a
retention time of 2.54 min was detected by the photodiode array detector (PDAD) (Figure 2(a)),
but this peak was not detected by mass spectrometry. It was only at a retention time of 5.47 min
Figure 1. FTIR spectrum of the synthesized TMSeI.

376 Q.-X. Zhao et al.
(a)
180
2.54
160
140
120
100
80
60
40
20
0
0
2.5
5
7.5
10
12.5
15
17.5
20
Retention time (min)
(b)
50,000
45,000
40,000
35,000
30,000
25,000
20,000
15,000
10,000
5000
5.47
0
0
2.5
5
7.5
10
12.5
15
17.5
20
Retention time (min)
(c)
125.0
Max: 17,568
100
80
60
40
20
0
123.0
122.0
460.8
110.0
100
150
200
250
300
350
400
450 m\z
Figure 2. Chromatograms obtained from HPLC coupled with photodiode array detector-electrospray ionization-mass
spectrometer. Column: Pursuit XRs C18 250 × 4.6 mm, particle size: 3 μm; mobile phase: 0.01% TFA/0.01% HFBA/5%
methanol (pH 2.8); flow rate: 1.0 mL min−1. Fragmentation voltage: 70V; sample injection volume: 50 μL; TMSeI
solution concentration solution: ∼100 μM. (a) HPLC chromatogram of I− (UV wavelength 226 nm); (b) the total ionic
chromatogram of (CH3)3Se+ (positive mode) and (c) mass spectrum of the peak (ESI set at positive mode).
that an intense peak corresponding to positively charged ions was found by the mass detector
(Figure 2(b)). The mass spectrum (Figure 2(c)) shows a cluster of ions with m/z of 125.0, 123.0
and122.0 amu, respectively.ThesehavebeenassignedtotheisotopomersofTMSe+, i.e.TM80Se+
(natural abundance (NA) of 80Se = 49.8%), TM78Se+ (NA of 78Se = 23.5%) and TM77Se+ (NA

Journal of Sulfur Chemistry 377
of 77Se = 7.6%). A similar ESI-MS spectrum was also obtained by Wrobel et al. (35) from their
synthesized TMSeI compound.
2.3. UV absorption properties of TMSeI
The fact that the species with a retention time of 2.54 min was not detected by the mass detector
was further studied. A series of standard potassium iodide solutions were prepared and injected
into the HPLC column under the same chromatographic and detection conditions. Iodide (I−) was
eluted from the column and detected by PDAD at 226 nm at the same retention time of 2.54 min.
The intensity of absorption corresponded linearly to the concentration of I− at least from 1.0 to
100 μM. This confirms that the peak at retention time 2.54 min in Figure 2(a) corresponds to the
I− ion UV absorption resulting from a charge-transfer-to-solvent state (36). This phenomenon has
been used to determine iodide in sea water by ionic chromatography with the UV detector (37).
The negatively charged I− was not seen because the detection mode of the MS was set at positive.
Since there is no UV absorption peak at the retention time of 5.47 min, the UV absorption property
of TMSeI was further checked using a freshly prepared TMSeI solution (∼40 μM). There was
no molecular absorption from 190 to 1100 nm, except for some sharp line peaks in the range of
190–250 nm, which were probably produced by I− UV absorption. This confirms that TMSe+
does not absorb UV/visible light, thus this peak was not detected by PDAD when it was eluted
out at 5.47 min. It is thus important that the UV signal produced by I− not be mistakenly regarded
as that of TMSe+.
