Extractive Spectrophotometric Determination of Platinum in Cisplatin ...

Columbia International Publishing Journal of Trace Analysis in Food and Drugs (2016) Vol. 2 No. 1 pp. 1-24 doi:10.7726/jtafd.2016.1001

Research Article

Extractive Spectrophotometric Determination of Platinum in Cisplatin Injection, Alloys and Catalysts Assisted by 2-nitrobenzaldehydethiocarbohydrazone Sunil B. Zanje1, Arjun N. Kokare1, Vishal J. Suryavanshi1, Gurupad D. Kore1, Balaji T. Khogare1, and Mansing A. Anuse1* Received: 2 August 2015; Published online 2 April 2016 © Columbia International Publishing 2016.Published at www.uscip.us

Abstract A simple, rapid, selective and sensitive spectrophotometric method for the determination of platinum(IV) was developed, based on the color reaction between platinum(IV) and 2nitrobenzaldehydethiocarbohydrazone (2-NBATCH) in the pH range 6.4-7.8. The red colored species have been developed after heating the reaction mixture in boiling water bath for 5 min and it was extracted into chloroform. The complex has an absorption maximum at 440 nm. A 20 fold of excess of reagent was required for complete complex formation. Beer’s law was obeyed for platinum(IV) concentration in the range of 4-12 µg mL-1 and the optimum concentration range was 6-12 µg mL-1 of platinum(IV) as evaluated by Ringbom’s plot. The molar absorptivity and Sandell’s sensitivity were 1.03  104 L mol-1 cm-1 and 0.0189 µg cm-2, respectively. The effect of pH, heating and extraction time, concentration of reagent and interference from various ions were investigated. The stoichiometry of the extracted complex was determined by Job’s method of continuous variation, mole ratio method and slope ratio method. It was found that metal to ligand ratio was 1:2. The developed method has been successfully applied to the determination of platinum(IV) in pharmaceutical samples, catalyst and synthetic alloy sample. Keywords: Platinum(IV); Spectrophotometry; 2-Nitrobenzaldehydethiocarbohydrazone; Analysis of real samples

1. Introduction Platinum is a rare element, however, its use has increased in recent years and is grouped among the most precious metals (http:/unctad.org/infocomm/anglais/platinum/uses.htm). The consumption of platinum is in ornaments and jewellery and in different industries like automobiles in catalytic ______________________________________________________________________________________________________________________________ *Corresponding e-mail: [email protected] 1 Analytical Chemistry Research Laboratory, Department of Chemistry, Shivaji University, Kolhapur-416004, India 1

Sunil B. Zanje, Arjun N. Kokare, Vishal J. Suryavanshi, Gurupad D. Kore, Balaji T. Khogare, and Mansing A. Anuse/ Journal of Trace Analysis in Food and Drugs (2016) Vol. 2 No. 1 pp. 1-24

exhausts gas converters, chemical, petrochemicals, electrical, glass and aircraft manufacturing (http:/www.ebullionguide.com/platinum.aspx). There are many sources through which platinum can enter into the environment. Platinum as a metal is not considered as toxic as for e.g. lead but its salts/drugs do cause changes in DNA and is therefore hazardous to health (Lu et al., 2007). Over a past 20 years, pollutants in exhausts gases from motor vehicles have been treated a successfully by autocatalytic converters containing precious metals, mainly platinum together with palladium and rhodium autocatalysts remove about 90 % of CO, unburned hydrocarbons and nitrogen oxides, three major gaseous environmental pollutants (Barefoot, 1997). Taking into account a substantial amount of forms decontaminated autocatalyst and substantial concentrations of precious metals in them, autocatalyst should be considered as an important secondary raw material for production of platinum metals. Owing to the high price of platinum group metal, analytical control over the process of their extraction as well as the analysis of feedstock and the products of its processing should be performed using methods characterized by high accuracy and selectivity (Dal’nova et al., 2010). The compound cis diaminedichloroplatinum(II), clinically known as cisplatin, a square planar platinum complex is used in routine alone or in combination with other drugs and with radiotherapy for the treatment of testicular and ovarian cancers and also of survical bladder and head/neck tumors (Anilanmert et al., 2001). Spectrophotometric methods for the determination of platinum have been reviewed by Marczenko (Marczenko, 1976). Numerous spectrophotometric determination of platinum(IV) has been reported with chromogenic reagents such as N-(m-methylphenyl)-N’-(sodium paminobenzenesulfonate)-thiourea (Ma et al., 2001), N-(3,5-dimethylphenyl)-N’-(4aminobenzenesulfonate)-thiourea (Zhang et al., 2006), o-phenylenediamine (Anilanmert et al., 2001). Anisaldehyde-4-phenyl-3-thiosemicarbazone (Prakash et al., 1987), 1,5-diphenylcarbzide (Brajter et al., 1987), benzyldimethylphenylammonium chloride [Das & Das, 1994). 4-[N,N(diethyl)amino] benzaldehyde thiosemicarbazone (Naik et al., 2010), mercapto carboxylic acids (Crisponi et al., 2000), tin(II) chloride and amides (Patel et al., 2004; Lintz, 1991). Dimethyl sulphoxides (Grigoryan et al., 2008) have been reported as a chromogenic reagent for platinum(IV) but these reagents have lower selectivities. Other methods used for determination of platinum(IV) which are highly sensitive but lack of the selectivity. These are leuco xylene cyanol FF (Revanasiddappa & Kiran Kumar, 2003), 3-(2’-thiazolylazo)-2,6-diaminopyridine (Toral et al., 2000), 5-(4-nitrophenylazo)-8-(p-toluenesulphonamido)-quinoline (Jianwei & Qiheng, 1991) and astrafloxin FF (Bazel et al., 2012). Various instrumental technique have recently been used for determination of platinum such as atomic absorption spectrometry (AAS) (Dal’nova et al., 2010; Dal’nova et al., 2010; Junior et al., 2010), electrothermal-atomic absorption spectrometry (ET-AAS) (Moskvin et al., 2005; Najafi et al., 2010; Tsogas et al., 2008; Godlewska-zylkiewicz et al., 2008; Meeravali et al., 2014), and graphite furnace-atomic absorption spectrometry (GF-AAS) (Ye et al., 2014; Resano et al., 2015; Dobrowolski et al., 2015; Puig & Alvarado, 2006; Chappuy et al., 2010; Ojeda et al., 2006). Due to its high level of selectivity high performance liquid chromatography (HPLC) (Lanjwani et al., 2006) with UV detector has been established itself on the most widely used for this purpose. Furthermore a sensitive method of separation of platinum from complex matrix has been achieved by inductively coupled plasma-mass spectrometry (ICP-MS) (Hanada et al., 1998; Yamada et al., 2005; Alonso et al., 2015), inductively coupled plasma-atomic emission spectrometry (ICP-AES) (Dyachkova et al., 2


