Anal. Methods Environ. Chem. J. 5 (1) (2022) 75-85
Research Article, Issue 1
Analytical Methods in Environmental Chemistry Journal
Journal home page: www.amecj.com/ir
AMECJ
Rapid analysis of chromium (III, VI) in water and
wastewater samples based on Task-specic ionic
liquid by the ultra-assisted dispersive ionic liquid-liquid
microextraction
Vahid Saheba and Tayebeh Shamspur b,*
a Department of Chemistry, College of Science, Shahid Bahonar University of Kerman, Postal code:7616914111, Kerman, Iran
bDepartment of Chemistry, College of Science, Shahid Bahonar University of Kerman, 7616914111, Iran
ABSTRACT
Exposure to hexavalent chromium (Cr VI) causes cancer in cells of the
human body. So, the speciation and determination of the Cr (VI) and
Cr (III) in water and human samples based on sensitive techniques are
necessary. In this research, 2-mercapto-1-methylimidazole a novel
Task-specic ionic liquid (C4H6N2S; HS-CH3-IM) was used with a new
approach for speciation of Cr (III, VI) from water samples by ultra-
assisted dispersive ionic liquid-liquid microextraction procedure
(USA-D-ILLME). Due to the procedure, 100 mg of HS-CH3-IM and
0.2 mL of acetone were mixed and injected into 10 mL of water or
standard Cr (III) and Cr (VI) solution in the conical tube. After stirring
for 5 min, the Cr (VI) and Cr (III) were extracted with a positive and
negative charge of the thiol group (HS2+, HS-) in pH 2 or 8 and pH
5, respectively. The mixture of the HS-CH3-IM was collected at the
bottom of the conical tube by centrifuging. The upper liquid phase
was vacuumed with a peristaltic pump and the Cr (III, VI) loaded
on the HS-CH3-IM was back-extracted in a liquid solution. Finally,
the concentration of the Cr (III, VI) ions in a remained solution were
measured with ET-AAS after dilution up to 0.5 mL with DW. The
total chromium was determined in water samples by summarizing
the Cr (VI) and Cr (III) contents. All parameters such as the amount
of HS-CH3-IM, the sample volume, pH, and the shaking/centrifuging
time were optimized. Under the optimal conditions, good linear
range (LR), LOD, and enrichment factor (EF) were obtained 0.05–
1.7 μg L−1, 15 ng L−1, and 19.82 respectively (RSD% < 1.45). The
procedure was validated by spiking samples and good accuracy and
precision results were achieved.
Keywords:
Chromium III, VI;
Water samples;
2-Mercapto-1-methylimidazole;
Dispersive ionic liquid-liquid
microextraction,
Electrothermal atomic absorption
spectrometry
ARTICLE INFO:
Received 28 Oct 2021
Revised form 10 Jan 2022
Accepted 4 Feb 2022
Available online 27 Mar 2022
*Corresponding Author: Tayebeh Shamspur
Email: tsh@uk.ac.ir
https://doi.org/10.24200/amecj.v5.i01.170
------------------------
1. Introduction
Heavy metals have a toxic effect on environmental
matrixes (air, soil, water). they can enter from
waters, food, or vegetables and accumulate in brain,
liver, or renal tissues. A trace amount of heavy
metals can cause cellular damage in the human
body. Chromium(VI) is a major pollutant for the
environment and enters from many sources such as
chemical industries, steelworks, and electroplating.
The chromium cause diseases such as gene mutations,
carcinogen effect, and DNA lesions in human [1,2].
Two different oxidation forms of chromium exist
in the environment (Cr III and Cr VI). Cr (III)
76
compounds have an important role in the metabolism
of glucose and protein in humans[3]. Moreover, the
Cr (VI) has carcinogenic effects in cell tissues with a
strong oxidation potential in the human body which
enables to provide damage to DNA. Also, Cr (VI) is
harmful to the lungs and kidneys [4,5]. Chromium
values in drinking water are lower than 2 µg L-1
[6]. The World Health Organization (WHO) was
reported that the genotoxicity of Cr (VI) in humans is
50 µg L-1. The ACGIH announced the normal range
for chromium levels in human blood and urine were
achieved at 1.8 µg L-1 and 2.0 µg L-1, respectively
[7,8]. The Federal Committee on drinking water
(FCDW) has reported new information on Cr(III,
VI) and guideline technical documents on Cr(III,
VI) in drinking water. The FCDW showed a
maximum acceptable concentration (MAC) of 50 µg
L-1 to Cr(VI). This document focuses on the health
effects of Cr(VI) and total chromium considered
about 100 µg L-1. Some of the analytical methods
measure the total chromium Cr(III, VI) in drinking
water at the lower limit of the reported MAC[9].