2.4. Thermodynamic properties of TMSeI
Information on the chemical and physical properties of TMSeI is scarce. Hashimoto et al. (27)
interchangeably used “fusion” and “decomposition” points of this compound at 162–163 ◦C in
their paper. Furthermore, due to the lack of measurement of the purity of their compound, the exact
“fusion” or “decomposition” point reported in their work remains questionable. Using a simple
melting point apparatus, we observed that the colorless crystal TMSeI was gradually transformed
to a white solid and its crystallinity seemed to deteriorate with increasing temperature. At about
149 ◦C, the sample was losing its mass rapidly which was accompanied with an evolving gas
with the characteristic odor of (CH3)2Se. When the temperature reached 153–154 ◦C, the solid
sample had completely disappeared. Therefore, we can now confirm that (CH3)3SeI possesses
the “decomposition temperature” rather than the “fusion temperature”. A more precise measure-
ment was made with a differential scanning calorimeter (DSC). The measurement shows that, at
a temperature of 122.8 ◦C, the compound underwent a phase transition in which an enthalpy of
4.3 kJ mol−1 was involved. This agrees well with our earlier observation where a white amor-
phous precipitate appeared before its crystallization. The decomposition point of this compound
was measured at 157.7 ◦C and the enthalpy of the decomposition reaction was 100.7 kJ mol−1
(Figure 3). Again, the characteristic smell of the decomposed (CH3)2Se gas was detected at the
decomposition temperature. No residue was found after the measurement, which confirmed the
formation of gaseous compounds during the decomposition. Based on the above experiments, the
following reactions are suggested:
◦
(CH3)3SeI(crystal) 12ꢀ2.8 C (CH3)3SeI(amorphous)
,
ꢀH = 4.3 kJ mol−1
(1)
low temp.
◦
(CH3)3SeI(amorphous)
15ꢀ7.7 C
(CH3)2Se(g) + CH3I(g)
,
ꢀH = 100.7 kJ mol−1
.
low temp.; anoxic conditions
(2)

378 Q.-X. Zhao et al.
Temperature (°C)
100
0
50
150
200
3
–2
–7
–12
–17
–22
–27
–32
–37
Figure 3. Decomposition of TMSeI measured with differential scanning calorimeter (DSC).
The same quantities of heat should be released when the reversed reactions occur. This also
explains why it is preferred to carry this synthesis under a low temperature.
The amount of dimethyl selenide used in the reaction was 6.5 mmol, and the final amount of
TMSeI obtained was 3.63 mmol (0.908 g) for a yield of around 56%. The low yield could be
probably due, in part, to the high volatility of (CH3)2Se (b.p. 42–43 ◦C) and to the incompleteness
of the reaction. The results of the supernatant showed that only 0.045 mmol of Se was found in the
aqueous solution, which represents approximately 0.7% of the (CH3)2Se initially added for the
synthesis. This suggests that a significant amount of dimethyl selenide was lost probably through
the evaporation during the several steps of manipulation.
2.5. The stability studies of TMSe+
Although TMSe+ has been reported as a difficult compound to breakdown during acid digestion,
there is little experimental evidence in the literature to demonstrate it. This is partially due to
the fact that pure TMSe+ is not easily available; therefore, very few people have conducted
systematic studies on its properties. Still we know even less in what form(s) Se would be present
under UV irradiation and different chemical attacks, if it does break down. Hydride generation-
atomic fluorescence spectrometry (HG-AFS) is not only a very sensitive analytical method for
several hydride-forming elements (Se, As, Sb, Sn, etc.), but it also possesses an advantage to
identify the formation of different Se species in an aqueous digestion system. The understanding
of the forms of final products of TMSe+ breakdown is crucial for developing an on-line detection
of TMSe+ with the HPLC–HG-AFS system.
2.5.1. The stability of TMSe+ under UV irradiation
The stability of TMSe+ under UV irradiation was first studied. It was found that, unlike many
other organo-selenium compounds (38, 39), the chemical bonds between Se and C in TMSe+
become very stable once it is dissolved in water. It was shown that after 2.5 h of UV irradiation
(300 nm), neither Se (IV) nor Se (VI) – two possible decomposition products by UV cleavage –
was formed, indicating that no Se–C bond had been broken under a strong UV attack with a total
output power of 336W. A close to 100% recovery of Se in this solution as measured by graphite
furnace-atomic absorption spectrometry (GF-AAS) suggests that there should be no significant
loss in Se by the formation of any volatile selenium compounds, such as dimethyl selenide, during
UV treatment (Table 1). The same phenomenon was observed both in 1.0% (v/v) HNO3–2% (v/v)
HCl and in pure water.

Journal of Sulfur Chemistry 379
Table 1. Study on the stability of TMSe+ in different matrices under a UV (300 nm) irradiation of 336W for
2.5 h (n = 3).
