摘要:

ANALYST. APRIL 1989, VOL. 113 505 Computerised Compensation Method for the Spectrophotometric Determination of a Single Substance in the Presence of Interferences Abdel-Aziz M. Wahbi, Hoda Mahgoub and Magda Barary Pharmaceutical Analytical Chemistry Department, Faculty of Pharmacy, Alexandria University, Alexandria 21521, Egypt The difference curves obtained using the compensation method for the spectrophotometric determination of a single substance in the presence of interferences were computed using a BASIC computer program. The exact balance-point (end-point) was defined on a plotter. When the absorption characteristics of the substance to be determined disappear, the resulting curve corresponds to the interferences, and the concentration of the substance in the sample solution is equal to that in the reference solution.The applicability of the method was illustrated by the determination of atropine sulphate in an injection solution and ephedrine hydrochloride and nadolol in tablets. The results showed good agreement with those obtained using the experimental compensation method and a second-derivative ultraviolet spectrophotometric method. Keywords: Computerised compensation spectrophotometry; interferences; pharmaceutical analysis; BASK program The compensation method’ is a non-mathematical method for the detection and elimination of unwanted absorption during spectrophotometric analysis. The unwanted absorption curve is assumed to possess the simplest possible shape and none of the characteristics of the pure compound. The method may therefore be regarded as an analogue of the more advanced types of mathematical correction which involve similar assumptions.The compensation method involves a compari- son of several difference spectra (sample, s, - reference, r) using different concentrations of a reference solution (c,) in the reference cell. Hence, if ASi and Arj refer to the absorbances of the relevant cells against air at a wavelength, i , then AAi = ASj - Arj. The characteristic peak of the pure compound, which may be observed in the difference curve, gradually decreases as c, increases and finally disappears at the balance-point (end- point), for which c, = c,. A further increase in c, then leads to an over-compensated difference curve which exhibits an inversion of the pure compound’s characteristic peak (Figs.The difference curve at the balance-point coincides with the unwanted absorption, if present. The accuracy of the compen- sation method for the determination of a single substance and for the analysis of multi-component mixtures depends on correct evaluation of the balance-point.*-4 Apart from its ability to compensate for unwanted absorp- tion, the method also possesses the usual advantage of a “null method” in that it cancels the non-linearities of both the instrument and the chemical system. Hence, when the balance-point is associated with a negligible difference curve, the spectrophotometer is little more than a “balance detector” and all the usual errors of measurement5 (excluding those due to cell path length) are eliminated.With regard to the chemical system, Beer’s law deviations,h which may be accentuated by constituent interactions, disappear at the final stage, when both “sample” and “reference” mixtures have been equalised. Further, although the interactions between the constituent(s) and the unwanted absorption remain, they usually represent only a minor problem. The work described in this paper involves replacing the practical compensation steps by a suitable BASIC program that can carry out the entire operation and define the balance- point. Only two solutions are required, a reference solution of suitable, known concentration and a sample solution. The absorbances of the two solutions are measured over a wide wavelength range in order to cover all the absorption 2-4).characteristics. The proposed method was applied to the determination of atropine sulphate in an injection solution (1 mg ml-I), ephedrine hydrochloride in tablets (30 mg per tablet) and nadolol in tablets (80 mg per tablet). Experimental Reagents Atropine sulphate crystals Merck, Darmstadt, FRG. Ephedrine hydrochloride crystals. Knoll, Chemische Fab- Nadolol. Squibb Laboratories, Princeton, NJ, USA. All other reagents and solvents were of analytical-reagent riken, Ludwigshafen am Rhein, FRG. grade. Instrumentation A Perkin-Elmer Model 550s UV - visible spectrophotometer with 1-cm quartz cuvettes and a Hitachi Model 561 recorder. an Olivetti M24 personal computer, 128 k byte, and an Epson HI-80 plotter were used. Reference Solutions Atropine sulphate. 0.08% mlV in 0.1 M hydrochloric acid.Ephedrine hydrochloride, 0.06% mlV in 0.05 M sulphuric Nadolol, 0.025% mlV in 0.1 M hydrochloric acid. acid. Pharmaceutical Preparations and Sample Solutions Atropine sulphate injection USP X X . Misr, 1 mg ml-1, used as received. Ephedrine hydrochloride tablets. Nile, labelled to contain 30 mg of ephedrine hydrochloride per tablet; average mass, 0.1345 g. Ephedrine hydrochloride sample solution. Weigh and powder 20 tablets. Transfer an amount of the powder equivalent to about 0.090 g of ephedrine hydrochloride into a 100-ml calibrated flask. Add about 70 ml of 0.05 M sulphuric acid, shake mechanically for 30 min, and then make up to the mark with 0.05 M sulphuric acid. Mix and filter, discarding the first few millilitres. Nadolol tablets (Corgard tablets).Squibb, Egypt, labelled to contain 80 mg of nadolol per tablet; average mass, 0.22597 g.ANALYST. APRIL 1989. VOL. 114 Start c2 Read data for sample, Read data for reference wavelength ( i ) and A,; lnitialise the plotter and draw x and y axes t I t -1 Enter the variable; K 1 Compute the data to be plotted AA; = [A,; - (KA,;)] 1 I Plot AA, against i I K7 Exit Fig. 1. Flow chart for the BASIC computer program Nadolol sample solutiorz. Weigh and powder 20 tablets. Transfer an amount of the powder equivalent to about 0.100 g of nadolol into a 100-ml calibrated flask. Add about 70 ml of 0.1 M hydrochloric acid, shake mechanically for 30 min and make up to the mark with 0 . 1 ~ hydrochloric acid. Mix and filter. discarding the first few millitres.Dilute 20 ml of the filtrate to 100 ml with 0.1 M hydrochloric acid. Second-derivative Spectra7.8 These were recorded between 290 and 240 nm at a scan speed of 60 nm min-1 and a chart speed of 120 nm min-1 with the response set at 6 and the ordinate minimum and maximum settings of -0.05 and 0.05, respectively. The amplitude was measured in millimetres for both the standard and sample solutions. Procedures Compiiterised compensation method Measure the absorbances of the reference, A,,, and sample, A,,, solutions against the solvent from 230 to 290 nm at 2-nm intervals. Using the BASIC program (Fig. I ) , plot A,, against wavelength, i. Note the absorption characteristics of the sample solution. Select the variable, K , so that KA,, is about 0.5A,, at the wavelength of maximum absorbance.Plot AA, (= A,, - KA,,) against the wavelength. Continue changing K and plotting the difference curves until the characteristics of the peak for the substance to be determined disappear completely and the balance-point (end-point) is reached at K = K, . The calculations are performed as follows: atropine sulphate in injection solution (mg ml-1) = ephedrine hydrochloride (mg per tablet) = KCP x 0.080 x (10001100) K, X 0.060 X (average masdmass taken) X 1000 0.6 0.4 a, U C ru e 0.2 n Q cn 0 - _ _ _ _ - - - - - _ -0.2 , j 240 250 260 270 280 Wavelengthinm Fig. 2. (A) Absorption curve of atropine sulphatc injection solution; (B and C) the computed difference curves obtained by compensation; (Z) the balance-point; and (D and E) over-compensated difference curves nadolol (mg per tablet) = K, x 0.025 x (average massimass taken) x (100120) x 1000 Experimental compensation method Record the absorption curve of the sample solution against the solvent. Prepare a series of reference solutions (by appro- priate dilution of a suitable reference solution) starting with concentration differences of 10, 5 and 2 mg per cent.for atropine sulphate, ephedrine hydrochloride and nadolol. respectively, followed by a second series with concentration differences of 1, 1 and 0.5 mg per cent., respectively, near the balance-point. The concentration increments are selected to give effective difference curves when using the compensation technique. Reducing the increments does not lead to notice- able differences. Keeping the sample solution in the sample cell, fill the solvent cell with the reference solutions in succession starting with the most dilute reference solution and recording the difference absorption curve in each instance under the sample absorption curve.Follow the disappearance of the absorption characteristics of the substance to be determined by increasing the concentration of the reference solution, c,. Determine the exact balance-point at which the concentration of the substance in the sample solution is equal to that in the reference solution. Results and Discussion The compensated difference curves, AA,, can be regarded as being equal to A,, - KA,,, where A, and A, represent the absorbance of the sample and reference solutions, respect- ively, at a wavelength, i ; the value of K can be varied to reach the balance-point in the computerised compensation method.If the sample is as pure as the reference, then A,, - KA,, = 0 , i.e., the balance-point coincides with the wavelength scale. Fig. 1 shows a flow chart for the BASIC program used. Fig. 2 shows the difference curves obtained with the computerised compensation method for atropine sulphate in an injection solution. The peak characteristics decrease as K increases and finally disappear at the balance-point (end-point) where K = K , p . The curve obtained at the balance-point represents the absorption curve of the interferences present in the injection solution. This is not surprising because the atropine sulphate injection solution9 is a sterile solution of atropine sulphate in water (0.1%); the acidity of the solution is adjusted to pH 3. Owing to the relatively low molar absorptivity of atropine sulphate, the injection solution is measured without any further dilution.The additives used to adjust the pH of the solution are the source of the absorbing interferences.ANALYST. APRIL 1989, VOL. 114 507 Table 1. Spectrophotometric determination of atropine sulphate in an injection solution using the computerised compensation, experimental compensation and second-derivative UV methods Q) m 0.4 +? 8 2 0.2 0 -0.2 1 I I 230 240 250 260 270 Wavelengthhm Fig. 3. (A) Absorption curve of ephedrine hydrochloride \ample solution in 0.05 M sulphuric acid; (B and C) the computed difference curves obtained by compensation; ( Z ) the balance-point; and (D and E ) over-compensated difference curves 8 0.2 c m 11 L g o a 11 -0.2 -0.4 250 260 270 280 290 Wavelengthinm Fig.4. (A) Absorption curve of nadolol sample solution in 0.1 M hydrochloric acid; (B and C) the computed difference curves obtained by compensation; and (D and E) over-compensated difference curves. Note that the balance-point coincides with the wavelength axis A further increase in K so that it exceeds Kc.p. leads to an inversion of the pure compound's characteristic peak and results in over-compensated difference curves (Fig. 2). This last step is sometimes necessary to locate the balance-point accurately. Figs. 3 and 4 show the difference curves obtained with the computerised compensation method for ephedrine hydro- chloride and nadolol sample solutions, respectively.The curve obtained at the balance-point shown in Fig. 3 represents the unwanted absorption caused by tablet fillers and excipients. In the example shown in Fig. 4, the balance-point was found to coincide with the wavelength axis, indicating that the interfer- ence from tablet fillers and excipients was negligible owing to excessive dilution during the preparation of the final sample solution. In these instances, the absorption curves of the interferences are linear. Accordingly, they can be eliminated by recording derivative absorption curves7.10.11 and, in par- ticular, second-derivative spectra.7.8,' The computerised compensation, experimental compensa- tion and second-derivative spectrophotometric methods were applied to the determination of atropine sulphate in an injection solution and ephedrine hydrochloride and nadolol in tablets.The results obtained are shown in Tables 1, 2 and 3, respectively. In view of the fact that location of the balance- point is subjective and in order to eliminate any personal bias, Method Computerised Experimental co m pe n s a t i o n Experi- compensation ment No. K , * Found, Yo f c, , Yo $ Found. (Yo j- 1 1.24 99.2 0.100 100.0 2 1.25 100.0 0.101 101.0 3 1.25 100.0 0.100 100.0 4 1.25 100.0 0.101 101.0 K , = K at the balance-point. + Percentage of label claim (1 mg ml-1) found. ri: c, = reference concentration at the balance-point. Second derivative Found. '%t 100.4 100.6 100.1 - Table 2. Spectrophotometric determination of ephedrine hydrochloride in tablets using the computerised compensation.experimental compensation and second-derivative UV methods Method Computerised Experimental Second Experi- compensation cornpensation derivative ment No. K , Found. % ' c,/mg o/o Found, Yo* Found, % * 1 1.40 93.3 85 94.4 94.3 2 1.41 94.0 85 93.4 93.9 3 1.40 93.3 84 93.3 93.4 4 1.41 94.4 85 94.4 93.6 * Percentage of label claim (30 mg per tablet) found. Table 3. Spectrophotometric determination of nadolol in tablets using the computerised compensation. experimental compensation and second-derivative UV methods Method Computerised Experimental Second Experi- compensation compensation derivative ment No. K , , Found, cJmg Yo Found, o/o * Found. "/C, * 1 0.78 97.5 19.5 97.5 97.4 2 0.77 96.2 19.5 97.5 97.6 3 0.77 96.6 19.5 97.5 97.3 4 0.78 97.5 19.5 97.5 97.2 * Percentage of label claim (80 mg per tablet) found.four analysts determined the exact balance-point indepen- dently using both methods (i.e., computerised and experimen- tal compensation methods ) for the three compounds investi- gated. Each assay result was obtained by one analyst. With regard to precision, all the results were within ~ 1 % of each other and of their mean. Regarding the accuracy of the computerised and experimental compensation methods, the average percentage value found deviated from that obtained using the second-derivative method by less than 1%. This indicates that both compensation methods give precise and accurate results. However, the computerised method needs only two solutions, a reference and a sample solution.The final result is obtained on the plotter by applying the BASIC program. The repeatability of the computerised and experimental compensation methods cannot be evaluated from the results obtained by one analyst due to bias. Further comparative studies between the computerised and experimental compensation methods were carried out. Hence, the difference curves obtained mid-way through the compensation technique and at the balance-point for the three compounds were compared over the wavelength range used.508 ANALYST. APRIL 1989. VOL. 114 The differences between the experimental and computed difference curves were found to be negligible and only affected the third decimal place of the values obtained. This is further confirmation that the computerised version of the experimen- tal Compensation technique can be applied successfully to the determination of a single substance in the presence of unknown interferences.The proposed method is vercatile, fast and easily automated for routine analysis. Further, with the advent of modern spectrophotometers, which can be interfaced to a computer, the entire operation can be carried out with the minimum of time and effort. The procedure can be concidered to be a specfrophotometric titration technique for the determination of a single substance in the presence of interferences. Work is continuing to extend the method to two- and multi-component analyses. It should be noted that for successful application of the computerised method, the substance should obey Beer‘s law over the concentration range involved in the compensation process and it should not interact with the interferences present or with the solvent used.Adherence to Beer’s law can be tested by conventional means. Possible interaction between compounds can be checked by testing for the additive properties” of their absorbances. I . 2. 3 . 4. 3. 6. 7 . 8. 9. 10. 1 1 . 12. 13. References Jones. J . 1 1 . . Clark. G. R . , and Harrow, L. S . , J . A.ssoc. Ojy. Agric. (‘hem.. 1951, 34, 135. Schiaffino, S . S . , Loy, H. W., Kline, 0. I-., and Harroiv, L. S., J . Assoc. Off. Agric. Chcrn., 1956. 39. 180. , J . Ptiarm. Sci., 1961. 50, 693. . F.. Anal. Chrm., 1961, 33, 927. Goldring, L. S., Hawes, R. C., Hare, G. H . . Bcckman, A . 0.. anti Stickncy, M. E., Anal. Chrwz., 1953. 2 5 . 869. Loth i a t i , G . F . , “Absorption Spec t rop h o t o m e t ry . ’’ S e co ti d Edition, Hilger and Watts, London, 1958, p. 75. Davidson, A . G., and Elsheikh, H . , Analysi. 1982. 107, 879. Davidson, A . G . , and Hassan, S. M.. .I. Pharm. Sci., 1984. 73, 413. L‘United States Pharmacopeia XXl.” Twinbrook Parkway. Rockville, MD, 1985, p. 80. Wahbi, A. M.. and Ebel, S., Anal. Chirri. Actu. 1974, 70. 57. Fell, A . F.. Proc. Anal. Div. C‘hem. SOC.. 1978, 15, 260. Davidson, A . G . , and Hassan, S. M . , J . Pharrri. Phurmucol.. 1984, 36. 7 . Wahbi, A. M., and Barary. M., Anal. Lett., 1983. 16(A20), 1617. Puper 8101 H50F Received May I I th, I988 Accepted Decmzber 7th, I088

