A simple, rapid, and powerful microextraction technique was used for determination of palladium (II) ion in water samples using dispersive liquid-liquid microextraction (DLLME) followed by graphite furnace atomic absorption spectrometry (GF AAS). The different variables affecting the complexation and extraction conditions such as extraction and disperser solvent type, extraction time, pH, and concentration of chelating agent were optimized. Under the optimum conditions, the calibration graph was linear in the ranges of 0.05–1
Palladium has been used in different areas of science and technology including agents, brazing alloys, petroleum, electrical industries, and catalytic chemical reactions. The metal may enter the environment and interact with complexing materials, such as humic substances. Palladium has no biological role and all palladium compounds should be regarded as highly toxic and carcinogenic. Thus, because of its increasing use, on one hand, the toxicity of palladium (II) compounds to mammals, fish, and higher plants, on the other hand [
The complexity of matrix and low concentration levels of palladium in industrials (
Liquid-liquid extraction has been widely used for separation of platinum metals [
In previous research, we demonstrated a novel microextraction technique which was named dispersive liquid-liquid microextraction (DLLME) that was used for the extraction and determination of polycyclic aromatic hydrocarbons (PAHs) [
The purpose of this paper is to demonstrate the feasibility of DLLME combined with GF AAS for determination of palladium (II) ion in water samples.
The experiments were performed using a Shimadzu atomic absorption spectrometer (AA 6300G) with a graphite furnace atomizer (GFA-EX7i). A palladium hollow cathode lamp, operated at a current of 10 mA and a wavelength of 247.6 nm with a spectral band pass of 0.7 nm was used. Pyrolytic graphite-coated graphite tubes were purchased from Shimadzu.
The sample injection volume was 20
Graphite furnace temperature for determination of palladium.
Step | Temperature (°C) | Ramp time (s) | Hold time (s) | Argon gas flow (mL min−1) |
---|---|---|---|---|
Drying | 150 | 20 | 10 | 100 |
Pyrolysis | 1000 | 3 | 10 | 250 |
Atomization | 2700 | 0 | 2 | 0 |
Cleaning | 2800 | 0 | 2 | 1000 |
Separation of phases was assisted using a centrifuge (centurion scientific model: K 240R). The pH values were measured with a Metrohm pH-meter (model: 713) supplied with a glass-combined electrode.
All reagents used were of analytical grade. All solutions were prepared using doubly distilled deionized water. Stock solution of palladium (1000.0 mg L−1) was prepared by dissolving appropriate amounts of metallic Pd in aqua regia. Working solutions were prepared from the stock solution by serial dilutions with doubly distilled deionized water.
Chloroform, methanol, and ethanol were of analytical-grade from Merck (Darmstadt, Germany). 2 × 10−3 mol L−1 solution of 4,4′-Bis (dimethylamino) thiobenzophenone, Thio-Michler’s ketone (TMK), (Merck, Darmstadt, Germany) was prepared by dissolving appropriate amount of TMK in chloroform. This solution was kept in a dark place at room temperature.
A stock standard acetic acid/sodium acetate buffer solution (0.1 mol L−1, pH 3.0) was prepared by dissolving an appropriate amount of sodium acetate in doubly distilled deionized water and neutralizing to pH 3.0 with hydrochloride acid.
The pipettes and vessels used for trace analysis were kept in 10% nitric acid for at least 24 h and subsequently washed four times with deionized water before use.