Direct analyses
(Se (IV), HG-AFS (i))
Pre-reduction (Se (IV)–Se (VI),
HG-AFS (ii))
Direct analyses
(total Se, GF-AAS (iii))
1% HNO3 (v/v)–2% HCl (v/v)
Se detected (μg L−1
)
)
<Detection limit
1.6
1.0
62.5
1.6
105.3
0.9
0.9
SD (μg L−1
)
n.a
n.a
0.0
RSD (%)
Recovery (%)a
102.2
Deionized water
Se detected (μg L−1
4.8
0.7
7.5
0.8
104.0
0.004
0.004
100.9
SD (μg L−1
)
RSD (%)
13.6
4.6
10.2
7.3
Recovery (%)a
Note: aRecovery % is the measured Se in each treatment compared with total Se introduced before the digestion treatment.
Se can be present in four different chemical oxidation states. However, in a strong oxic envi-
ronment, (CH3)3Se+ could only be either intact or oxidized to Se (0), Se (IV) or Se (VI). The
formation of Se (0) was excluded, as there was no formation of characteristic reddish elemental
Se in any of the tested solutions, even at a concentration as high as 10.3 mg L−1. Based on the
previously established knowledge in the studied matrices, the formation of any other non-hydride-
forming Se species, other than Se (IV) and Se (VI), is quite unlikely. Considering the chemical
nature of this compound and our previous results, we hypothesize that all (CH3)3Se+ in these
solutions remained intact after a strong UV irradiation treatment.
2.5.2. The stability of TMSe+ under chemical attacks
The stability of TMSe+ in different chemical reagents was investigated in a microwave digestion
system using two types of Teflon digestion vials: 100 or 6 mL (38). The obtained results (Table 2)
are not in agreement with those obtained by D’Ulivo et al. (31, 32). In the tests carried in 100 mL
vials, the average Se (IV) found after digestion was 29%, 23% and 30% of the initial TMSe+
for digestion system (A), (B) and (C), respectively. A significantly smaller percentage of Se (VI)
was found in these digestion systems, representing only 5–7% of the initial TMSe. The total Se
Table 2. Percentage of Se (IV), Se (VI) measured by HG-AFS compared with total Se by GF-AAS after microwave
digestion (100 mL vial).
(A): 7.0 mL 15.0 M
HNO3–1.0 mL
30% H2O2
(B): 8.0 mL 15.0 M
HNO3–0.2 mL
18.4 M H2SO4
(C): 7.0 mL 15.0 M
HNO3–0.5 mL
Br solutiona
Replicate
analysis
Se (IV)
Se (VI)
Total Se
Se (IV)
Se (VI)
Total Se
Se (IV)
Se (VI)
Total Se
1
2
3
4
5
6
52.0
24.5
40.5
25.8
20.8
13.2
29.5
14.2
48.2
9.9
7.2
6.0
7.6
4.6
5.7
6.8
1.9
27.5
97.0
98.3
100.0
97.9
98.7
97.5
98.3
1.1
18.1
6.3
4.8
4.6
5.9
7.7
4.4
n.a
5.5
1.4
25.4
142.2
159.5
146.3
130.0
116.5
n.a.
138.9
16.3
11.8
8.3
6.4
2.1
60.1
69.8
32.3
29.8
29.4
98.3
7.9
4.8
2.4
5.8
2.1
8.5
5.3
2.7
50.7
100.3
97.8
96.9
106.5
103.4
101.8
101.1
3.6
15.4
35.9
39.3
23.0
23.0
14.1
61.1
Average (%)
SD (%)
RSD %
1.1
3.5
Note: aBr solution is 1.1 M KBr–0.22 M KBrO3 saturated solution.

380 Q.-X. Zhao et al.
Table 3. Percentage of Se (IV) and Se (VI) measured by HG-AFS after the microwave digestion (6 mL vial).
(I): 1.0 mL 15.0 M
HNO3–0.20 mL
30% H2O2
(II): 1.0 mL 15.0 M
HNO3–0.10 mL
18.4 M H2SO4
(III): 0.7 mL 15.0 M
HNO3–0.15 mL
Br solutiona
Vial
number
Se (IV)
Se (VI)
Se (IV)
Se (VI)
Se (IV)
Se (VI)
1
2
3
4
5
6
89.8
85.8
67.3
62.7
90.4
92.1
81.4
12.9
15.9
8.2
9.0
8.2
10.1
6.5
2.3
7.4
2.8
37.4
52.9
50.2
11.8
9.9
17.3
17.1
26.5
19.6
73.8
9.5
10.6
3.5
2.9
8.9
13.2
8.1
4.1
10.0
9.2
5.5
2.7
1.2
0.9
4.9
4.0
81.6
52.3
55.5
24.1
24.0
75.0
73.5
50.8
22.6
44.6
Average (%)
SD (%)
RSD (%)
50.1
Note: aBr solution is 1.1 M KBr–0.22 M KBrO3 saturated solution.