Many sample preparations based on adsorbents or
ligands were was used for extraction chromium
from water samples. In addition, Cr(III) is likely to
be converted to oxidized form [Cr(VI)] after sample
preparation. Therefore, it is important to analyze
chromium species and total chromium(TCr) in
waters. In conventional studies, the best method for
the treatment TCr is coagulation based on ltration
and ion exchange [10]. Coagulation-based ltration
and ion exchange are favorite methodologies for
extracting Cr(VI) from drinking water. The drinking
water treatment technologies able to be certied to
international standards for reduction of TCr, Cr(VI),
and Cr(III) individually, include adsorption, reverse
osmosis, and distillation [11]. Recently, the different
techniques, include, ion chromatography(IC),
inductively coupled plasma mass spectrometry
(ICP-MS) [12], stripping voltammetry (SV) [13],
co-precipitation [14], ame atomic absorption
spectrometry (F-AAS) [15], , inductively coupled
plasma optical emission spectrometry (ICP-OES)
[16], ion chromatography inductively coupled
plasma-mass spectrometry (IC-ICP-MS) [17] and
electrothermal atomic absorption spectrometry
(ETAAS) [18] were used for determination of
chromium species in water samples. Due to
difculty matrixes and low detection for chromium
in water samples, treatment process such as liquid-
liquid extraction (LLE) [19], dispersive liquid-
liquid microextraction (DLLME) [20], magnetic
solid-phase extraction (SPE) [21], dithiocarbamate-
modied magnetite nanoparticles (DC-MNPs) [22]
and cloud point extraction (CPE) [23] are developed.
Dispersive liquid-liquid microextraction (DLLME)
is a conventional technique, where the extraction
phase (a microliter of hydrophobic solvent) was
dispersed in the water sample. Many organic
solvents (ethanol, methanol, toluene) were used in
the extraction phase. Recently, ionic liquids (IL) as
green solvent, low vapor pressure, high stability, and
large viscosity have been used in LLE [24,25].
The aim of this study is the speciation of Cr (III)
and Cr (VI) in water samples based on HS-CH3-IM
by the USA-D-ILLME procedure. The important
parameters for the extraction of chromium were
optimized and the concentration of chromium was
determined by ET-AAS.
2. Experimental
2.1. Instrumental
Chromium was determined with an atomic absorption
spectrometer (AAS, GBC Plus 932, Australia) using
a graphite furnace accessory (GF3000, ET-AAS).
The main parameters such as temperature (ash,
atomized, drying), auto-sampler into graphite tube,
owrate Ar gas, and temperature programming for the
chromium were adjusted by the book manufacturer.
A hollow cathode lamp of chromium (HCLcr) tuned
at a current (6 mA) and a wavelength of 357.9 nm
with a slit of 0.2 nm was used. The linear range (1.5-
33 µg L-1) and sample injection of 20 μL was used
(Peak Area). The pH of samples was controlled by
a digital pH meter (Metrohm 744). A centrifuge and
shaker (Germany, Product N: SIAL311GZ2F) was
used for dispersing and separating IL from samples.
For validation results, ICP-MS (Perkin Elmer) was
used for ultra-trace determination of chromium in
standard and water samples.
Anal. Methods Environ. Chem. J. 5 (1) (2022) 75-85
77
2.2. Reagents and materials
Ultra-trace reagents with HPLC or AAS analytical
grade purchased from Merck or Sigma Co.
(Germany). The modier for chromium [Mg(NO3)2]
for increasing ashing temperature, hexane, ethanol,
acetone, HNO3, H2SO4, and HCl were prepared
from Merck, Germany. The standard solution of
Cr (III) was prepared from an appropriate amount
of Cr(NO3)3 in 0.01 mol L-1 HNO3 (1000 mg L-1
Cr III, 1.0 g L-1). The standard solution of Cr (VI)
was purchased from Merck which was prepared by
1.0 g of K2CrO4 in 1 % HCl (1000 mg L-1 CrVI).
