American Journal of Anal yt ical Chemistry, 2011, 2, 217-222
doi:10.4236/ajac.2011.22026 Published Online May 2011 (
Copyright © 2011 SciRes. AJAC
Investigation of Distribution for Trace Lead and Cadmium
in Chinese Herbal Medicines and Their Decoctions by
Graphite Furnace Atomic Absorption Spectrometry
Hanwen Sun, Lixin Li
Key Laboratory of Analytical Science and Technology of Hebei Province, College of Chemistry and
Environmental Science, Hebei University, Baoding, China
Received February 16, 2011; revised March 7, 2011; accepted March 15, 2011
Lead and cadmium in herbal medicines are highly toxic to living organisms even in low concentrations. An
effective method is developed for analysis of trace lead and cadmium in Chinese herbal medicines and their
decoctions by graphite furnace atomic absorption spectrometry (GFAAS). The effects of analytical condi-
tions on absorbance were investigated and optimized. A water-dissolving capability for Pb and Cd was in-
vestigated, and the contents of different species in five Chinese herbal medicines and their decoctions were
analyzed. The content ratios (kow) of n-octanol-soluble Pb or Cd to water-soluble Pb or Cd were evaluated,
and the distribution of Pb and Cd in water decoction at stomach and intestine acidities was developed, in the
first time. The contents of water-soluble Pb and Cd, n-octanol-soluble Pb and Cd, and their content ratios
were related with the kind of medicine and the acidity of the decoction. The proposed method has the advan-
tages of simple operation, high sensitivity and high speed, with 3 σ detection limits of 4.2 pg for Pb and 0.1
pg for Cd.
Keywords: Distribution, Lead, Cadmium, Herbal Medicines, Decoctions, Graphite Furnace Atomic
Absorption Spectrometry
1. Introduction
Chinese herbal medicine has been used as a form of
treatment for a multitude of ailments ranging from acute
infections to chronic fatigue. Study on the trace elements
in Chinese herbal medicine can provide science provi-
dence for pharmacology and toxicology. Lead has well-
documented toxic effects on plants, animals, and micro-
organisms. Cadmium exposure can produce a wide vari-
ety of acute and chronic effects in humans, leading to a
build-up of cadmium in the kidneys that can cause kidney
disease. Some cases of intoxication with Pb and Cd re-
sulting from the ingestion of Chinese herbal medicines
have been reported [1,2]. Therefore, the analysis of trace
Pb and Cd in herbal medicines and their decoctions is
very important for pharmacological and toxicological
A series of atomic spectrometric methods were re-
ported for the determination of Pb and/or Cd in herbal
medicines. Atomic absorption spectrometry is the ana-
lytical technique, most employed for metal analysis due
to its low interference level and reasonable sensitivity. A
pre-concentration flow injection analysis–flame atomic
absorption spectrometry (FAAS) method was reported
for determination of Pb content in medicinal plants with
the limit of detection (LOD) of 19 µg·L–1 [3]. A solid
sampling–FAAS method was used for determination of
Cd and Pb in medicinal plants, relative standard devia-
tions (RSDs) were below 10% (n = 5) and LODs were
0.1 µg·kg–1 and 12 µg·kg–1 for Pb and Cd, respectively
[4]. To increase method sensitivity graphite furnace
atomic absorption spectrometry (GFAAS) was frequently
used to determine heavy metals for the quality control in
herbal medicines. Several GFAAS methods had been
reported with higher sensitivity, such as for the determi-
nation of Pb in Chinese herbal medicine with the LOD of
0.1 μg·kg–1[5], and for the determination of Pb and Cd in
Chinese crude drugs with the LOD of 11.6 pg and 2 pg
[6], and 6 μg·kg–1 and 0.208 μg·kg–1 [7] for Pb and Cd,