in the digested solutions (A) and (C), measured by GF-AAS, was closed to 100% of the initial
TMSe+, whereas for system (B), the recovery of Se was significantly higher, probably due to
interference from H2SO4 in the sample (Table 2). A 100% recovery of Se by GF-AAS indicates
that there was no loss of Se in forms of volatile Se during the microwave digestion. Similarly, these
results indicate that even under a temperature of 210 ◦C and in the presence of large quantities
of strong chemicals, only a small percentage of (CH3)3Se+ was broken down and most of the
compound remained stable. The reagent blanks for digestion systems (A), (B) and (C) were all
negligible.
The TMSe+ stability was also examined using 6 mL vials using the same chemical reagents but
in much smaller volumes (Table 3). Since there is no formation of volatile Se compound (CH3)2Se
(based on the data fromTable 2) and since the formation of other Se species, apart from Se (IV) and
Se (VI), is quite unlikely in the investigated chemical digestion systems, the difference between
the Se added and the sum of Se (IV) and Se (VI) measured in digested solutions can be attributed
to the remaining (CH3)3Se+. It was noticed that, with group (I) tests, although chemical reagents
(HNO3–H2O2) were the same as those used with 100 mL vial trial (Table 2, (A)), an average of
81% of TMSe+ was converted to Se (IV) in 6 mL vials compared with less than 30% in 100 mL
vials. In addition, a remarkable difference between 6 and 100 mL vial digestions was observed in
group (III) in Table 3 and group (C) in Table 2. In the 6 mL vials after digestion, about 50% of
TMSe+ was converted to Se (VI) and 5% in Se (IV), whereas in 100 mL vials these values were
somewhat reversed, with 5% and 30% for Se (VI) and Se (IV) present, respectively. This suggests
that the chemical environment between these two types of digestion vials was not the same.
This difference can be explained by the difference in temperature measurement and chemical
environment created in the two types of vials. When using 100 mL vials, the temperature probe
was set directly in the reagent solution, whereas in 6 mL vials, it was set in the deionized water
placed between two sets of digestion vials; therefore, the temperature inside the 6 mL vials may
differ from that in 100 mL vials. The presence of deionized water in the digestion system and
smaller quantity of digestion reagents in the small vials also produce different chemical conditions
in the 6 mL vials digestion system.
Despite these differences, data in Tables 2 and 3 have a remarkable common feature – the large
variations in results related to Se (IV) and Se (VI) in the same chemical treatment group. To
check this variation, the experimental work was repeated several times and they all showed the
same trend. It is also important to mention that in the 6 mL vials, although the percentage of Se
(IV) and Se (VI) varied largely within the same digestion system (Table 3), the variations were
much smaller between the samples located in the same 100 mL vial, remembering that vials 1

Journal of Sulfur Chemistry 381
and 2, 3 and 4 and 5 and 6 were grouped into three individual 100 mL vials. This phenomenon
suggests that the small vials inserted in the same 100 mL vial were subjected to the same digestion
conditions, whereas the digestion conditions varied from one to another 100 mL vial. The reagent
blank in each group was negligible, indicating that no spill had occurred during the digestion. The
large variation in the results strongly suggests heterogeneity in the distribution of the microwave
energy. It is also clear that a larger quantity of chemical reagents added in 100 mL vials did not
promote the breakdown of TMSe+, but rather the opposite result.
Our study with a chemical system containing Br−/BrO3− did not show a significant advantage
in breaking down TMSe+ over the other types of chemical systems. This could be explained as
below. In the acidic solution and in the coexistence of Br− and BrO3−, the comproportionation
reaction occurs:
BrO−3 + 5Br− + 6H+ −→ 3Br2 + 3H2O.