The standard solutions fthe or calibration curve of
chromium (0.1, 0.2, 0.4, 0.5, 1.0, 1.5 µg L-1) were
prepared daily by dilution of the stock solution. The
pH adjustments were made using appropriate buffer
solutions including sodium phosphate for pH 2.0-2.5,
ammonium acetate for pH 4.0-5.5 and ammonium
chloride for pH 8-10 (Merck). 2-Mercapto-1-
methylimidazole as Task-specic ionic liquid was
purchased from Sigma, Germany (HS-CH3-IM,
CAS N: 60-56-0, 25 g). Ultra-pure water (DW) was
obtained from a pure Water System (RIPI).
2.3. Water Sampling
The glass tubes were washed with HNO3 solution
(1 M) for two days and rinsed 10 times with DW.
Due to low concentrations of chromium in water
samples, even trace contamination, and sample
storage caused to affect the accuracy of the results.
The acidied water sample was put into the conical
tube (10-20 mL) and kept at -20OC. After ltering,
water samples were prepared from river water from
Karaj, well water from Varamin city, drinking water
from Tehran city, industrial wastewater, Tehran, Iran
prepared by ASTM procedure for waters.
2.4. Extraction Procedure
A pre-concentration procedure based on HS-CH3-
IM by the USA-D-ILLME was performed as
follows: rst, 100 mg of HS-CH3-IM as a TSIL, 0.2
mL of acetone were mixed and injected into 10 mL
of water and chromium standard samples (Fig.1).
After shaking for 5 min, the Cr VI and Cr III were
extracted by thiol group of HS-CH3-IM at pH 2 and
5, respectively. For optimizing, 10 mL of 0.1 - 1.5
μg L-1 Cr (III) and Cr (VI) standard solutions as the
lower and upper limit of quantication was used
instead of water samples in a conical centrifuge
tube. First, 100 mg of HS-CH3-IM dispersed in 0.2
mL of acetone in a I mL syringe and injected to 10
mL of chromium standard in a conical tube. The
pH was adjusted at 2 and 5 by the buffer solutions,
then the mixture solution was shaken for 5 min, and
chromium extracted by TSIL at 25 OC. To separation
phase, the turbid solution was centrifuged for 5 min
at 4000 rpm and the liquid phase was vacuumed
with an autosampler. Then, Cr (III) and Cr (VI)
were back-extracted from TSIL in acidic and basic
by adding 0.25 mL of 1.2 mol L-1 HNO3 and 0.2
mL of 1.0 mol L-1 NaOH, respectively. Finally,
the remained aqueous phase was determined by
ET-AAS after dilution with DW up to 0.5 mL. In
the optimum pH conditions, total chromium was
calculated by summarizing Cr (VI) to Cr (III)
contents. The blank solutions proceeded in the same
way and were used for the calibration ET-AAS. The
extraction conditions based on the HS-CH3-IM (IL)
for chromium speciation were shown in Table 1.
Fig.1. The extraction and speciation chromium based on HS-CH3-IM by the USA ─D-ILLME procedure
Speciation Chromium by Task-specic ionic liquid Vahid Saheb et al
78
3. Results and discussion
The TSIL (HS-CH3-IM) with the USA-D-ILLME
procedure was used for chromium speciation in the
standard solution and water samples. The results
showed us, the mean concentrations of Cr (III
and VI) in wastewater samples were signicantly
higher than water samples [(5.13 ± 0.22 μg L-1,
3.92 ± 0.18 μg L-1) and (0.19 ± 0.02μg L-1, 0.12 ±
0.01 μg L-1)], respectively.
The extraction recovery (Equation 1) was obtained
as the percentage of the ratio of the extraction
chromium (Cex) into the IL phase vs total chromium
in water(Ctotal).
Extraction Recovery =
(Eq. 1)
3.1. FTIR spectrum
The FT-IR spectra of HS-CH3-IM are presented in
Figure 2. The peak of FT-IR spectra at 1600 cm-1
is related to C=O bond vibration of the carboxylic
acid groups. The spectrum shows a band around
3100 cm-1 which can be attributed to the hydroxyl
groups. In addition, bands around 2900 cm-1 are
due to regular C-H stretching of the CH2 groups of
HS-CH3-IM.
