ЖУРНАЛ АНАЛИТИЧЕСКОЙ ХИМИИ, 2014, том 69, № 10, с. 1024-1028
ОРИГИНАЛЬНЫЕ СТАТЬИ =
УДК 543
A NEW SENSITIVE SPECTROPHOTOMETRIC DETERMINATION OF SODIUM 2-SULFANYLETHANESULFONATE USING
LEUCO XYLENE CYANOL FF © 2014 Barbara Szpikowska-Sroka1, Aleksandra Guz, Justyna Po+edniok
Institute of Chemistry, University of Silesia 9 Szkolna Street, Katowice, 40-006 Poland 1E-mail: barbara.szpikowska-sroka@us.edu.pl Received 10.10.2012; in final 09.01.2014
A simple and accurate spectrophotometry method for determination of sodium 2-sulfanylethanesulfonate (MESNa) with leuco xylene cyanol FF (LXCFF) has been developed. The proposed method is based on the reaction of MESNa with potassium iodate(V) in acidic medium, to liberate iodine, which oxidized leuco xylene cy-anol FF to its blue form xylene cyanol FF. The xylene cyanol FF dye formed shows maximum and stable absor-bance at pH 4.1—4.2. Absorbance of the obtained colored products was measured at 613 nm. The molar absorptivity, limit of detection and limit of determination of the method were found to be 3.64 x 104 L/mol cm, 0.29 and 0.33 p.g/mL, respectively. The colour system obeys Beer's laws in the range 0.4—4.0 p.g/mL of MESNa. All the variables were studied in order to optimize the reaction conditions. The procedure was used for determination of MESNa in pharmaceutical preparations. Reliability of determination was confirmed applying standard iodometric method, recommended by European and Polish Pharmacopoeia.
Keywords: sodium 2-sulfanylethanesulfonate, sodium 2-mercaptoethanesulfonate, leuco xylene cyanol FF, spectrophotometry, pharmaceutical analysis.
DOI: 10.7868/S004445021410017X
Thiols are chemically and biochemically very active components of the sulfur cycle of the natural environment, but for all their similarities in structure and common chemistry, the functions of thiols in organism are remarkably different. These compounds are highly polar and water soluble, which makes their extraction from biological matrices without derivatization almost impossible. The redox chemistry of thiols is dominated by the sufhydryl group (-SH), which enables them to undergo oxidation in the presence of an electron acceptor to form the disulfides (-S—S-) [1]. Almost all known thiol-containing compounds tend to scavenge free radicals. Recent studies show that numerous disorders originate from free radical attacks on biological macromole-cules such as proteins, lipids and DNA. Therefore, the search for new antioxidants is essential [2].
MESNa (HS—CH2—CH2—SO3Na) is an antioxidant used particularly in renal protection. MESNa, a low-molecular-weight thiol, is also highly effective in the prevention of urothelial toxicity associated with high doses of oxazaphosphorines, such as ifosfamide or cyclophosphamide, as describe Links and Lewis (1999). Upon entering the bloodstream, MESNa is immediately converted to an inactive disulfide form, dimesna (dithiodiethanesulfate) which is subsequently filtered and secreted by the kidneys. The protective ca-
pability of MESNa to the bladder mucosa is ascribed to the chemical reactions of the thiol group with the urotoxic acrolein and other metabolites. The drug is frequently prescribed in the treatment of cancer or as part of the immunosuppressive conditioning regimens in bone marrow recipients [3—4]. It especially helps prevent hemorrhagic cystitis, ulcerative colitis and bladder tumors induced by anti-tumor agents and external nephrotoxins [5—7].
Therefore it is of great importance for better understanding the pharmacology, simple and reliable analytical methods are needed for determination this compound. Different analytical methods have been already developed for MESNa determination in urine, kidney, biological samples, and pharmaceuticals. They include HPLC with various detection [1—3, 8—11], coulometry [12], LC [13]. However, these methods often require complicated pretreatment procedures, are costly and require instrumentation. Some of these methods did not show its applicability to determining MESNa in biological tissues, or responses from other chemical groups could cause interference and invalidate results. Several spectrophotometric methods based on colour reactions of the investigated thiol are known [14], however, they are not highly sensitive.
In the proposed method, LXCFF has been used as a new reagent for sensitive and simple spectrophoto-metric determination of MESNa. Up till now, LXCFF has been used only as a reagent for determination of oxidants, for example: iron(III) [15], platinum(IV) [16], gold, chromium(VI) [17], cerium(IV) [18], and
IO- ions [19]. In the literature there are only few applications to determine organic reductors by the colorless reduced form of dye, for example: methionine in complex preparations [20], N-acetyl-L-cysteine in pharmaceutical preparations [21]. In this paper we use LXCFF, which is a reduced form of xylene cyanol FF, as a new reagent for determination of others reductors (MESNa).
EXPERIMENTAL
Apparatus. A HACH DR/2010 spectrophotometer with 1 cm-in-width glass cells used for absorbance measurements; pH measurements were performed using an N-517 pH-meter (Meratronic, Poland). Water obtained from Elix 3 system (Millipore, Molsheim, France) was used during the experiments.