A 5.0 mL of doubly-distilled water was placed in a 10 mL screw cap glass test tube with conic bottom and spiked at levels of 0.05–1
In order to obtain a high recovery and enrichment factor, the effect of different parameters affecting the complexation and extraction conditions such as pH, concentration of buffer and chelating agent, kind of extraction and disperser solvent and volume of them, extraction time, and salt addition were investigated and optimized. In order to study the explained parameters, extraction recovery and enrichment factor have been calculated by the following equations:
These parameters are known except
The separation of metal ions by dispersive liquid-liquid microextraction involves prior formation of a complex with sufficient hydrophobicity to be extracted into the small volume of sedimented phase; thus obtaining the desired preconcentration. pH plays a unique role on metal-chelate formation and subsequent extraction. The influences of the pH on the quantitative recovery values of palladium ions were investigated at the pH range of 1.0–10.0 using HCl and NaOH while other parameters were kept constant. The results illustrated in Figure
Effect of pH on extraction recovery of palladium obtained from DLLME. Extraction conditions: water sample volume, 5.0 mL; disperser solvent (methanol) volume, 500
Dispersive liquid-liquid microextraction of 2.0 ng of palladium using TMK from 5.0 mL of the sample solutions was conducted by varying the concentration of TMK in chloroform (70
Effect of TMK on extraction recovery of palladium obtained from DLLME. Extraction conditions: water sample volume, 5.0 mL; disperser solvent (methanol) volume, 500
Careful attention should be paid to the selection of the extraction solvent. It should have higher density rather than water, extraction capability of interested compounds and low solubility in water. Chloroform, carbon tetrachloride, tetrachloroethylene, carbon disulfide, and chlorobenzene were compared in the extraction of palladium. A series of sample solution were studied by using 500
To examine the effect of the extraction solvent volume, solutions containing different volumes of chloroform were subjected to the same DLLME procedures. The experimental conditions were fixed and include the use of 500
Effect of the volume of extraction solvent (CHCl3) on the enrichment factor and extraction recovery of palladium obtained from DLLME. Extraction conditions: water sample volume, 5.0 mL; disperser solvent (methanol) volume, 500
According to Figure
The main criterion for selection of the disperser solvent is its miscibility in the extraction solvent and aqueous sample. For this purpose, different solvents such as acetone, acetonitrile, tetrahydrofuran, and methanol were tested. A series of sample solutions were studied by using 500
Investigation of the effect of different volume of methanol (disperser solvent) on the extraction recovery would be very rough. Since, variation of the volume of methanol makes change in the volume of settled phase at constant volume of chloroform (extraction solvent). Thereby, to avoid this matter and in order to achieve a constant volume of settled phase (30
Extraction time is one of the most important factors in the most of extraction procedure. In DLLME, extraction time is defined as interval time between injection mixture of disperser and extraction solvent, and starting to centrifuge. The effect of extraction time was examined in the range of 0–45 min with constant experimental conditions. The results showed that the extraction recovery increased by increasing extraction time up to 1 min and after that remained constant. Thus, 1 min was used for extraction time in the subsequent experiments.
For investigating the influence of the ionic strength on performance of DLLME, various experiments were performed by adding different amount of NaCl (0.0–1.0 mol L−1). Other experimental conditions were kept constant. The results showed (Figure
Effect of the salt on the enrichment factor and extraction recovery of palladium obtained from DLLME. Extraction conditions: water sample volume, 5.0 mL; disperser solvent (methanol) volume, 500
The effects of common coexisting ions in natural water samples on the recovery of palladium were studied. In these experiments, 5.0 mL of solutions containing 0.2
Table
Analytical characteristics of proposed method.
Parameter | Analytical feature |
---|---|
Linear range ( |
0.05–1.0 |
Limit of detection ( |
0.02 |
Repeatability (RSDa, %) ( |
3.5 |
Enrichment factorb | 166.5 |
The enrichment factor (the volume ratio (
The proposed DLLME-GF AAS methodology was applied to the determination of Pd in several water samples. Water samples (i.e., tap water, sea water, river water and mineral water) were filtered using a 0.45
Determination of Pd(II) in different water samples.
Sample | Pd2+ spiked |
Pd2+ detected |
RSDg |
Recovery |
---|---|---|---|---|
Tap watera | 0.000 | n.d.f | — | |
0.100 | 0.098 | 3.6 | 98.0 | |
0.200 | 0.198 | 3.5 | 99.0 | |
| ||||
Sea waterb | 0.000 | n.d. | — | |
0.100 | 0.085 | 3.7 | 85.0 | |
0.200 | 0.172 | 3.8 | 86.0 | |
| ||||
River waterc | 0.000 | n.d. | — | |
0.100 | 0.092 | 3.6 | 92.0 | |
0.200 | 0.188 | 3.5 | 94.0 | |
| ||||
Mineral waterd | 0.000 | n.d. | — | |
0.100 | 0.097 | 3.4 | 97.0 | |
0.200 | 0.192 | 3.5 | 96.0 | |
| ||||
Synthetic samplee | 0.100 | 0.095 | 3.8 | 95.0 |
0.200 | 0.193 | 3.3 | 96.5 |
aFrom drinking water system of Tehran, Iran.
bCaspian sea water, Iran.
cZiarat River, Gorgan, Iran.
dFrom Abali mineral water, Tehran, Iran.
eCu2+, Co2+, Cd2+, Fe3+, Ag+, Cr3+, 500
fNot detected.
gRSD of three replicate experiments.
Dispersive liquid-liquid microextraction combined with graphite furnace atomic absorption spectrometry allows tackling the determination of palladium in natural waters in a simple way. The method is simple, rapid and economical. High preconcentration factor was obtained easily through this method and a detection limit at sub
The authors thank the research council at the University of Tehran and Iran University of Science and Technology for financial support.