2012; Petrova et al., 2010) and inductively coupled plasma-optical emission spectrometry (ICPOES) (Yu et al. 2010; Zhang & Tian 2015). However, most of these methods need prior separation and enrichment to avoid matrix interference and to enhance the sensitivity (coprecipitation, fire assay, solvent extraction and floatation). These methods have also disadvantages in terms of cost and instrument used in routine analysis. The aim of this study is to develop simple, low cost, sensitive, accurate and reliable spectrophotometric method for the determination of trace amount of platinum(IV) using 2nitrobenzaldehydethiocarbohydrazone (2-NBATCH) as a reagent. The proposed method has been successively applied in determination of platinum in pharmaceutical preparation, catalyst and synthetic mixture corresponding to composition of alloys and minerals.

2. Experimental 2.1 Apparatus Absorption measurements were made with a Mecasys digital spectrophotometer model optizen  using 1-cm quartz cells. A model LI-120 Elico digital pH meter with combined glass electrode was used for pH measurement. A shimadzu AA – 6800 atomic absorption spectrometer with the primary radiation source was a platinum hollow cathode lamp operated at 15 mA for platinum was used throughout measurements which was made at 266 nm with a dual background correction. Mettler Toledo single pan electronic balance model ML 204 was used for weighing. Glasswares were cleaned by soaking in acidified solutions of potassium dichromate, followed by washing with soap solution and rinsing two times with double distilled water. 2.2 Standard platinum(IV) solution Pure platinum wire (0.100 g) was dissolved in aqua-regia. The solution was repeatedly evaporated by the addition of concentrated hydrochloric acid until all the nitric acid was removed. The residue was dissolved in 2 mL concentrated hydrochloric acid and diluted to 100 mL with water and standardized (Tikhomirova et al., 1991). The solution was suitably diluted to obtain a working solution 100 µg/mL of platinum(IV). 2.3 Reagent and solutions 2-Nitrobenzaldehydethiocarbohydrazone (2-NBATCH) was synthesized and recrystallised as reported by (Li et al., 2008). Stock solution (0.02 mol L-1) was prepared by dissolving 0.239 g of 2NBATCH in 50.0 mL of 1,4-dioxane. All of the other reagents and solvents used were of analytical grade. Stock solutions of interfering ions were prepared by dissolving suitable salts of metals in water or in suitable dilute acids and making upto known volume. The solutions of anions were prepared by dissolving the alkali metal salts in water. Double distilled water was used throughout the experiment. 2.4 Recommended Procedure An aliquot of the sample solution containing 100 µg of platinum(IV) solution (100 µg/mL) was 3


taken in 25 mL volumetric flask. The pH was adjusted to 7.0 and followed by 5 mL of 0.02 mol L-1 2NBATCH in 1,4-dioxane. It was then diluted to 25 mL with water. The mixture was heated in boiling water bath for 5 min. The mixture was cooled and transferred into a 125 mL separatory funnel. The yellowish red colored platinum(IV)-2-NBATCH complex was extracted in 10 mL of chloroform with a 5 min equilibration time. The two phases were allowed to separate and the yellowish red colored complex layer was dried over anhydrous sodium sulfate, transferred into 10 mL calibrated volumetric flask and made up to mark with chloroform. The absorbance of platinum(IV)-2-NBATCH complex was measured at 440 nm against reagent blank prepared in a similar manner. Percentage extraction (%E) and a distribution ratio (D) were calculated according to Eqs. (1) and (2), respectively 𝐴1−𝐴 %E= x 100 (1) 𝐴1−𝐴0 Where, the cation

A0 - is the absorbance of 2-NBATCH solution without metal. A1 - is the absorbance of the 2-NBATCH solution containing known concentration of cation before the extraction A - is the absorbance of the 2-NBATCH solution containing known concentration of after extrcation.