Br2 possesses a strong oxidative power. As the bromine solution was prepared in 1.1 M KBr –
0.22 M KBrO3, a 5:1 molar ratio, therefore, no Br− (nucleophilic reagent) remained after the
above reaction. Unlike the open digestion system (31, 32), the usage of a large quantity of the
HBr reagent was carefully avoided to prevent high pressures generated during the digestion in a
closed digestion system. The discrepancy in observation between our study and that of D’Ulivo
et al. (31, 32) may be due to these differences in digestion systems, open vs. closed vials and large
vs. restricted quantity of HBr.
2.6. Other observed properties related to (CH)3SeI
It was observed that soon after the synthesis of TMSeI, the aqueous solutions in both the glove box
and the refrigerator were heavily contaminated for Se determination with HG-AFS, possibly due
to the dissolution of (CH3)2Se into these solutions. By flushing the glove box with abundant N2
gas and evacuation of air in the refrigerator, the falseAFS signals produced in such a way were all
eliminated. Therefore, it is recommended to safeguard sample solutions if they are to be analyzed
by HG-AFS. Apparently, (CH3)2Se emits a very strong fluorescent signal which overlaps with
that of atomic fluorescence signal produced by Se atoms after the H2Se breakdown in the flame.
3. Conclusion
This work presents a detailed protocol to synthesize TMSeI with a high purity, which makes it
qualified as a primary standard substance (99.8 1.1%). The synthesis is simple, straightforward
and affordable. Differential scanning calorimetric analysis shows that a phase transition occurred
at 122.8 ◦C with an enthalpy of 4.3 kJ mol−1, and decomposition of (CH3)3Se+ happened at
157.7 ◦C with an enthalpy of 100.7 kJ mol−1. Once it is dissolved in water, TMSe+ becomes very
stable under strong UV irradiation. Under harsh chemical attacks at a high temperature (210 ◦C)
and a high pressure in a microwave digestion system, this compound also appeared quite stable
as indicated by relatively small percentage of broken down products such as Se (IV) and Se (VI)
species in most digested solutions. The poor reproducibility in results is possibly produced by
the heterogeneity of microwave energy; the inadequate amount of Br− and reagent combination,
therefore, needs to be further studied.
TMSeI is stable when stored under frozen conditions. No structure modification was found after
1 year of storage. The chemical structure of TMSe+ in an aqueous solution remained unchanged
4 months after storage at 4 ◦C.

382 Q.-X. Zhao et al.
4. Experimental
4.1. Instrumentation
The synthesis was carried in a controlled atmosphere chamber (Vacuum Atmospheres Company,
Omni-Lab System) in which high-purity nitrogen gas was flushed to maintain the chamber oxy-
gen level at around 400 ppmv (parts per million in volume) prior to synthesis. The compound
was characterized with the aid of a Varian Gemini 2000 NMR spectrometer, an FTIR spec-
trometer (MB102, BOMEM Hartman & Braun, Inc.), a HPLC–ESI-MS (Agilent 1100 series,
Agilent 6120 quadrupole LC/MS) in the positive mode of detection. The decomposition point and
decomposition enthalpy of TMSeI were studied with a melting point apparatus (MEL-TEMP®,
Electrothermal) and a DSC Q20, TA Instrument calibrated with indium (m.p. 156.6 ◦C). The
UV–visible spectrum of the synthesized product and that of sodium iodide were recorded on an
Ultraspec 3000 UV–visible spectrometer (Pharmacia Biotech).
The purity of the synthesized product was determined with three different analytical techniques:
inductively coupled plasma mass spectrometry (ICP-MS; ELAN DRC-e, Perkin Elmer), GF-AAS
(Perkin Elmer, AAnalyst 600) and flame atomic absorption spectrometry (FAAS; Perkin Elmer,
AAnalyst 400).
In the studies of photochemical stability of TMSe+, a Rayonet photochemical chamber reac-
tor (RPR-100, Southern New England Ultraviolet Company) equipped with 16 lamps of 300 nm
wavelength (21W each) was employed. The chemical stability of TMSe+ under strong diges-
tion conditions was examined with a microwave Labstation (Milestone Ethos 1600 URM, HPR
1000/10 system, Bergamo, Italy) equipped with 100 or 6 mL Teflon digestion vials. HG-AFS
(PSA 10.055 Millennium Excalibur) was also used in the studies to identify the formation of Se
(IV) and Se (VI) species under different chemical digestion systems. A five-digit microbalance
(Mettler Toledo, Switzerland) was employed when a small sample size was required.