ISSN:0003-2654    

DOI:10.1039/AN9891400505

出版商:RSC    

年代:1989

数据来源: RSC

摘要:

509 Simultaneous Determination of Benzodiazepines by Ultraviolet - Visible Spectrophotornetry in Micellar Media M. de la Guardia, M. V. Galdu, J. Monzo and A. Salvador Departamenio de Quimica Analiiica, University of Valencia, C/Dr. Moliner 50, Burjassot 46700, Valencia, Spain A method for the simultaneous determination of benzodiazepines in binary mixtures is proposed, based on the acid hydrolysis of benzodiazepines to benzophenones and the spectrophotometric determination of the latter in the presence of Nemol K 1030, a non-ionic surfactant condensate of ethylene oxide with nonylphenol. The experimental conditions for the hydrolysis of several benzodiazepines in sealed Pyrex tubes were determined. The addition of Nemol K 1030 to acidic solutions of benzophenones modified the positions of the absorption bands and made possible the simultaneous analysis of binary mixtures of benzodiazepines.Keywords : Benzodiazepines; benzophenones; hydrolysis; surfactants; UV spectrophotometry Benzodiazepines are psychotherapeutic drugs widely used in the treatment of different nervous diseases such as anxiety, insomnia and epileptic convulsions, owing to the wide variety of the properties of the benzodiazepinic structure. 1-3 The therapeutic interest in these compounds justifies research to establish analytical methods for the determination of benzo- diazepines in pharmaceutical preparations and biological samples. Methods proposed for the determination of benzodiaze- pines include liquid chromatography,"5 polarography,h,7 atomic absorption spectrometry8 and molecular spectroscopic techniques such as f-luorimetryy.1(' and infrared" and UV - visible spectrophotometry.For the spectrophotometric determination of this type of compound either the benzodiazepine itself or the benzophe- none obtained by hydrolysis can be employed.12-13 Other methods involve the use of colour reagents that react with these compounds to form species that absorb in the visible region. 14.15 The acid hydrolysis of benzodiazepines to benzophenones has been reportedl.16 and used for the chromatographic determination of these compounds in biological matrices. The hydrolysis is carried out with hydrochloric acid at elevated temperature. One of the methods proposed for obtaining 5-chloro-2-(methylamino)benzophenone (CMAB)l7 involves the treatment of diazepam in stoppered tubes with 6~ hydrochloric for 1 h at 100°C in a boiling water-bath, but in the paper cited the experimental conditions of the hydrolysis reaction were not discussed.In this work we have extended the acid hydrolysis in closed tubes to a wide variety of benzophenones and studied the effect of various experimental conditions. Ultraviolet spectrophotometry is not a selective method because many benzodiazepines have very similar spectra. The use of organised media, such as micellar media, can improve the sensitivity and selectivity of spectrophotometric methods by providing hyperchromic and bathochromic shifts in the spectra of metallic complexes and organic molecules. 18-20 Previous work has demonstrated that the addition of anionic surfactants to solutions of some benzodiazepines in dilute sulphuric acid improves their spectrofluorimetric deter- mination.However, the increase in the fluorescence of benzodiazepines in micellar media is due to the increase in the fluorescence quantum yield without a simultaneous increase in the molecular absorption bands.21-22 In this paper, a method is proposed for the determination of benzodiazepines in binary mixtures based on their hydrolysis to benzophenones and the spectrophotometric determination of the latter in the presence of a non-ionic surfactant. Experimental Apparatus and Reagents A Shimadzu UVi240 UV - visible spectrophotometer equipped with 1-cm quartz cells and a PR-1 graphic printer was used for the absorbance measurements. Powdered samples of diazepam, oxazepam, potassium chlorazepate, temazepam, prazepam, nitrazepam, clonaze- pam and lorazepam were obtained from the Clinical Hospital, Madaus Cerafarm and the Bromatology Department of Valencia University.The following surfactants were used: sodium dodecyi sulphate (SDS) (Fluka), cetyltrimethylammonium bromide (CTAB) (Merck), Descoxid 728, a fatty acid condensate with ethylene oxide (Tensia Surfac), Nemol K 539, 1030 and 1032 condensates of ethylene oxide with nonylphenol and Genapol PF 80 condensate of ethylene oxide and propylene oxide (Hoestch Iberica) and Triton X-100 condensate of tert-octyl- phenol with ethylene oxide (Probus). Hydrolysis of Benzodiazepines Solutions containing 125 pg of diazepam or oxazepam in dilute hydrochloric acid (1 + 1) were used to study the conditions for the hydrolysis of benzodiazepines to benzophenones.Experimental parameters such as temperature, time and acid volume were modified using sealed Pyrex tubes to carry out this reaction in all instances. The recommended procedure consists of placing 1 4 ml of the solution of a benzodiazepine or mixtures of benzodiaze- pines in 6 M hydrochloric acid in a 15-ml Pyrex tube. The tube is hermetically sealed and allowed to stand in an oven at 100-120 "C for 1-1.5 h, allowed to cool and then the contents are diluted to an appropriate volume. Diazepam and oxazepam have strong absorption bands at 240 and 235 nm, respectively, and two other common bands at 285 and 360 nm. The related benzophenones CMAB and 2-amino-5-chlorobenzophenone (ACB) both have a maxi- mum absorbance at 260 nm (see Fig.2 ) . The hydrolysis reaction was monitored by spectrophotometric measurements in the UV region. Determination in the Presence of Surfactants A series of cationic, anionic and non-ionic surfactants were added to the CMAB solutions obtained after hydrolysis of different amounts of diazepam. Calibration graphs in the ultraviolet range were obtained in both the presence and absence of surfactants to determine the effect on the intensityAKALYST, APRIL 1989, VOL. 114 A A 250 3CO 350 400 C 250 300 350 400 hln m Ultraviolet - visible spectra of diazepam, oxazepam and their related benzophenones. Spectra were obtained for 5 p.p.m. solutions of (A) diaze am and (C) oxazepam and the correspondin benzo- phenones, 6) 5-chloro-2-(methylamino)benzophenone (SCMAB) and (D) 2-amino-5-chlorobenzophenone (ACB) and shift of the absorption bands.A 1% surfactant concentra- tion was used in all instances except for solutions of CTAB, for which a 0.05% solution was used owing to its low solubility. Simultaneous Analysis of Mixtures of Benzodiazepines Binary mixtures of benzodiazepines were hydrdysed using the experimental conditions determined previously and the UV spectra recorded in the presence of 1% Nemol K 1030. The absorbance values at the maximum absorbance wavelengths of each benzodiazepine make it possible to determine the concentration of each compound in the mixture using the experimental data obtained for solutions containing only one of the compounds concerned and solving simultaneous equa- tions.Results and Discussion Hydrolysis of Benzodiazepines When samples of diazepam or oxazepam are heated in an oven for 1 h with 1 ml of 6 M hydrochloric acid in pressurised Pyrex vessels, the absorbance of the bands corresponding to benzophenones (260 nm) increases and the absorbance of those of the benzodiazepines (240 and 235 nm) decreases as the temperature is increased. At temptratures higher than 100 "C a constant absorbance was obtained in both instances (see Fig. 2). Using this temperature, the absorbance of the benzophenones obtained by hydrolysis of diazepam and oxazepam increases as the digestion time increases. For a time shorter than 1 h the hydrolysis is not complete, but for longer times the absorbance values remain constant (Fig.3). A volume of 6~ hydrochloric acid greater than 0.75 mi is required for the hydrolysis of diazepam and oxazepam under the previously determined conditions, as can be seen in Fig. 4. Spectroscopic Characteristics of Benzophenones Using the experimental conditions determined previously, the hydrolysis of a series of benzodiazepines was carried out and the following benzophenones were obtained: CMAB from diazepam and temazepam, ACB from oxazepam and potas- sium chlorazepate, 2-amino-S,2'-dichlorobenzophenone (ADCB) from lorazepam, S-chloro-2-(cyclopropylmethyl- amino)benzophenone (CCMB) from prazepam, 2-amino-5- nitrobenzophenone (ANB) from nitrazepam and 2-amino-2'- chloro-5-nitrobenzophenone (ACNB) from clonazepam. The corresponding absorbance maxima and molar absorptivities are given in Table 1.These data indicate the existence of strong overlapping of the absorption bands corresponding to 0.4 - a c 4 0.3 - n Q: $ 0.2 - 0.1 ' I I 20 60 100 140 50 80 110 140 TemperaturePC Fig. 2. Effect of temperature on the acid hydrolysis of diazepam and oxazepam. (a) (U) Absorbance at 240 nm and (@) absorbance at 260 nm of a 5 p.p.m. solution of diazepam after treatment for 1 h with 1 ml of 6~ hydrochloric acid, ( b ) (m) Absorbance at 235 nm and (@) absorbance at 260 nm of a 5 p.p.m. solution of oxazepam treated for 1 h with 1 ml of 6~ hydrochloric acid at different temperatures 0.4 a 0.3 2 2 0.2 I , I I I 0.1 ' 15 ' 45 75 105 15 45 75 105 Timeimi n Fig. 3. Effect of time o n the hydrolysis of diazepam and oxazepam. (a) (M) Absorbance at 240 nm and (@) absorbance at 260 nm of a 5 p.p.m. solution of diazepam after treatment at 100 "C with 1 ml of 6 M hydrochloric acid.( b ) (U) Absorbance at 235 nm and (0) absorbance at 260 nm of a 5 p.p.m. solution of oxazepam after treatment at 100°C with 1 ml of 6~ hydrochloric acid I I I 0 0.5 1 0 1 2 0.1 I VHcliml Fig. 4. Effect of the volume of hydrochloric acid used on the hydro1 sis of diazepam and oxazepam. (a) (H) hbsorbancc at 240 nm and (d) absorbance at 260 nm of a 5 p,p.m. solution of diazepam treated at 100 "C for 1 h with different amounts of hydrochloric acid. (b) (M) Absorbance at 235 nm and (@) absorbance at 260 nm of a 5 p.p.m. solution of oxazepam treated at 100 "C for 1 h with different volumes of 6 M hydrochloric acid the different benzodiazepines, which makes their differentia- tion difficult. Determination of Beozophenone in Micellar Media Calibration graphs for C,MAB in both the absence and presence of different surfactants were obtained.Table 2 gives the equations corresponding to the systems studied. It can be seen that the absorbance maximum at 260 nm is little affected by the addition of anionic, cationic or non-ionic surfactants. However, when a caticnic surfactant such as CTAB or a non-ionic ethylene oxide condensate was added to CMAB solution, a new absorbance band appeared at 415 nm, which makes possible a more selective determination of this benzo- phenone. The addition of Nemol K 1030 to the different benzophe- nones provides a bathochromic shift of the UV bands except for ANB and ANCB, in all instances good linearity of the Cali bration lines corresponding to each of the benzopheno- nones being obtained (Table 3).ANALYST, APRIL 1989, VOL.114 511 Table 1. Spectroscopic characteristics of benzophenones Benzophenone hrn.3, h m CMAB . . . . . . 260 ACB . . . . . . . . 25 8 ADCB . . . . . . . . 2.50 CCMB . . . . . . . . 260 ANB . . . . . . . . 240 365 ACNB . . . . . . . . 250 355 &/moll-1 cm I 11 100 k 300 10300 k 100 10 100 k 100 10200 k 100 13 800 f 100 14800 k 100 11 600 t 100 10200 k 100 Table 2. Effect of addition of surfactants on the spectrophotometric determination of diazepam as CMAB Concen- Regression tration, Calibration coefficient Surfactan t Yo graph* ( r ) None . . . . . . - = 11.057C + 0.02 0.99995 SDS .. . . . . 1 A,,, = 10.565C + 0.01 0.99995 A 4 1 5 = 1.819C - 0.001 0.99995 CTAB . . . . . . 0.05 A,,, = 11 .S48C - 0.05 0.999995 Nemol K 1030 . . 1 AdI5 = 3.931C + 0.006 0.999995 Genapol PF80 . . 1 A260 = 10.811C + 0.01 0.999995 * A = absorbance; C = concentration in mmol 1 - 1 . Table 3. Influence of Nemol K 1030 micelles on the spectrophotometric determination of benzophenoncs Benzo- Calibration graph Calibration graph Ah/ phenone in acidic media" in micellar media* nm CMAB . . A,,,) = 11.057C + 0.008 (Y = 0.99995) ( r = 0.9995) ACB . . A 2 5 8 = 10.161C + 0.020 ADCB . . AZsn = 10.13SC + 0.020 ( r = 0.99995) (Y = 0.99995) CCMB . . A260 = 10.093C + 0.006 ANB . . A T 6 5 = 14.774C-0.004 (Y = 0.99995) ( r = 0.99995) ACNB . . A 3 5 5 = 10.238C-t 0.003 A420 = 4.361C + 0.004 A190 = 2.540C + 0.009 ( r = 0.995) ( r = 0.9995) ( r = 0.99995) A,,,) = 14.S32C + 0.01 1 + 160 +I32 ( r = 0.9995) A395 = 4.179C - 0.003 + 145 A410 = 4.658C - 0.003 +I50 -5 = 12.17SC + 0.011 0 (Y = 0.999995) ( r = 0.999995) * A = absorbance; C = concentration in mmol 1 - 1 .The new bands obtained in acidic micellar media are the same as those obtained in absolute ethanol, which indicates that the micellar microenvironment has similar characteristics to alcohols. In the micellar media the absorbance bands of some of the benzophenones derived from different benzo- diazepines differ significantly, in contrast to the benzodiaze- pine and benzophenone spectra obtained in acidic media, hence allowing the selective determination of these com- pounds in binary mixtures and the determination of diazepam and its metabolites.Analysis of Mixtures of Benzodiazepines It can be see in Fig. 1 that diazepam and oxazepani have very 4 .? 3 400 450 500 J 5 0 A/n m Fig. 5 . Absorption spectra of CMAB and ACB in acidic and micellar media. (a) Absorption spectra of (1) 5 p.p.m. of CMAB; (2) 5 p.p.m. of ACB; and (3) a mixture of 5 p.p.m. of both CMAB and ACB. ( b ) Absorption spectra in the presence of 1% Nemol K1030 for (4) 10 p.p.m. of CMAB; ( 5 ) 10 p.p.m. of ACB; and (6) a mixture of 5 p.p.m. of both CMAB and ACB Table 4. Analysis of binary mixtures of benzodiazepines. Concentrations in p.p.m. Compound Present Oxazepam . . . . . . . . 2.62 5.24 2.62 1.31 5.24 1.37 2.74 5.48 Diazepam . . . . . . . . 1.23 2.46 1.23 4.92 1.23 2.46 1.23 4.92 Diazepam .. . . 1.23 2.46 1.23 4.92 1.25 2.50 1.25 5.00 Found 2.72 5.66 2.88 1.10 5.97 1.36 2.99 6.02 1.32 2.62 1.31 5.20 1.30 2.51 1.10 5.10 1.28 2.71 1.18 5.22 1.34 2.73 1.40 5.33 Relative difference, Yo Compound -3.8 Diazepam . . . . -8.02 -9.9 + 16.03 - 13.9 +0.7 -9.1 -9.8 -7.3 Chlorazepate . . -6.5 -6.5 -5.7 -5.7 -2.03 + 10.6 -3.7 -4.1 Lorazepam . . - 10.2 +4.1 -6.1 -7.2 -9.2 - 12.0 -6.6 Present . . . 2.70 1.35 2.62 5.24 1.31 2.82 2.82 1.41 . . , 2.54 2.54 5.08 1.27 2.46 2.46 4.92 1.23 . . 2.60 2.60 5.20 1.30 2.60 2.60 5.20 1.30 Found 2.92 1.35 2.62 5.29 1.41 2.96 2.97 1.44 2.70 2.54 5.15 1.14 2.60 2.66 5.41 1.32 2.91 2.44 5.30 1.30 2.59 2.39 5.02 1.20 Relative difference, O/* -8.1 0 0 -0.95 -7.6 -5.0 -5.3 -2.1 -6.3 0 -1.4 + 10.2 -5.7 -8.1 - 10.0 -7.3 -11.9 +6.2 -1.9 0 +0.4 +8.1 +3.5 +7.7512 ANALYST, APRIL 1989, VOL.114 similar absorption spectra in the UV - visible region. The spectra of CMAB and ACB are also very similar and as a consequence it is not easy to determine the individual compounds in a mixture of the two [Fig. 5(a)]. However, when Nemol K 1030 is added to the benzophenone solutions the absorption spectra of the two benzophenones differ substan- tially and the binary mixture could be resolved by solving a conventional system of simultaneous equations [Fig. 5(b)]. The same situation occurs for mixtures of diazepam and lorazepam and diazepam and potassium chlorazepate (see Table 3). Hence the simultaneous determination of these benzodiazepines in binary mixtures was carried out by measuring the absorbance at the maximum absorption wavelength for each compound in micellar media after hydrolysis to the corresponding benzophenone.Table 4 summarises the results obtained and the relative differences between the concentrations found and added. References 1. 2. 3. 4. 5. Schutz, H., “Benzodiazepines,” Springer, New York, 1982. Daudon, M., Pharm. Biol., 1977, 11, 389. Civera, J., Master Thesis, University of Valenica, 1982. Mehta, A. C., Tafanta, 1984, 31, 1. de Silva, J. A. F., and Puglisi, C. V., in Garrett, E. R., and Hirtz, J. L., Editors, “Drug Fate and Metabolism,” Volume 4, Marcel Dekker, New York, 1963, p. 245. 6. Barrett, J., Smyth, W. F., and Hart, J. P., J . Pharm. Pharmacol., 1974, 26, 9. 7. Oelschager, H., Biolectrochem. Bioenerg., 1983, 10, 25. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. Gonzalez-Pdrez, C., Gonzilez-Martin, M. J., Herniindez- Mendez, J., and Recio-Robuster, R., Qiiim. Anal., 1986, 5 , 420. Gifford, L. A., Miller, J. N., Bridges, J. W., and Burns, D. T., Talanta, 1977, 24, 273. Rodriguez Procopio, J., Hernandez Hernandez, P., and Hernandez Hernandez, L., Analyst, 1987, 112, 79. Taylor, N. F., Jr., and Randall, J., J. Assoc. Off. Anal. Chem., 1979, 62, 799. Giusiani, M., Poggi, G., and Martinelli, G., Riv. Ztal. Zg., 1981, 41, 258. Seitzinger, R. W. T., Pharma. Weekbl., 1975, 110, 1073. Stevens, H. M., J . Forensic Sci. SOC., 1978, 18, 69. Fernandes-Magalhaes, J., and Gisela Pirds, M., Rev. Brasil. Farm., 1970, 195. Lafargue, P., Meunier, J., and Lemontey, Y., J . Chrumutogr., 1971,62,423. de Silva, J. A. F., Schartz, M. A., Stefanovic, V., Japlan, J., and d’Arconte, L., Anal. Chem., 1964, 36, 2099. Hinze, W. L., in Mittal, K. L., Editor, “Solution Chemistry of Surfactants,” Volume 1, Plenum Press, New York, 1979, p. 79. Pelizzetti, E., and Pramauro, E., Anal. Chim. Acta, 1985,169, 1. Cline Love, L. J . , Habarta, J. G., and Dorsey, J. G., Anal. Chem., 1984, 56, 1133A. de la Guardia, M., and Rodilla, F., J. Mol. Struct., 1986, 143, 493. Rodilla, F., Master Thesis, University of Valencia, 1986. Paper 8/02 781 A Received July 11 th, 1988 Accepted November 2nd, 1988