3.2. PH effect
The effect of pH on extraction of Cr (III) and Cr(VI)
ions on the HS-CH3-IM as a TSILwas investigated
using different pH from 2 to 12 for 0.1 μg L-1 Cr (III)
and Cr(VI) ions as a lower LOQ and 1.5 μg L-1 Cr
(III) and Cr(VI) ions as upper LOQ. The extraction
was strongly dependent on the pH of solutions and
subsequently affected recovery. The results show
that the highest extraction efciency for Cr (III) was
achieved at pH 4 to 6 by the thiol group of the HS-
CH3-IM and the Cr (VI) extracted at pH 2-3. Thus,
the procedure was applied to speciation of two
forms of chromium at pH 5 and 2 for the Cr (III)
Table 1. Extraction conditions for chromium (III, VI) based on HS-CH3-IM by the USA ─D-ILLME method
ValueParameters
4 for Cr(III) and 2 for Cr(VI)
10 mL
0.2 mL for KOH/0.25 mL for HNO3
1 mL
1.0 mol L-1 for KOH/1.2 mol L-1 for HNO3
100 mg
200 mL
5 min
5 min
pH
Sample volume
Volume of back-extraction reagents
Volume of Buffer (0.1-0.2 mol L-1)
Concentration of back-extraction
Amount of IL
Volume of Acetone
Shaking time
Centrifugation time
Fig.2. FTIR spectra for HS-CH3-IM
Anal. Methods Environ. Chem. J. 5 (1) (2022) 75-85
79
and Cr(VI), respectively (Fig. 3). The mechanisms
of Cr (III) and Cr(VI) ions on the HS-CH3-IM were
obtained by complex formation between Cr (III)
and Cr(VI) ions and HS groups of the HS-CH3-IM
at optimized pH. The HS can be deprotonated (SH-
) at a wide range of pH from 4 to 9. The extraction
efciency of Cr (III) can be attributed to the afnities
of HS of the HS-CH3-IM as a TSIL for the Cr 3+
cations existing at pH from 4 to 6. The different
anionic species of Cr (VI) exist at low and high
pH (pH=2 and pH > 8), namely HCrO4
-, CrO4
2- and
Cr2O7
2- and negatively charged of anionic species
can be extracted by positive charges of SH2+ group.
3.3. Sample volume
Sample volume is the main parameter for the
extraction of chromium in the water sample. So, the
effect of sample volume was studied in a range of
2- 25 mL for 0.1 - 1.5 μg L-1 of Cr (III) and Cr(VI),
respectively. High extraction was obtained between
2 mL and 12 mL of the water sample. At more
volumes, the extraction efciency was decreased.
On the other hand, TSIL can be soluble partially
in water at higher sample volumes and cause non-
reproducible results. Therefore, a sample volume
of 10 mL was used for this study with HS-CH3-IM
by the USA-D-ILLME method (Fig. 4).
Fig.3. Effect of pH on extraction and speciation of Cr (III) and Cr(VI) ions based
on HS-CH3-IM by the USA ─D-ILLME procedure
Fig. 4. Effect of sample volume on extraction and speciation of
Cr (III) and Cr(VI) ions based on HS-CH3-IM by the USA ─D-ILLME procedure
Speciation Chromium by Task-specic ionic liquid Vahid Saheb et al
80
3.4. Amount of HS-CH3-IM
The results showed us that the extraction efciency
of Cr (III) and Cr(VI) ions was remarkably affected
by the amount of TSIL. Therefore, the amount of
TSIL was evaluated within the range of 50–250
mg. The extraction recovery was observed at more
than 80 mg TSIL. So, 100 mg of TSIL (HS-CH3-
IM) was chosen as optimum IL for extraction of
Cr (III) and Cr(VI) ions in water samples at pH 2
and 5 by the HS group (Fig. 5). For salty water
such as seawater, 120 mg of TSIL for 10 mL of
seawater must be used at optimized pH.
3.5. Centrifuge and sonication time
The sonication and centrifuge time are crucial to
achieving an efcient extraction based on HS-
CH3-IM by the USA-D-ILLME procedure. In this
research, the various sonication and centrifuge
times between 1-10 min was evaluated for
chromium extraction in water samples. The result
showed us, by increasing the sonication time
the relative response for extraction of chromium
increased and reached the maximum value at
4.5 seconds for HS-CH3-IM, and then remained
constant. Therefore, the ultrasonic times of 5.0
minutes for the Cr (III) and Cr(VI) extraction was
used. Also, the centrifuge time of 5.0 minutes
was selected for Cr (III) and Cr(VI) extraction in
water.