4.2. Reagents and standards
Dimethylselenide(>99%), methyliodide(99%)andn-hexane(99%)werepurchasedfromSigma-
Aldrich and used for synthesizing TMSeI. Water used in all studies was purified using an NANO
Pure DiamondTM Water Purification System (Barnstead, NH, USA). The primary standard Se
(IV) solution of 1000 mg L−1 (as Se) was prepared in 3.0 M HCl from SeO2 (99.8% Aldrich) and
stored at 4 ◦C. This solution is stable for at least 12 months. Trifluoroacetic acid (TFA) (>99.5%,
Fisher) and heptafluorobutyric acid (HFBA) (>99.5%, Fisher) were employed in HPLC as eluents
for TMSe+. All other chemicals used in this work are at least of analytical purity.
4.3. Protocol for synthesis
The synthesis was conducted in a controlled atmosphere chamber kept at an oxygen level of
∼400 ppmv. The reaction vessel was a 15 mL conical bottom-graded Pyrex glass centrifuge tube
with a ground glass stopper. Mixture I (1.0 mL of CH3I and 1.0 mL of n-hexane) and mixture II
(0.5 mL of dimethyl selenide and 0.75 mL of hexane) were both prepared in the pre-cleaned and
dried Pyrex glass centrifuge tubes and placed in an ice-water bath to reduce the rapid evaporation
of the solvents and moved into the glove box. The solvent of mixture II was added into mixture I
dropwise with a gentle stirring until it was all added and the stopper was tightened. Within a few
minutes after mixing the two solutions, a white amorphous precipitate was formed. The reaction
vessel together with the icy bath was withdrawn from the glove box and placed in a refrigerator
overnight, and at this point, the amorphous precipitate was transformed into colorless crystals.

Journal of Sulfur Chemistry 383
By then, the supernatant was evaporated to dryness. It is important to close the tubes tight and
perform the mixture (II) addition as swift as possible, due to the low boiling points of methyl
iodide (42.5 ◦C), dimethyl selenide (42–43 ◦C) and n-hexane (69 ◦C).
The solid was washed with ∼1 mL of n−hexane and recrystallized in ∼1 mL of methanol
(100%). The dried crystals were then transferred into a clean conical bottom-graded Pyrex glass
centrifuge tube; a small and just sufficient volume of hot methanol (HPLC grade) was introduced
to dissolve the crystals and then added another aliquot of hot methanol of about 10% of existing
volume. The sample was left at 4 ◦C overnight. The crystals were then filtered through a #1
Whatman filter paper under vacuum to remove the solvent and dried at 50 ◦C for 2 h in an oven.
The resulting transparent crystals (0.908 g, yield 56%) were stored at −23 ◦C.
In laboratories with no access to a sophisticated commercial glove box, a simple plastic glove
box can be used providing that a thorough removal of the air and a 2 h N2 flush is performed
prior to the synthesis. The inert atmospheric conditions prevent a fast oxidation of CH3I, and the
formation of I2 thus increases the purity of the synthesized compound.
4.4. Characterization of the synthesized TMSeI
To obtain NMR spectroscopic information, a solution containing 10 mg of synthesizedTMSeI was
dissolved in 0.50 mL of D2O. For FTIR analysis, 2.0 mg of the product was mixed and ground with
0.20 g of KBr and pressed into a disc. The chromatographic behavior and mass spectroscopic data
were collected by HPLC–ESI-MS. A solution of synthesized TMSeI (∼80 μM), prepared with
pure water, was injected (20 μL) on the column (Pursuit XRS – C18, 250 × 4.6 mm,A6001250 ×
046, Varian) and the chromatographic peaks detected with a 6120 Quadrupole MS.
4.5. Investigation of the purity of TMSe+
To determine the purity of the synthesized TMSeI, the compound was assumed as 100% pure.