ISSN:0003-2654    

DOI:10.1039/AN9891400509

出版商:RSC    

年代:1989

数据来源: RSC

摘要:

ANALYST. APRIL 1989, VOL. 113 513 Extractive Spectrophotometric Determination of Some Anti-inflammatory Agents with Methylene Violet C. S. P. Sastry, A. S. R. Prasad Tipirneni and M. V. Suryanarayana Foods and Drugs Laboratory, School of Chemistry, Andhra University, Waltair 530 003, India A fairly sensitive spectrophotometric method for the determination of ibuprofen, ketoprofen, piroxicam, diclofenac sodium, mefenamic acid or enfenamic acid in bulk samples and pharmaceutical preparations is described, based on the formation of a chloroform-solu ble, coloured ion-association complex between the drug and Methylene Violet a t pH 7.6. Keywords: Anti-inflammatory agents determination; extractive spectrophotometry; Meth ylene Violet Many of the reported visible spectrophotometric methods for the determination of anti-inflammatory agents such as ibu- profen (IB).] ketoprofen (KT),2.3 piroxicam (PX),".' diclo- fenac sodium (DS),b mefenamic acid (MA)'-9 and enfenamic acid (EA)lO suffer from lack of sensitivity or simplicity.In contrast, the extractive spectrophotometric technique pro- vides a highly sensitive method for the determination of pharmaceuticals." This technique has not yet been used for the determination of these drugs with the exception of MA.9 CH3 I CH-COOH R' -3 COOR' / I MV NH2 As the six anti-inflammatory agents studied in this work are acidic in nature, attempts were made to utilise the basic dye Methylene Violet (MV; CI No. 50210) for their extractive spectrophotometric determination. Experimental Apparatus A Systronics Model 105 (MK 1) spectrophotometer with 1-cm matched glass cells was used for all absorbance measurements.All pH measurements were made with an Elico Model LI-120 digital pH meter. Reagents All chemicals were of analytical-reagent grade. Buffer solution (PH 7.6). Prepared by mixing 88.5 ml of 0.067 M disodium hydrogen phosphate solution and 11.5 ml of 0.067 M potassium dihydrogen phosphate solution. Methylene Violet, 0.068% mlV (1.95 x 10-3 M) solirtion. Prepared in buffer solution. Standard drug solutions. Stock solutions containing 500 pg ml-1 of the anti-inflammatory agents were prepared by dissolving 50 mg of each drug separately in the minimum volume of 0.1 M sodium hydroxide solution and diluting to 100 ml with distilled water. Working standard solutions were prepared as required (IB, 100 pg ml-1; KT, 50 pg ml-1; PX and EA, 40 pg ml-1; and DS and MA, 20 pg ml-1) by suitable dilution of the stock solutions with distilled water.Procedure Aliquots of the standard drug solution (0.5-3.0 ml for IB or PX; and 0.5-4.0 ml for KT, EA, MA or DS) were transferred into a series of 125-ml separating funnels and then 8 ml of buffer (pH 7.6) and 1 ml of MV solution were added to each separating funnel. The total volume of the aqueous phase was adjusted to 15 ml by the addition of distilled water. Chloro- form (10 ml) was added to each separating funnel and the contents were shaken for exactly 1 min. The absorbance of the separated chloroform layer was measured at 540 nm against a reagent blank. The amount of each drug present was calculated from its calibration graph.Procedure for the assay of dosage forms An amount of the tablet powder, capsule powder or suspen- sion equivalent to 50 mg of the anti-inflammatory agent was weighed accurately (or measured) and treated as described above for the standard drug solution. Filtration was per- formed in instances where insoluble matter remained during preparation of the sample solutions.5 14 ANALYST, APRIL 1989. VOL. 114 Results and Discussion Figs. 1 and 2 show the absorption spectra of the MV - anti-inflammatory agent ion-association complexes extracted into chloroform and of the reagent blank. All these spectra have an absorption maximum at 540 nm, hence this wavelength was used for all subsequent measurements. In order to establish the optimum pH range, each anti- inflammatory agent was allowed to react with MV in aqueous solutions buffered to pH 6.C8.0 and the complex formed was extracted into chloroform for measurement.Constant ab- sorbances were obtained over the pH range 7.4-8.0 in phosphate buffer. Hence a pH of 7.6 was used in all subsequent work. The extent of the extraction of the ion-association complex was found to be affected by the concentration of MV used. To establish the optimum amount, 1-ml aliquots of 3.5 X 10--4-2.8 x l o - 3 ~ MV solutions were used under the conditions given above. The calibration graphs obtained using 1 ml of a 3.5 x 10-4 or 7.1 x 1 0 - 4 ~ solution were not linear, although the reagent bianks had low absorbances. The graphs obtained with 9.2 x 10-4-2.8 x 1 0 - 3 ~ MV solutions were linear, but the use of more MV resulted in higher absorbances for the reagent blanks.In subsequent work 1 ml of a 1.95 X 1 0 - 3 ~ MV solution was employed. Other organic solvents were tested. but chloroform was found to be the most suitable. Shaking times of 0.5-4 min produced a constant absorb- ance, hence a shaking time of 1 min was used throughout. The zbsorbances of the separated extracts were stable for more than 1 h; some data are presented in Table 1. Regression plots showed that there was a linear dependence of absorbance on concentration over the Beer’s law ranges given in Table 1. The optimum conditions were those used in the procedure. The molar absorptivities, slopes, intercepts and correlation coefficients obtained by a linear least-squares 400 440 480 520 560 600 Wavelengthinm Fig.1. Absorption spectra of (A) MV - DS; (B) MV - MA; and ‘C) MV - EA systems. [MV] = 1.95 x 10-3; DS] = 6.2 x 10 h ; [MA) = 8.2 x 10-6: and [EA] = 1.65 x 1 0 ~ ~ ~ . [D) Reagent blank treatment of the results are also given in Table 1. The precision of the method was tested by analysing six replicate samples of each anti-inflammatory agent (60 yg of DS or MA; 100 yg of EA; 150 yg of KT; 200 pg of IB; and 80 pg of PX); the relative standard deviation and range of error obtained are given in Table 1. The stoicheiometric ratio of drug to MV in each of the coloured complexes was determined using the slope-ratio method.12 It is apparent from the data that ion-association complexes with varying drug to dye ratios (2 : 1 for IB, PX, DS, MA or EA; and 1 : 1 for KT) are formed by the reaction of these drugs with MV.Other components normally found in combination with anti-inflammatory agents, such as paracetamol (PT), diaze- pam (DI) and dextropropoxyphene hydrochloride (DP), and commonly used excipients, diluents and acidic analytes (e.g., benzoic acid, ascorbic acid, and citric acid) do not interfere with the proposed method even when present in a ten-fold excess. Some pharmaceutical dosage forms were analysed by both the proposed and official methods (DS, as for sodium benzoate,13 viz., titration with hydrochloric acid using Bromo- phenol Blue as indicator; MA, titration with sodium hydrox- ide solution using Phenol Red as indicator”; EA, a visible spectrophotometric method using sodium nitroprusside and hydroxylamine hydrochloridelfl; PX, a UV spectrophoto- metric methods; IB, titration with sodium hydroxide solution using phenolphthalein as indicator14; and KT, a UV spectro- photometric method13) (Table 2) in order to confirm the accuracy of the proposed method for the determination of the six anti-inflammatory agents. As can be seen from Table 2 the proposed method has the advantage of being virtually free from interferences; it may, therefore, be of value for the determination of trace amounts of anti-inflammatory agents in other samples.0.6 a, 0.4 -e :: Q 0.2 0 ([I a t 0 400 440 480 520 560 600 Wavelengthhm Fig. 2. MV - KT systems. [MV] = 1.95 X l(1-3; [IB] = 4.84 X 1.96 X 10-5; and [PX] = 1.2 X 10-SM. (D) Reagent blank Absorption spectra of (A) MV - IB; (B) MV - PX; and C) [KT\ = Table 1.Optical characteristics and precision data IB KT PX DS MA EA Beer’slawlimits/ugml-l . . . . Molar absorptivityil mol-1 cm--’ Sandell’s sensitivity/ pgcm-2per0.001A . . . . Correlationcoefficient . . . . Regression equation (A)* Slope ( b ) . . . . . , . . Intercept(a) . . . . . . Relative standard deviation, Yo Range of error (95% confidence limit). % . . . . . . . . Stability of drug - dye complexih . . 5-30 . . 4.74 x 103 . . 0.044 . . 0.9999 . . 2 . 2 8 9 ~ 10- . . 2.0 x 10-3 . . 1.20 k1.23 1 2.5-20 2-12 1-8 1-8 2-16 6.10 x 10’ 1.72 x 104 3.10 x 104 2.29 x 104 9.64 x 103 0.042 0.019 0.01 0.01 1 0.025 0.9997 0.9998 0.9999 0.9999 0.9998 * 2.365 X 10 2 5.186 x 10-2 9.912 x lop2 9.45 x 10-2 3.941 x 10-2 5.196 x 10 5.333 x 10-3 5.196 x lo-’ 3.119 x lo-’ 3.873 x 10-3 1.38 1.18 1.30 1.37 1.08 k1.42 L1.21 i1.34 21.41 k1.11 2 6 4 4 4 * A = u + bc, where c is the concentration in pg m1-I.ANALYST, APRIL 1989, VOL.114 515 Table 2. Determination of anti-inflammatory agents in pharmaceutical preparations using the proposed and reference methods Composition of Amount foundimg pharmaceutical preparation/ Labelled amount/ Recovery, “10 Sample mg mg Proposed method Reference method* (proposed method)t Tablets- S1 , . . . IB200 200 192.8 194.6 99.6 S2 . . . . IB400 400 386.6 389.3 99.4 S3 . . . . IB600 600 582.0 585.7 99.8 S4 . . . . IB400,PT325 400 388.6 390.2 99.6 S5 . . . . IB400,PT325,DI2 400 389.4 391.3 99.5 S6 . . . . IB 200, PT 250, D P 32.5 200 194.7 196.0 99.9 s7 .. . . PX10 10 9.8 9.9 99.8 S8 . . . , PX20 20 19.2 19.3 99.6 S9 . . . . DS25 25 24.3 24.4 99.7 S10 . . . DS50 50 48.3 48.6 99.3 S11 . . . . MA250,PT250 250 246.6 247.5 99.7 S12 . . . . EAS00,PT500 500 484.3 486.9 99.6 S13 . . . . EA300 400 389.7 391.3 99.5 S13 . . . . IB200 200 192.4 193.2 99.4 S15 . . . . IB300 300 291.6 292.4 99.8 S16 . . . . IB400 400 388.7 390.2 99.7 S17 . . . . IB200, DP32.5 200 192.5 193.2 99.9 S18 . . . . IB400,DP65 400 384.8 386.3 99.8 S19 , . . . KTSO 50 48.6 48.7 99.9 S20 . . . . KT100 100 96.4 96.7 99.8 S21 . . . . KT50, PT500 50 47.7 47.9 99.6 s22 . . . . PX10 10 9.80 9.84 99.7 S23 . . . . PX20 20 19.3 19.4 99.8 S23 . , . . MA50 50 48.6 48.9 99.4 S25 . . . , MA250 250 242.8 244.1 99.9 S26 . . . . MA500,PT500 500 486.7 488.8 99.6 S27 .. . . MA500,D12 500 484.6 487.2 99.2 S28 . . . . IB50ml 100 98.4 99.1 99.6 S29 . . . . MA50ml 10 9.86 9.89 99.9 f After adding 10 mg; each value is the average of three replicate determinations. Capsules- Susperzsion (mg ml-1)- Reference methods: BPI1 for DS, MA and KT; IPl4 for IB; Guoguanys for PX; and Sastry and RaoI0 for EA. The proposed procedure is simple, sensitive, rapid, precise and accurate compared with many of the reported methods and can be used for the routine determination of anti- inflammatory agents in their dosage forms. 7. 8. 9. Khier, A. A . , El-Sadek, M.. and Baraka, M., Analyst, 1987, 112, 1399. Hassib, S. T., Safwat, H. M., and El-Bagry, R . I., Egypt. J. Pharm. Sci., 1987, 28 (1-4), 203. Issa, A. S . , Beltagy, Y.A . , Gabr Kassem, M., and Daabees, The authors thank the Quality Control Managers of Torrent Pharmaceuticals, India. and Unichem Laboratories, India, for providing the reference samples and the UGC, New Delhi, for the award of a Junior Research Fellow to one of us (A. S. R. P. T.). References 1. Matsuda. R., Takeda, Y . , Ishibashi, M., Vchiyama. M., Suzuki. M., and Takitami, S . , Bunseki Kagaku, 1986,35, 151. 2. Vachek. J., Cesk. Furm., 1987, 36, 168. 3. Emmanuel, J . , and Fernandes. N. N . , East. Pharm.. 1988, 31, 366. 139. 4. Sastry, C. S. P., Prasad Tipirneni. A. S. R . , Suryanarayana, M. V., and Prasad, T. N . V., East. Pharm., 1988,31,367,131. 5. Guoguany. P., Yayao Gongge, 1985, 16. 248. 6. Agarwal, Y. K., Upadhyay, V. P., and Menon, S. K., Indian J . Pharm. Sci., 1988, 50, 58. H. G . , Talanta, 1%5, 32, 209. Sastry, C. S . P., and Rao, A. R. M., Indian Drugs, 1987, 24, 303. Das Gupta, V., Indian J. Pharm., 1973, 35, 77. Irving, H., Rossotti, F. J . C., and Williams, R. J . P.. J. Chem. Soc., 1955, 1906. “British Pharmacopoeia 1980,” HM Stationery Office. Lon- don, 1980, DS: p. 406; and MA: p. 273; Addendum 1983, KT: p. 130. “Pharmacopoeia of India,” Ministry of Health and Family Welfare. Government of India, New Delhi, 1985, IB: p. 251. 10. 11. 12. 13. 14. Paper 8103770A Received September 26th, 1988 Accepted November 23rd, I988