3.6. Effect of reagents on back-extraction
Due to the viscosity and organic structure of ionic
liquids, injection of IL into the graphite tube of the
furnace of ETAAS was not possible. So, based on
the USA-D-ILLME procedure, Cr (III) and Cr(VI)
were back-extracted from the HS-CH3-IM with
acid and base reagents. Due to previous research,
decreasing pH leads to dissociation and releasing
of chromium ions released into the aqueous phase
by decreasing or increasing pH. So, the different
concentrations of reagents such as HCl, HNO3,
H2SO4, KOH (0.5 -2.0 mol L-1) were used for
chromium back-extraction from the TSIL (Fig.
9). The research showed that 1.2 mol L-1 of HNO3
Fig. 5. Effect of HS-CH3-IM on extraction and speciation of Cr (III)
and Cr(VI) ions by the USA ─D-ILLME procedure
Anal. Methods Environ. Chem. J. 5 (1) (2022) 75-85
81
(0.25 mL) can be back-extracted Cr (III) from the
HS-CH3-IM to the liquid phase. Also, 1.0 mol
L-1 of KOH (0.2 mL) can be back-extracted Cr
(VI) from the HS-CH3-IM phase. After back-
extraction, the resultant solution was adjusted
to 0.5 mL with DW in a centrifuge conical tube
before determining by ET-AAS (Fig. 6).
3.7. Validation of methodology
The USA ─D-ILLME method was applied to
determine Cr (VI) and Cr (III) found in 10 mL
of water samples. The Cr (VI) and Cr (III) in
wastewater and water samples were evaluated (20
n). The mean concentration of Cr (VI) and Cr (III)
in wastewater was higher than in water samples.
Also, the mean concentration of Cr (VI) in well
water was lower than Cr (III) concentration. The
coloration analysis was achieved between Cr
(III) and Cr (VI) in industrial water and drinking
waters and there was a high correlation (r > 0.66).
In addition, in drinking waters, no correlation and
regression were shown between Cr (III) and Cr
(VI) (r > 0.12). The spiked water and wastewater
samples were used to demonstrate the reliability
and validation of the method for speciation and
determination of Cr (III) and Cr (VI) (Table 2). By
back-extraction process, the remaining solution
was spiked with standard solutions of Cr (VI) and
Cr (III) and analyzed with ET-AAS after extraction
based on the HS-CH3-IM by the USA-D-ILLME
method (Table 3). The recovery of spiked samples
is satisfactorily results, which shows the ability of
the procedure for determination and speciation of
the Cr (VI) and Cr (III)
in water samples. For validation of the proposed
method, certied reference materials in waters
(CRM) were obtained by ICP-MS. The spiking
CRM with the chromium standard solution showed
us the validation of methodology for speciation
and determination of Cr (VI) and Cr (III) in water
samples (Table 4). Due to results, high efciency
and accuracy were achieved for the determination
and speciation of Cr (VI) and Cr (III) in water
samples.
Fig. 6. Effect of reagents (acid and base) on back-extraction of Cr (III) and Cr(VI) ions
by the USA ─D-ILLME procedure
Speciation Chromium by Task-specic ionic liquid Vahid Saheb et al
82
Table 2. The coloration analysis for chromium determination of wastewater and water samples
in different cities, Iran (n=20, μg L-1)
City *Wastewater (n=20) water (n=20) Wastewater
Cr III Cr VI Cr III Cr VI r P-value
Tehran 1.07 ± 0.77 4.28 ± 0.04 0.09 ± 0.22 0.11 ± 0.02 0.098 <0.002
Karaj 2.51 ± 0.03 2.03 ± 0.69 0.14 ± 0.02 0.07 ± 0.04 0.331 <0.001
Kerman 0.75 ± 0.13 1.94 ± 0.81 0.10 ± 0.11 0.06 ± 0.05 0.113 <0.005
