Reversed-Phase Liquid Chromatographic Separation and Determination of Ni ( II ) , Cu ( II ) , Pd ( II ) , and Ag ( I ) Using 2-Pyrrolecarboxaldehyde-4-phenylsemicarbazone as a Complexing Reagent

is paper reports the utilization of 2-pyrrolecarboxaldehyde-4-phenylsemicarbazone (PPS) as a complexing reagent for the simultaneous determination and separation of Ni(II), Cu(II), Pd(II), and Ag(I) by reversed-phase high-performance liquid chromatography with UV detector. A good separation was achieved usingMicrosorb C18 column (150× 4.6mm i.d.) with amobile phase consisted of methanol : acetonitrile : water : sodium acetate (1mM) (68 : 6.5 : 25 : 0.5 v/v/v/v) at a �ow rate of 1mL/min. e detection was performed at 280 nm. e linear calibration range was 2–10 μμg/mL for all metal ions. e detection limits (S/N= 3) were 80 pg/mL forNi(II), 0.8 ng/mL for Cu(II), 0.16 ng/mL for Pd(II), and 0.8 ng/mL for Ag(I).e applicability and the accuracy of the developedmethod were estimated by the analysis of Ni(II) in hydrogenated oil (ghee) samples and Pd(II) in palladium charcoal.


Introduction
iosemicarbazones bonded through the sulphur and hydrazine nitrogen atom generally behave as a chelating ligand with transition metal ions.Free thiosemicarbazones and semicarbazones are less active in comparison to metal complexes.iosemicarbazones and their complexes have been considered extensively because of their pharmacological activities like anticancer, antibacterial, antiviral, antifungal, anti-HIV, antitumour, and many others [1,2].
e important part of analytical chemistry is the continuous monitoring of the level of heavy metal ions in the environmental samples because of their positive and/or negative effects on the human body [3].Few metal ions are toxic and carcinogenic, and they assert dangerous effects.ese metal ions can easily be accumulated in the tissues of organisms and cause serious physiological disorders [4].ey can affect the respiratory system and lungs, causing asthma, pneumonia, wheezing, and also nasal and throat cancers due to acute toxicity [5,6].Due to their hazardous effects, the researchers have increasing interest in the determination of these metal ions in biological and environmental samples.A number of methods have been reported employing various separations and detection techniques including atomic absorption spectrometry [7], ion chromatography [8], HPLC with solid-phase microextraction [9], inductively coupled plasma-atomic emission spectrometry [10], inductively coupled plasma-mass spectrometry (ICP-MS) [11], and capillary electrophoresis [12].Although the most sensitive and reliable techniques reported so far are the ICP-MS and AAS, these are very costly.However, HPLC is the most commonly used technique, which ful�lls all the requirements for analytical determination/separation of metals at very small scale.e purpose of this work is not only to synthesize and characterize the transition metal complexes with some ligands but also to develop a simple method to determine hazardous as well as essential metal ions at a very low concentration.e current study highlights a new loom for separation and simultaneous determination of Ni(II), Cu(II), Pd(II), and Ag(I) using 2pyrrolecarboxaldehyde-4-phenylsemicarbazone (PPS) as a complexing reagent.), Tokyo, Japan) with dual 1 cm cuvette was used to study absorption spectra for metal complexes.F 2: e effect of variation of pH on the formation of Pd(II), Ag(I), Ni(II), and Cu(II) as complexes of PPS against reagent blank.e �nal concentrations were 2, 1, 1, and 1 g/mL, respectively.

Synthesis of the
4-phenylsemicarbazone was dissolved in methanol : water (1 : 1) (20 mL).Both solutions were mixed well by adding glacial acetic acid (1 mL).e mixture was re�uxed for 30 minutes, concentrated to 10 mL, and cooled at −5 ∘ C overnight.Slightly yellow-colored crystals of PPS were obtained, and product was recrystalized twice from methanol.e PPS melted at 194 ∘ C (Figure 1).

Spectrophotometric
Procedure.e appropriate volume of Ni(II), Cu(II), Pd(II), and Ag(I) solutions containing 1.0-70 g of metal ion was transferred to a volumetric �ask (10 mL), and reagent PPS solution (1 mL, 0.2% w/v in methanol) was added. 2 mL of buffer solution (pH 6-7) was added and made up to mark with methanol.e solutions were scanned in the wavelength range of 700-300 nm against reagent blank in the same solvent.e same procedure was adopted to study the effect of pH (1-10) on absorption spectra of metal PPS complexes.e variation in absorbance with pH was investigated (Figure 2).Similarly, the stability of metal PPS complexes was investigated by recording the Detection was performed at 280 nm.e analytical column was re-equilibrated for 5 min aer each run, and the chromatographic peak height was used for quanti�cation purpose.

Determination of Pd(II) in Palladium
Charcoal.5 mL of hydrochloric acid (37%) was added to 0.3 g of palladium charcoal with Pd 10% (E.Merck) and re�uxed for half an hour, and then 5 mL of water was added to the solution, cooled, and �ltered.e �nal solution was adjusted to 25 mL.e solution (0.5 mL) was transferred to 10 mL of volumetric �ask, and the above analytical procedure was followed.e amount of Pd(II) in palladium charcoal was calculated from the calibration curve prepared from the standard Pd solution.