Reagents. All chemicals used in the experiments were analytical grade and used as received. All solutions were prepared using deionized water; 1 mg/mL standard solutions of sodium 2-sulfanylethane-sulfonate was prepared by dissolving MESNa in water; 10 ^g/mL working solution was prepared daily by an appropriate dilution of the standard solution. The following solutions were used in this study: potassium io-date(V) (Merck Darmstadt, Germany), 0.1 M aqueous solution; hydrochloric acid (POCh, Poland), 1 M aqueous solution; sodium hydroxide (POCh, Poland), 1, 0.1, 0.025 and 0.0025 M aqueous solutions; leuco xylene cyanol FF 0.1% solution was prepared by dissolving 100 mg of xylene cyanol FF (Fluka, Buchs, Switzerland) in 25 mL of water containing 2 mL of 1 M acetic acid and 400 mg of zinc dust. The mixture was stirred well and left to equilibrate for 24 h. Afterwards, the resulting solution was diluted to 100 mL with water and filtered. Leuco xylene cyanol FF 0.01% solution was obtained by an appropriate dilution of the 0.1% solution of this compound.
The pharmaceutical preparations examined were: Anti-Uron, Pliva Krakow, Poland vials 0.2 g; Mistabron, UCB S.A. Pharma Sector, vials 0.2 g/mL; Mucofluid, UCB S.A. Pharma Sector (Next Pharmas SAS) aerosol — 50 mg/mL (5 mg per dose); Uromitexan, Baxter Oncology GmbH, vials 100 mg.
RESULTS AND DISCUSSION
Optimization of reaction conditions. The optimum conditions for spectrophotometric determination of MESNa were established by performing systematic investigations to achieve rapid formation of the colored product with maximum stability and sensitivity. Con-
trolled experiments were performed by measuring the absorbance at 613 nm for a series of solutions by varying one and fixing the other parameters. These studies established the optimum amounts of reagents are added according to the following scheme:
1. The oxidation of the analyte by iodate(V) anion:
Analyte + IO- ^ Analyteox + I-.
2. The iodide ions react with the excess of iodate(V) ions in acidic medium (addition of HCl, pH about 1) and quantitatively oxidize iodide ions to form free iodine:
5I-
+ IO- + 6H+ ^ 3I2 + 3H2O.
The redox potential of the systems IO3 + 6H+ + 5e- ^ 3I2 + 3H2O in acidic medium is +1.2 V, but with increasing pH (to the value about 4) the potential significantly decreased. It has been found that under optimum conditions of this experiment (pH value abou 4) iodate(V) ions do not oxidize iodide ions.
3. The iodine oxidized leuco xylene cyanol FF to give colored xylene cyanol FF dye (pH of these system was increased to value 4.1-4.2, in these conditions io-date(V) ions do not oxidize leuco form of the dye to its colorful form):
LXCFF + 1/2I2 ^ XCFF+ + I-.
The iodine can be dissolved in the iodide ions-containing solution to give triiodide ions, which prevent the loss of iodine due to its volatility.
After this step, the samples were heated in order to obtain constant and maximum absorbance. While examining the stability of absorbance in time, it was found that xylene cyanol FF absorbance is stable for more than a week. The optimal range of pH to create xylene cyanol FF was found 4.1-4.2.
Spectral characteristics. Iodine quantitatively oxidized LXCFF into its blue colored xylene cyanol FF dye at pH 4.1-4.2. The dye shows maximum absorption at 613 nm. Reagent blank absorbs negligibly at this wavelength.
Effect of temperature. The effect of temperature and heating time on the oxidation MESNa was examined. It was found that the absorbance does not depend on this factor that is why we omitted this step. However, the effect of temperature and heating time after the creation of xylene cyanol FF has been also examined. Constant and maximum absorbance was obtained when temperature was kept in range 75-90°C. It was found the temperature and time needed to set the maximum and constant absorbance is over 80°C. To achieve this temperature, the contents were placed in a water bath maintained at 80 ± 2°C, and 20 min time was necessary for full colour development.
Effect of pH. The effect ofpH ofthe solution at 613 nm with solution containing 2.4 ^g/mL of MESNa was also examined (Fig. 1). The spectrum of the solution
2 XyPHAtf AHAtfHTH^ECKOH XHMHH tom 69 № 10 2014
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SZPIKOWSKA-SROKA и др.
0.70 0.65
о
S 0.60
га -р
0.55
0.50
0.45
3.7
3.9
4.1 pH
4.3
4.5
Fig. 1. Effect of pH on absorbance (2.4 p,g/mL of MESNA).
0.70
<D
1 0.60
ra
-O
л 0.50 A
0.40
0.5 1.0 1.5 2.0 ?kio3 x 10 mol
2.5
3.0
Fig. 2. Effect of amount (q) of KJO3 on absorbance (2.4 p,g/mL of MESNa).
0.8 г
0.6
<D о Й ce -О
0.4
s
0.2
0.5 1.0 1.5 2.0 2.5 qHCl x 10mol
was found to be strongly dependent on the pH
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