D= Where,

(𝑉𝑤/𝑉𝑜)×%𝐸 (100−%𝐸)

(2)

D - is the distribution ratio, Vw - volume of aqueous phase, Vo - is the volume of organic phase

3. Results and Discussion 3.1 Absorption spectra and spectral characteristics of colored complex A yellowish red color complex of platinum(IV)-2-NBATCH showed a maximum absorbance at 440 nm and 2-NBATCH in 1,4-dioxane showed maximum absorbance at 315 nm (Fig. 1). Thus, all further spectral measurements of the complex were made at 440 nm against the reagent blank. The physico-chemical characteristics are given in (Table 1).

Fig. 1. (A) Absorption spectrum of 2-NBATCH vs. 1, 4-dioxane blank (λmax = 315 nm and 345 nm) 4


(B) The absorption spectrum of Pt(IV)-2-NBATCH complex vs. 2-NBATCH blank (λmax = 440 nm) (Pt(IV)= 10.0 µg mL-1; pH = 7.0 ; 2-NBATCH = 5.0 mL of 0.02 mol L-1; Equilibrium time = 5 min; Solvent = chloroform) Table 1 Physico-chemical characteristics and precision data of platinum(IV)-2-NBATCH complex Characteristics of complex pH Reagent solvent 2-NBATCH Heating time Extraction solvent Equilibrium time λmax Molar absorptivity Sandell’s sensitivity Beer’s law range Ringbom’s optimum range Standard deviation Relative standard deviationa Stoichiometry Stability of complex

Parameters 7.0 (6.4 – 7.8) 1,4-Dioxane (20 %) 5.0 mL, 0.02 mol L-1 5 min (5-30 min) Chloroform 5.0 min (single extraction) 440 nm 1.03 X 104 L.mol-1.cm-1 0.0189 µg. cm-2 4-14 µg mL-1 6-12 µg mL-1 0.2 0.22 % 1:2 > 48 h

3.2 Effect of pH. The effect of pH on the formation of the platinum(IV)-2-NBATCH complex was investigated by varying the pH of platinum(IV) solution in the range of 1 to 10 before the addition of the organic phase. The results in (Fig. 2) showed that the absorbance increases from pH 2.0 to 6.4 and then it remains constant from pH 6.4 – 7.8. The optimum pH range of complex was 6.4-7.8. A further increase in the pH caused a sharp decrease in the percentage extraction, may be due to hydrolysis of the complex. Hence, pH 7.0 was recommended for further studies.

Fig. 2. Effect of pH on the extraction Pt(IV)-2-NBATCH complex, Pt(IV)= 10.0 ug mL-1, 2-NBATCH = 5.0 mL of 0.02 mol L-1, λmax = 440 nm, Solvent = chloroform 5


3.3 Effect of 1, 4-dioxane, ethanol, dimethylsulfoxide and N, N-dimethylformamide medium The percentage of solvents in aqueous phase were studied by ethanol, 1,4-dioxane, dimethylsulfoxide and N,N-dimethylformamide (Fig. 3) with the optimum range varied 10 – 40 % (V/V) keeping other parameter constant. In the presence of 1, 4-dioxane the absorbance increases from 10 % to 14 % (V/V), absorbance remained constant from 14 % to 24 % (V/V) and further absorbance decreases above 24 % (v/v) of 1,4-dioxane. Similarly, in the presence of dimethylsulfoxide, ethanol and N, N-dimethylformamide the complexation was found to be incomplete and showed lower absorbance. In order to ensure complete complexation excess of 1, 4dioxane 20 % (V/V) in aqueous phase was maintained for further study.

Fig. 3. Effect of 1,4-dioxane, DMSO, ethanol and DMF medium (10 - 40 %):Pt(IV)= 10.0 ug mL-1 , 2NBATCH = 5.0 mL of 0.02 mol L-1, λmax = 440 nm, Solvent = chloroform 3.4 Effect of 2-NBATCH concentration

Fig. 4. Effect of 2-NBATCH concentration on extraction of Pt(IV)-2-NBATCH complex, Pt(IV)= 10.0 ug mL-1 , 2-NBATCH = 0.1 – 10 mL of 0.01 mol L-1 in 1,4-dioxane, λmax = 440 nm, Solvent = chloroform, Equilibrium time = 5 min. The effect of 2-NBATCH concentration on the complexation of platinum(IV) was studied by varying its concentration from 4  10-4 mol L-1 to 2  10-2 mol L-1 (Fig. 4) for full color development at pH 7.0. Absorbance goes on increasing from 4  10-4 mol L-1 to 4  10-3 mol L-1 and above the 6