ISSN:0003-2654    

DOI:10.1039/AN9891400513

出版商:RSC    

年代:1989

数据来源: RSC

摘要:

ANALYST. APRIL 1989. VOL. 114 517 SHORT PAPERS p-Anisaldehyde Thiosemicarbazone: a Reagent for the Polarographic Determination of Platinum(l1) Rasappan Palaniappan and Vedachalam Revathy Department of Analytical Chemistry, University of Madras, Guindy Campus, Madras 600 025, India p-Anisaldehyde thiosemicarbazone (PATSC) is proposed as a reagent for the rapid, relatively sensitive and selective determination of platinum(1l) in the approximate range 0.05-8.0 mM by d.c. polarography. This reagent quantitatively formed a yellow complex with platinum(l1) in 0.1-0.25 M HCI medium, which yielded a reversible, diffusion-controlled, two-electron reduction wave. Various polarographic parameters for the quantitative determination have been studied and the reliability of the method has been checked by statistical analysis.The senstivity of the method was increased approximately ten-fold by employing differential-pulse polarog ra p hy. Keywords : p -A nisalde h yde thiosem ica rbazo n e; pla tin urn (11); pola rograp h y Thiosemicarbazones have aroused special interest in the fields of medicinal and analytical chemistry. 1-3 These compounds act as complexing agents for various metal ions. Recently, several analytical applications of thiosemicarbazones in com- plexometric, gravimetric, spectrophotometric, fluorimetric, potentiometric and polarographic studies of many metal ions, especially the platinum group elements, have been reported.49 This work was undertaken with the objective of evolving a new method of analysing very dilute solutions of platinum as only a few sensitive methods10." have been reported.The proposed method was found to be highly selective, as the analysis was carried out at relatively low pH; interferences from other ions were, therefore, found to be a minimum. Experimental Analytical-reagent grade chemicals and doubly distilled water were used. Anhydrous PtC1, (Arora Metthey, India) was used as the source compound. Each 100-ml stock solution (ca. 0.01 hi) contained 4 ml of 4 M hydrochloric acid and was standardised as described in the literature.12 The stock solution (ca. 0 . 0 1 ~ ) was diluted further to the relevant concentration of platinum(I1) as required. For the study of interferences, other noble metal solutions such as palladium(II), rhodium(III), ruthenium(II1) and iridium(II1) in 2~ HC1 were freshly prepared as stock solutions from analytical-reagent grade salts PdCl2, RhC13.3H20, RuC13.3H20 and IrC13.3H20 (Arora Metthey) respectively. The solution of palladium( TI) was standardised gravimetric- ally by precipitation with dimethylglyoxime.13 The rho- dium( 111) solution was also standardised gravimetrically by precipitation as the sulphide, followed by ignition to the oxide and then reduction to the metal in the presence of hydrogen.13 The iridium(II1) solution was standardised using 2-mercap- tobenzothiazole and the ruthenium(II1) solution by spectro- photometry with thionalide. 12313 Osmium tetraoxide (Merck), weighed carefully in an ampoule, was dissolved in 0 . 5 ~ NaOH. neutralised with acid and diluted to a known volume, before being standardised by titrimetry.13 y-Anisaldehyde thiosemicarbazone (PATSC, m.p. 175 "C) was prepared according to Sah and Daniels.14 For polarographic work, a 50-fold excess of concentration of ligand over metal was used to ensure complete complexation. Potassium chloride (0.2 M) was used as supporting electrolyte. All d.c. polarographic experiments were carried out at a dropping-mercury electrode (DME) referenced to a saturated calomel electrode (SCE) using a Model CL-25D (Elico, India) automatic instrument. Polarograms were recorded at 25 k 0.5"C and purified nitrogen was used for de-aeration. The capillary characteristics in 0.2 M KC1 (open circuit) were as follows: mass flow of Hg, m = 2.72 mg s-1; drop time, t = 2.89 s at a mercury column height of 40 cm; m t = 2.3260 mg s-f.Differential-pulse polarograms were recorded using a Model CL-90 (Elico) instrument. The electrode system used was a DME working electrode, an SCE reference electrode and a platinum counter electrode. The pH was measured using an Elico digital pH meter (Model LI-120). Results and Discussion Polarogram of Platinum(I1) in the Presence of PATSC In highly acidic medium ( 0 . 6 ~ HCl), Pt" and PATSC in the presence of 0 . 2 ~ KC1 produced a wave with E+ = 0.006 V versus SCE. Simultaneously a black deposit was observed on the pool of mercury. This deposit may be due to incomplete complexation between Pt" and PATSC. By virtue of the positions of Hg and Pt in the e.m.f. series the chemical reaction (1) preceded the electrode reaction (2).15.16 The oxidised Hg22+ underwent cathodic reduction at Et = +0.006 V versus SCE.. . (1) Pt" + 2 Hg -+ PtO (black deposit) + Hg22+ . . . . (2) 0.25 0.75 1.25 - E N versus SCE Fig. 1. Polarograms of the Pt" - PATSC system. A, 50 mM PATSC in 0.2 M KCl + 0.2 M HCl; B. 1.4 mM Pt" + 50 mM PATSC + 0.2 M KCl + 0.6 M HCl; C, as B but in 0.4 M HCl; D, as B but in 0.2 M HCI518 ANALYST, APRIL 1989, VOL. 114 When the total acid concentration in the solution exceeded 0.25 M, the reduction wave for mercury(1) appeared resulting in an apparent two-wave pattern (reduction of Hg22+ and Pt" complex) (Fig. 1). Characteristics of the Polarographic Wave A single well defined wave was obtained at Et = -0.430 V versus SCE in the acid (HC1) concentration range 0.25-0.1 M (Fig.1). When the concentration of HCl decreased from 0.6 to 0.2 M the wave shifted to more negative potentials indicating complex formation of higher stability. The limiting current value remained almost constant within 0.25-0.1 M HC1 and thereafter progressively decreased. The reduction wave was found to be diffusion controlled [constant id/V%-; h , mercury column height (cm)] and reversible [plots of log(ilid - i) versus EDME were linear with a slope = 0.029 k 0.002 V] involving a two-electron transfer electrode process. Exhaustive con- trolled potential electrolysis in the limiting current region of the wave (-0.600 V versus SCE) at 0.13 M HCl gave a value of 2 for n. the number of electrons involved in the electrode reaction, providing further support to the two-electron electrode process.The electrode reaction rate constant ( k f " ) was evaluated at optimum experimental conditions and found to be 1.06 x 10-2 s-1; the diffusion current constant and the diffusion coefficient were calculated as 3.382 and 7.66 X 10-6 cm2 s-1, respectively. Analytical Applications and Sensitivity of the Method The polarographic curves were found to be analytically useful in the HCI concentration range 0.1-0.25 M for accurately determining Pt" in solutions in the range 8-0.05 mM (error <1%); even a 0.025 mM solution could be determined with an error of ca. 3%. The interferences of diverse ions were also studied. Of the various cations and anions tested individually in the determination of 1 mM of platinum(II), no interference was observed in the presence of a 200-, 50-, 25-,lo- or 5-fold excess of ethylenediaminetetraacetate (EDTA), zinc( II), barium(I1) , cadmium(II), molybdenum(VI), tungsten(VI), fluoride , acetate, oxalate , chloride or sulphate; chromium(III), aluminium(III), nickel(II), manganese(II), cobalt(I1) or thiocyanate; osmium(VIII), iron(II,III), bromide or thiosulphate; ruthenium(II1); and rhodium(II1) or iridium(III), respectively.The method was found to be selective; only a few ions, i.e., palladium(II), copper(I1) and iodide interfered seriously even to the same level of concentra- tion of platinum(I1). The major interfering ions such as copper(I1) and palladium(I1) could be tolerated by adding EDTA (masking agent) and selectively precipitating17 before determination. I -I- 0.00 0.40 0.80 1.20 - E N versus SCE Fig.2. Typical differential-pulse polarograms of the Pt" - PA'TSC system. A, 50 mM PATSC in 0.2 M KCI + 0.2 M HCl; B, 0.5 mM Pt" + 50 mM PATSC + 0.2 M KCI + 0.6 M HCI; C, as B but in 0.4 M HCI; D, as B but in 0 . 2 ~ HCl Statistical Treatment of the Proposed Method The precision of the proposed method was evaluated by determining the same amount of platinum(I1) (2 mM) in six different samples. The average was found to be 1.994 mM and the corresponding standard deviation was 0.060. From the observations of linearity the value of the correlation coeffi- cient was 0.9994; this implied that the best linear association between the measured signals and the true (theoretical) concentrations was observed in the proposed method. Differential-pulse Polarographic (DPP) Determination of Platinum( 11) The polarograms were recorded under the following condi- tions: drop time, 1 s; pulse amplitude, 25 mV; sweep rate, 5 mV s-1.When platinum(I1) with PATSC was subjected to DPP analysis, at the concentration of HCl (0.25-0.1 M) applied for d.c. polarographic analysis, a single, symmetric, reversible, diffusion-controlled peak with high reproducibility was observed. In highly acidic medium, an apparent two-peak pattern was observed, the former being due to the reduction of mercury(1) and the latter to the reduction of the platinum(I1) - PATSC complex (Fig. 2). The peak current (&) - concentration relationship was found to be linear for 0.005-3.5 mM of platinum(I1). Linear calibration plots were obtained in two concentration ranges: 0.005-0.1 and 0.1-3.5 m M .The limit of determination was 0.005 mM. The average sensitivities were 24.58 and 22.88 pA mM-1 for 0.005-0.1 and 0.1-3.5 mM of platinum(I1) respectively. The standard deviations and coefficients of variation were 0.29,0.27 and 0.47, 2.16 for 0.06 and 2.0 mM of platinum( 11), respectively. Correlation coefficients of 0.9924 and 0.9894 were observed for 0.005-0.1 and 0.1-3.5 mM of platinum(II), respectively. As the proposed method proved to be sensitive, rapid and free from interferences from many ions (selective), it can be applied to the determination of platinum in real samples such as dental alloys, catalysts, electrical standard resistors or thermocouplesll~lx-2(~ by using either the d.c. or DPP mode. The authors thank Professor Agnes Paul, University of Madras, for providing necessary facilities.1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. References Petering, H. G., Buskirk, H. J . , and Underwood, C E., Cuncer Res., 1964, 64, 367. Dwyer, F. P., and Haro, R. T., Prog. Exp. Tumour Res., 1969, 12, 102. Singh. A. K., Katyal, M., and Lal, K . , Ra.cayan Savrzrksha, 1986, 2, 41. Gandhi, M. H., and Lahiri, S . A., Acta Crenc. Inllica [Ser] Chem., 1985, 11, No 3, 195. Can0 Pavon, J . M., and Pino, F., Talanta, 1973, 20, 1973. Palaniappan, R., and Revathy, V., Pakictun J. Scr. Ind. ReJ., 1988, 31, 378. Harumi, K., Norikagu, B., Satoshi, K., and Taheo, H., Bunseki Kagaku, 1971, 20, 1315. Garg, B. S . , Singh, S. R., Basnet, R. B., and Slngh, R. P., Polyhedron. 1988. 7, 147. Palaniappan, R., and Paul, A., Zndiun J. Clzem., Sect. A , 1987, 26, 625. Medyantsera, E. P., Romanova, 0. N . , Budnikov, G. K.. Sturis, A. P., and Bankovskii, Yu. A , , Zuvod. Lab., 1987, 53. No. 7, 12. Jaya, S . , Rao, T. P., and Ramakrishna, T. V., Analyst, 1984, 109, 1405. Beamish, F. E. and van Loon, J . C., "Recent Advances in Analytical Chemistry o f Noble Metals," Pergamon Press, London, 1972. Beamish, F. E., and van Loon, J. C., "Analysis of Noble Metals," Academic Press, New York, 1977.ANALYST, APRIL 1989, VOL. 114 519 14. 15. 16. 17. 18. Sah, P. T., and Daniels, T. C., Rrcl. Truv. Chim. Puys-Bas, 1950, 69, 1545. Cozzi, D . , and Pantani, E. F., 1. Znorg. Nucl. Chem., 1946, 8, 385. Feigl, F., and Angler, V., “Spot Tests in Inorganic Analysis,” Elsevier, New York, 1972, p. 305. Poddar, S . N . , Anal. Chim. Acta, 1963, 28. 586. Sanke Gowda, H., Padmaji, K. A . , and Thimmaiah, K. N . , Analysr, 1981, 106, 198. 19. Rowlands, J . A . , and Woods, S. B.. Rev. Sci. Instrum., 1976, 20. Peroutkova. V., and Beranek, L., Collect. Czech. Chem. 47, 795. Commun., 1976, 41, 526. Paper 8103039A Received July 26th, 1988 Accepted October 24th, 1988