respectively. GFAAS was utilized to the determination
of 4 metal element in 13 herbs of tocolysis formulation
with the LOD of 0.45 ppb (μg·L–1) for Pb and 0.03 ppb
(μg·L–1) for Cd [8], and to the quality control in Argen-
tinian herbal medicines with the LOD of 0.06μg·L–1 for
Pb and 0.008 μg·L–1 for Cd [9]. GFAAS and inductively
coupled plasma mass spectrometry (ICP-MS) had been
used for the determination of arsenic, cadmium and lead
for quality control monitoring purposes of Bulgarian
herbs and their infusions, and the LODs using GFAAS
were 0.5 μg·L–1 for Pb and 0.01 μg·L–1 for Cd [10]. Hy-
dride generation-atomic fluorescence spectrometry
(HGAFS) method was described for simultaneous de-
termination of trace Cd and arsenic in biological samples
with the LOD of 0.01 μg·L–1 for Cd [11]. Otherwise,
a–reversed-phase high-performance liquid chromatogra-
phy (RP-HPLC) method, was developed for the simulta-
neous determination of heavy metal ions in Chinese
herbal medicine. The method had low LOD value of
0.004 μg·L–1 for Pb and 0.003 μg·L–1 for Cd, but analyti-
cal procedure was complicated, and required pre-column
derivatized with tetra-(4-chlorophenyl)-porphyrin (T4-
CPP) to form the colored chelates [12]. All the methods
reported above were used for effective determination of
total content of analyte. However, because the action of
trace elements in Chinese herbal medicine on human
body is mostly depended on the combination forms of
elements, so the distribution analysis of trace elements is
more important than total content analysis.
The n-octanol system was used to study the distribu-
tion of major-element or micro-element in water decoc-
tion in our stomach and intestine, and to appraise the
medicine affection in pharmacology [13]. The combina-
tion forms of Zn and Mn in some Chinese herbal medi-
cines was investigated by FAAS using n-octanol system,
but since FAAS normally allows the quantification of
elements only at µg·g–1 levels [14,15]. A new method
was developed for simultaneous determination of trace
arsenic and antimony in Chinese herbal medicines by
HGAFS with a Soxhlet extraction system and n-octanol-
water extraction system [16]. Lead and cadmium in her-
bal medicines are highly toxic to living organisms, how-
ever there was no report for analysis of trace Pb and Cd
in Chinese herbal medicines and their decoctions up to
The main purpose of our work is to study the distribu-
tion of Pb and Cd at stomach and intestine acidities.
Chemical modification technique was used for GFAAS
to increase the analytical sensitivity and to overcome
matrix interference. The n-octanol-water extraction sys-
tem was used for the analysis of trace Pb and Cd in the
decoctions of Chinese herbal medicines. The content of
water-soluble and n-octanol-soluble analyte and its ratio
were investigated. The proposed method was used to ex-
amine the distribution of Pb and Cd at stomach and in-
testine acidities. The method was used for the determina-
tion of total Pb/Cd, water-soluble and n-octanol-soluble
Pb/Cd in Chinese herbal medicines and their decoctions
with satisfactory results.
2. Materials and Methods
2.1. Instrumentation
A PE-1100B graphite furnace atomic absorption spec-
trometer (Perkin Elmer Co.) equipped with Pb and Cd
hollow cathode lamps (Beijing Haiguang Instrument Co.,
China) was used for all the measurements. Pyrocoated
graphite tubes were used. The instrument operating pa-
rameters are given in Table 1.
2.2. Reagents and Samples
All reagents were of analytical-reagent grade except
when indicated otherwise. De-ionized water was used
throughout this work. The working solutions of Pb and
Table 1. The operating parameters of GFAAS.