concentration 4  10-3 mol L-1 absorbance remains constant up to 2.0  10-2 mol L-1. However, 5.0 mL of 2.0  10-2 mol L-1 of the reagent was recommended in order to ensure the complete complexation. A further excess of 2-NBATCH has no adverse effect on absorbance of platinum(IV) 2-NBATCH complex. 3.5 Effect of extracting solvents Different organic aliphatic and aromatic solvents were studied for the quantitative extraction of platinum(IV)-2-NBATCH complex. The percentage extraction (%E) values increased in order of kerosene (16.8) < cyclohexane (22.7) < n-butanol (33.1) < amyl acetate (35.9) < toluene (47.3) < xylene (53.9) < methyl isobutyl ketone (MIBK) (73.2) < dichloromethane (80.7) < 1,2dichloroethane (93.8) < chloroform (99.9). It was found that there is no direct correlation between percentage extraction and dielectric constant (€) of the extracting solvents examined (Table 2). Among these, chloroform was used for extraction, as it shows high absorbance of the complex at λmax. Table 2 Effect of extracting solvents on extraction of platinum(IV)-2-NBATCH complex Platinum(IV) = 100 µg, pH = 7.0 , 2-NBATCH = 5 mL 0.02 mol L-1 , Heating time = 5 min, Contact time = 5 min, λmax = 440 nm. Solvent

Dielectric constant(€)

Percentage extraction(%E)

MIBK Chloroform

13.11 4.81

73.2 99.9

Distribution ratio (D) 6.82 24997.5

1,2-Dichloroethane

10.4

93.7

37.56

Dichloromethane Kerosene Xylene Toluene n-Butanol Cyclohexane Amyl acetate

1.25 1.80 2.30 2.38 17.80 2.02 4.80

80.7 16.8 53.8 47.2 33.1 22.7 35.9

10.46 0.50 2.91 2.23 1.23 0.73 0.88

.

3.6 Effect of heating time There is no formation of complex at room temperature. Therefore, platinum(IV)-2-NBATCH mixture was heated with time interval of 01 – 30 min. The absorbance goes on increasing up to 5 min and above 5 min, absorbance remained constant up to 30 min (Fig. 5). Hence 5 min was optimized for subsequent study. There is no any undesirable effect of time of heating on the absorbance of the complex.

7


Fig.5. Heating time of Pt(IV)-2-NBATCH complex, Pt(IV)= 10.0 ug mL-1 , 2-NBATCH = 5.0 mL of 0.02 mol L-1,Equilibrium time = 5.0 min, λmax = 440 nm, Solvent = chloroform 3.7 Effect of equilibrium time The equilibrium time was varied from 15 s to 45 min in order to extract the coloured complex into chloroform (Fig. 6). Absorbance increases from 15 s to 2 min, furthermore 2 to 45 min it remains constant. Prolonged shaking has no adverse effect on the absorbance of platinum(IV)-2-NBATCH complex. Hence a contact time of 5 min was selected for subsequent experiment.

Fig. 6. Effect of equilibrium time, Pt(IV)= 10.0 ug mL-1 , 2-NBATCH = 5.0 mL of 0.02 mol L-1, λmax = 440 nm, Solvent = chloroform, Equilibrium time = 15 s to 45 min. 8


3.8 Effect of color stability of complex The color stability of platinum(IV)-2-NBATCH complex was studied at room temperature by measuring the absorbance at regular time intervals. The absorbance of the complex was stable for more than 60 h (Fig. 7). Therefore, measurement of absorbance of complex the time was not critical.

Fig. 7. Stability study, Pt(IV)= 10.0 ug mL-1 , 2-NBATCH = 5.0 mL of 0.02 mol L-1,Equilibrium time = 5.0 min, λmax = 440 nm, Solvent = chloroform 3.9 Effect of temperature The effect of temperature on complexation of platinum(IV) at pH -5.0 using 5 mL of 0.02 mol L-1 2-NBATCH at varying temperature from 313 to 373 K was studied (Table 3). It was shown that, the distribution coefficient increases with increase in temperature. The extraction equilibrium constant (Kex) with change in temperature is expressed by Vant Hoff’s equation. d(log Kex) / d(1/T) = -H/2.303 R

(3)

The plot of log Kex versus 1000/T is linear with slope value -0.1087 (Fig. 8) and enthalpy change H = 2.082 KJ mol-1. It means that extraction of platinum(IV) with 2-NBATCH is a endothermic process. The free energy G and entropy S were calculated from the equation G = - 2.303 RT log Kex S = (H - G) / T

(4) (5)

The negative values of free energies G indicate that reaction is spontaneous. The positive enthalpy (H) value indicates that the extraction of platinum(IV) with 2-NBATCH was favorable with rise in temperature. 9


Table 3 Effect of temperature on complexation of platinum(IV)-2NBATCH complex Temp .K

1000/T

Absorb ance

%E

D

Log D

G (KJ mol)

H (KJ mol)

S

313 3.194 0.089 16.79 0.5044 -0.2972 1.6957 0.0012 323 3.095 0.264 50.09 2.51 0.4 -2.2823 0.0135 333 3.003 0.456 86.36 15.84 1.2 -6.8470 0.0268 343 2.915 0.517 97.77 109.64 2.04 -11.639 2.082 0.0400 353 2.832 0.526 99.60 630.95 2.8 -15.976 0.0511 363 2.754 0.528 99.92 3162.27 3.5 -19.970 0.0607 373 2.680 0.529 99.99 24997.5 4.3978 -25.093 0.0728 T – temperature, %E – Percentage extraction, D – Distribution ratio, ∆G – Gibb’s free energy, ∆H – enthalpy, ∆S - Entropy