ISSN:0003-2654    

DOI:10.1039/AN9891400517

出版商:RSC    

年代:1989

数据来源: RSC

摘要:

ANALYST, APRIL 1989, VOL. 114 521 Polarographic Study of Cobalt(l1) and Manganese(l1) at a Dropping Mercury Electrode Using 2-Amino-3-hydroxypyridine as a - Complexing Agent Ashok Kumar, Ashok Joshi and Rama Kant Shukla Department of Chemistry, University of Indore, lndore 452 00 I , India The polarographic behaviour of cobalt(l1) and manganese(l1) has been studied using 2-amino-3-hydroxy- pyridine as a complexing agent at a constant ionic strength, 1.1, of 0 . 6 ~ NaC104 and a t pH 6.0 & 0.5. Well defined diffusion-controlled irreversible waves were obtained for both metals. The forward rate constant (@f,h) and the charge-transfer coefficient (an) were calculated. The diffusion current constants were 3.83 for cobalt and 3.16 for manganese, and were constant over the concentration ranges 0.50-6.00 and 0.50-8.50 mM, respectively.Based on the large difference in their half-wave potentials, a method is proposed for the simultaneous determination of these metals when they occur together in pure solutions. The method was applied to the determination of these metals in a number of standard alloys. Keywords: 2-Amino-3-hydroxypyridine; polarograph y; alloys; cobalt and manganese determination The polarographic reduction of cobalt and manganese at a dropping mercury electrode has been studied in the presence of various complexing agents such as rn-aminobenzoate, 4aminosalicylate, 2-aminopyrimidine , I sulphothalein deriva- tives,' sulphosalicylate ,3 ~-tryptophan,4 thiodiethanol,5 glycineh and E-caprolactam .7.8 In most instances mixed elec- trolytes were used and in some instances a maximum suppressor was also required. Hence, the sensitivity and accuracy of the diffusion current measurements were low.2-Amino-3-hydroxypyridine (AHP) has been used as a sensitive and selective reagent in several analytical tech- niques, e.g., spectrophotometry,g potentiometry") and polar- ography.11 However, few polarographic studies using the complexes of cobalt(I1) and manganese(I1) with AHP have been reported. One advantage of using this complexing agent is that a maximum suppressor is not required. In this work the method was applied to the determination of cobalt and manganese in various reference materials. The kinetic parameters are reported. Experimental Reagents Stock solutions of the metal ions were prepared by dissolving their analytical-reagent grade nitrate salts in doubly distilled water.A solution of 2-amino-3-hydroxypyridine (Aldrich) was prepared in purified ethanol. A NaC104 solution was used to keep the ionic strength (p) constant at 0 . 6 ~ . All chemicals were checked polarographically before use. Apparatus and Procedure For each polarographic measurement, the volume of the solutions was kept constant (20 ml) by adding the necessary volumes of doubly distilled water. Purified nitrogen was also passed through the solutions to effect deaeration. The polarograms were recorded at 298 K with a Toshniwal manual polarograph. A saturated calomel electrode (SCE) was used as the reference electrode, which was connected to the polarographic cell by means of a potassium chloride agar - agar bridge.The dropping mercury electrode had the follow- ing characteristics: mass of mercury flowing th<o;igh the capillary, rn = 2.80 mg s-1; drop time, t = 2.9 s; rn Itz = 2.43 mg + S-f ; and height of the mercury column, h,,,, = 58.8 cm. The number of electrons ( n ) involved in the reduction processes was determined by the millicoulometric method of Devries and Kroon. 12 This gave a value for n of two at pH 6.0 k 0.5 for both metals. Results and Discussion Effect of pH The polarograms for a solution containing 1 mM cobalt(I1) or manganese(I1) and 0.1 M AHP were recorded between pH 1.5 and 11.0. It was observed that the negative shift in the half-wave potential (EB) reached a maximum at pH 6.0 in both instances. Hence, this pH was chosen for all subsequent work.Effect of the Pressure of Mercury Polarograms for 0.5 mM metal and 0.1 M A€1P solutions were recorded at various heights of the mercury column. The linear dependence of the limiting current on the square root of the height of the mercury column indicates that the reduction of the metal ion is diffusion-controlled. Effect of AHP The shape of the wave does not change when the concentra- tion of AHP is increased from 0.1 to 0.5 M. The formation of the complex is evident, as the half-wave potential becomes more negative (Table 1) with increasing concentrations of AHP. The various criteria for irreversibility'3J4 indicate that the electrode reactions are irreversible at the dropping mercury electrode. Hence, kinetic parameters such as the charge-transfer coefficient (an) and forward rate constant (lcof,J were calculated by Koutecky's theoretical treatment as developed by Meites and Israel.15 The value of an was calculated by equating the slope of the graph of Ed,, versus log i/(id - i) to -0.0542/an, where id is the diffusion current and Ed,,, is the potential corresponding to this current; the value of E+ was calculated from the intercept of this graph and was used to calculate kOf,h.The data presented in Table 1 show that there is a decrease in the charge-transfer coefficient (an) and the forward rate constant (kOf,h) with an increase in the concentration of AHP, indicating the tendency of the wave to move towards irreversibility. Because of this irreversibility, no deduction could be made regarding the composition of the complexes.However, on the basis of the values of n (determined coulometrically) , the electrode reaction may be represented as M2+ + 2e- + MO(Hg), where M = cobalt(I1) or manganese(I1). The stability of the complexes is reflected in the difference between the half-wave potentials obtained for a simple metal ion and a complex metal ion. Therefore, a comparison of the values for E+ may yield information about the relative522 ANALYST, APRIL 1989, VOL. 114 Table 1. Polarographic data for the cobalt(I1) and manganese(I1) systems. Cobalt(I1) or manganese(I1) concentration = 0.5 x 10 -3 M; pH = 6.0 k 0.05; p = 0 . 6 ~ NaClO, - E; vs. Slope of AHPi iCll SCE/ logplot/ D,+/lO--? k", .h/ M pA V mV cm's-1 an cms-1 Cobalt(l1) - AHP- 0.1 4.65 1.110 81 2.71 0.669 1.77 x 10-13 0.2 4.45 1.145 84 2.59 0.645 1.58 x 10-11 0.3 4.15 1.175 86 2.42 0.630 1.20 x 10-13 0.4 3.90 1.200 88 2.27 0.616 9.80 x 10 14 0.5 3.75 1.250 91 2.16 0.590 6.48 x 10 IJ Manganese( / I ) -A HP- 0.1 3.85 1.368 86 2.29 0.630 9.76 x 10-16 0.2 3.55 1.400 88 2.07 0.616 7.77 x 10 16 0.3 3.40 1.435 90 1.98 0.602 6.15 x 10-16 0.4 3.25 1.484 93 1.89 0.583 4.67 x 10-16 0.5 3.10 1.518 95 1.81 0.571 3.75 x 10-lf~ Table 2.Polarographic determination of cobalt(I1) and manganese(I1) with AHP. [AHP] = 0.1 M ; pH = 6.0 k 0.05; sensitivity = 0.02 Amount of metalimg Relative standard Metal Taken Found* deviation, o/o Cobalt . . . Manganese . 0.590 1.179 1.768 2.358 4.715 0.549 1.098 2.196 3.794 4.392 0.585 1.188 1.784 2.380 4.675 0.552 1.105 2.210 3.752 4.370 1.02 0.76 0.91 0.93 0.85 0.55 1.01 0.64 1.10 0.50 * Average of ten replicate determinations.stabilities of the complexes under study. However, for the irreversible process the half-wave potential also depends on a, hence values of anAE, should be compared; it is found that the ZnIJ - AHP complex is stronger than the CO" - AHP complex. Effect of Metal Ion Concentration Polarograms over the concentration ranges 0.50-6.00 and 0.50-8.50 m~ CO" and Mn", respectively, were recorded in the presence of 0.1 M AHP at pH 6.0 k 0.05. The value of the diffusion current constant ( I ) was calculated using the Ilkovic equation,l-l I = i,/cm$tb , and was found to be 3.83 for COT' and 3.16 for MnII. These values were constant over the above concentration ranges.Polarographic results can, therefore, be used for the determination of these metals. General Procedure for the Determination of Cobalt(I1) and Manganese(I1) A calibration graph was constructed for both metals by recording the polarograms of each metal at various concentra- tions in a 0.1 M AHP solution at pH 6.0. The id values obtained from the polarograms were plotted against the concentration of the metal ions; the polarogram of a solution containing the metal in an unknown concentration was then recorded under identical conditions. The id values obtained from this wave were referred to the calibration graph and the concentration of the metal could then be determined. The results are given in Table 2. Ten replicate analyses of the same sample solution gave mean diffusion currents of 4.65 and 3.85 pA for Co" and Mn".respectively, with relative standard deviations of 0.95 and 1.02%, respectively. Table 3. Simultaneous polarographic determination o f cobalt(I1) and manganese(I1). [AHP] = 0.1 M ; pH = 6.0 -t 0 . 5 ; sensitivity = 0.02 Amount addedimg Amount found*/mg Error, "/o Sample Cobalt Manganese Cobalt Manganese Cobalt Manganese 1 0.560 1.605 0.554 1.620 -1.07 +0.93 2 1.585 1.900 1.598 1.916 +0.82 +0.84 3 2.575 2.225 2.562 2.205 -0.50 -0.90 4 3.540 2.870 3.560 2.892 +0.56 +0.77 5 4.126 4.118 4.160 4.148 +0.82 +0.72 * Average of seven replicate determinations. Table 4. Polarographic determination of metals in standard reference materials. [AHP] = 0.1 M ; pH = 6.0 k 0.05; sensitivity = 0.02. Alloy samples were supplied by The Iron and Steel Institute of Japan, Tokyo, Japan Amount of Relative metal/mg standard Certified composition, deviation, Sample YO Taken Found* NBS SRM 171 Magnesium Alloy .. Mn: 0.65;Zn:l.OS; Mn: 1.922 1.940 Pb: 0.0033; Ni: 0.009; Cu: 0.01 1 ; Si: 0.01 18; Al: 2.98; Fe: 0.0018 3A-30 A1 alloy (NiPPon Alumin- Mn: 0.042; Mg:O.Ol; Mn: 2.470 2.442 ium . . Zn: 0.043; Ni: 0.042; Ti: 0.638; Zn: 0.038; S: 9.96; Fe: 0.633 JSS, 607-6 High Speed Steel . . Co: 4.72; V: 0.86; Co: 1.050 1.042 W: 16.96; Mo: 0.30; Mn: 2.175 2.160 Cr: 4.14; Ni: 0.0158; Cu: 0.028; S: 0.006; P: 0.012; Mn: 0.30; Si: 0.32; C: 0.75 JSS, 655-4 Stainless Steel . . Co:0.28;Nb:0.60; Co: 2.58 2.52 Te: 0.03; W: 0.024; Mn: 1.55 1.52 Mo: 0.051; Cr: 18.54; Mn: 1 .58; Si: 0.060; S + P + C: 0.094 * Average of seven replicate determinations.Y O 0.94 1.13 0.86 0.95 0.98 1.02 Effect of Foreign Ions The following ions (in the amounts shown in parentheses) do not interfere: Pb", Cd", Hg", BPI, A+, Sb"1 and CrIII (80 mg each); Ba", Ca", Sr", Mg", RUT", Rh"*, WVI, MoVI, UVI, AuIII, PtIV, VV and Ag[ (100 mg each); Zn" (50 mg); and PdII (60 mg). Nickel(I1) interferes in both instances but can be masked by adding 15 ml of 10% sodium cyanide solution. Sodium chloride, sodium acetate, sodium sulphate, potassium bromide and potassium tartrate (350 mg each); sodium dihydrogen phosphate (400 mg) ; potassium thiocyanate and sodium citrate (850 mg each); sodium oxalate (230 mg); and EDTA, disodium salt (100 mg) are also tolerated. Mixed Polarograms of the Cobalt(I1) and Manganese(I1) Systems From the individual polarograms for cobalt(I1) and man- ganese(I1) it is apparent that it is possible to differentiate between the two metals when they are complexed with AHP as their E+ values differ by 0.3 V.Consequently, a series of polarograms were recorded for mixed, synthetic solutions ofANALYST, APRIL 1989, VOL. 114 523 these metals and the id values obtained for each metal were referred to the respective calibration graph and the metal concentrations calculated. Table 3 shows the concentrations of cobalt(I1) and manganese(I1) determined in the mixed solutions. The results obtained are accurate and reproducible. Analysis of Standard Reference Materials A 1.0-g sample of the standard reference material was decomposed with 30-40 ml of 1 + 1 hydrochloric acid and 10-20 ml of concentrated nitric acid.A 3.5-ml volume of 30% hydrogen peroxide was then added and the solution was heated on a hot-plate until the sample had dissolved com- pletely and until the volume had been reduced to about 5 ml. After cooling, the solution was diluted to 1 1 with doubly distilled water. An aliquot of this solution was taken and the metal was determined using the proposed method. The results obtained are given in Table 4. 1. 2. 3. References Corw, D. R., and Zanopoulos, J . , Anal. Chim. Acta, 1980,109, 231. Bhasin, S. K., Gaur, J . N., and Jain, D. S . . J. Electrochem. SOC., 1979, 20, 147. Ogura, K.. Murakani. S . , and Seno, K . , J. Inorg. Nucl. Chem., 1981, 43, 1243. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. Dubey, M. C., and Singh, M., Indian J. Chem., Sect. A , 1979, 18, 177. Khatri, K. C., Varshney, A., Shivahare, K., and Singh, M., Indian J. Chem., Sect. A , 1981, 20, 1144. Gritzner, C., and Redhenger, P., J. Electroanal. Chem. Interfacial Electrochem., 1980, 109, 334. Reddy, S . V. V.. Sethuram, B., and Rao, N. T., Indian J. Chem., Sect. A , 1981, 20, 1138. Puri, B. K., and Kumar, A . , Electrochim. Acta, 1984. 29, 345. Mehta, Y. L., Garg, B. S . , and Singh, R. P., Talanta, 1976,23. 53. Kalra, H. L., Malik, J. S . , and Gcra, V.. J. Indian Chem. SOC., 1982, 59, 1427. Swellen, R. S . , Pandega. K. B., and Singh, R. P., Indian J . Chem., Sect. A , 1976, 14,913. Devries, T., and Kroon, J . L., J . Am. Chem. Soc., 1953, 75, 2484. Kivaro, P., Oldham, K. B., and Laitenen, H. A., 1. Am. Chem. Soc., 1953, 75, 4146. Meites, L., “Polarographic Techniques,” Interscience, New York, 1965, p. 235. Meites, L., and Israel, Y. L., J. Am. Chem. Snc.. 1961. 83, 4403. Paper 8104504F Received November 11 th, 1988 Accepted December 5th, 1988

