摘要:

,-1 rznlyst, December, 1973, 1-01. 98, PP. 895-899 895 Polarographic Studies of the Zinc(I1) Complex Formed with Tyrosine in Aqueous and Mixed Aqueous and Non-aqueous Media BY DAYA NAND CHATURVEDI AND C. M. GUPTA (Chemical Laboratories, University of Rajasthan, Jaipuv-4, India) The reduction of zinc(J.1) in tyrosine solutions has been studied a t a dropping-mercury electrode in aqueous and mixed aqueous and non-aqueous media. The effects due to variation of pH, temperature, ligand concentration and height of the mercury column on the wave characteristics have been investigated and the results interpreted. Under all experimental conditions the reduction has been found to be irreversible and diffusion controlled. Hence, the kinetic parameters, transfer coefficient (a,,) and formal rate constant (K'I,~) have been calculated by use of Koutecky's method as im- proved by Meites and Israel.The analytical implication of the sytem has also been suggested. THE importance of amino-acids and several other nitrogen-containing compounds has been recognised in the biochemical, analytical and pharmaceutical fields. Such compounds are therefore attracting wide attention in different areas of research. Polarographic investigation of the complexation behaviour of various metal ions with tyrosine and other amino-acids has recently been carried out in our laboratorie~.l-~ However, there is no reference to the pursuit of polarographic studies on the zinc(I1) - tyrosine complex, therefore the present investiga- tions were undertaken. This paper reports the detailed polarographic investigation of the formation of the zinc(I1) - tyrosine complex in aqueous and mixed aqueous and non-aqueous media.EXPERIMENTAL APPARATLJS- A manual polarograph with a Scalamp galvanometer acting as a current recorder was used in all the investigations. The dropping-mercury electrode had the characteristics m = 2.422 mg s-l and f = 3.2 s. The experiments were carried out by using a polarographic H-cell (containing a 4 per cent. agar-saturated potassium chloride salt bridge) with a saturated calomel electrode as reference electrode. Measurements of the pH were made on a Toshniwal pH meter with combined electrodes and 0.1 N solutions of nitric acid and sodium hydroxide were used for adjusting the pH of solutions. De-oxygenation of polarographic solutions was carried out by bubbling purified nitrogen through them for 15 minutes immediately prior to the polaro- graphic examination.The temperature of the polarographic solution was maintained constant by means of a thermostat. REAGENTS- All the reagents used were of analytical-reagent grade and all the solutions were prepared in double-distilled water. Freshly prepared solutions were always used in order to avoid the effects of ageing and oxidation by air. Purified methanol, ethanol, propan-2-01 and 2-methylpropan-2-01 were used as the non-aqueous solvents. Potassium nitrate was the supporting electrolyte while gelatine, 0.004 per cent. in the final solutions, served as the maximum suppressor. Experiments were carried out with a 0.5 mM solution of zinc(II), while the concentration of tyrosine was varied from 0.0 to 0 .0 7 0 ~ . The ionic strength of the electrolyte was kept constant at 0.5 M by addition of appropriate amounts of potassium nitrate. @ SAC and the authors.896 REDUCTION- A single, well defined wave appeared for each solution. The reduction Kas been found to be diffusion controlled, as is evident from the constant value of id/hifl. (0-597 0.003 pA cm-lI2). The diffusion-controlled nature of the reduction wave has been further corroborated by the temperature coefficient values of diffusion currents, which fall in the range4 from 1.0 to 1.2 per cent. per "C (Table I). Conventional logarithmic graphs yielded good straight lines but the resulting slopes were found not to be in agreement with the theoretical values for a reversible process, thus indicating the irreversible nature of the reduction process.CHATURVEDI AND GUPTA: POLAROGRAPHIC STUDIES OF THE F.4 nalyst, Vol. 98 RESULTS AND DISCUSSION TABLE I EFFECT O F VARIATION OF TEMPERATURE ON WAVE CHARACTERISTICS Sample Temperature1 Ratio of id a t indicated Temperature coefficieiit, number "C i d / p A temperature to i d a t 25 "C per cent. per "C 1 25 3.542 1.000 - 2 30 3.7345 1.054 1-050 3 35 3.9655 1.1 19 1.123 4 40 4.235 1-195 1.186 5 46 4.5045 1.272 1.204 6 50 4.7355 1.337 1.162 Concentration of zinc(II), 0.5 m M ; concentration of tyrosine, 0.050 M ; p, 0.5 M (potassium nitrate) ; pH, 11.0; concentration of gelatine, 0.004 per cent. EFFECT OF pH- The polarographic investigations of the zinc( 11) - tyrosine complex were carried out systematically over the pH range 8.0 to 12.5 on solutions 0.5 mM in zinc(II), 0.025 M in tyrosine, 0.5 M in potassium nitrate and 0.004 per cent. in gelatine.The half-wave potential shifts to more negative values with the increase in pH and such a cathodic shift suggests the formation of the complex in this pH range. The lower limit of these measurements is imposed by the insolubility of the ligand below pH 8.0. Further studies on this system were carried out a t pH 11.0. EFFECT OF LIGAND CONCENTRATION- To investigate the effect of change of ligand concentration, polarograms of 0.5 mIvi zinc(I1) mixed with various concentrations (0.0 to 0.070 M) of tyrosine (p = 0-5 M) were recorded at 25 & 1 "C. The zinc(I1) - tyrosine reduction wave remained irreversible and diffusion controlled in all of the solutions investigated.The shift in half-wave potential to more negative values, along with a decrease in diffusion current on increasing tyrosine concentration, indicated the formation of the complex. The nature of the wave did not change at higher concentrations of tyrosine. KINETIC PARAMETERS- The Koutecky5 treatment for irreversible waves, as modified by Meites and Israel,6 was applied in order to determine the kinetic parameters. It follows from this treatment that for a totally irreversible wave (at 25 "C) with Ellz greater than -1.0 V versus S.C.E.- and Epp = -0.2412 + log DY2 ' .. . . .. 0.059 15 1.349 K&, an (In these equations both E d e and The kinetic parameters have been calculated by use of equations (1) and (2).The value of an was obtained by equating the slope of the straight-line graph of Ede vcrszcs are referred to S.C.E.) .i 0.0542 (log - -0.546 log t ) with - . 8d- anDecember, 19731 ZINC(I1) COMPLEX FORMED WITH TYROSINE 897 The intercept of the same graph, when the quantity being plotted as abscissa is equal to zero, gives a value for the parameter E;,2, defined by equation (2), which is then used to calculate K&,. at various ligand concentrations (pH = 11.0, p = 0.5 M) are summarised in Table 11. The values of an and Ligand concentration / PA 0.0 0.025 0.030 0.035 0.040 0-045 0-050 0.060 0.070 TABLE I1 POLAROGRAPHIC RESULTS FOR THE ZINC(IL) - TYROSINE SYSTEM ialpA 5-313 3.927 3.773 3.7345 2.696 3.619 3.542 3.311 3.157 -%2/ s .C.E.) V (veysus 1.001 1.2460 1-2550 1.2630 1-2700 1-2740 1.2770 1.2800 1.2820 Slope/ mV 37 50 50 50 51 51 50 50 51 N n 1.4649 1.0840 1.0840 1.0840 1.0627 1.0627 1.0840 1.0840 1.0627 DiP2/cm2 s-l 3-996 x 2.969 x 2.839 x lop3 2.809 X 2.781 x 2.724 x 2.668 x 2.491 X 2.375 x 1ci.h /cm s-1 2.236 x 1.190 x 10-81 1.827 x 2.586 x 1.433 X 1.719 X 4.919 X 5.978 x 2.754 x Concentration of zinc(II), 0.5 mM; p, 0-5 M (potassium nitrate) ; concentration of gelatine, 0.004 per cent.; pH, 11.0; temperature, 25 "C. EFFECT OF TEMPERATURE- In order to investigate the effect of temperature on the wave, a series of polarograms of a solution 0.5 mM in zinc(II), 