Fig. 8. Effect of temperature on the extraction of Pt(IV)-2-NBATCH complex, Pt(IV)= 10.0 ug mL-1 , 2-NBATCH = 5.0 mL of 0.02 mol L-1,Equilibrium time = 5.0 min, λmax = 440 nm, Solvent = chloroform 3.10 Beer’s law and sensitivity of the method A linear calibration curve indicates that Beer’s law was obeyed within the concentration range of 414 µg mL-1of platinum(IV) (Fig. 9). The optimum concentration range was evaluated by Ringbom’s plot method (Ringbom 1939) and it was confirmed to be 6-12 µg mL-1 (Fig. 10). Molar absorptivity was found to be 1.03 X 104 L.mol-1.cm-1 while the sensitivity of the method as defined by Sandell’s was 0.0189 µg. cm-2.

10


Fig. 9. Beer-Lamberts law, 2-NBATCH = 5.0 mL of 0.02 mol L-1, Equilibrium time = 5.0 min, λmax = 440 nm, Solvent = chloroform

Fig. 10. Ringbom plot, 2-NBATCH = 5.0 mL of 0.02 mol L-1, Equilibrium time = 5.0 min, λmax = 440 nm, Solvent = chloroform 3.11 Precision and accuracy of the method Five aliquots of different concentrations of each ten samples were taken and platinum(IV) was determined by employing the general procedure in order to assess the accuracy and precision of the method. The standard deviation was found to be not more than 0.02 and the relative standard deviation is less than 0.23 %. The values showed that this method has a greater accuracy and enhanced precision. 11


3.12 Stoichiometry of the complex The composition of extracting species was ascertained by a Job’s method of continuous variation (Job, 1928) (Fig. 11). The probable composition of extracting species was calculated to be 1:2 (Metal: ligand). The composition of the complex was also confirmed by Mole ratio method (Yoe and Jones, 1944) (Fig. 12) and slope ratio method by plotting the graph (Fig. 13) of logD[Pt(IV)] vs. log C[2NBATCH] at pH – 4.0 and pH – 10.0 with platinum(IV) having slope values 1.8 and 1.9, respectively. 2NBATCH acts as a bidentate ligand, sulfur from thiol group, and nitrogen from the amine group (NH2) coordinate with platinum(IV) to form a 1:2 (platinum(IV):2-NBATCH) complex. Sulfur containing ligands (2-NBATCH) first reduces the platinum (IV) to platinum (II) and then forms complex with it (Beamish and Van Loon 1977). Based on this investigation, the reaction mechanism for the formation of the complex and the probable structure of the complex are as follows. NO2 NO2 H H H N N N N NH2 N NH N 2

SH

S

….(6)

Keto form of 2-NBATCH NO2 N

Enol form(acidic) NO2

H N

N

Dissociation

NH2

N

NH2

+

H+

….(7) Anionic form of 2-NBATCH

Enol form(acidic) NO2

NO2 N

+

N S-

SH

PtCl 4

H N

NH

N

NH2

S-

N

NH

N

+

4 Cl

-

NH2

S Pt 2

General reaction

PtCl4 + 2 R-SH →[Pt-(S-R)2] + 2HCl + 2 Cl-

…(8)

…..(9)

The probable structure of the platinum(IV)-2-NBATCH complex is

12


NO2 N

H N

N NH2

S Pt

NH2 S N

N H

N NO2

Fig. 11. Job’s method of continuous variation, Pt(IV)= 2-NBATCH = 5.12  10-4 and 7.68 10-4 mol L1, Equilibrium time = 5.0 min, λmax = 440 nm, Solvent = chloroform, (M = Metal ion, L = Ligand)

Fig.12. Mole ratio method, Pt(IV)= 2-NBATCH = 5.12  10-4 and 7.68 10-4 mol L-1, 2-NBATCH = 5.0 mL of 0.02 mol L-1, Equilibrium time = 5.0 min, λmax = 440 nm, Solvent = chloroform, M = Metal ion, L = Ligand 13


Fig. 13. Slope analysis method, Pt(IV)= 10.0 ug mL-1,pH – 4.0 and 10.0, 2-NBATCH = 5.0 mL of 0.0002-0.005 mol L-1, Equilibrium time = 5.0 min, λmax = 440 nm, Solvent = chloroform