*Wastewater diluted with DW up to 50 mL (1:5)
Table 3. Validation of chromium speciation based on the HS-CH3-IM with spiking water samples
by the USA-D-ILLME method
Sample* Added (μg L-1)*Found (μg L-1) Total Recovery (%)
Cr (III) Cr (VI) Cr (III) Cr (VI) Cr (III) Cr (V)
Water 1
--- --- 1.235 ± 0.034 1.028 ± 0.037 2.263 ± 0.088 --- ---
1.0 --- 2.205 ± 0.104 1.055 ± 0.032 3.260 ± 0.126 97.0 ---
--- 1.0 1.229 ± 0.029 1.996 ± 0.097 3.225 ± 0.127 --- 96.8
Water 2
--- --- 0.224 ± 0.012 0.188 ± 0.013 0.412 ± 0.022 --- ---
0.2 --- 0.419 ± 0.019 0.191 ± 0.012 0.610 ± 0.028 97.5 ---
--- 0.2 0.226 ± 0.011 0.393± 0.021 0.619 ± 0.031 --- 102.5
**Wastewater 1
--- --- 4.213 ± 0.186 2.450 ± 0.105 6.663 ± 0.298 --- ---
2.0 --- 6.197 ± 0.304 2.447 ± 0.094 8.644 ± 0.386 99.2 ---
--- 2.0 4.198 ± 0.191 4.406 ± 0.178 8.604 ± 0.411 --- 97.8
**Wastewater 2
--- --- 2.155 ± 0.086 3.175 ± 0.128 5.330 ± 0.237 --- ---
2.0 --- 4.163 ± 0.204 3.179 ± 0.132 7.342 ± 0.335 100.4 ---
--- 3.0 2.162 ± 0.094 6.104 ± 0.275 8.266 ± 0.403 --- 97.6
Water 5
--- --- 0.532 ± 0.025 0.082± 0.004 0.614 ± 0.031 --- ---
0.5 --- 1.026 ± 0.045 0.079 ± 0.003 1.105 ± 0.048 98.8 ---
--- 0.1 0.528 ± 0.024 0.177 ± 0.005 0.705 ± 0.032 -- 95.0
*Mean of three determinations ± condence interval (P = 0.95, n =5)
**wastewater diluted with DW (1:5), so the result calculated after dilution factor (DF× 5)
Water 1: River water from Karaj
Water 2: Drinking water from Tehran city
Water 5: Well water from Varamin city
Anal. Methods Environ. Chem. J. 5 (1) (2022) 75-85
83
4. Conclusions
In this study, a novel method based on HS-CH3-IM as
TSIL was used for the speciation and determination
of the Cr (III) and Cr (VI) in water samples by the
USA-D-ILLME procedure. The important factors
for high extraction were optimized. By procedure,
a sensitive, efcient, low cost, and simple method
for speciation and preconcentration of the Cr (III)
and Cr (VI) in water samples were achieved. Under
optimized conditions, the working range (WR),
LOQ, and RSD% were obtained 0.05–3.6 μg L−1, 50
ng L−1, and 1.45, respectively. The performance of
the method for quantication analysis of chromium
in water samples was obtained. The analytical
performances of detection of Cr (III) and Cr (VI)
in water samples are comparable to previously
reported methods. Finally, the speciation chromium
based on HS-CH3-IM was revealed that most of Cr
(VI) and Cr (III) exist in industrial wastewaters.
5. Acknowledgments
The authors thank from Department of Chemistry,
College of Science, Shahid Bahonar University of
Kerman, Iran
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Table 4. Comparing chromium speciation and determination based
on the HS-CH3-IM/ET-AAS with CRM analysis by ICP-MS
CRM
ICP-MS (μg L-1)HS-CH3-IM (μg L-1)
Cr III Cr VI Total Cr III Found Cr VI Found Total
SS a
0.205 ± 0.012 0.198 ± 0.010 0.403 ± 0.019 0.195 ± 0.013 0.211 ± 0.014 0.406± 0.021
0.714 ± 0.031 0.508 ± 0.024 1.222 ± 0.048 0.698 ± 0.034 0.494 ± 0.026 1.192± 0.055
Water
--- ---- 1.321 ± 0.054 1.005 ± 0.054 0.318 ± 0.014 1.323 ± 0.068
0.50 ---- 1.804 ± 0.086 1.493± 0.069 0.305 ± 0.018 1.798± 0.087
--- 0.50 1.818 ± 0.081 1.012 ± 0.051 0.811± 0.042 1.823± 0.093
*Mean of three determinations ± condence interval (P = 0.95, n =5)
aSS: Standard Solution
Speciation Chromium by Task-specic ionic liquid Vahid Saheb et al
84
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Speciation Chromium by Task-specic ionic liquid Vahid Saheb et al