0.05 M in tyrosine, 0.5 M in potassium nitrate and containing 0.004 per cent. of gelatine were recorded at different temperatures varying from 25 to 50 "C.The value of the temperature coefficient of id for each temperature interval, calculated by using the term7 log (i2/il), is given in Table I. EFFECT OF NON-AQUEOUS MEDIA- Our earlier s t u d i e ~ ~ ~ ~ of the complexation phenomenon in aqueous and mixed aqueous and non-aqueous solvents (with different alcohols) gave significant results. As a sequel to this attempt to establish certain useful generalisations, polarograms of solutions 0.5 mM in zinc(II), 0.025 M in tyrosine (p = 0.1 M) and containing various amounts (0 to 60 per cent. v/v) of non-aqueous solvents such as methanol, ethanol, propan-2-01 and 2-methylpropan-2-01 were polarographed. The investigations of the zinc - tyrosine system with methanol and ethanol as solvents revealed that the half-wave potential is shifted to more negative values as the organic solvent concentration is increased from 0 to 60 per cent.With propan-2-01, the half-wave potential is shifted towards more negative values up to a concentration of 40 per cent., beyond which a positive shift in half-wave potential is observed. With 2-methylpropan-2-01 as solvent the half-wave potential shifts in the negative direction as the concentration of 2-methylpropan-2-01 is increased up to 30 per cent., but beyond 30 per cent. the half-wave potential is shifted to more positive values. The probable cause of the variation of half-wave potential in the instances of propan-2-01 and 2-methyl- propan-2-01 is that the inter-ionic attraction is large in solvents of low dielectric constant, so that the polarographic waves in such media are influenced significantly by the supporting electrolyte even if complex formation is not involved.Addition of increasing amounts of the non-aqueous solvents causes the diffusion current to decrease. The decrease in diffusion current may partly be caused by an increase in the viscositylO of the medium and partly by ion-pair formation.11 In non-aqueous media with low dielectric constants, electroactive ions are largely converted into neutral species known as ion pairs, and this ion-pair formation must be considerable because a continuous decrease in diffusion current is observed. It was observed that in all of these investigations zinc(I1) continued to be irreversibly reduced at the dropping-mercury electrode.However, it can be concluded from the decreasing values of the slopes of the graphs that the electrode reaction becomes faster and less irreversible898 CHATURVEDI AND GUPTA : POLAROGRAPHIC STUDIES OF THE [AlZabSt, VOl. 98 in the presence of increasing amounts of non-aqueous solvents, resulting in comparatively lower values of Kiqh at higher alcohol concentrations. The polarographic results were processed by the method of Koutecky, as modified by Meites and Israel, as discussed above. The values of the formal rate constant (%,J and transfer coefficient (cc,) are summarised in Table 111. TABLE I11 EFFECT OF VARIOUS NON-AQUEOUS SOLVENTS ON THE REDUCTION OF ZINC(II) I N TYROSINE SOLUTION Content of non-aqueous solvent in solvent mixture, &fethanol- per cent.id/PA 0 3.154 10 3.030 20 2.850 30 2.660 40 2.546 50 2.318 60 2.071 10 2.849 20 2.618 30 2.175 40 1-7095 50 1.694 60 1.540 10 3.080 20 2.387 30 1.7095 40 1.617 50 1.4245 60 1.078 10 2.992 20 2.299 30 2.090 40 1-748 50 1.482 60 1.140 Ethanol- P~opan-2-0l- 2-Methylp~opan-2-ol- - E d S.C.E.) V (versus 1.2450 1.2560 1.2650 1.2750 1.2870 1.2980 1.3130 1.2630 1.2790 1.3030 1.3270 1-3350 1-3450 1.2770 1.2910 1.3140 1.3400 1.3330 1.3220 1.2990 1.3060 1.3180 1.3130 1.3080 1.3030 Slope/ mV 53 53 52 52 52 51 50 53 52 52 51 49 46 53 49 47 47 45 43 51 48 47 46 45 41 an 1.0226 1.0226 1.0422 1.0422 1.0422 1.0627 1.0840 1.0226 1.0422 1.0422 1.0627 1.1061 1.1783 1.0226 1.1061 1.1534 1.1534 1.2044 1.2605 1.0627 1-1292 1.1534 1-1783 1.2044 1-3170 D;''/crn s-l 2.373 X lo-' 2.144 X 2.288 x 2.002 x 10-3 1.915 x 10-3 1.744 x lo-' 1.559 x 2.144 x 1-970 x 1.593 x lop3 1.286 x 1.275 x lo-' 1.159 x 10-3 2.318 x 1.797 x 1-286 X 1.217 x 1.072 x lo-' 8.112 x 10-4 2.252 X 1.730 x 1.315 x 1.115 x lo-% 8.578 x 1.572 x 1.322 x 2.230 x 7.163 x 1.152 x loe2' 1.960 x lo-" 7.863 x 3.693 x 2.999 x 1-372 x 4.512 X 3.545 x 10-'2 8.383 x 10-2.' 5.880 x 10-23 4.845 x 10-20 3.134 x 2.910 x 2-168 x 1.844 x 8.570 x 10-23 3.724 x 1.631 x 6.949 x 2-031 x 6.993 x 8.387 x 10-23 Concentration of zinc(II), 0.5 mM; concentration of tyrosine, 0.025 M ; p, 0.1 M (potassium nitrate) ; concentration of gelatine, 0.004 per cent.; temperature, 25 "C; pH, 11.0. QUANTITATIVE DETERMINATION AND DIFFERENTIATION OF ZINC AND NICKEL IN THE PRESENCE The conventional gravimetric and titrimetric methods for the determination of zinc and nickel in the presence of each other have recently been described.12 These methods, being manual, are relatively inaccurate and high sensitivity cannot be achieved on account of their inherent limitations.The half-wave potentials of Zn2+ (1.001 V vemw S.C.E.) and Ni2+ (1.012 V zleysus S.C.E.) ions in a non-complexing medium (0.5 M potassium nitrate solution) are very close to each other. Therefore the polarographic waves due to the discharge of Zn2+ and Ni2+ ions in the medium merge with each other and it is not possible to determine zinc in the presence of nickel and vice versa. The presence of a small amount of tyrosine (0.07 M) results in a marked separation of the respective reduction waves, thus providing a convenient method for their individual determination; the half-wave potentials of Zn2f and Ni2+ ions in 0.07 M tyrosine solution have been found to be 1.2820 V and 1.1170 V versus S.C.E., respectively.The waves resulting from the two complexation reactions are irreversible and diffusion controlled and the wave height is directly dependent on the concentration of the metal ion in the solution. As this is an electroanalytical technique, more accurate results are achieved than with a O F EACH OTHER-December, 19731 ZINC(II) COMPLEX FORMED WITH TYROSIKE 899 manual method. This method can also be used for the determination of zinc and nickel in nickel-silver and silver coin. Zinc can be determined in the presence of cadmium, lead and copper -by use of solutions of tyrosine as these metals are reduced at relatively more positive potentials than zinc.1 The authors acknowledge with thanks the facilities given by Dr. R. C. Mehrotra, Professor and Head of Chemistry Department, University of Rajasthan, Jaipur, India. One of the authors (D.N.C.) also thanks the University of Rajasthan, Jaipur, for the award of a scholarship. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. REFERENCES Chaturvedi, D. N., and Gupta, C. M., 2. analyt. Chem., 1972, 260, 120. -- , J . prakt. Chem., in the press. Raw& P. C., and Gupta, C. M., Indian J . Chem., 1973, 11, 186. Meites, L., “Polarographic Techniques,” Second Edition, Intersc ience Publishers, New York, Koutecky, J., Colln Czech. Chem. Coinmztn., 1953, 18, 597. Meites, L., and Israel, Y., J . Amer. Chem. SOG., 1961, 83, 4903. Shrivastava, 0. N., and Gupta, C. M., Analyst, 1972, 97, 204. Rawat, P. C., and Gupta, C. M., Talanta, 1972, 19, 79% Muller, M., “The Polarographic Method of Analysis, Schaap, W. B., J . Amer. Chem. SOG., 1960, 82, 1837. Vogel, A. I., “A Text Book of Quantitative Inorganic Analysis,” Longmans, Green and Co. Ltd., Received January 29th, 1973 Accepted July 20th, 1973 1965, p. 139. -, 09. Git., p. 140. Chemical Education Publishing, Easton, Philadelphia, 1951, p. 74. London, 1968, p. 635.