4 Applications To check the applicability and versatility of the present method for the extractive spectrophotometric determination of platinum(IV), several different samples and products were employed for the quantitative extractive spectrophotometric determination of platinum(IV) from the synthetic mixture, composition of synthetic mixture corresponding to alloys and minerals and real samples. 4.1 The effect of foreign ions The Influence of interfering ions (viz. anions and cations) on the extractive spectrophotometric determination of platinum(IV) was investigated by adding the known amount of diverse ion to a standard platinum(IV) solution and by comparing the final absorbance with the standard. Initially the foreign ion was added to the platinum(IV) solution in large excess; 100 mg for anions and 25 mg for cations. When interference was found to be intensive, the test was repeated with successively smaller amounts of foreign ion. The tolerance limit of diverse ion which do not cause a deviation of more than ± 0.2 % in the absorbance measurement of platinum(IV)-2-NBATCH complex (Table 4). The most common ions do not interfere in the extractive spectrophotometric determination of platinum(IV). The interference due to cations was eliminated by the use of suitable masking agents and therefore the method becames more selective. The species showing interference in the procedure were ascorbate, oxalate due to formation of strong metal chelates, while thiourea, thiosulphate and thiocyanate form strong complexes with platinum(IV) because platinum group metals (PGMs) belong to soft acids which possess a strong affinity to ligands containing donating type sulphur atoms which acts as a soft bases (Pearson, 1963 & Pearson, 1968).

14


Table 4 Effect of foreign ions in the determination of 10 µg mL-1 platinum(IV) with 2-NBATCH (relative error ± 2 %) Amount tolerated, Foreign ion mg 100 Phosphate, sulphate, acetate, salicylate 75 Malonate, succinate, nitrate, bromide 50 Fluoride, citrate, tartrate 25 Sn(II), U(VI), Cd(II), La(III), Ge(IV), Fe(II),Chloride, Nitrite, EDTA 15 Ca(II), Sr(II), Ba(II), Tl(I), Al(III), Ga(III), Cr(VI), Zr(IV), Mo(VI), Re(VII), Ir(III) 10 Pb(II), Sn(IV), V(V), Zn(II), Ni(II)d, Cr(III), In(III) 5 W(VI), Co(II), Mn(II), Th(IV), Ag(I)c, iodide 3 Os(VIII)e, Ru(III)d, Pd(II)e, Rh(III)d, Mn(VII)b, Se(IV)b, Te(IV)b, Sb(III)b 2 Au(III)c, Bi(III)a, Cu(II)e, oxalate, ascorbate a Masked with 25 mg of Chloride b Masked with 50 mg of Fluoride c Masked with 50 mg of Bromide d Masked with 25 mg of Citrate e Masked with 25 mg of Tartrate

4.2 Separation of platinum(IV) from associated metal ions The proposed method successfully permits the separation and determination of platinum(IV) from associated metal ions containing Co(II), Ni(II), Fe(II), Au(III), Rh(III), Ir(III), Pd(II), Ru(III), Se(IV), Te(IV), Cd(II), Zn(II), Pb(II), and Cu(II). Method showed the separation of platinum(IV) from commonly associated metal ions on the basis of differences in the extraction conditions for other metal ions. Platinum(IV) was separated from Co(II), Ni(II), Fe(II), Ir(III), Cd(II), and Pb(II) by extracting it with chloroform over the heating mixture of platinum(IV), at pH – 7.0 and 0.02 mol L-1 2-NBATCH in 1,4-dioxane. Under the optimum conditions of platinum(IV), Co(II), Ni(II), Fe(II), Ir(III), Cd(II), and Pb(II) do not form complex with 2-NBATCH and hence they were remained quantitatively in the aqueous phase. Cobalt(II) and Fe(II) from the aqueous phase were determined by the thiocyanate method (Marckzenko 1976), Cd(II), Zn(II) and Pb(II) were determined by the PAR method (Flaschka and Bernard 1972), while Ni(II) was estimated by DMG method (Marckzenko 1976), and Ir(III) was determined by SnCl2 method (Marckzenko 1976). Platinum(IV) was separated from Cu(II), Te(IV), Se(IV), Ru(III), Pd(II), Rh(III) and Au(III) by maintaining optimum complexation conditions of platinum(IV) such as pH – 7.0 and 0.02 mol L-1 2NBATCH in the presence of masking agents. Gold(III) was masked with 50 mg of bromide while Pd(II) and Cu(II) with 25 mg of tartrate, Rh(III) and Ru(III) was masked with 25 mg of citrate. The fluoride (50 mg) was used to mask Te(IV) and Se(IV). The masked metal ions were remained in aqueous phase quantitatively and absorbance of extracted platinum(IV)- 2-NBATCH complex in the organic phase was determined at λmax 440 nm. The metal ions remained in the aqueous phase, were demasked by 2.0 mL conc perchloric acid and followed by addition of (2  3 mL) conc HCl and the solution was evaporated to moist dryness. The residue was cooled, dissolved in dil. HCl. Copper(II) was estimated by 2’,4’-dinitroAPTPT (Kamble et al., 2011). Palladium(II) was determined by 4’chloroPTPT (Anuse et al., 1986), Se(IV) and Te(IV) were estimated by 4’-bromoPTPT (Kolekar and Anuse 1998; Kolekar and Anuse 1998), Au(III) was determined by SnCl2 method (Sandell 1965), Rh(III) was estimated by the KI-SnCl2 method (Marckzenko 1976) and Ru(III) was determined by thiourea method (Sandell 1965). The recovery of platinum(IV) and that of added ions were found to be quantitative (Table 5). 15


Table 5 Separation of platinum(IV) from binary synthetic mixtures Metal ions Pt(IV) Co(II)

Amount taken (µg) 100 600

Average Recovery* (%) 99.9 99.8

R. S. D. (%) 0.01 0.15

Chromogenic ligand

Ref.

