Anal. Chem. 2003, 75, 2092-2099
UV Va p o r Ge n e ra t io n fo r De t e rm in a t io n o f
S e le n iu m b y He a t e d Qu a rt z Tu b e At o m ic
Ab s o rp t io n S p e c t ro m e t ry
Xum ing Guo,† Ra lph E. Sturge on,* Zolta´ n Me s te r, a nd Gra e m e J . Ga rdne r
Institute for National Measurement Standards, National Research Council of Canada, Ottawa, Ontario, Canada K1A 0R9
tion is the most widely used. As a result, other generation methods
are rather limited in scope, not only to a few elements but to
generation conditions that may also be rather critical. However,
the principal problem with current hydride generation techniques
is that of interference arising from the presence of transition
metals,1 notably Ni, Co, and Cu, caused by their interaction with
the NaBH4 reductant or their catalytic decomposition of the analyte
hydride on the reduced interference metal surface. These are
especially severe for the generation of H2Se or H2Te. In addition,
NaBH4 is a potential source of contamination, and its aqueous
solution is unstable. The development of new vapor generation
systems for the determination of trace elements therefore remains
a fascinating research area in atomic spectroscopy.
In the past few decades, UV-induced photooxidation for the
decomposition of organic material in samples has been widely
described in the literature. Often, a strong oxidizing agent, such
as O3, K2S2O8, and K2Cr2O7, as well as HNO3 or H2O2, is added to
the system4-7 and intermediate radicals (mainly OH•), formed
during UV irradiation, play a crucial role in the process of
oxidation. Although UV irradiation itself is catalytic in nature,5 in
the presence of some organic substances it can result in formation
of radicals (such as H•, CO•) that elicit “photoreduction”, such as
for production of hydrogen,8 instead of stimulating oxidation. As
a typical example, volatile mercury species formed by photo-
chemical processes have been reported in earlier studies.9
Synthetic seawater, spiked with organoselenium compounds and
exposed to sunlight, produced methylated selenium, which was
not the case with spikes of inorganic selenium.10 Kikuchi and
Sakamoto11 reported formation of volatile species of selenium,
(presumably SeH2) when photolyzing aqueous solutions fortified
with formic acid in the presence of TiO2 photocatalyst. Despite
such progress, little is known in this area as there is too little
effort expended in clarifying UV “photoreduction” reactions so
as to permit their routine use in analytical chemistry.
A new vapor generation technique utilizing UV irradiation
coupled with atomic absorption for the determination of
selenium in aqueous solutions is described. In the pres-
ence of low molecular weight organic acid solutions,
inorganic selenium(IV) is converted by UV irradiation to
volatile selenium species, which are then rapidly trans-
ported to a heated quartz tube atomizer for detection by
atomic absorption spectrometry. Optimum conditions for
photochemical vapor generation and interferences from
concomitant elements were investigated. Identification of
the volatile products using cryotrapping GC/ MS analysis
revealed that inorganic selenium(IV) is converted to
volatile selenium hydride, selenium carbonyl, dimethyl
selenide, and diethyl selenide in the presence of formic,
acetic, propionic, and malonic acids, respectively. In
acetic acid solution, the efficiency of generation was
estimated to be 5 0 ( 1 0 %. No interference from Ni2 + and
Co2 + at concentrations of 5 0 0 and 1 0 0 mg L-1 , respec-
tively, was evident. A detection limit of 2 .5 µg L-1 and a
relative sensitivity of 1 .2 µg L-1 (1 % absorption) with a
precision of 1 .2 % (RSD, n ) 1 1 ) at 5 0 µg L-1 were
obtained.
The use of vapor generation as a means of sample introduction
for atomic spectrometry offers unique advantages for real sample
analysis, which arise as a result of the separation and concentration
of the analyte from the complex matrix. Higher sample introduc-
tion efficiency and improved limits of detection can also be
achieved. By selectively forming volatile species, vapor generation
enables the analysis of problematic samples having high dissolved
salt, acid concentrations, or other species, which would otherwise
cause serious spectroscopic or matrix interferences. Among the
existing methods that use various media for vapor generation1,2
(i.e., hydridization, cold vapor generation, halination, ethylation,
propylation, oxidization, etc.), and electrons3 (electrochemical
hydride generation), hydride generation using borohydride reduc-
This study was undertaken to characterize a new technique
for vapor generation based on UV irradiation of samples for
(4) Golimowski, J.; Golimowska, K. Anal. Chim. Acta 1 9 9 6 , 325, 111-133.
(5) Low, G. K.-C.; Mcevoy, S. R. Trends Anal. Chem. 1 9 9 6 , 15, 151-156.
(6) Lores, M.; Cabaleiro, O.; Cela, R. Trends Anal. Chem. 1 9 9 9 , 18, 392-400.
(7) Tsalev, D. L.; Sperling, M.; Welz, B. Spectrochim. Acta, Part B 2 0 0 0 , 55,
339-353.
(8) Lee, S. G.; Lee, S.; Lee, H. Appl. Catal., A 2 0 0 1 , 207, 173-181.
(9) Agaki, H.; Takabatake, E. Chemosphere 1 9 7 3 , 131-133.
(10) Amouroux, D.; Pe´cheyran, C.; Donard, O. F. X. Appl. Organomet. Chem.
2 0 0 0 , 14, 236-244.
* Corresponding author. Fax: 613 993 2451. E-mail: Ralph.Sturgeon@nrc.ca.
† On leave from the Department of Chemistry, Xiamen University, Xiamen,
China.
(1) Dedina, J.; Tsalev, D. Hydride Generation Atomic Absorption Spectrometry;
John Wiley & Sons: New York, 1995; Chapter 2.
(2) Sturgeon, R. E.; Liu, J.; Boyko, V. J.; Luong, V. T. Anal. Chem. 1 9 9 6 , 68,
1883-1887.
(3) Denkhaus, E.; Golloch, A.; Guo, X.; Huang, B. J. Anal. At. Spectrom. 2 0 0 1 ,
16, 870-878.
(11) Kikuchi, E.; Sakamoto, H. J. Electrochem. Soc. 2 0 0 0 , 147, 4589-4593.
2092 Analytical Chemistry, Vol. 75, No. 9, May 1, 2003
10.1021/ac020695h CCC: $25.00 Published 2003 Am. Chem. Soc.
Published on Web 04/02/2003