ISSN:0003-2654    

DOI:10.1039/AN9739800895

出版商:RSC    

年代:1973

数据来源: RSC

摘要:

900 Analyst, December, 1973, Vol. 98, pfi. 900-905 Determination of Organoisothiocyanates Alone and in Mixtures with Organoisocyanates or Thioureas BY BRLBIR CHAND VERMA AND SWATANTAR KUMAR (Defiartmmt of Chemistry, Punjabi University, Patiala, India) An iodatometric method for tlie determination of organoisothiocyanates is described. The isothiocyanates are quantitatively converted with n-butyl- ainine in dirnethylformamide medium into the corresponding symmetrical NN-disubstituted thioureas, which are titrated visually or potentiometrically in acidic medium with potassium iodate solution. Methods have also been developed for the analysis of isothiocyanate - isocyanate and isothio- cyanate - thiourea mixtures on the same sample solution. A known excess of the standard n-butylamine solution added to the mixture in dimethyl- formamide converts the isothiocyanate and isocyanate into the corresponding disubstituted thiourea and urea, respectively.Acidimetric titration of tlie excess of aniine, and iodatometric titration of the thiourea present and formed, enable the particular mixture to be analysed for both constituents. The end-points can be detected both visually and potentiometrically. The methods described are simple, accurate, reliable and widely applicable. MOST titrimetric methods that are used for the determination of organoisothiocyanates are based on the quantitative conversion of these compounds into the corresponding thioureas. This conversion was accomplished by some workers by heating the isothiocyanate with ammonia in aqueous or alcoholic solutions, but because of the significant reaction of isothio- cyanates with water or alcohol, ammonia was subsequently replaced with amines and the reaction carried out in non-aqueous media.The unreacted amount of amine, after completion of the reaction, was determined by acidimetric titration with hydrochloric or sulphuric acid in aqueous medium. The earliest and most commonly adopted method is that developed by Siggia and Hanna,l who determined organoisothiocyanates by treating the sample at room temperature with a known excess of standard n-butylamine in dioxan: RNCS + C,H,NH2 -+ RNHCSNHC,H, The alkyl isothiocyanates required 45 minutes for the reaction to occur. The aryl isothiocyanates, however, reacted immediately. The excess of amine was titrated with a standard solution of sulphuric acid, with methyl red as indicator. A blank was also run as the presence of acidic or basic impurities in the sample would give rise to erroneous results.Karten and Ma2 adapted this procedure to the micro-determination of isothiocyanates. Vinson3 succeeded in decreasing the reaction time between alkyl isothiocyanates and n-butyl- amine in Siggia and Hanna's method to only 5 to 10 minutes by replacing the dioxan with dirnethylformamide. Methods involving the reaction of isothiocyanates with n-butylamine in chlorobenzene,4 and with piperidine in dioxan,5 were also developed. The determination of isothiocyanates, based on their reactions with amines in non- aqueous media, can be achieved either by titration of the excess of amine or by titration of the substituted thiourea formed.The methods developed for the determination of isothio- cyanates involve the titration of the excess of amine acidimetrically. Some significant improvements in the determination of isothiocyanates can be effected if the substituted thioureas formed (rather than the excess :)f amine) can be determined oxidimetrically. The determination of thiourea, particularly by redox methods, has attracted much attention and titrimetric procedures with almost all the known oxidants have been developed. The oxidimetric methods for the determination of thiourea are based mostly on its oxidation under various conditions to urea and sulphate, to sulphate, carbonate and nitrogen or to formamidine disulphide. Reynolds ant1 Werner6 developed a method for the determination of thiourea based on its oxidation to formamidine disulphide with iodine in aqueous solution.Gilfillan' however, reported that this iiiethod gave accurate results only with very dilute @ SAC and the authors.VERMA AND KUlLIAIi 90 1 thiourea solutions. Skramovskys found that the reaction of thiourea with an alkaline solution of iodine was slow and developed an indirect method for the determination of thiourea with oxidant, and Guptas determined thiourea by titrating it with iodine solution in the presence of sodium hydrogen carbonate. The slow rate of reaction of thiourea with an alkaline solution of potassium hexacyanoferrate (111) enabled only an indirect determination of thiourea with the oxidant to be made ( Joshilo).Berka and Zykall titrated thiourea with N-bromosuccin- imide in a sodium hydrogen carbonate medium and Suchomelova and Zyka12 reported that the oxidation of thiourea with lead tetraacetate occurred in 50 per cent. acetic acid and also in the presence of sulphuric or hydrochloric acid. During detailed studiesl3 on the oxidimetric determination of thioureas, we found that potassium iodate is one of the oxidants that oxidise thiourea and its m0110-l~ and symmetrically disubstituted (B. C. Verma, unpublished work) derivatives smoothly, rapidly and quanti- tatively to corresponding disulphides a t room temperature without the use of a catalyst : 2 R,N>--SH --f \c-s--s-c/ + ZH+ + 2e (R and R’ = hydrogen atoms or alkyl or aryl groups) No indicator is required, the end-point being signalled by the appearance of iodine with the first excess drop of iodate solution, which imparts a distinct yellow colour to the solution.The end-point can, however, be made more perceptible by using amylose as an indicator. The titrations can also be carried out potentiometrically by using platinum-wire and saturated calomel electrodes. The potential attains a steady value immediately with each addition of oxidant, a sharp jump in potential being observed a t the equivalence point. The simplicity and reliability of the iodatometric method for the determination of thioureas prompted us to apply this method to the determination of isothiocyanates after their quantitative conversion into substituted thioureas in the manner described.The oxidimetric (iodatometric) method possesses some distinct advantages over the acidimetric method for the determination of isothiocyanates: (i) as in the oxidimetric method, the amine is required solely to convert isothiocyanates into the corresponding substituted thioureas and the excess of amine need not be measured, and an amine solution of approximate concentration (unstandardised) can therefore be used for the conversion. In addition, the excess of amine does not interfere in the iodatometric determination of thioureas; (ii) potassium iodate is a reliable and widely used primary standard and hence by using the oxidimetric method, the necessity of standardising the acid (hydrochloric or sulphuric acid) used in the acidimetric method can be eliminated; (iii) any acidic or basic impurities in the isothiocyanate samples would not affect the results owing to the oxidimetric character of the method; (iv) the iodato- metric titrations can be performed without the use of an additional indicator; and (v) isothio- cyanates can be determined in the presence of isocyanates by the iodatometric method, as the substituted ureas formed by the reaction of isocyanate with amine do not cause interferencein the titration of thioureas.RHN RHN NHR R‘NH NNR’ ANALYSIS OF ISOTHIOCYANATE - ISOCYANATE MIXTURES- Organoisothiocyanates and isocyanates are structurally similar compounds and are significantly similar in their reactions, especially with ammonia and amines to form sub- stituted thioureas and ureas, respectively. They also find extensive use as intermediates in the synthesis of polymers, hence their determination in the presence of each other is of great interest.A simple and accurate method for their determination in a single aliquot of sample solution consists in treating the solution of the mixture in dimethylfonnamide with a known excess of a standard solution of n-butylamine in dimethylformamide. The isothiocyanatcs and isocyanates are converted into the corresponding symmetrical NN-disubstituted thioureas and ureas, respectively. The excess of amine on titration with standard acid solution gives the total amount of isothiocyaiiate and isocyanate in the mixture. Titration with standard potassium iodate solution of the disubstituted thiourea formed gives the isothiocyanate content of the mixture and the amount of isocyanate present can be calculated by difference.Both the visual and potentiometric methods of detection of the end-points are reliable.902 VERMA AND KUMAR : DETERMINATION OF ORGANOISOTHIOCYANATES [Analyst, 1'01. 