ISSN:0003-2654    

DOI:10.1039/AN9891400521

出版商:RSC    

年代:1989

数据来源: RSC

摘要:

AYALYST, APRIL 1980. VOL. I13 525 Voltammetric Determination of Chlorpromazine Hydrochloride Saadet Dermi? and hci Biryol Department of Analytical Chemistry, Faculty of Pharmacy, University of Ankara, Ankara, Turkey The electrochemical behaviour of chlorpromazine hydrochloride (CPZ-HCI) in sulphuric acid was investigated voltammetrically using ruthenium electrodes and it was subsequently determined by the same method. From the recorded voltammograms it was concluded that CPZ-HCI can be determined in the concentration range 2 x 10-4-8 x 10-4 M (71-284. 3 pg ml-I). The proposed voltammetric method was applied to the determination of CPZ-HCI in tablets used for neuroleptic purposes in Turkey; the amount of effective compound was found to be within the ranges given for a pharmacopoeial procedure.Keywords 1 Chlorpromazine hydrochloride; ruthenium electrode; voltammetry In chlorpromazine hydrochloride (CPZ-HCI) [2-chloro-10-(3- d i me thy 1 amino prop y I) p hen o t hi azi n e mono h y d r oc h 1 o ride ] t h e d i ni e t h y 1 anii n o p r o p y l group h as i rn po r t an t t r a n q u i 11 is i ng effects. C h 1 or pr o m azi n e h y d roc h 1 o ri de can be determined by v ari - ous techniques including chromatographic1.2 gravimetric,'-5 tit r i m e t r i c , {vt-t; spec t r o p ho t om e t ric'). 1 0 and e 1 ect roc he m ical 1 I - I 1 methods. For the pharmacopoeial determination of CPZ-HCI a non-aqueous titrati0nl-~-l7 method is recommended. Typically. i n electrochemical studies, the polarographic behaviour of chlorpromazine has been investigated after chemical oxidation.18 Investigations carried out using solid electrodes were limited by the lack of reproducibilty of results caused by variations in the electrode surface due to surface reactions occurring in the metal itself. For solid electrodes pre-treatment of the electrode is very importantly and once a suitable pre-treatment procedure is used highly reproducible results can be obtained. This paper describes an investigation into the electroana- Iytical behaviour of CPZ-HC1 using ruthenium electrodes subjected to various pre-treatments and discusses the experimental results obtained under optimum conditions. A further aim of this study was to compare the results obtained by applying the proposed technique to the analysis of dosage forms of tablets containing CPZ-HCI.available in Turkey, \vith those of the pharmacopoeia1 technique. Experimental Apparatus The apparatus and the electrode used in the voltammetric determinations were a three-electrode Tacussel PRG-3 system and a ruthenium wire of 1.0 mm diameter (Engelhard). The reference electrode was a Tacussel Type C-10 saturated calomel electrode and a platinum wire (Johnson Matthey) electrode was used as the counter electrode. All electrochemical experiments and electrode pre-treat- ments were performed in a three-compartment experimental cell made of Pyrex glass. Chemicals The chlorpromazine hydrochloride used as a standard was obtained from Eczacibay Pharmaceuticals (Turkey) and the Largactil tablets containing CPZ-HCI (25-100-mg dosage) were obtained from local drugstores.To prepare a 10-3 M stock solution of the standard, CPZ-HCI was weighed and dissolved in 0.2 M HZS04 (as supporting electrolyte). Solutions of different concentrations, for which voltammograms were recorded, were prepared by dilution of this stock solution. Doubly distilled water was used in the preparation of all solutions and spectroscopic determinations were performed using a Pye-Unicam SP 8-100 spectrophotometer. Electrode Pre-treatment The electrodes were pre-treated in order to obtain reprodu- cible results. A potential of -20 mV was maintained between the electrodes in 0.5 M I12SOI for 5 min by bubbling nitrogen through the electrolyte. The electrodes were then washed with doubly distilled water after the circuit had been disconnected and an electrode potential of +400 mV was applied for 15 min.Such a pre-treated electrode is referred to as a non-oxidised electrode. Kecording of Voltammograms The voltammograms were recorded of CPZ-HCI solutions of different concentrations in 0.2 M H2S04 as supporting electrolyte. The experiments were carried out in a cell isolated from the light after each solution had been de-oxygenated by bubbling with nitrogen for 10 min. Throughout the experiment nitrogen was bubbled through the solution, which was stirred continu- ously by a magnetic stirrer. The current - potential graphs were recorded in the potential range +400 to +1500 mV at a scan rate of 0.01 V s-1. (All potentials are versiis a standard hydrogen electrode.) Analysis of pharmaceutical dosage forms Largactil, a commercial drug containing CPZ-HCI, was analysed under the electro-oxidation conditions used for the determination of standard CPZ-HC1.Comparison of the voltammograms obtained for the same concentration of CPZ-HCI in both the standard and drug solutions showed that the additives present in the drug did not affect the procedure. For the drug analysis, 20 tablets were weighed accurately and ground to a fine powder. Largactil tablets containing the equivalent of 100 mg of CPZ-HC1 were weighed accurately, dissolved in 0.2 M H2S04 and made up to 100 ml in a calibrated flask with the same solution. A 20-ml aliquot of the solution was stirred for 1 h with a magnetic stirrer, transferred to a tube and centrifuged. The clear solution (10 ml) at the top of the tube was then removed and made up to 100 ml in a calibrated flask with 0.2 M HZS04.Voltammograms of this solution were recorded under standard working conditions. Results and Discussion Investigation showed that 0.2 M H2S04 was the most suitable supporting electrolyte and that 0.01 mV s-1 was the optimum scan rate. Fig. 1 shows the oxidation graph of 0.2 M H2S04 in the potential range +400 to +1500 mV obtained by linear526 ANALYST, APRIL 1989, VOL. 114 800 600 N I k $400 200 I P i 500 600 700 800 900 1000 11 00 1200 1300 1400 EHlmV Fig. 1. Voltammograms obtained for 0.2 M H,S04 containing various concentrations of chlorpromazine. A non-oxidised electrode was used in stirred solutions. Scan rate, 10 mV s-1. +, 0.2 M H,S04. [Chlorpromazine hydrochloride]: A .10-4; 0 , 2 x 10-4; 0 , 3 x 10-4; x , 4 x 10-4; M, S x I O F ; A, 6.5 x 10-4; 0 , 7 x 10-4; and 0, 8 x lo-.‘ hf Table 1. Results of the analysis of Largactil tablets for chlorpromazine hydrochloride. Calculated Student’s t-value, 1.66; p < 0.05 Found by Found by spectrophotometric voltammetric Sample No. methodlmg per tablet methodimg per tablet 1 2 3 4 5 6 7 8 9 10 100.7 101.2 100.5 101.6 101.4 102. I 100.6 100.5 101.4 102.7 102.4 102.4 100.9 100.9 100.9 99.3 100.9 09.3 97.6 99.3 Mean value . . . . 101.27 +- 0.52 100.39 2 1.08 Standard deviation . . 0.73 1 .so Standarderror . . 0.23 0.47 Theoretical value . . 100 100 scanning before the anodic polarisation of CPZ-HC1 with an unoxidised ruthenium electrode. Although not very distinctive, two steps occur on the graph, at +500 and +900 mV, corresponding to oxidation of the ruthenium electrode surface.The sharp increase at + 1350 to +1300 mV is due to the formation of Ru04 and the evolution of oxygen. The voltammograms of 10-4-10-3 M CPZ-HCI in 0.2 M HzS04 show a distinctive increase in the current and a limiting current corresponding to this step is apparent on most of the graphs from +900 to +1200 mV. The limiting current density at 1000 mV obtained from the voltammogram for the 0.2 M H2S04 supporting electrolyte was subtracted from the corresponding current densities for the graphs shown in Fig. 1. For 2 X 10-4, 3 X 10-4, 4 X 10-4, 5 X 10-4, 6.5 X 10-4, 7 X 10-4 and 8 X 10-4 M solutions of CPZ-HCl the limiting current densities were 115, 150, 184, 215, 275, 295 and 315 PA cm-2, respectively.The calibration graph had the following charac- teristics: correlation coefficient, 0.998; slope, 3.45 x 105; y-intercept, 46.3; and regression standard deviation, 11.8. The linear relationship obtained between concentration and current density showed that the reaction took place by diffusion-controlled processes and it was concluded that CPZ-HCI could be determined quantitatively in a concentra- tion range of 2 x 10-4-8 x 10-4 M. The test solution was exposed to UV light for 30 min and a marked decrease in the current (about 26%) was observed on the voltammograms recorded at the end of this period. Hence the voltammetric method is selective in the presence of the decomposition products. For the quantitative analysis of Largactil tablets by a pharmacopoeia1 technique, the spectrophotometric determi- nation described in reference 20 was employed.The results of the analysis for CPZ-HCl in the tablets obtained by both voltammetric and spectroscopic methods are given in Table 1. The BP states that CPZ-HCl should be in the range 92.5-107.5% .20 The voltammetric and spectrophotometric analysis data obtained in this study fall within this range and, in addition, there is no significant difference between the two techniques. The authors thank the Research Fund of Ankara University and Eczacibay Tlaq Sanayii ve Ticaret A. $. , Turkey, for their financial support. 1 . 2. 3. 4. 5 . 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. References Gonnet, C., and Rocca, J . L . , J .Chromarogr., 1976, 126. 319. Laitem, L., Bello, I . , and Gaspar, P., 1. Chrornatogr., 1978, 156, 327. Blaiek, J . , and Stcjskal, Z., Cesh. Farm., 1955, 4, 246; Anal. AbJtr.. 1956, 3, 530. Blaiek, J . , Phurmazie, 1967, 22, 120. Blaiek, J . . Spinkova, V., and Stejskal, E., An. Farm. Hosp., 1967, 10, 7. Zivanov-Stakic, D.. and Djceric. L.,Arh. Farm., 1977,27,223. Walash, M. I., Rizk, M., Abou-Ouf, A.-M., and Belal, F., Analyst, 1983, 108, 626. Zakhari, N. A., Rizk. M., Walash, M. I . , and Ibrahim. F . , Anal. Lett., 1985, 18, 1405. El-Shabouri, S. R., Tulurzta. 1985, 32. 999. Jayarama. D., Souza, M. V., Yathirajan, H. S . , and Rangas- wamy, Talanta, 1986, 33, 352. Rhatt. S. K.. Arora, R. K., Chakrabarti, S., and Gode, K. D.. Indian J . Hosp. Pharm., 1979, 182. Takamura, K., Inoue, S., Kusu, F., Otagiri, M., and Uekama, K., Chern. Pharrn. Bull., 1983. 31, 1821. Oelschlager, H., and Bunge, K., Arch. Pharm., 1973, 18. 410. Wang, J . , Freiha, B. A . , and Deshmukh, B. K., Bioefectro- chem. Bioenerg., 1985. 14, 457. ‘.British Pharmacopoeia 1963.” Pharmaceutical Press, London, 1964. p.173. “Turkish Pharmacopoeia 1974,” Milli Egitum Basimcvi, Istan- “The United States Pharmacopeia 1985,’‘ 25th Revision, Mack, Easton, PA, 1985, p. 205. Oelschlager, H., Bioelectrochem. Bioenerg., 1983, 10, 25. Smyth, W. F. ~ -’Polarography of Molecules of Biological Significance,” Academic Press, London. 1979, p. 79. “British Pharmacopoeia 1980,” H.M. Stationery Office, Lon- don, 1980, p.748. bul, 1974, pp. 159-160. Paper 8101375F Received April 7th, I988 Accepted November 7th, 1988