A known amount of the synthesized product (32.8 mg) was weighed precisely and dissolved in
10.00 mL of ultra-pure water to obtain a solution with a concentration of 1030.5 mg L−1 as Se. The
above solution was sequentially diluted to a final concentration of 10.3 mg L−1, 103.1 μg L−1 and
25.7 μg L−1 as Se for FAAS, GF-AAS and ICP–MS determination, respectively. A wavelength of
196.03 nm and a Se electrodeless discharge lamp were employed in Se determination by FAAS and
GF-AAS. The graphite furnace program comprised five steps: drying at 110 ◦C (ramp 1, hold 30 s)
and at 130 ◦C (ramp 15, hold 30 s), ashing at 1300 ◦C (ramp 10, hold 20 s), atomization at 1900 ◦C
(ramp 0, hold 5 s) and cleaning at 2100 ◦C (ramp 1, hold 2 s). The addition of 6 μL MgNO3
(1000 mg L−1)–Pd (1500 mg L−1) matrix modifier is necessary to avoid the loss of TMSe+.
The determination by ICP-MS was done with both Se78 and Se82. In each method, at least three
individual analyses were carried and the overall average of measured Se in the synthesized TMSeI
was derived.
4.6. Stability studies of TMSe+
4.6.1. TMSe+ stability studies under UV irradiation
In the studies on the effect of UV radiation on the stability of TMSe+, two aliquots of 10.00 mL
of the 103.1 μg L−1 TMSeI solution (as Se) were prepared, one in deionized water and another
one in 1.0% (v/v) HNO3–2.0% (v/v) HCl. They were subjected to UV irradiation (300 nm) for
2.5 h (40). The UV irradiation studies were performed as below: (i) direct determination of Se
(IV) by HG-AFS without any treatment in order to check the possible formation of Se (IV) after

384 Q.-X. Zhao et al.
UV irradiation; (ii) pre-reduction of Se (VI) in 3.0 M HCl in a microwave oven (temperature
arising from 20 to 110 ◦C within 10.0 min, then hold at 110 ◦C for 15.0 min, venting for 20 min
in a sealed 100 mL digestion bomb) and determination of the sum of Se (IV) and Se (VI) with
HG-AFS, in case there is any Se (VI) formed in the solution during irradiation. The difference in
Se between (ii) and (i) should be the concentration of Se (VI) formed under UV radiation. (iii)
Direct determination of Se in the UV-irradiated solution by GF-AAS to investigate whether there
was any loss of Se in form of volatile Se compound such as (CH3)2Se during the UV irradiation.
4.6.2. TMSe+ stability studies under chemical attacks
The chemical stability of TMSe+ under a variety of strong digestion systems was studied using a
microwave oven digestion system with 100 or 6mLTeflon digestion vials. The microwave program
consists: (1) room temperature → 85 ◦C in 4 min; (2) 85 ◦C → 145 ◦C in 10 min; (3) 145 ◦C →
210 ◦C in 6 min; (4) maintained at 210 ◦C for 10 min and (5) vent (210 ◦C → 170 ◦C) in 20 min. A
standard TMSeI solution of 10.3 mg L−1 as Se was prepared. Three tested chemical systems were
(A) 7.0 mL 15 M HNO3–1.0 mL 30% (w/w) H2O2; (B) 8.0 mL 15.0 M HNO3–0.2 mL 18.4 M
H2SO4 and (C) 7.0 mL 15.0 M HNO3 – 0.5 mL of bromine solution (1.1 M KBr–0.22 M KBrO3
in saturation). HG-AFS was used to examine the possible formation of Se (IV) and Se (VI) during
the digestion. GF-AAS was used to determine the total Se that remained in the microwave digested
solutions. To avoid the possible matrix effect in GF-AAS determination, the Se concentration was
obtained based on a three point – spike, standard and addition – method for all measurements.
For the studies of chemical attacks using 6 mL vials, the microwave digestion program was
identical as for 100 mL vials. The chemical attack system was (I) 1.0 mL 15.0 M HNO3–0.2 mL
30% (w/w) H2O2; (II) 1.0 mL 15.0 M HNO3–0.10 mL 18.4 M H2SO4; (III) 0.7 mL 15.0 M HNO3–
0.15 mL Br solution (1.1 M KBr–0.22 M KBrO3 in saturation). Vial numbers 1 and 2, 3 and 4 and
5 and 6 were installed in three different 100 mL vials, and a reagent blank vial was included in
each group. The detailed description for low-volume digestion is provided in (39).
Acknowledgements
Funding from the Natural Sciences and Engineering Research Council of Canada through the Discovery Grant program
and the Strategic Network MITHE-SN is greatly acknowledged. We sincerely thank G. Arteca for his interpretation of
spectra. We also express our gratitude for the helpful comments from anonymous reviewers.
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