98 NALYSIS OF ISOTHIOCYANATE - THIOUREA MIXTURES- One of the simple and general methods for the preparation of substituted thioureas involves the reaction of isothiocyanates with ammonia or amines. As a large number of substituted thioureas have been prepared by such reactions, mixtures of isothiocyanate and thiourea may be encountered. A simple and accurate method has been developed so as to enable the same aliquot of sample solution to be used for the determination of both components of such mixtures. The solution of the mixture in dimethylformamide is allowed to react with a known excess of the standard n-butylamine solution.The excess of amine is titrated with standard acid followed by titration of total thiourea (already present in the sample solution as well as disubstituted thiourea obtained from isothiocyanate by the reaction with n-butylamine) with standard iodate solution. From the acidimetric titration the amount of isothiocyanate in the mixture can be calculated and from the iodatometric titration the total amount of isothiocyanate and thiourea in the mixture. The thiourea content of the mixture can be found by difference. APPARATUS- Redox potentiometric titrations were performed with an Osaw Crompton (India) potentio- meter, and an Osaw spot-reflecting galvanometer, a bright platinum-wire indicator electrode and a saturated calomel reference electrode.Acid - base potentiometric titrations were performed with a Philips pH meter (electronic millivoltmeter) and glass and saturated calomel electrodes. Microburette-Of 10-ml capacity, graduated in 0-02-ml divisions. REAGENTS- Dimethylformamide-Commercial grade material was purified by storing it over analytical- reagent grade anhydrous sodium carbonate for 2 days. The solvent was decanted off, distilled and the fraction distilling at 148.5 to 149-5 "C was collected in a coloured bottle. Potassium iodate solzttion, 0.05 N-This solution was prepared by dissolving 1-7834 g of the dried analytical-reagent grade compound in water and making the volume up to 1 litre.Sulfihuric acid, 0.1 N-This solution was standardised with potassium hydrogen phthalate, with phenolphthalein as indicator. n-Butylamine solution, 0.2 N-This solution was prepared by dissolving slightly more than the calculated amount of amine (purified by distillation over barium oxide) in dimethyl- formamide. The solution was standardised by titration with standard sulphuric acid, with methyl red as indicator. Alkyl isothiocyanates and alkylthioureas were prepared by well known methods.15 Phenyl isothiocyanate (commercial grade) was distilled before use; phenylthiourea (commercial grade) was recrystallised before use; phenyl isocyanate was prepared by the method of Allen and Be1116; butyl isocyanate (commercial grade) was distilled before use ; and o-methoxy- phenyl isothiocyanate was prepared by the method of Dains, Brewster and Olander.17 PROCEDURE- Determifiation of organoisothiocyanates-To an aliquot of the solution in dimethylform- amide of each isothiocyanate contained in a glass-stoppered titration flask 5 ml of approxi- mately 0.2 N n-butylamine in dimethylformamide were added. The volume of the solution was made up to 10ml with the solvent.The flask was stoppered, swirled in order t o mix the reactants and set aside for 10 minutes so as to ensure completion of the reaction. Sufficient water and sulphuric acid to maintain the normality of the solution at 2.0 to 2.5 N and its volume at 100 ml were added. The solution was cooled to room temperature (26 "C) in each instance and titrated with 0-05 N potassium iodate solution to the appearance of a distinct and permanent yellow colour.If desired, amylose (0.2 ml of a 1 per cent. aqueous solution) can be used as an indicator, the solution acquiring a blue colour at the end-point. In potentiometric titrations, the solution was stirred magnetically during the titration. A sharp jump in potential was observed at the equivalence point. From the volume of standard 0.05 N potassium iodate used corresponding to the end- point in visual and potentiometric titrations, the amount of disubstituted thiourea formed EXPERIMENTALDecember, 19731 ALONE AND WITH ORGANOISOCYANATES OR THIOUREAS 903 and consequently the amount of isothiocyanate present was calculated. The results are recorded- in Table I. TABLE I IODATOMETRIC DETERMINATION OF ORGANOISOTHIOCYANATES Values are means of six determinations with standard deviations Amount found*/mg Visual T P o t e n t i o m e t r i c Compound method method CH,NCS .. . . 8.05 f 0.020 7-99 f 0.017 CH,CH,CH,NCS . . 7-98 f 0.020 7.98 f 0.015 (CH,),CHNCS . . . . 8.04 f 0.031 8.01 f 0.025 CH,CH,CH,CH,NCS . . 8.05 f 0-024 8.03 f 0.015 (CH,),CHCH,NCS . . 7.97 f 0.031 7-98 f 0.015 C,H,NCS . . 8.05 f 0.034 8.00 f 0.028 o-(OCH,)C,H,NCS . . 8.03 f 0,030 7.99 f 0.028 CH,CH,NCS . . . . 8-04 f 0-028 8.00 f 0.011 * Amount taken 8 mg. t Amount taken 30 mg. Amount foundtlmg Visual T v m e t r i c method method 30.06 f 0.019 29.94 f 0.031 30.05 f 0.011 30.00 f 0.026 29.92 & 0.015 30.13 f 0.031 30-00 f 0.031 29-90 f 0.028 30.14 f 0.032 29.93 f 0.032 30.14 & 0.031 30.17 & 0427 30.14 f 0.032 30.23 f 0.037 29.96 f 0.038 29.90 5 0.042 Determination of organoisothiocyanates a.nd isocyanates in the j?wesence of each other- Aliquots of the solution in dimethylformamide of synthetic nlixtures with various proportions of isothiocyanate and isocyanate were placed in glass-stoppered titration flasks containing a known excess (7 ml) of standard (0.2 N) solution of n-butylamine in dimethylformamide. The volume of each solution was made up to 15 ml with the solvent. The flask was stoppered, swirled in order to mix the reactants and set aside for 10 minutes so as to ensure completion of the reaction.The solution was diluted with 30 to 40 ml of distilled water, cooled to room temperature and titrated with standard 0-1 N sulphuric acid, with methyl red as indicator.To the same solution sufficient water and sulphuric acid to maintain the normality of the solution at 2.0 to 2-5 N and its volume at 125 ml were added. The solution was cooled to room temperature (26 "C) and titrated with standard 0.05 N potassium iodate solution, with amylose as indicator. The colour changed sharply from red to blue at the end-point. Both the acidimetric and iodatometric titrations were also performed potentiometrically. The solution was stirred magnetically in these titrations. The volume of standard acid used in the acidimetric titration corresponds to the total amount of isothiocyanate and isocyanate present in the sample, and that of iodate solution used in the iodatometric titration corresponds to the amount of