Parameters Pb Cd
Measurement wavelength/nm 283.3 228.8
Lamp current/mA 6 6
Slit/nm 0.7 0.7
Charring temperature/˚C 60 120 60 120
Ramp time/s 5 10 5 10
Hold time/s 10 10 10 10
Pyrolysis temperature/˚C 800 800
Ramp time/s 10 15
Hold time/s 10 15
Atomization temperature/˚C 1700 1800
Ramp time/s 0 0
Hold time/s 5 4
Cleaning temperature/˚C 2500 2500
Ramp time/s 1 1
Hold time/s 3 3
Background correction D-lamp D-lamp
Measurement model Peak area Peak area
Integral time/s 3 3
Carries gas flow/mL·min–1 300 300
Copyright © 2011 SciRes. AJAC
H. W. SUN ET AL.219
Cd were prepared by diluting appropriate aliquots from
the stock solution (1 mg·mL–1, provided by the National
Steel Material Testing Center, China). Mg(NO3)2,
NH4NO3, NH4H2PO4 and PdCl2 were used to study modi-
fication effects. A n-octanol solution was used for analy-
Samples of Chinese herbal medicines, Common ane-
marrhena rhizome, Liquorice, Dioscorea nipponica ma-
kino, Radix salviae miltiorrhizae and Fructus ligustri
lucidi, were bought from a market.
2.3. Procedure
For the analysis of total Pb/Cd in herbal medicines, com-
plete digestion of a herbal sample was performed by wet
digestion with a mixture of nitric acid and hydrochloric
acid. A 1.000 g sample of Chinese herbal medicine was
digested with 8 mL of nitric acid and 2 mL of perchloric
acid in a beaker covered with a watch glass on an electric
hot-plate for about one hour, then each digest solution
was gently heated, and any excess acid was removed.
After cooling to room temperature (25˚C), the residues
were dissolved with 1% nitric acid. The content was
transferred to a volumetric flask and diluted to 50 mL
with 1% nitric acid for the determination of total Pb/Cd.
The sample blank preparation and recovery test were
carried out in the same way.
For the analysis of total water-soluble Pb/Cd in water
decoctions, a 20.00 g sample of Chinese herbal medi-
cines in a 400 mL beaker was extracted with triplet de-
ionized water (200 mL, each) and heated on an electric
hot-plate to slight boiling of 1 h. The obtained decoctions
were filtered with a 0.45 µm membrane. The water de-
coction was obtained by concentrating the filtrate to 100
mL. An aliquot of the water decoction (30.0 mL) was
used for the determination of total water-soluble Pb/Cd.
The 30.0 mL solution was heated until about 5 mL of
solution was obtained, then 8 mL of nitric acid and 2 mL
of perchloric acid were added and gently heated on a hot
plate to dryness. After cooling, the residue was dissolved
with 1% (v/v) nitric acid and diluted to 25 mL of volume
with de-ionized water.
For the analysis of Pb and Cd in water decoctions at
stomach and intestine acidity, two aliquots of the above
water decoction (30.0 mL, each) were added into two
beakers, respectively. One was adjusted to the acidity of
the stomach (pH 1.3) with 2.0 mol/L hydrochloric acid
and 30% (v/v) NH3·H2O, the other was adjusted to the
acidity of intestine (pH 7.6). They were translated into a
separatory funnel, and then 10.0 mL of n-octanol was
added, oscillating for extraction for 2 h. The water phase
obtained was diluted to 25.0 mL with 1% (v/v) nitric acid
for the determination of water-soluble Pb/Cd in the water
decoctions. Then contents of n-octanol-soluble Pb/Cd
were obtained by subtracting the content of water-soluble
Pb/Cd from that of total Pb/Cd in the water decoctions,
3. Results and Discussion
3.1. Effect of Acid Medium and Acidity
The effects of hydrochloric acid, nitric acid, phosphoric
acid and sulfuric acid acidity from 1% to 2% (v/v) on the
absorbance of Pb and Cd were investigated. Used hy-
drochloric acid or phosphoric acid as a medium, the back-
ground interferences would be increased, and the ab-
sorbance would be lower than using sulfuric acid as a
medium. Nitric acid in the range of 0.7% - 1.5% (v/v)
was selected as a medium with higher sensitivity and
stability for the determination of Pb and Cd. A 1% nitric
acid was used in this work.
