Plasma Science and Technology, Vol.16, No.7, Jul. 2014
Simultaneous Determination of Trace Lead and Chromium in Water
Using Laser-Induced Breakdown Spectroscopy and Paper Substrate
∗
YU Youli (於有利)
1
, ZHOU Weidong (周卫东)
1
, QIAN Huiguo (钱慧国)
1
,
SU Xuejiao (苏雪娇)
1
, REN Ke (任可)
2
1
Institute of Information Optics, Zhejiang Normal University, Jinhua 21004, China
2
Physics Department, University of Science and Technology of China, Hefei 230026, China
Abstract Toxic metals such as lead and chromium in aqueous solutions have been analyzed
simultaneously by laser-induced breakdown spectroscopy (LIBS), in which the ordinary printing
pap er is used as a liquid absorber which was immerged into Pb(NO
3
)
2
and Cr(NO
3
)
3
aqueous
solution to enrich the heavy metals. This method overcomes the drawbacks of splashing and low
sensitivity in ordinary LIBS analysis of water, in which a laser beam is directly focused on a liquid
surface. A good signal intensity and reproducibility has been demonstrated. The Pb 405.78 nm
and Cr 427.48 nm spectral lines are used as the analytical lines. The variation of line intensity with
immersion time was investigated. The calibration curve for quantitative measurement of Pb and
Cr in water was established, and the detection limits are 0.033 mg/L and 0.026 mg/L respectively,
which is about 2-3 orders of magnitude better than that in the ordinary LIBS analysis of heavy
metal in solution.
Keywords: LIBS, solution, quantitative analysis, paper substrate
PACS: 52.50.Jm, 42.62.Fi, 52.25.Os
DOI: 10.1088/1009-0630/16/7/09
(Some figures may appear in colour only in the online journal)
1 Introduction
It is widely known that heavy metals have seriously
detrimental effects on human health
[1,2]
, such as brain
damage
[3−5]
, cancer
[6]
, infertility
[7]
etc. Polluted wa-
ter can be ingested directly into the human body
[8]
or
ingested through vegetables irrigated by such polluted
water
[9]
. Therefore, the development of a technique to
monitor water that could b e at risk of heavy metal con-
tamination is very important, and the analysis of trace
toxic metals in water is also desirable for drinking water
quality control, analysis of industrial waste water and
other environmental pollution monitoring.
In the last decade, a relatively simple technique,
laser-induced breakdown spectroscopy (LIBS) has
proved to be a versatile trace element analysis technique
for any form of materials: solid, liquid, or gaseous sam-
ples
[10−16]
. In this technique, an intense laser pulse is
used to ablate and vaporize a tiny portion of the sam-
ple, and create ionized plasma. When the plasma cools
down, electron transfer occurs b etween different energy
levels in atoms. Accordingly, each species in the plasma
emits its characteristic spectral radiation. The spec-
tral emission of plasma contains qualitative and quan-
titative information about the elemental composition
in plasma. The direct analysis of liquid samples by
the LIBS technique is implemented by focusing a laser
pulse on the surface or the bulk of a static liquid. These
experimental configurations have some inherent draw-
backs such as splashing, surface ripples, quenching of
emitted intensity, and a shorter plasma lifetime
[17,18]
.
Various experimental methodologies have been devel-
oped to eliminate these problems
[19−30]
. One of these
methodologies is the use of a liquid-to-solid conversion
technique, i.e. transferring the liquid sample into a solid
sample. To date, different solid substrates have been
successfully performed by some groups, such as bulk
ice
[19]
, mixed with calcium hydroxide
[20]
, deposited
on carbon planchet
[21]
, absorbed to solid absorbers
such as wood slices
[22]
or filter paper
[23−25]
, or even
by attracting ions onto membranes
[26,27]
and electrode
plates
[28]
.
To date, filter papers have been used as the sub-
strates for both transforming aqueous solutions to solid
samples and pre-concentrating dissolved heavy metal
ions, and have successfully improved the limit of detec-
tion (LOD) of metal ions in solution in using LIBS tech-
nique. Recently, Pb(NO
3
)
2
solution was transferred
dropwise to the filter paper
[23]
, and the limit of detec-
tion of Pb in solution was found to be 3.87 mg/L. Sim-
∗
supported by National Natural Science Foundation of China (No. 61178034), Key Research Project of University of Zhejiang
Province, China (No. ZD2009006) and the Program for Innovative Research Team, Zhejiang Normal University, China
683