disubstituted thiourea formed and consequently the amount of isothiocyanate present.The iosocyanate content of the sample can therefore be determined by difference. The results of the analysis of phenyl iso- thiocyanate and plienyl isocyanate mixtures by both visual and potentiometric titrations are recorded in Table 11. TABLE I1 DETERMINATION OF PHENYL ISOTHIOCYANATE AND PHENYL ISOCYANATE Values are means of six determinations with standard deviations IN ADMIXTURE Amount of C,H,NCS in the mixture1 mg 10.00 10.00 10.00 10.00 20.00 30.00 40.00 Amount found/mg r Visual metric method method Potentio- 10.03 f 0.055 10.05 rf 0.054 10.05 f 0.024 9-94 & 0.028 20-12 f 0.075 30.23 f 0.077 40.29 f 0.080 9-97 f 0.039 10.02 f 0.015 10.02 f 0.028 9-97 f 0.015 20.08 f 0-056 30.10 f 0.057 40.18 & 0,052 Amount of C,H,NCO in the mixture/ mg 10.00 20.00 30.00 40.00 10.00 10-00 10.00 Amount found/mg V i o - Visual metric method method 10-04 f 0.076 9.98 f 0.058 19-96 f 0.093 20.00 & 0.084 29.93 f 0.124 29.90 rf 0.084 39.85 3 0-124 38.89 f 0.031 10.04 f 0.065 9.96 f 0.040 9-96 f 0-065 9.98 rf 0.022 10.03 f 0.063 9-96 0.040 Ratio of C,H,NCS to C,H,NCO 1 : l 1:2 1:3 I:4 2: 1 3: 1 4: 1904 VERMA AND RUMAR: DETEKMIKATION OF ORGANOISOTHIOCYANATES [Analyst, Vol.98 Determination of organoisothiocyanates and thioureas in the presence of each other-The procedure adopted was similar in detail to that used for mixtures of organoisothiocyanates and isocyanates, except that an excess of 5 ml of 0.2 N solution of n-butylamine in dimethyl- formamide was used.The value for total thioureas included that originally present in the mixture. Both the acidimetric and oxidimetric titrations were also carried out potentiometrically. From the volume of standard acid used in the acidimetric titration, the amount of isothiocyanate in the mixture was calculated. The total amount of isothiocyanate and thio- urea in the mixture was calculated from the volume of standard potassium iodate used in the oxidimetric titration. The thiourea content of the mixture was calculated by difference. The results of the analysis of a mixture of ethyl isothiocyanate and ethylthiourea by both visual and potentiometric methods are given in Table 111. Amount of C,H ,N CS in the mixture! mg 10.00 10.00 10.00 10.00 20.00 30.00 40.00 TABLE I11 DETERMINATION OF ETHYL ISOTHIOCYANATE AND ETHYLTHIOUREA Values are means of six determinations with standard deviations IN ADMIXTURE Amount found/mg r Visual method 10-00 f 0.059 10.04 f 0.043 10.03 f 0.071 10-04 f 0.041 20.08 f 0.043 30.22 0.058 40-37 f 0.058 1 Potentio- metric method 10.00 & 0.038 9-96 f 0.027 9.97 f 0.015 10.03 f 0.030 19.97 f 0.022 30.12 f 0.022 40.33 f 0.043 Amount of ethyl- thiourea in the mixture/ mg 10.00 20.00 30.00 40-00 10.00 10.00 10.00 Amount found/mg Visual metric method method P o t e z i o - 9.96 f 0.045 19.87 f 0.051 30.24 f 0.072 39.64 & 0.057 10.05 f 0.020 10.04 f 0.026 10.04 f 0.049 9.96 & 0.015 20.00 f 0.047 30-12 f 0.067 39.73 f 0-032 9.96 f 0.015 10.03 -& 0.011 10.02 f 0.022 Ratio of CBH,NCS to qH,NHCSNH, 1 : l 1:2 1:3 1:4 2: 1 3: 1 4 : 1 RESULTS AND DISCUSSION The results recorded in Table I show that methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, phenyl or o-methoxyphenyl isothiocyanate can be determined visually and potentio- metrically after conversion into symmetrical NN-disubstituted thioureas by reaction with n- butylamine in dimethylformamide medium.The over-all standard deviation from the pooled results of all the visual and potentiometric titrations performed with 8 mg of each isothio- cyanate have been found to be -+0.027 and &O.OlO, respectively, and for 30 mg of each com- pound h0.034 and 50.024, respectively. The method is free from interferences from organoisocyanates, thiocyanates or ureas even when present in up to five-fold amounts.Thioacet amide, thiosemicarbazide, t hioureas, dit hiocarbamat es and xant hat es, however, interfere. w Although efforts had been made to develop methods that are applicable to the analysis of pure samples of organoisothiocyanates, organoisocyanates or thioureas, no attention appears to have been directed towards determining these compounds in mixtures containing them. The proposed methods for the analysis of isothiocyanate - isocyanate and isothio- cyanate - thiourea mixtures, besides being simple, accurate and reliable, have the added advantage that the analyses can be conducted on the same sample solution, thus resulting in a saving of time and effort. The acidimetric titration of the excess of amine added to the mixture, followed by iodatometric titration of thiourea present and formed, enables the mixture to be analysed for both constituents.The red colour of the acidic form of methyl red will persist throughout the iodatometric titration, which is carried out in sulphuric acid medium immediately after the acidimetric titration. There is, however, a sharp colour change from red to blue at the end-point. The analysis with both visual and potentiometric end-point detection is reliable, but blanks are required to be run if the samples or the solvents used are likely to be contaminated with acidic or basic impurities. The synthetic mixtures of phenyl isothiocyanate and phenyl isocyanate with ratios in the range 1 : 4 to 4: 1 can be analysed by both visual and potentiometric methods with anDecember, 19733 ALONE AND WITH ORGANOISOCYANATES OR THIOUREAS 905 average standard deviation of 0.29 per cent.(for isothiocyanate) and 0.44 per cent. (for iso- cyanate), respectively (Table 11). The method has also been applied to the analysis of a mixture of n-butyl isothiocyanate and n-butyl isocyanate, the results agreeing well with those obtained for the above mixture of aromatic compounds. The results recorded (Table 111) for the analysis of synthetic mixtures of ethyl isothiocyanate and ethylthiourea with ratios also in the range 1 : 4 to 4 : 1 show that they can be analysed by the visual and potentiometric methods with an average standard deviation of 0.29 per cent. (for ethyl isothiocyanate) and 0.23 per cent. (for ethylthiourea), respectively. The method has also been extended to other mixtures such as methyl isothiocyanate - methylthiourea, n-propyl isothiocyanate - n-propyl- thiourea, isopropyl isothiocyanate - isopropylthiourea, n-butyl isothiocyanate - n-butyl- thiourea, isobutyl isothiocyanate - isobutylthiourea and phenyl isothiocyanate - phenyl- thiourea, the components of which have been determined with the same degree of accuracy. The authors thank the Council of Scientific and Industrial Research (Indial for the award 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. \ I of a research fellowship to one of them (S.K.). REFERENCES Siggia, S., and Hanna, J. G., Analyt. Chem., 1948, 20, 1084. Karten, B. S., and Ma, T. S., Microchem. J . , 1959, 3, 507. Vinson, J. A., Analyt. Chem., 1969, 41, 1661. Roth, H., Mikrochim. Acta, 1958, 773. Venkataraghavan, R., and Rao, C. N. R., Chemist Analyst, 1962, 51, 48. Reynolds, J . E., and Werner, E. A., J . Chem. SOG., 1903, 83, 1. Gilfillan, F. A., J . Amer. Chem. SOG., 1920, 42, 2072. Skramovsky, S., Chem. ZentBl., 1941, 11, 379. Gupta, P. C., J . lndian Chem. Soc., 1960, 37, 213. Joshi, M. K., Naturwissenschaften, 1957, 44, 537. Berka, A., and Zyka, J., Chemicke’ Listy, 1957, 51, 1823. Suchomelova, L., and Zyka, J., J . Electroanalyt. Chem., 1963, 5, 57. Singh, B., and Verma, B. C., J . Scient. Ind. Res.. 1965, 24, 536. -___ , 2. analyt. Chem., 1963, 194, 112. Drake, N. L., Org. Synth., 1941, 21, 81 and 83. Allen, C. F. H., and Bell, A., Ibid., 1955, Collect. Vol. 3, 846. Dains, F. B., Brewster, R. Q., and Olander, C. P., Ibid., 1955, Collect. Vol. 3, 447. Received May Zlst, 1973 Accepted September 3 4 1973