ISSN:0003-2654    

DOI:10.1039/AN9891400525

出版商:RSC    

年代:1989

数据来源: RSC

摘要:

ANALYST, APRIL 1989, VOL. 114 527 Determination of Selenium in Fish Flesh by Hydride Generation Atomic Absorption Spectrometry Lena Hansson, Jean Pettersson and Ake Olin Department of Analytical Chemistry, University of Uppsala, P.O. Box 531, S-751 21 Uppsala, Sweden Selenium was determined in freeze-dried fish flesh from perch, pike-perch and the fish flesh reference materials MA-A-2 No. 1174 and MA-6-3 No. 151 (both from the International Atomic Energy Agency) by hyd ride generation atomic absorption spectrometry. Fou r different decom position procedures were tested. They yielded consistent results for the four specimens, but the certified concentration level of selenium in the reference material MA-A-2 was not reached. This indicated losses or the presence of very stable selenium-containing compounds in this fish flesh.Neutron activation analysis of the reference material, however, was in agreement with those results obtained. Keywords: Decomposition procedures; selenium; h ydride generation atomic absorption spectrometry; fish flesh; reference material The determination of selenium in biological specimens of aquatic origin can present problems. Reports indicate that low recoveries of the element are sometimes obtained. 1.2 It is possible that organic compounds containing selenium that are resistant to oxidative attack are present in the samples. Recently, we were asked to determine selenium in fish muscle in a project initiated by the Swedish National Environmental Protection Board.3 Therefore, the perform- ance on fish flesh samples of our procedure developed previously for the determination of selenium in biological materials has been investigated.The procedure uses hydride generation atomic absorption spectrometry (HG-AAS) for the final determination of selenium and is combined usually with a magnesium nitrate - nitric acid - hydrochloric acid digestion step to break up the sample. This method has proved reliable for a number of biological materials.”s Freeze-dried flesh from perch, pike-perch and fish flesh reference materials were subjected to four different decomposition procedures prior to HG-AAS. Experimental Reagents and Materials All the reagents and chemicals were of pro analysi quality. The water used for dilution and washing was de-ionised, distilled and filtered through a Milli-Q system.The reference materials were MA-A-2 No. 1174 and MA-B-3 No. 151 fish homogenate (International Atomic Energy Agency. Monaco). The filter-paper used in the closed flask combustion procedure had a low ash content (OOM class 1, Munktells, Grycksbo, Sweden). Apparatus The instrumentation for HG-AAS and the equipment for sample work-up have been described previously.4 Procedure Decomposition Three digestion methods were applied to the samples: (i) the “magnesium” method, (ii) the nitric acid - perchloric acid - sulphuric acid method and (iii) digestion with nitric acid in a closed bomb. These methods are described in reference 4. In addition, method (iv), closed flask combustion in an oxygen atmosphere, was tested and is described below. Weigh about 0.05 g of the sample accurately on to a filter- paper cut out as described in reference 6.Fold the paper to form a small package containing the sample and place the package in a platinum gauze fastened to the stopper of a 1-1 Erlenmeyer flask by a platinum wire (gauze, 20 x 20 mm; wire, 50 mm). Allow a wick to protrude from the paper. Add 15 ml of 4~ hydrochloric acid to the flask as an absorbing medium. Fill the flask with oxygen from a gas tube by flushing for about 10 s, then ignite the wick and introduce the sample package quickly into the flask. Hold the stopper firmly in place and turn the flask upside-down so that the hydrochloric acid can provide a liquid seal for the gases formed. After a few seconds the combustion is complete. Allow the combustion products to be absorbed by the hydrochloric acid for 30 min.Swirl the flask occasionally to facilitate the absorption. Remove the stopper and boil the contents for 15 min to remove the dissolved gases and to reduce any selenate to selenite. After cooling, dilute the solution to 50 ml. Table 1. Concentrations (ug g-1) of selenium in fish samples obtained using four decomposition methods. SD = standard deviation, n = number of deter 111 in at io ns (i) (ii) (iii) (iv) Sample Mcan SD n Mean SD n Mean SD rz Mean SD n Perch . . , . . . . . , . . . 1.29 0.06 7 1.18 0.06 5 1.1s 0.06 4 1.32 0.07 4 MA-A-2No.1174’ . . . . . . 1.15 0.06 12 1.11 0.07 6 1.13 0.06 3 1.29 0.07 4 MA-B-~No. 151t . . . . . . 1.34 0.03 6 1.44 0.03 3 1.41 0.02 3 1.43 0.08 2 Certified concentration, 1.7 & 0.3 pg g-1.Pike-perch . , . . . . . , . . 0.51 0.02 7 0.48 0.03 3 0.48 0.02 5 0.54 0.03 4 NAA result: direct measurement, 1.10 k 10 pg g 1 ; after chemical separation, 1.12 * 0.06 pg g-I (Studsvik AB, Nykoping, Sweden). i Certified concentration, 1.46 pg g-1 (90°/, confidence interval, 1.35-1.70 pg g-I).528 ANALYST, APRIL 1989, VOL. 114 Evaluation The concentration of selenium was evaluated from a calibra- tion graph obtained from standards prepared by adding known amounts of selenite to combusted blanks. Application of the standard additions method to the samples did not change the results significantly. Results and Discussion Concentrations of selenium found in the fish specimens are shown in Table 1. They were calculated on a dry mass basis.The result from the analysis of one of the reference materials using neutron activation analysis (NAA) is also included. In general, the results are consistent both between the digestion procedures and between HG-AAS and NAA. The certified mean value for MA-A-2 of 1.7 k 0.3 pg g-* of selenium, however, was not obtained. This could indicate a systematic error in our procedures of about -30% (over-all mean value was 1.17 pg g-1). but in that instance NAA suffers from the same error (over-all mean value, 1.11 pg g-1). Neutron activation analysis was performed both directly on the irradiated sample and after chemical separation. A further explanation for the discrepancy may be that the MA-A-2 is certified incorrectly for selenium. This is supported by the fact that the result obtained for MA-B-3 was consistent with the certified value References 1. Welz, B., and Melcher, M., Anal. Chem., 1985, 57, 427. 2. Bye, R., and Lund, W., 2. Anal. Chem., 1985, 321, 483. 3. H$kansson, L., "Liming and Mercury," Swedish Environment Protection Board, Stockholm. 4 Pettersson, J . , Hansson, L., and Olin, A,. Talanra. 1986, 33, 249. 5 Hansson, L., Pettersson, J . , and Olin, A., Tafanta, 1987, 34, 829. 6. Gorsuch, T. T., "The Destruction of Organic Matter," Pergamon Press, Oxford, 1970. p, 32. Paper 8f04535F Received November 14th, 1988 Accepted December 12th, I988

ISSN:0003-2654    

DOI:10.1039/AN9891400527

出版商:RSC    

年代:1989

数据来源: RSC

摘要:

