Moisture Influence Reducing Method for Heavy Metals Detection in
Plant Materials Using Laser-Induced Breakdown Spectroscopy: A
Case Study for Chromium Content Detection in Rice Leaves
Jiyu Peng,
†,∥
Yong He,
†,∥
Lanhan Ye,
†
Tingting Shen,
†
Fei Liu,*
,†
Wenwen Kong,
‡
Xiaodan Liu,
†
and Yun Zhao
§
†
College of Biosystems Engineering and Food Science, Zhejiang University, Hangzhou 310058, China
‡
School of Information Engineering, Zhejiang A & F University, Linan 311300, China
§
School of Information and Electronic Engineering, Zhejiang University of Science and Technology, Hangzhou 310023, China
*
S
Supporting Information
ABSTRACT: Fast detection of heavy metals in plant materials is
crucial for environmental remediation and ensuring food safety.
However, most plant materials contain high moisture content, the
influence of which cannot be simply ignored. Hence, we proposed
moisture influence reducing method for fast detection of heavy
metals using laser-induced breakdown spectroscopy (LIBS). First,
we investigated the effect of moisture content on signal intensity,
stability, and plasma parameters (temperature and electron
density) and determined the main influential factors (exper-
imental parameters F and the change of analyte concentration) on
the variations of signal. For chromium content detection, the rice
leaves were performed with a quick drying procedure, and two
strategies were further used to reduce the effect of moisture
content and shot-to-shot fluctuation. An exponential model based on the intensity of background was used to correct the actual
element concentration in analyte. Also, the ratio of signal-to-background for univariable calibration and partial least squared
regression (PLSR) for multivariable calibration were used to compensate the prediction deviations. The PLSR calibration model
obtained the best result, with the correlation coefficient of 0.9669 and root-mean-square error of 4.75 mg/kg in the prediction
set. The preliminary results indicated that the proposed method allowed for the detection of heavy metals in plant materials using
LIBS, and it could be possibly used for element mapping in future work.
H
eavy metals contamination has become a globe problem
due to the deposition and accumulation in soils and
water resources.
1
People might be exposed to heavy metals
from polluted air, food, and water. As a consequence, chronic
exposure to heavy metals can cause severe healthy problems to
humans, plants, and animals if critical levels are exceeded.
2,3
Some strategies such as conventional physicochemical or more
recently biological treatments have been developed to decrease
the concentration of heavy metals.
4
However, one of the
important points in remediation is to real-time monitor the
concentration of heavy metals in contaminated creatures for
indication and biosorption. What’s more, there is also a need
for developing robust, rapid methods to determine the heavy
metals content and to ensure the food safety.
Currently, atomic absorption spectrometry (AAS), induc-
tively coupled plasma optical emission spectroscopy (ICP-
OES) and inductively coupled plasma with mass spectrometry
(ICPMS) are the conventional methods to detect heavy metals.
However, these methods are limited by complex sample
preparations and cannot meet the demands of real-time
monitoring. Laser-induced breakdown spectroscopy (LIBS) is
a novel atomic emission spectroscopy, which has advantages of
fast analytical speed, no or little sample preparation, and in situ
or stand-off detection capability.
5
By analyzing the spectral
signal emitted from laser plasma, LIBS have been used to
characterize sample features and quantify elemental contents in
various kinds of samples (gases, liquids, and solids).
6−8
However, the detection capability of LIBS is limited by the
moisture content in the plant materials. It has been reported
that moisture content in samples might reduce the emission
intensities and worsen the signal stability.
9−11
Two strategies
have been used to deal with it. One is to freeze the samples
with a freezer,
12
and the other one is to reduce the moisture
content with the drying process.
13,14
The frozen samples are
likely to thaw when analyzing, and it is not suitable for practical
application. For dried samples, drying, grinding, and pressing
are usually preferred, and good repeatability and accuracy have
been achieved for the detection of nutrient elements in plants
Received: April 18, 2017
Accepted: June 17, 2017
Published: June 17, 2017
Article
pubs.acs.org/ac
© 2017 American Chemical Society 7593 DOI: 10.1021/acs.analchem.7b01441
Anal. Chem. 2017, 89, 7593−7600