Analysis of Ni(II) in a Hydrogenated Vegetable Oil (Ghee)
Sample.20 g of a hydrogenated vegetable oil sample (Pakistan Oil Mills, Pvt. Ltd., karachi and Tullow Oil Mills, Hyderabad, Pakistan) was transferred to conical �ask, and 30 mL of HNO 3 (1 M) was added.Aer shaking on mechanical shaker for one hour, the layers were allowed to separate, and aqueous layer was collected and concentrated to nearly 5-7 mL, and the �nal volume was adjusted to 10 mL with water.In a 10 mL �ask, 0.5 mL of solution was transferred, pH was adjusted to 6.0, and analytical procedure was followed as mentioned in a previous section.External calibration curve was used for the quanti�cation of Ni.To compare the results obtained with the proposed method, content of Ni in aqueous extract was also determined by using �arian AA-20 �ame atomic absorption spectrophotometer.Samples were run in triplicate with delay and integration time of 3 seconds.

Results and Discussion
e reagent PPS was prepared as reported and reacted with Cu(II), Ni(II), Co(II), Fe(II), Hg(II), Pd(II), and Ag(I) to form colored complexes.e maximum color reaction was observed within pH 5-8 and was stable for 6 to 24 hrs.Ag(I) complex developed turbidity and required solvent extraction procedure in chloroform.All complexes were absorbed maximally within 370-380 nm with molar absorptivity in the range of 8.5 to 45×10 3 L mole −1 cm −1 .e Ag(I) indicated the minimum and Ni(II) the maximum value of molar absorptivity.e beer's law was obeyed with 0.1-7.0g/mL of the metal ions (Table 1).e reagent PPS has high a spectrophotometric permittivity, but the complexes were absorbed within the narrow range of 377-390 nm in visible region; therefore, HPLC was examined for their simultaneous determinations.e complexes were injected on Microsorb C18 column and eluted isocratically with a mixture of methanol water and acetonitrile.However, a separation between Ni(II), PPS, Cu(II), Pd(II), and Ag(I) was obtained when eluted with a mixture of methanol : water : acetonitrile : sodium acetate (1 mM) (68 : 25 : 6.5 : 0.5 v/v/v/v) with a �ow rate of 1 mL/min at 280 nm wavelength (Figure 3).e retention times for Ni(II), Cu(II), Pd(II), and Ag(I) were observed as 2.0, 2.9, 3.9, and 12 min, respectively.Linear calibration curves were plotted by recording the average peak height (  ) versus concentration and were obtained with 2.0-10 g /mL of each metal ion, corresponding to 5-50 ng/injection.e detection limits remained as three times the signal-to-noise ratio (3 : 1) and were obtained as 0.8 ng/mL for Ag(I), 0.16 ng/mL for Pd, 0.8 ng/mL for Cu, and 80 pg/mL for Ni.e coefficient of determination ( 2 ) for Ag, Ni, Cu, and Pd with six-point calibration was observed as 0.995, 0.994, 0.998, and 0.996, respectively (Table 2).Nickel(II) eluted before the complexing reagent PPS with retention time of 2.0 min and palladium aer the reagent show very good separation and indicated high permittivity.erefore, the determination of Ni(II) and palladium from real samples was considered.e method was used for the determination of palladium in palladium charcoal and nickel in hydrogenated oil (ghee) samples.e results of Ni are also compared with AAS method and summarized in Table 3. e effect of different ions at least twice the concentration of Ni(II) and Pd(II) was also examined.Cu(II), Fe(II), Cd(II), Zn(II), Pb(II), Mn(II), Cr(III), Ca(II), Mg(II), Bi(III), Cl − , Br − , 1 − , SO 4 −2 , citrate, and tartrate did not interfere.

Conclusion
A rapid, precise, reproducible, and sensitive method for simultaneous determination and separation of metal complexes using RP-LC was developed.Enhanced detection sensitivity (pg to ng levels) with quantitative data was successfully demonstrated.PPS was found to be a very efficient reagent for the determination of these metal ions aer complex formation.PPS reacts with the number of metal ions but is more selective and sensitive for Ni(II), Cu(II), Pd(II), and Ag(I).e applicability of method to a variety of matrices reveals the ruggedness of the proposed method.

Con�ic� of �n�eres�s
All the authors of the paper declare that they do not have a direct �nancial relation with any commercial identity mentioned in the paper that might lead to a con�ict of interests for any of the authors.

T 1 : 1
Quantitative spectrophotometric data of color reaction of PPS with metal ions.S. no.Metal ions Solvent pH  max (nm)  = 10 3 L mol −1 cm −Solution aer preparation and aer lapse of different intervals.e variations in absorption spectra at different time intervals and the effects of time on the characteristic of absorption spectra were evaluated and shown in Table1.2.5.HPLC Procedure.A solution (1-5 mL) containing Ni(II), Cu(II), Pd(II), and Ag(I) (1-100 g) was transferred to a 10 mL volumetric �ask and was added reagent PPS solution (0.5 mL, 0.2% w/v in methanol) and 1 mL of bicarbonate buffer solution of pH 8.0.e contents were mixed well, and the volume was adjusted to the mark with methanol.e solution (2 L) was injected on column Microsorb C18, 5 m (150 × 4.6 mm i.d.), and complexes were eluted with a mixture of methanol : water : acetonitrile : sodium acetate (68 : 25 : 6.5 : 0.5 v/v/v/v) using a �ow rate of 1 mL/min.
T 2: Quantitative HPLC data for metal ions Cu(II), Ni(II), Pd(II), and Ag(I) using PPS complexing reagent.Palladium was not analyzed by AAS; e result was compared with the standard value provided by E. Merck. *