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DOI:10.1039/AN9739800900

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年代:1973

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906 Analyst, December, 1973, Vol. 98, pp. 906-90’7 Determination of Bacitracin in Animal Feeds that Contain Copper BY B. GRYNNE, E. HOFF, T. SILSAND AND K. VAAJE ( A IS Apothekeriaes Laboratorium for Specialpraepayater, Oslo, Novway) A modification of the method involving the use of acidified methanol for the analysis of animal feeds that contain bacitracin and copper sulphate as additives has been developed. Because of the interference of copper in the bacitracin assay, the copper is precipitated by the addition of 3 to 4 mol of sulphide ions per mole of copper. The method has been used for feed samples that contain 5 to 20 p.p.m. of bacitracin and 100 to 300 p.p.m. of copper. THE determination of bacitracin in animal feeds that contain zinc bacitracin and copper sulphate as growth promotorsl gave low recoveries (30 to 60 per cent.) when the feeds were analysed by methods in which pyridine2 and methanol3 are used.In this work attempts have been made to precipitate the interfering copper as a solid salt during the extraction procedure with acidified methanol. METHOD REAGENTS- Ammonium sulphide solution-Minimum content as hydrogen sulphide, 10 per cent. m/ I/. All other reagents and the zinc bacitracin standard solution were prepared according to Grynne’s EXTRACTION AND ASSAY OF BACITRACIN- Carry out the extraction and microbiological assay as described in procedure B in the method of G r ~ n n e , ~ with the following modification: add 0.4 ml of ammonium sulphide solution immediately after the acidified methanol, before triturating. To avoid any possible interference of the sulphide with the test bacteria, it is always recommended that the super- natant liquid is evaporated to dryness before the dissolution and the microbiological assay.RESULTS AND DISCUSSION A known aniount of zinc bacitracin feed supplement was mixed with the feed samples with a high content of copper. The samples were assayed by the original method involving methanol3 as well as by the modified method. It can be seen in Table I that the results found by the modified method compare favourably with the added content of zinc bacitracin. TABLE I COMPARISON OF RESULTS BY THE ORIGINAL METHOD^ AND MODIFIED METHOD FOR THE EXTRACTION OF BACITRACIN FROM ANIMAL FEEDS CONTAINING COPPER* Bacitracin content, p.p.rn. 6-0 9-4 10.0 10.0 10.0 10.0 20-0 20.0 Copper content, p.p.m.188 125 190 200 200 300 200 300 Bacitracin found by original method, p.p.m. 1.7 3.3 6.6 5.6 5.3 5.9 15.7 9.9 Bacitracin found by modified method, p.p.m. 6.0 9.6 10.3 9.7 9.7 9-3 21.3 18.9 * Each result is the mean of three determinations, Le., extraction and biological test (I-point assay). 0 SAC and the authors.GRYNNE, HOFF, SILSA4ND AND VAAJE 907 The assay of bacitracin in feeds containing copper as additive also gave low recoveries when the method involving pyridine was used. Attempts were therefore made to modify the latter method by the precipitation of the copper as its sulphide during the extraction with hydrochloric acid. The assay results found, however, were even lower than those obtained by the original method with pyridine. The authors thank Dr. H. P. Throndsen for critically reading the manuscript and for assistance in its preparation, and Mrs. S. Irgens Karlsen for assistance with the experimental work. REFERENCES 1. 2. 3. Livingstone, R. M., and Livingston, D. M. S., J . Agric. Sci., Camb., 1968, 71, 419. Craig, G. H., U.S. Patent 3 306 827, 1967. Grynne, B., Analyst, 1971, 96, 338. Received July 5th. 1972 Amended May 23rd, 1973 Accepted June lst, 1973