Thiocyanate

Marczenko (1976)

Pt(IV) Ni(II)

100 60

99.8 99.7

0.11 0.16

DMG

Marczenko (1976)

Pt(IV) Fe(II)

100 40

99.9 99.6

0.09 0.11

Thiocyanate

100 150

99.9 99.8

0.09 0.11

Tin chloride

Marczenko (1976) Sandell (1965)

Pt(IV) Au(III)a Pt(IV) Rh(III)b

100 400

99.8 99.6

0.12 0.21

KI method

Marczenko (1976)

Pt(IV) Ir(III)

100 60

99.9 99.4

0.01 0.12

Tin chloride

Marczenko (1976)

Pt(IV) Pd(II)b

100 200

99.6 99.8

0.16 0.11

4-ChloroPTPT

Anuse et al., (1986)

Pt(IV) Ru(III)c

100 300

99.8 99.9

0.21 0.07

Thiourea

Pt(IV) Se(IV)d

100 400

99.8 99.7

0.08 0.16

4-BromoPTPT

Kolekar and Anuse 1998

Pt(IV) Te(IV)d

100 200

99.9 99.9

0.19 0.14

4-BromoPTPT

Pt(IV) Cd(II)

100 30

99.9 99.7

0.09 0.20

Kolekar and Anuse 1998

PAR

Pt(IV) Zn(II)

100 50

99.9 99.9

0.11 0.09

PAR

Flaschka and Bernard (1972) Flaschka and Bernard (1972)

Pt(IV) Pb(II)

100 80

99.7 98.9

0.18 0.17

PAR

Sandell (1965)

Flaschka and Bernard (1972) 16

Sunil B. Zanje, Arjun N. Kokare, Vishal J. Suryavanshi, Gurupad D. Kore, Balaji T. Khogare, and Mansing A. Anuse/ Journal of Trace Analysis in Food and Drugs (2016) Vol. 2 No. 1 pp. 1-24 Pt(IV) Cu(II)b

100 300

99.7 99.3

* Average of five determinations b Masked with 25 mg of tartrate d Masked with 50 mg fluoride

0.11 0.09 a c

APTPT

Kamble et al., (2011)

Masked with 50 mg of bromide Masked with 25 mg of citrate

4.3 Determination of platinum(IV) from ternary synthetic mixtures Platinum (IV) is one of the noble metals, therefore, platinum(IV) was separated and determined from other noble metal ions such as Au(III), Ru(III), Pd(II), Rh(III), Os(VIII), and Ir(III) with the varying compositions. The interfering metal ions were masked with suitable masking agents (Table 6) and extraction of platinum(IV) was carried out by employing the recommended procedure. The platinum(IV) was also separated and determined from Bi(III), Mo(VI), Sb(III), W(VI), Zn(II), Pb(II), Se(IV), Te(IV), Fe(II), Ni(II), Co(II) and Cu(II). The results obtained were accurate and good agreement with the amount added. Table 6 Determination of platinum(IV) from ternary synthetic mixtures Composition (µg)

Average R.S.D. (%) recovery* % Pt(IV)100; Ru(III)a 200; Pd(II)b 200 99.7 0.09 Pt(IV) 100; Rh(III)b 400;Ir(III) 500 99.8 0.33 Pt(IV) 100; Fe(II) 300; Cu(II)b 200 99.8 0.09 Pt(IV) 100; Ni(II) 500; Co(II) 500 99.9 0.17 Pt(IV) 100; Bi(III)c 300; Pb(II) 300 99.7 0.09 Pt(IV) 100; Bi(III)c 300; Zn(II) 500 99.8 0.16 Pt(IV) 100; Se(IV)d 200; Te(IV)d 200 99.4 0.18 Pt(IV) 100; Au(III)e 200; Cu(II)b 200 99.8 0.31 Pt(IV) 100; Mo(VI) 300; W(VI) 300 99.6 0.13 Pt(IV) 100; Sb(III)e 500; Au(III)e 200 99.7 0.28 * Average of five determinations a Masked with 25 mg of citrate b Masked with 25 mg of tartrate c Masked with 25 mg of Chloride d Masked with 25 mg Fluoride e Masked with 50 mg of bromide

4.4 Analysis of platinum(IV) from a synthetic mixture corresponding to the composition of alloys and minerals The applicability of the present method was investigated by the analysis of platinum(IV) containing alloy and mineral samples. The standard alloy samples were not available at this working place, therefore we have prepared the synthetic mixture corresponding to the composition of alloys, minerals and analyzed platinum in alloys, platinum iridium alloy, osmiridium alloy, Garutit (IMA 2008 - 055), Iridium mineral and Bowieite mineral in which a known amount of platinum(IV) was added. The results were found to be in good agreement with the amount added (Table 7 ).

