Development of a reliable analytical method for extraction spectrophotometric determination of ruthenium(III) from catalyst and fissium alloy using o-methylphenyl thiourea as a chromogenic chelating ligand

Abstract

A simple and selective method is developed for the extraction spectrophotometric determination of ruthenium(III) using o-methylphenyl thiourea (OMPT) as a chromogenic chelating ligand. The basis of the proposed method is ruthenium(III)–OMPT complex formation in aqueous hydrochloric acid media (3.0 mol L⁻¹) after 5.0 min heating on a boiling water bath and the complex formed is extracted into chloroform. The absorbance of green colored ruthenium(III)–OMPT complex is measured at 590 nm against the reagent blank. Beer’s law was obeyed up to 42.5 μg mL⁻¹ of ruthenium(III) and the optimum concentration range is 7.56–39.81 μg mL⁻¹ of ruthenium(III) as evaluated by Ringbom’s plot. Molar absorptivity and Sandell’s sensitivity of ruthenium(III)–OMPT complex in chloroform are 2.34 × 10³ L mol⁻¹ cm⁻¹ and 0.043 μg cm⁻² respectively. The composition of ruthenium(III):OMPT complex (1:2) was established from slope ratio method, mole ratio method and Job’s continuous variation method. Complex was stable for more than 48 h. The interfering effect of various foreign ions was studied and suitable masking agents are used wherever necessary to enhance the selectivity of the method. Proposed method is successfully applied for determination of ruthenium(III) from binary and ternary synthetic mixtures, synthetic mixtures corresponding to fissium alloy and ruthenium catalyst. Repetition of the method was checked by finding relative standard deviation (R.S.D) for 10 determinations which was 0.23%. A scheme for sequential separation of palladium(II), ruthenium(III), rhodium(III) and platinum(IV) has been developed.

Introduction

Ruthenium is a rare metal found in metallic state together with other platinum group metals and coinage metals. Its abundance is 0.0001 ppm by weight [1]. It is a precious metal with widespread applications as high resistance to chemical attack, stable electrical properties, used in jewelry and as one of the most effective hardener in high density alloys. It acts as a versatile catalyst, used for removal of NO_x from air stream [2]. Ruthenium complexes are biologically important in detection of amino acids [3], iodine/iodide [4], vitamin A [5], and chlorophenaramine [6] and are investigated as anticancer drug [7]. Trace concentration, enhanced properties along with significant applications demands a necessity of precise and reliable detection method for ruthenium(III).

A review of different techniques used for determination of ruthenium is reported by Balcerzak [7]. A sensitive determination of ruthenium has been carried out using microwave radiations [8] and naturally occurring flavanoids [9]. In comparison with available techniques solvent extraction is a potent analytical technique used to obtain quantitative recovery allied with spectrophotometric determination. Thiourea plays a vital role in spectrophotometric analysis of ruthenium [10], [11], [12]. Though other reagents are reported by Sandell and Marckzenco, however determination using thiourea method is sensitive and easily practicable but suffers from drawbacks viz. higher hydrochloric acid concentration (6.0 mol L⁻¹), 10 min heating time or one hour standing and interferences from other platinum group metals. A derivative of thiourea, o-methylphenyl thiourea (OMPT) which forms an intense green colored 1:2 (ruthenium(III):OMPT) complex in hydrochloric acid media (3.0 mol L⁻¹) is investigated in present study. A number of reagents are reported for spectrophotometric determination of ruthenium as thiocyanate [13], sodium isoamyl xanthate [14], derivatives of diantipyrlmethane [15] and as-triazines [16]. Derivative spectrophotometry is also employed for determination of ruthenium [17], [18], [19].

Considering the catalytic property of ruthenium(III) it is determined based on the oxidation of pyronin B [20], dimethyl yellow [21] and l-phenylalanine [22]. Ruthenium(III) is determined based on its catalytic kinetic effect on oxidation of giemsa pigment [23], acid fushine [24], acid chrome black [25], o-nitrophenyl fluorine [26], malachite green [27], xylene cyanol FF [28] and neutral red [29]. Flow injection catalytic kinetic spectrophotometric determinations of ruthenium have been investigated [30], [31], [32], [33]. The methods reported for determination of ruthenium(III) based on catalytic, catalytic kinetic, flow injection catalytic kinetic mechanism are sensitive and applicable at race level but are restricted around oxidation systems like periodate, permanganate and peroxide while only the colored dye being changed. They have minimum and restricted applications, narrow Beer’s range, temperature controlled oxidation condition and laborious procedure, demerits these methods.

Literature survey reveals that the existing spectrophotometric determination methods lack with simplicity and novelty and predict that there is a wide range for the work in development of a precise, inexpensive, easy and sensitive method with quantitative recovery of ruthenium.

In our laboratory we have developed extraction spectrophotometric determination method for palladium(II) and rhodium(III) [34], [35] using OMPT. As a part of further extension of the work using OMPT as a chromogenic chelating ligand and to enhance its analytical applications we have developed a precise and reliable extraction spectrophotometric determination method for ruthenium(III). A scheme has been developed for sequential separation of palladium(II), ruthenium(III), rhodium(III) and platinum(IV).