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DOI:10.1039/AN9739800906

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年代:1973

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908 AnaZyst, December, 1973, To]. 98, @p. 908-911 Analytical Methods Committee REPORT PREPARED BY THE PROPHYLACTICS IN ANIMAL FEEDS SUB-COMMITTEE TheJDetermination of Nifursol in Animal Feeds THE Analytical Methods Committee has received the following Report from its Prophylactics in Animal Feeds Sub-committee. The report has been approved by the Analytical Methods Committee and its publication has been authorised by the Council. REPORT The constitution of the Sub-committee responsible for the preparation of this report was : hlr. J. Markland (Chairman), Mr. B. J. Allen, Mr. R. J. Anderson, Dr. I. E. Burrows, Mr. ,4. G. Croft, Mr. G. Drewery, Mr. C. E. Dodd, Dr. I<. Field, Mr. R. S. Hatfull, hlr. J. S. Leahy, Slr. D. H. Mitchell, Mr. R. C. Spalding, Mr. J. A. Stubbles and Dr.D. R. \Villiams, with Mr. P. W. Shallis as Secretary. INTRODUCTION Nifursol [3,5-dinitrosalicyl-(5-nitrofurfurylidene) hydrazide] is an anti-blackhead drug and growth-promoting agent that is incorporated in animal feeds at a level of about 75 p.p.m. Polarographic,l spectrophotometric2 and gas-chromatographic3 methods have been proposed for its determination in animal feeds. Neither the polarographic procedure, which is based on reduction of the nitro group, nor the spectrophotometric procedure, which involves for- mation of a phenylhydrazone, is specific for nifursol. The gas-chromatographic method, in which the derivative methyl 3,5-dinitrosalicylateJ prepared by cleavage of the nifursol mole- cule and esterification of the 3,5-dinitrosalicylic acid formed, is determined with an electron- capture detector, is virtually specific for nifursol. EXPERIMENTAL M.l'hen the Sub-Committee began its work only the polarographic and syectrophotometric methods were available.It was decided first to investigate the spectrophotometric procedure and preliminary work by some members indicated that good recovery of nifursol could be obtained. However, in this preliminary work one point of considerable difference emerged : in the method as written2 the wavelength of maximum absorption of the final coloured product was stated to be 555 nm, but all members who tried the method found that maximuni absorption was at a shorter wavelength than this, one finding it to be at 455 nm and another at about 510 nm. When details of the gas-chromatographic metliod involving the use of electron-capture detection3 were published it was realised that this technique offered a more specific approach to the determination of nifursol.Some members who had electron-capture detectors avail- able carried out preliminary investigations of this method. Difficulties were encountered by all members, either with the conditions of the derivative formation, or in reproducing the gas-chromatographic conditions specified. As only a few members had access to electron- capture detectors it was decided not to pursue this investigation, but to concentrate on the spectrophotometric method. A collaborative test of the spectrophotometric method was arranged for which three different feed samples were distributed to each collaborator and medication was carried out in each laboratory at levels of 50, 75 and 100 p.p.m.Four laboratories took part in this work and eighteen determinations were carried out at each level; the mean recoveries were 96.0 per cent. (s.d. 4.80) at the 50 p.p.m. level, 94-9 per cent. (s.d. 3.75) at the 75 p.p.m. level and 93.0 per cent. (s.d. 4.20) a t the 100 p.p.m. level. However, again the collaborating laboratories reported that they had not all found the same wavelength of maximum absorption. It was discovered during this work that the concentration of hyamine hydroxide reagent used affected the colour of the final product and hence influenced the wavelength of maximum absorption. In the written account of the method use of 0.1 ml of 1 M hyamine hydroxide in methanol was specified, and it was found that when reagent of this concentration was used 0 SAC.ANALYTICAL METHODS COMMITTEE 909 the absorption maximum of the final coloured product was at about 565 nm.However, a 10 per cent. solution of the reagent in methanol is more readily obtainable in this country and most inembers had been using this concentration. The wavelength of maximum absorption when 0.2 ml of such a solution was used was found to be at about 515 nm. A further collab- orative test of the method, slightly modified in accordance with these findings, was carried out for which three samples of different feedingstuffs were circulated and medication was again carried out in each laboratory at levels of 50, 75 and 100 p.p.m. The results of this test are given in Table I.TABLE I DETERMINATION OF NIFURSOL IN FEEDS BY USE OF THE RECOMMENDED METHOD Feed Laboraory 1 A B C D E 2 A B C D E 3 A B C D E 1 A B C D E 2 A B C D E 3 A B C D E 1 A B C D E 2 A B C D E 3 A B C D E Nifursol added, Nifursol found, p.p.m. p.p.m. 50 57.0, 60.0 49.0, 65.6 50.3, 49.5 51.0, 52.5 45.0, 43-2 54.0, 57.0 51.0, 52.0 50.6, 49.5 51.0, 52-5 40.3, 40.9 53.0, 54.0 50.0, 51.0 48-7, 48.4 49.5. 51-0 42.0, 40.6 Over-all mean .. Standard deviation . . Coefficient of variation 75 80.0, 76.0 79.5, 79.5 74.3, 73-8 79.5, 79.0 63.1, 68.9 83.0, 82.0 79.5, 78.5 74.3, 73.5 77.5, 80.0 61.6, 60.4 82.0, 80.0 76.0, 76.5 73.4, 72-4 76.5, 77.0 61.3, 63.9 Over-all mean * . Standard deviation . . Coefficient of variation 100 108*0,104*0 104.0, 97.0 98.3, 97.2 105.2, 107-5 90.8, 87.0 110*0,110*0 102.6, 95.5 97.8, 97.4 104*0,106*0 90.8, 85.3 110*0,107-0 95.6, 95.5 97.2, 96-7 102-0,102*5 86.7, 85.8 Over-all mean ..Standard deviation . . Coefficient of variation Recovery, per cent. 114.0, 100.0 98.0, 111.0 100.6, 99.0 102.0, 150-0 90.0, 86.4, 108.0, 114.0 102.0, 104.0 101.2, 99.0 102.0, 105.0 80.6, 81.8 106.0, 108.0 100.0, 102.0 97.4, 96.8 99.0, 102.0 84.0, 81.2 . . 99.3 . . 3.76 . . 3.78 106.6, 101.3 106.0, 106.0 99.2, 98.4 106.0, 105.3 84.0, 91-8 110.6, 109.3 106.0, 104.5 99.0, 98.1 103.3, 106.7 82.2, 80.4 109-3, 106.6 100.0, 102.0 97.8, 96-5 102-0, 102.7 81.8, 85.1 . . 99.6 . . 2.79 . . 2.80 108.0, 104.0 104.0, 97.0 98.3 97.2 105.2, 107.5 90.8, 87.0 110.0, 110.0 102.5, 95.5 97.8, 97-4 104-0, 106.0 90.8, 85.3 110.0, 107.0 95.5, 95.5 97.2, 96.7 102.0, 102.5 86.7, 85-5 .. 99.3 . . 2.55 . . 2.57910 ANALYTICAL METHODS COMMITTEE : THE DETERMINATION OF [Analyst, Vol. 98 The Sub-committee recommends that the method given in the Appendix should be used RECOMMENDATION for the determination of nifursol in compound feedingstuffs. Appendix RECOMMENDED METHOD FOR THE DETERMINATION OF NIFURSOL IN ANIMAL FEEDS The method is applicable to the determination of nifursol in animal feeds at concentra- Other substances that will provide a nitro group under the con- SCOPE AND FIELD OF APPLICATION- tions of up to 125 p.p.m. ditions of the method, e.g., nitrofurazone and furazolidone, will interfere, PRINCIPLE OF THE METHOD- Nifursol is extracted from the feed with dimethylformamide and the extract is cleaned up on a column of alumina.Phenylhydrazinium chloride solution is added to a test portion of the cleaned-up extract, which is then extracted with toluene. The colour is developed with hyamine hydroxide solution and measured at the absorbance maximum at about 515nm. The concentration of nifursol present in the sample is calculated by reference to a calibration graph. REAGENTS- Toluene-Analytical-reagent grade. NifiwsoZ-Purified for use as a standard. Alumina, 80 to 200 mesh, alkaline, Brockmann activity 1-To one hundred parts of the alumina add six parts of analytical-reagent grade powdered magnesium hydroxide. Shake them in a screw-capped bottle to mix, add eight parts of water, and mix again until free from lumps. Sand-Acid washed. DimethyZfornzamide solution, aqueous, 95 per cent.V/V. Dimethylformamide solution, aqueous, 50 per cent. V/V. Phenylhydrazinium chloride solution-Shake 0.25 5 0.005 g of analytical-reagent grade phenylhydrazinium chloride in 25 ml of water, add 25 ml of concentrated hydrochloric acid, and shake the mixture to dissolve the solid. Prepare this reagent freshly immediately before use and filter it if necessary. Hyamine 10-X hydroxide sol.ution-An approximately 10 per cent. m/V solution in methanol. Nifursol standard solution-Weigh, to the nearest 0.1 mg, 25 mg of nifursol into a 100-ml calibrated flask, add 5 ml of 95 per cent. V/V dimethylformamide solution, and mix until all of the solid has dissolved. Prepare this solution freshly each day. APPARATUS- in length, plugged at the bottom end with glass-wool, was used.Dilute to the mark with methanol. Chyomatographic column-A glass column, 20 to 25 mm in diameter and 100 to 150 rnm PREPARATION O F TEST SAMPLE- Feeds in the form of pellets or crumbs should be finely ground before being weighed out for analysis. PROCEDURE- Test portion-Weigh, to the nearest 0.01 g, approximately 5 g of the test sample into a 125-ml conical flask. Add 50.0 ml of 95 per cent. V/V dimethylformamide solution, insert a stopper loosely, and place the flask in a water-bath at 60 5 5 "C, leaving it for 30 minutes. Swirl the contents of the flask occasionally during this period. Next, shake the flask on a mechanical shaker for 30 minutes and then filter the contents through a rapid-flow filter- paper, preferably under vacuum on a Biichner funnel.Transfer 40.0 ml of the filtrate to a beaker, add 40.0 ml of water, and stir. Set the beaker aside in the dark for 30 minutes.December, 19731 NIFURSOL I N ANIMAL FEEDS 91 1 Chromatograg%iy-Pack the chromatographic column to a depth of 70mm with the prepared alumina and on top of the alumina add a layer of sand 15 mm deep. Wash the column with 50 ml of 50 per cent. V/V dimethylfonnamide solution and theri pass the dimethyl- formamide extract of the test sample through the column; reject the first 45 ml of extract and collect the next 17 ml. Determination-By means of a pipette transfer 5.0 ml of the eluate into a 20-ml centrifuge tube, add 5 ml of phenylhydrazinium chloride solution, mix, and place the tube in a water- bath at 40 & 2 "C for 20 minutes.Remove the tube from the water-bath and cool it in running water for 5 minutes. Add 5 0 m l of toluene to the contents of the tube, insert a glass or plastic stopper (a rubber stopper must not be used), and shake the tube vigorously forty times. Spin the tube in a centrifuge for 5 minutes to clear the toluene layer, and then transfer 3.0 ml of the toluene layer to a 10-mm spectrophotometer cell. To the contents of the cell add 0.2 ml of hyamine hydroxide solution, mix the liquids immediately, and within 1 minute measure the absorbance of the solution at 515 nm against toluene in the reference cell. Calibration gra@h--With a pipette transfer 5.0 ml of nifursol standard solution into a 200-ml calibrated flask, add 100 ml of 95 per cent. V/V dimethylformamide solution, and dilute to the mark with water. Into separate 20-ml centrifuge tubes transfer by pipette 0,2,3,4 and 5-ml portions of this solution and dilute the contents of each tube to 5 ml with 50 per cent. V/V dimethylformamide solution. Treat the contents of each tube as described under Determina- tion beginning at ". . . add 5 ml of phenylhydrazinium chloride solution. . . ." Construct a graph of micrograms of nifursol versus absorbance, Expression of results-Calculate the concentration of nifursol in the test sample from the expression : 20 A Nifursol, p.p.m. =- m where A is the amount, in micrograms, of nifursol read from the calibration graph equiva- lent to the absorbance of the test solution and m is the mass, in grams, of the test sample taken for analysis. REFERENCES 1. 2. 3. Koul, G. L., and Nigam, S. S., RieGhstofle Arom. Kdrperjbflegem., 1969, 17, 223. Zietlow, D. C., and Morrison, J. L., J . Ass. Off. Analyt. Chem., 1970, 53, 1085. Wheals, B. B., and Weston R. E., Aflalyst, 1971, 96, 78.