3.2. Matrix Modification Effect
The modification effects of several chemicals, such as
NH4NO3, (NH4)2SO4, NH4H2PO4 and PdCl2 as well as
NH4H2PO4 + Mg(NO3)2, on the determinations of Pb and
Cd were investigated comparatively. The absorbance-
pyrolysis temperature curves are shown in Figure 1.
Using NH4H2PO4 as a modifier, the critical pyrolysis
temperature for the determination of Pb was raised from
300˚C to 900˚C with a higher sensitivity and lower back-
ground absorption because of the formations of more
stable lead phosphate and easy volatile ammonium chlo-
ride in the presence of NH4H2PO4. (NH4)H2PO4 was used
as a matrix modifier for Cd determination [8]. In our
work, use of NH4H2PO4 plus Mg(NO3)2 as a matrix
Figure 1. The absorbance- pyrolysis temperature curves. a.
Pb + NH4H2PO4, b. Pb, c. Cd + NH4 H2PO4 +Mg(NO3)2, d.
Cd. Data point is the average value of three measurements
with < 2% of RSD.
Copyright © 2011 SciRes. AJAC
Copyright © 2011 SciRes. AJAC
modifier made the critical pyrolysis temperature of Cd
raised from 400˚C to 800˚C, and obtained higher sensi-
tivity than NH4H2PO4 alone. Thus, the optimum pyroly-
sis temperature of 800˚C was chosen for the determina-
tion of Pb and Cd in the presence of the modifiers.
The effects of modifier amounts on the sensitivity
were investigated. The sensitivity increased obviously
with the increase of the modifier concentration from 0 to
200 μg. The result showed that the best sensitivities
were achieved using 100 μg NH4H2PO4 and 120 μg
NH4H2PO4 + 5 μg Mg(NO3)2 for the determination of Pb
and Cd , respectively. Plateaus of the atomization tem-
perature were observed over 1700˚C - 2000˚C using
NH4H2PO4 and NH4H2PO4 + Mg(NO3)2 modifiers, re-
spectively. Therefore, the optimal atomization tempera-
tures were selected as 1700˚C for Pb and 1800˚C for Cd.
In addition, the “maximum power” and gas stop modes
were used for the determination of Pb and Cd in order to
obtain high sensitivity.
3.3. Linearity, Detection Limit and Precision
The calibration graph was linear up to 70 µg·L–1 for Pb
and up to 4 µg·L–1 for Cd. Linearity relation between
absorbance (A) and concentrations (C) can be described
by a regression equation: for Pb, A = 454.802C – 2.600,
and for Cd, A = 37.068C – 0.123, with a correlation co-
efficient of > 0.999. The detection limit calculated ac-
cording to the IUPAC rules on the basis of 3σ criterion
for 11 replicate measurements of the blank signal was
0.21 µg·L–1 for Pb and 0.005 µg·L–1 for Cd (4.2 pg Pb
and 0.1 pg Cd for sampling 20 µL solutions). For 1 g
sample and 50 mL final solution, the method LOD was
10.5 µg·kg–1 for Pb and 0.25 µg·kg–1 for Cd. The relative
standard deviation (RSD, n = 7) was 1.54% for Pb at 40
ng·mL–1 level and 2.4% for Cd at 0.4 ng·mL–1 level. It is
indicated that the proposed method has good linearity,
high sensitivity and precision, and can permit the accu-
rate detection of trace Pb and Cd in herbs and their de-
3.4. Determination of Pb and Cd in Herbs and
Their Decoctions
A water decoction is the one used for people to treat dis-
ease, and the content of Pb and Cd in the water decoction
was the actual contribution to the toxicity. The prepara-
tion of water decoctions and determination of total Pb/Cd
in herbs and total water-soluble Pb/Cd in water decoc-
tions were carried out according to the method described
in the procedure. The results are listed in Table 2.