17


Table 7 Analysis of platinum(IV) in synthetic mixtures corresponding to the composition of alloys and minerals Alloy sample Pt(IV) Amount of Pt(IV) found by R.S.D. Pt(IV) found by proposed (%) taken (µg) AAS (%) method* (%) Platinum alloy Pt – 850, Rua-100 100 99.8 99.6 0.19 Osmiridium alloy Rhb – 110, Osc – 325, Pt – 100, Rua – 80, 100 99.7 99.7 0.17 d Ir – 400, Au - 10 Garutit Fe -19.64%, Co -0.52% Ni – 27.49 %, Cub – 0.42 % Rua – 0.45%, Rhb – 0.69%, Osc -0.64%, Ir – 43.20%, Pt – 6.95% 100 99.9 99.7 0.13 Iridium mineral Ir -52.58%, Osc -31.22 %, Rua -5.53%, Pt -10.67%, 100 99.8 99.8 0.17 Bowieite mineral Ir -29.84%, Pt -10.09%, Rhb – 31.95 %, S – 28.12% Platinum Iridium alloy i) Pt – 70%, Ir – 30% ii) Pt – 80%, Ir – 20% Average of five determinations Masked with 25 mg of tartrate d Masked with 50 mg of bromide

100

99.9

99.8

0.13

100 100

99.9 99.8

99.6 99.7

0.11 0.13

*

a

b

c

Masked with 25 mg of citrate Masked with 25 mg of Tartrate

4.5 Analysis of platinum(IV) in catalysts Platinum group metals (PGMs) are showing good catalytic activity in many organic reactions. Platinum(IV) is the important contents in various catalysts (Pt-Rh catalyst on alumina, Pt-Pd catalyst on alumina, Pt-Rh monolith on cordierite, Pt-Pd-Rh monolith on cordierite) was determined by the proposed method. A known weight of catalyst samples was dissolved in aquaregia. The solution of catalyst is then heated with conc HCl to remove the oxides of nitrogen. The residue was dissolved in 10 mL of 1.0 mol L-1 HCl and filtered through the Whatman filter paper No.1. It was diluted to a 50 mL volumetric flask with water. An aliquot of the platinum(IV) solution was taken and determined by recommended procedure. Reliability of the results was checked after inter comparison with the results obtained from AAS and results were in good agreement with the certified values (Table 8).

18


Table 8 Analysis of platinum(IV) catalysts Alloy sample

Pt-Rha catalyst on alumina Pt-Pdb catalyst on alumina Pt-Pda-Rha catalyst on alumina Pt-Rha monolith on cordierite Pt-Pda-Rha monolith on cordierite * Average of five determinations

Certified Platinum Platinum value of found by found by AAS platinum proposed (%) taken (µg) method* (%) 100 99.9 99.8 100 99.8 99.8 100 99.9 99.8 100 99.9 99.7 100 99.8 99.6 a Masked with 25 mg of tartrate

R.S.D. (%) 0.16 0.13 0.17 0.14 0.19

4.6 Analysis of platinum(IV) from real samples Cisplatin The present method was used for the determination of platinum(IV) pharmaceutical sample such as cisplatin injection. A known volume (4 mL) of cisplatin injection solution (1 mg/mL) was digested in a concentrated perchloric:nitric acid mixture (10:1), and evaporated to dryness until organic matter was removed (Zhang et al., 1994). Therefore obtained residue was dissolved in concentrated HCl and diluted with water to 50 mL volumetric flask. An aliquot of 2.0 mL of sample solution was taken and platinum(IV) was determined using recommended procedure. (Table 9 ) Thermocouple wire A known weight (0.100 g) of Pt-Rh thermocouple wire (Kallman 1987) was fused with zinc powder and the residue was cooled and dissolved in hydrochloric acid. The black powder remained was treated with 5 mL of aqua-regia. After the reaction was over the entire solution was heated with two 5 mL portions of concentrated HCl until complete removal of oxides of nitrogen and diluted to 10 mL in standard volumetric flask. An aliquot of sample solution taken and platinum(IV) was determined using the recommended procedure (Table 9). Table 9 Analysis of platinum(IV) from real samples. Sample Cisplatin (anticancer injection) Platinumrhodiuma thermocouple wire (Pt – 87, Rha - 13) * Average

Certified value of Pt(IV)

Platinum found by AAS

Platinum found by proposed method

Recovery* (%)

R. S. D. (%)

1 mg

0.995 mg

0.990 mg

99.8

0.17

0.1 mg

0.09 mg

0.09 mg

99.7

0.09

of five determinations

a

Masked with 25 mg of tartrate

19


5. Conclusion The important characteristics of this method are i) It permits selective separation of Platinum(IV) from platinum group metals (PGMs) and base metals which are commonly associated with it. ii) It is free from interference from a large number of diverse ions which are associated with Pt(IV) in its natural occurrence, iii) Low 2-NBATCH concentration is required, iv) Single stage extraction, v) The method is applicable to the analysis of Pt(IV) in synthetic mixture, synthetic mixture corresponding to the composition of alloys and minerals. This method also applicable to analysis of real samples such as cisplatin injection, thermocouple wire and catalysts.

Acknowledgement One of the author Mr. S. B. Zanje is very much thankful to DST-PURSE, New Delhi and UGC-BSR for providing a financial support.

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