ISSN:0003-2654    

DOI:10.1039/AN9739800908

出版商:RSC    

年代:1973

数据来源: RSC

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912 Book Reviews [AnaEyst, Vol. 98 MODERN ANALYTICAL METHODS. By D. BETTERIDGE and H. E. HALLAM. Monogvaphs for Teachers No. 21. Pp. viii + 227. London: The Chemical Society. 1972. Price L2. This monograph reviews modern methods of analytical chemistry on a broad front with the objective of informing teachers and students of the current situation on the analytical scene. The treatment is descriptively quantitative, rather than mathematical, although a moderate algebraic treatment is involved in the key discussions of solution equilibria, liquid - liquid dis- tribution (solvent extraction), etc. The text initially treats dissolution of the sample, organic reagents for inorganic analysis, separation techniques for isolation, purification and pre-concentration, then moves on to titrimetry, electrochemical methods, thermal and kinetic methods and nuclear and X-ray methods, before ending on spectroscopic methods, with a final chapter on automatic and combined methods of analysis.Each chapter is monographic and carries its own references, but there is a list of twenty- five general references to comprehensive or broad-based texts on modern analytical chemistry. There is also a very useful subject index. The concept of this book is excellent and i t is timely for, as readers of The Analyst well know, the past few years have seen tremendous developments and an overriding shift of the centre of gravity of analytical chemistry towards physico-chemical techniques in the general area of spectro- scopy, nuclear, electrochemical and thermal methods. Both authors have made considerable contributions to modern techniques of analysis-Dr.Hallam principally in infrared work and Dr. Betteridge in solvent extraction, absorptiometry and, more recently, in photoelectron spectro- scopy-and are very well qualified to write this survey. The treatment is excellent and, bearing in mind the limited introductory nature of the book, the over-all effect is very satisfactory. There are few errors in the book, but one surprising error on page 38 is the perpetuation of the 2-methyl-8-hydroxyquinoline - 8-hydroxyquinoline myth concerning aluminium. The former reagent may not precipitate aluminium but, as has been shown in The Analyst (1965, 90, 13), it does appear to form a partially extractable fluorescent complex with it.Even here, however, the error, if such i t is, comes only in one of the many informative “asides” which the authors allow themselves from time to time. There are one or two typographical errors, e.g., Schwarzenback, page 40, transposition of the structural formulae for DMG and oxine, page 33, but they are not critical errors. Diagram 65 suggests an unfortunate admixture of total consumption (turbulent) and pneumatic nebulisation (laminar flow) burners and on page 199 there appears to be the possibility of confusion over mechanical modulation of a light signal and a pseudo double-beam type of measurement. On the same page, it is slightly misleading to attribute interpretation of the Fraunhofer lines to Bunsen and Kirchoff (1860), as they were first explained by Brewster in 1832 (some may also dispute that the lines were first discovered in 1802 by Wollaston). On a purely personal note, the reviewer found the use of the “f” symbol in the chapters on kinetics and titrimetry to be confusing because of the old activity coefficient symbol.However, these are minor blemishes in an excellent monograph which, if widely read-as it deserves to be-should inspire many more students to engage their interests in analytical chemistry as a vital and fascinating branch of chemistry. T. s. WEST MOSSRAUEK EFFECT DATA INDEX. COVERING THE 1971 LITERATURE. Edited by JOHN G. STEVENS AND VIRGINIA E. STEVENS. Pp. x + 430. London: Adam Hilger. 1972. Price L12-60. The information collected in this index is invaluable raw material for anyone who is using or is contemplating the use of Mossbauer spectroscopy. Not only are the numerical and decay scheme data well presented and easily retrieved, but the latest version contains over 1100 references culled from the literature of 1971 and part of 1972. P. A. Flinn’s short contribution on equipment calibration is very readable and could be of value to a newcomer in the field. A mild criticism relates to the section somewhat pretentiously labelled “Equipment, sources and supplies for Moss- bauer spectroscopy.” Essen- tially, the publication is a data handbook and a t L12.60 it is very reasonably priced. This section is simply a list of not very informative advertisements. R. BLACKBURN

ISSN:0003-2654    

DOI:10.1039/AN9739800912

出版商:RSC    

年代:1973

数据来源: RSC