The contents of Pb in the five herbs were higher than
for Cd in the same herbs. Though the content of total Pb
in Common anemarrhena rhizo me was the highest in the
five herbs, but the content of water-soluble Pb was the
lowest. In contrast, the contents of total Pb in Liquorice
was the lowest, but the contents of water-soluble Pb were
near to that in Common anemarrhena rhizome. It was
indicated that the dose of trace element taken in human
body could not be evaluated with total content of the
element in herb.
The practical feasibility of the proposed system was
tested on the five kinds of Chinese herbal medicines.
Since standard reference materials with certified Pb and
Cd values were not available, the selectivity and accu-
racy of the method were tested by a standard spiking
method. The recovery test was carried out in the same
way for spiked samples in the range of 0.15 - 10 µg·g–1
for Pb, and 0.01 - 0.2 µg·g–1 for Cd (each added content
nears real content in the sample). The recoveries of ana-
lyte from Common anemarrhena rhizome, Liquorice,
Dioscorea nippon ica makino, Rad ix sa lviae miltio rrh izae
and Fructus ligustri lucidi were 98.6, 99.3, 96.9, 102 and
98.4% for total Pb, and 97.3, 98.7, 95.8, 97.7 and 98.9%
for total water-soluble Pb, and 97.9, 100, 99.3, 98.8 and
96.9% for total Cd, and 98.9, 97.3, 98.6, 101 and 98.5%
for total water-soluble Cd, respectively. The data showed
that recovery was in the range of 95.8% - 102% for Pb
and 96.9% - 101% for Cd. The relative standard devia-
tions (R.S.D., n = 3) were in the range 1.7% - 3.4%,
demonstrating the general reproducibility of this method
Table 2. Determination of total Pb/Cd and total water-soluble Pb/Cd in herbs and their decoctions ( n = 3).
Sample Total Pb
(µg g–1)
Total Cd
(µg g–1)
Total water-
soluble Pb
Total water-
soluble Cd
Dissolving ratio
Pb Cd
(%) (%)
Common anemarrhena
rhizome 9.29 0.19 0.17 0.01 1.83 5.26
Liquorice 1.54 0.15 0.18 0.01 11.7 6.04
Dioscorea nipponica makino 4.77 0.14 0.38 0.03 7.97 21.4
Radix salviae miltiorrhizae, 4.94 0.19 0.25 0.02 5.06 10.5
Fructus ligustri lucidi 5.11 0.21 1.21 0.02 23.7 9.52
Copyright © 2011 SciRes. AJAC
3.5. Dissolving Capability
Based on above result, water-dissolving capability of the
analytes was examined. Table 2 showed the dissoluble
ratios (total water-soluble Pb/Cd contents to total Pb/Cd
content). The dissoluble ratio was related to the kind of
herb and element. For Fructus ligustri lucidi, the dis-
solving ratio of Pb was the highest. Although the content
of Pb in Common anemarrhena rhizome was the highest,
the dissolving ratio was the lowest. The content of Cd in
Dioscorea nipponica makino was the lowest, and the
dissolving ratio also was the highest. For Common ane-
marrhena rhizome the dissolving ratio of Cd was the
lowest. Otherwise, except for Liquorice and Fructus li-
gustri lucidi, the dissolving ratios of Cd were higher than
for Pb in the same herbs. The dissolving capability of Pb
and Cd in each of the five herbs has their own distributed
regularity. The kind of herb has a strong relationship to
the dissolving ratios.
3.6. Distribution of Pb and Cd in Water
Decoction at Stomach and Intestine
A decoction is one of the well known herbal preparations
that are used for healing many diseases and ailments.
The stomach and intestine are the main absorption or-
gans in the human body. The n-octanol-soluble Pb and
Cd have stronger lipophilic and biological activity. Since
the structure of n-octanol is similar to aqua-carbon com-
pound and ipide’s structure, so the distribution of Pb and
Cd in water decoction at stomach and intestinal acidity in
the presence of n-octanol is represented by their distribu-
tion in the stomach and intestine.
The content ratio ow (kowo w
kcc, where o is n-
octanol-soluble content; w is water-soluble content)
was employed to evaluate the lipophilic and biological
behaviors of organic compounds [17]. In this study, the
concentrations of water-soluble and n-octanol-soluble Pb
and Cd under gastric acidity (pH = 1.3) and intestinal
acidity (pH = 7.6) conditions were investigated. The re-
sults are listed in Table 3.
For the studied herbs, ow for Pb and Cd under intes-
tinal acidity was higher than that under gastric acidity, it
showed that analyte would be removed from water-
soluble to n-octanol-soluble Pb with raising pH of water
decoction. Otherwise, ow values for the five herbs also
had some differences. It is indicated that the content of
water-soluble and n-octanol-soluble analyte and its ratio
were related with the kind of herbal medicine and the
acidity of the decoction.
When , the quantum of n-octanol-soluble Pb
and Cd taken in gastric and intestinal part would be
higher than that of water-soluble Pb and Cd. When kow <
1, it was reverse. Therefore, when pharmacology actions
of herbal medicines were studied, medicine effects of
water decoction would not be evaluated only with total
content of Pb or Cd in water decoction. The component
of medicines, acted target, acidity of target and compati-
bility of medicines should be taken into account when
studying toxicology of herbal medicine.
4. Conclusions
It was indicated that the dose of trace element taken in
human body could not be evaluated with total content of
Table 3. Distribution of water-soluble and n-octanol-soluble Pb and Cd at gastric and intestinal acidity (n = 3)
Stomach acidity (pH 1.3) Intestine acidity (pH 7.6)
Sample Element
soluble ow
k Water-
soluble ow
Pb 0.098 0.083 0.85 0.059 0.123 2.10
Common anemarrhena
rhizome Cd 0.008 0.004 0.50 0.004 0.009 1.78
Pb 0.073 0.097 1.33 0.060 0.111 1.82
Cd 0.007 0.003 0.42 0.007 0.003 0.45
Pb 0.360 0.017 0.05 0.246 0.131 0.53
Dioscorea nipponica makino
Cd 0.010 0.004 0.40 0.008 0.007 0.82
Pb 0.226 0.022 0.10 0.215 0.034 0.16
Radix salviae miltiorrhizae,
Cd 0.009 0.004 0.45 0.007 0.007 1.00
Pb 0.878 0.333 0.40 0.806 0.406 0.50
Fructus ligustri lucidi
Cd 0.015 0.009 0.62 0.017 0.011 0.65
Copyright © 2011 SciRes. AJAC
the element in herb. A n-octanol system can be used to
study the distribution of Pb and Cd in water decoction in
our stomach and intestine. By using NH4H2PO4 as a
modifier for Pb and NH4H2PO4 plus Mg(NO3)2 as a ma-
trix modifier for Cd, the critical pyrolysis temperature
could be raised to 900˚C and 800˚C, respectively, assur-
ing high analytical sensitivity and lower background ab-
sorption. The detection limits of the proposed method for
Pb and Cd were lower than that of FAAS [3,4], GFAAS
[5,6,8,10] and HGAFS methods[11]. The proposed me-
thod is a reliable and effective for the determination of
Pb and Cd in Chinese herbal medicines and their de-
coctions. The distribution of Pb and Cd in water decoc-
tion at stomach and intestine acidities was developed in
the first time. The proposed method can help us make a
further study on the chemical and biological behaviors,
regularity of elements movement and toxicity of Pb and
Cd in Chinese herbal medicines, and gives some advice
on Chinese traditional herbs’ plant and use.
5. Acknowledgements
We express thanks to the Natural Science Foundation of
Hebei province of China for much support to the studied
subject (B2008000583).
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