ANALYST. APRIL 1989, VOL. 114 529 Terbium Chelate Labels for Fluorescence lmmunoassays Jerzy Siepak Department of Instrumental Analysis, A. Mickiewicz University, 60-780 Poznan, Poland Bovine serum albumin was labelled with a terbium complex by means of a reagent prepared from d i et h y I e net r i a m i n e pen ta a cet i c acid o r d i et h y I en et r i a m i n e pe n t a p h 0s p h o n ic a ci d a n d p-a m i n osa I icy I ic acid . The ternary mixed ligand complexes showed strong fluorescence and were stable in very dilute solution (10-10 M). The fluorescence of the conjugated products was compared with regard to their application in the fluoroimmunoassay of bovine serum albumin. Keywords: Fluoroimmunoassa y; terbium chelates; carboxylic and phosphonic complexones; bovine serum albumin In the immunoassay field the use of lanthanides is of growing interest.1 Some lanthanides, especially europium, terbium, erbium. samarium and gadolinium, form highly fluorescent chelates with many different organic ligands."." Lanthanide chelates with complexones, used as reagents in the fluorescent labelling of proteins, are widely applied in histochemistry3 and immunochemistry.5 Complexes of lanthanides with complex- ones have high stability and solubility in water, and the formation ccinstants with lanthanides are > 10'5.&X Bailey et used terbium chelates with diethylenetriaminepentaacetic acid (DTPA) and p-aminosalicylic acid @-AS) and human serum albumin (HSA) for determining nanogram amounts of HSA. We describe here the application of the terbium complexes of DTPA and diethylenetriaminepentaphosphonic acid (DTPP) with p-AS to the simple fluoroimmunoassay of bovine serum albumin (BSA). Experimental Apparatus The corrected fluorescence spectra were recorded using a Perkin-Elmer MPF-3 spectrofluorimeter with a xenon lamp as the radiation source. The excitation wavelength was 328 nm for TbI" and the emission was monitored at 545 nm.All measurements were carried out in 1 X 1 cm square quartz fluorescence cells. Reagents DTPA and DTPP were prepared as described previously.9310 Dimethyl sulphoxide (DMSO), triethylamine and p-AS sodium salt were obtained from Sigma (Poole, Dorset). Terbium chloride was prepared by dissolving the oxide (Tb407. 99.9% ; Fluka) in hydrochloric acid and evaporating the excess of the acid.The concentration of TbC13 in aqueous acidic solution (pH d 3) was measured by complexometric titration with standard EDTA using xylenol orange (Merck) as the indicator.8 Bovine serum albumin (BSA) monomer ( 5 pg ml-I) (Pierce) was used as a standard solution. Coomassie Brilliant Blue G-250 (CBB) (Pierce) was used as a standard solution (1 X 10-3 M) for the spectrophotometric method. Bovine IgG (11.3 mg 1-1) (Bio-Rad Laboratories) was used as a standard solution. Procedure The conditions for the preparation of ternary fluorescence complexes with DTPA and DTPP have been described.9-11 By applying the earlier tested methods, the following ternary complexes, showing strong fluorescence, were obtained: Tb"' - p-AS + DTPA - BSA and Tb"' - p-AS + DTPP - BSA.The properties of these complexes were compared in this work. DTPP or DTPA (0.1 mmol; 57.8 mg) and triethylamine (2 ml) were dissolved in 2 ml of DMSO. p-AS was dried at 110 "C until no further decrease in mass occurred and 0.1 mmol (18 mg) of the anhydrous salt was dissolved in 2 ml of DMSO. The p-AS solution was added dropwise to the stirred DTPP or DTPA solution and the mixture was stirred for 30 min at room temperature. BSA was labelled with the p-AS + DTPP or p-AS + DTPA derivative by adding 0.1 ml of the rapidly stirred suspension to a solution of 67 mg of BSA in 5 ml of 0.1 M phosphate buffer (pH 7) with continuous mixing. The mixture was kept overnight at 4°C and the excess of label was removed by dialysis for 36 h against three 1-1 volumes of 9 g 1-1 sodium chloride solution.For use in a fluorescence immunoassay, 0.4 ml of the labelled BSA preparation was mixed with 0.2 ml of 0.04 M terbium chloride solution and this mixture was diluted 1 + 99 with 0.1 M phosphate buffer (pH 7). The excess of terbium ions was precipitated as phosphate and could be removed by centrifugation at 1500 g for 5 min. Diluted label (0.1 ml) was mixed with 0.1 ml of a 1 + 49 dilution of BSA antibodies. After allowing it to stand for 30 min at room temperature. 1 ml of polyethylene glycol 6000 (200 g 1-1 in 0.1 M phosphate buffer, pH 7) was added to each centrifuge tube and the precipitates were sedimented by centrifugation at 1500 g for 20 min. The supernatants were removed by aspiration and the precipitates resuspended in 2 ml of 0.1 M phosphate buffer (pH 7).The assay tubes were placed directly in the cell compart- ment of a Perkin-Elmer spectrofluorimeter. Results The strong fluorescence of the stable terbium chelates was utilised for the determination of trace amounts of BSA (Fig. 1). It was demonstrated that the spectrofluorimetric method is significantly more sensitive than the spectrophotometric method, and that the sensitivity of the determination of BSA is higher when the DTPP (Table 1) is cross-linked. It was found that the spectrophotometric method permits the deter- mination of only microgram amounts of BSA, whereas the spectrofluorimetric method is applicable to nanogram amounts (Table 1). As shown in Fig. 2, fluoroimmunoassay of BSA showed a good correlation with the spectrophotometric method (CBB).The spectrofluorimetric and spectrophotometric methods showed a linear dependence on BSA concentration within the range 2-1000 ng ml-1. In the regression analysis of determinedANALYST, APRIL 1989, VOL. 114 530 ;; 0.8 z 0.6 - Q) 6 0.4 f a n 6 0.2 0 300 400 500 600 Wavelengthin m Fig. 1. Typical absorption (broken line) and excitation and emission (solid line) spectra of terbium chelates with p - A S + DTPP and BSA (2.1 x 10-8 \I) Table 2. Comparison of fluorescence properties of terndry complexes with phosphonic (DTPP) and carboxylic (DTPA) complexones Values i n parenthews refer t o DTPA Fluorescence Stability of complex intensity. "/" with ti m e/d Concentration of pH 7.0. pH 4.0. complexh DTPP DTPA DTPP DTPP 1.0 x lo-" 29.8 7.0 7 (6) 3 (2) 4.0 x lo-" 60.5 14.2 7 (6) 3 (2) 8.0 x lo-" 91.6 22.1 7 (6) 3 (2) Table 1.Dependence o f the rangc of determination of BSA on pH for the studied complexes Rectilinear Ternary Limit of range of BSA PH complex detection concentration range DTPA . . 0.5ngml-1 10-29.5 ng ml-1 4.0-11.0 DTPP . . 0.1 ngml-1 2-29 ng ml-1 2.5-1 2 .0 CBB . . 0.1pgml-1 0.5-7.5 pg ml-1 5.5-1 1.25 10.5 500 1000 Fig. 2. Calibration graphs for BSA detcrmination by ( u ) fluoroim- munoassay (A. DTPP; B, DTPA) and ( b ) spectrophotometric (CBB) methods versus found BSA concentrations, the slopes were 0.955 (DTPP), 0.940 (DTPA) and 0.830 (CBB). Rectilinear calibration graphs of fluorescence intensity versus BSA concentration were obtained for the ranges 2.&29 ng ml-1 (DTPP) and 1@29 ng ml-1 (DTPA).The relative standard deviation for 10 ng ml-1 of BSA was 3.0% for DTPP and 4.2% for DTPA for 15 measurements. The spectroflu- orimetric assay showed good reproducibility, the coefficients of variation being 0.46% for DTPP and 0.30% for DTPA. From comparisons of the rectilinearity range, BSA determi- nations, detection limits, pH determinations and stabilities of the DTPP and DTPA complexones with time, we concluded that the application of the DTPP complexone provides more favourable analytical results. The differences can be attri- buted to the difference in the stabilities of these complexes (fluorescence intensity, Table 2), and also their acid - base properties and the complex-forming properties of DTPP and DTPA. It was demonstrated that bovine TgG can be determined according to the proposed procedure, allowing fluoro- immunoassay to be performed.Discussion The ternary mixed ligand complexes of Tb11' - p-AS + DTPA (or DTPP) - BSA form highly fluorescent chelates (Fig. 1). The absorption of light by the ligands is followed by efficient energy transfer from the excited singlet state through the triplet state to the resonance levels of the terbium ion. The terbium ion emits energy as a narrow-band line-type emission. The fluorescence of the chelate is characterised by broad excitation in the absorption region of the ligand (328 nm) with a large Stokes shift (>215 nm) and emission lines typical of terbium. Typical excitation and emission spectra of terbium chelates are shown in Fig. 1. The 488- and 545-nm bands are the strongest and are due to the SD4 -+ 7F6 and sD4 -+ 7Fs transitions, which are also hypersensitive.The hypersensitive band observed for TbI" arises as a result of vibronic coupling connected with the influence of the ligand field on the 4f orbital of the Tb"1 ion. The oscillator strengths of certain 4f + 4f transitions in lanthanide(II1) complexes exhibit an espe- cially strong sensitivity to the structural details and chemical nature of the ligand environment. A terbium cation with a high coordination number is capable of binding strongly p-AS + DTPP (or DTPA) with BSA. Hence the high stability of the chelate complex is confirmed by intense fluorescence in dilute solutions. The ternary mixed ligand complexes, TbIII - complexones - BSA, are strongly fluorescent and stable in very dilute solution (10-10 M)? The sensitivities of the two DTPP and DTPA complexones were compared in the determination of BSA, BSA monomer being used as the reference material.The differences in the sensitivities of the two complexones should be attributed to the different acid - base properties. The dissociation constants for DTPA are pK1 = 1.95. pK2 = 2.55, pK3 = 4.23, pK4 = 8.56 and pK5 = 10.45,7,11.13 and those for DTPP are pK1 = 1.05, pK2 = 1.90, pK8 = 8.15, pK9 = 10.10 and pKlo = 12.04.7.11.13 These dissociation constants indicate a much wider range of the acid - base properties for DTPP than for DTPA (ApKlo =: 11, ApKs = 8.5). This provides more favourable conditions for the complexation reaction in a wider pH range. The stability constants of TbIII complexes with DTPP, DTPA, BSA and p-AS are log f3 = 21.90, 19.90, 9.40 and 11.40, respec- tively.7.11.1-i As follows from the stability constants of com- plexes with the Tb"' cation, the Tb - DTPP system has the greatest strength.Further increases in the stability of the fluorescent ternary complexes may be possible by using polyaminocarboxylic, phosphonic, phosphinic and arsonic ligands. This procedure for the determination of proteins may be applied to many similar compounds. Work on such com- pounds and their lanthanide complexes is in progress. P K ~ = 2.80, P K ~ 1 4.45, PKS = 5.50, pK6 = 6.38, pK7 = 7.77, References 1. 2. 3. Soini, E., and Kojola, 13.. Clin. Chem., 1983. 29. 65. Hemmila, I . , Clirz. Chem., 1985, 31, 359. Petersson. K., Siitari, H.. Hemmila, I., Soini, E.. Liivgren, T.. Hanninen. V., Tanner, P.. and Stenman, U . , Clin. Chem., 1983, 29, 60. Chen, F. F., and Scott, C . H., Anal. Lett., 1985, 18, 393. Ferrara, A. I . . Meroni. G., and Bacigalupo, M., Fre.senius Z. And. Chem., 1985. 322, 509. 4. 5 .ANALYST, APRIL 1989, VOL. 114 53 1 6. 7. 8. 9. 10. Moeller, T., Martin, D. T., Thompson, L. L., Ferrus. R., Feistel, G. R.. and Randall. W. J . , Chem. Rev., 1965, 65. 1. Smith. R . M., and Martell, A . E., “Critical Stability Con- stants,” Volume 5 , Plenum Press, New York, 1982. Welcher, F. J . , “The Analytical Uses o f Ethylenediarninetetra- acetic Acid,” Van Nostrand, New York. 1958. Bailey, M. P., Rocks, B. F., and Riley, C., AnalyJt, 1984, 109, 1449. Siepak, J . , Bull. Soc. Amis. Sci. Lett. Poznari. Ser. D, 1988,26, 5 . 11. Siepak, J . , “Properties and Applications of New Organophos- phorus Complexones in Analytical Chemistry.” A. Mickiewicz University, Poznan, 1987. Siepak, J . , paper presented at Euroanalysis VI. Paris, 1987. Kabachnik, M. I., Dyatlova, N. M., Medved, T. Ya, Belgugin, Yu. F., andsidorenko. W. W., Dokl. Akad. NaukSSSR, 1967, 175, 351. Paper 8101 624K Received April 25th, 1988 Accepted September 27th, 1988 12. 13.

ISSN:0003-2654    

DOI:10.1039/AN9891400529

出版商:RSC    

年代:1989

数据来源: RSC

摘要:

ANALYST. APRIL 1989, VOL. 113 533 Ion-pair Extraction and Spectrophotometric Determination of Potassium Using Dibenzo-18-crown-6 and Bromothymol Blue Rosario Escobar, Concepcion Lamoneda, Fernando de Pablos and Alfonso Guiraum Department of Analytical Chemistry, Faculty of Chemistry, University of Seville, 4 lOI2-Seville, Spain A sensitive extractive - spectrophotometric method for the determination of potassium using dibenzo-I 8- crown-6 and bromothymol blue as the counter ion is described. The absorbance was measured at 410 nm and the value of the molar absorptivity was 18 000 I mol-1 cm-1. A linear working range from 0.1 to 3.0 pg ml-1 of potassium was obtained and the relative standard deviation was 2.3%. Rubidium and ammonium ions gave the highest interference. The method was applied to the determination of potassium in fruits and beverages. Keywords Potassium determination; crown ether complex; potassium extraction; spectrophotometry; fruits and beverages Crown ethers show a remarkable ability to extract alkali and alkaline earth metal ions selectively' and also other ions such a s Ag'.Cu7+ and Cu+' and organic cations and anions.3 These macrocyclic ligands have been widely used and scveral revieus+g have been published. The determination of potass- ium by means of ion-selective electrodes".lO involving the use of crown ethers has been reported. as has their use as potentiometric titrants. 1 1 Crown ethers have also been used for chromatographic ~eparations.3~12 Photometric or fluori- metric determinations, particularly of alkali and alkaline earth metal ions, can be carried out by solvent extraction of the ion pair formed between the crown ether complex and a col- ouredl3 or fluorescent14 counter ion.Also, direct photometric determinations have been performed by using crown ethers having a chromogenic crown.2.15-17 This paper describes the extractive - spectrophotometric determination of potassium using dibenzo- 18-crown-6 and bromothymol blue as the coloured counter ion. In addition, a study of the extraction of the crown ether - K+ complex using various counter ions and organic solvents was carried out. The method was applied successfully to the determination of potassium in fruits and beverages. Experimental Apparatus A Perkin-Elmer 554 spectrophotometer with 1 .O-cm glass cells and a Philips PW-9408 pH meter with a combined glass - calomel electrode were used.Reagents All chemicals used were of analytical-reagent grade or better, and water purified with a Millipore Nanopure system was used throughout. Dibenzo-18-crown-6 was obtained from Merck. A 0.1 'YO im V solution in chloroform was prepared. A 0.04% rrzlV bromothymol blue (BTB) solution was prepared by dissolving 0.04 g of BTB in 10 ml of ethanol and diluting to 100 ml with water. A 1 .0 g 1 - 1 stock solution of potassium was prepared from potassium chloride. Working standard solutions were pre- pared fresh by dilution of the stock solution. A buffer solution (pH 5.1) was prepared by mixing EDTA (2.0 g), lithium hydroxide (4.8 g) and glacial acetic acid (13 ml) and diluting to 1 1 with water.Recommended Procedure Determinution of potassium To a solution containing between 1 and 30 pg of potassium in a 50-ml separating funnel add 1 ml of buffer solution and dilute to 7 ml with water. Add 10 ml of dibenzo-18-crown-6 solution and shake for 2 min. Then add 3 ml of BTB solution and shake for a further 5 min. Discard the aqueous layer and measure the absorbance of the chloroform extract at 410 nm against a blank prepared in the same way but without the potassium solution. Use this procedure to construct a calibration graph. Fruit. Mineralise about 1 g (weighed accurately) of fruit in a muffle furnace for 30 min at 500 "C. Allow the residue to cool, then dissolve it in water, filter the solution and dilute to 100 ml with water. Take suitable aliquots of this solution and proceed as described under Determination of potassium.Orange urid lemon juice. Evaporate about 2 g of the sample to dryness, then follow the procedure described above for fruit . Beer. Take a 5-ml aliquot of the sample and dilute it to 100 ml; allow the C02 evolved to escape at room temperature overnight. Use suitable aliquots of this solution and proceed as decribed under Determination of potassium. Results and Discussion Selection of Counter Ion and Extraction Solvent Several acidic, coloured dyes, including methyl orange, congo red, bromocresol green, bromophenol blue, thymol blue and BTB, were used as counter ions; the highest absorbance was obtained with BTB. In addition, a study of the influence of the solvent on the efficiency of the extraction was carried out; chloroform was found to be the best solvent.The dibenzo-18- crown-6 - K+ complex, extracted into chloroform. with BTB as the counter ion, had an absorption spectrum with a maximum at 410 nm (Fig. 1). 300 400 500 600 Wavelengthin m Fig. 1. (A) Absorption spectrum of the dibenzo-18-crown4 - K+ - BTB system in chloroform. (B) Blank against water. cK = 1.5 pg ml-I534 ANALYST, APRIL 1989, VOL. 114 Table 1. Effect of foreign ions on the determination of 10 ug of potassium 1 0.8 I I L 0 4 PH 2 8 Fig. 2. BTB system. cK = 2.0 pg ml-1 Absorbance - pH graph of the dibenzo-18-crown-6 - K+ - Influence of pH Dibenzo-18-crown-6 and other crown ethers have been reported to be proton complexing agents18319 and this, together with the fact that BTB behaves as a weak acid, probably explains the influence of pH on the absorbance of the chloroform extract. Fig.2 shows the absorbance - pH graph; as can be seen the absorbance is independent of the pH in the range 4.2-5.8. A pH 5.1 buffer solution was used to adjust the pH of the aqueous phase within this range. Several buffer solutions were tested (glycine - HC1, imidazole - HC1) but none of them had a good buffer capacity in the optimum pH range. As the Li+ ion does not interfere with the formation of the dibenzo-18-crown4 - K+ complex14 an acetic acid - lithium acetate buffer was used; good results were obtained. Further, as EDTA also produces no interference, a buffer solution consisting of acetic acid, lithium hydroxide and EDTA (pH 5.1) was employed.This solution had a good buffer capacity and a better selectivity. Extraction of Potassium and Extraction Variables The influence of the crown ether and BTB concentrations was studied for a constant amount (2.6 X 1 0 - 5 ~ ) of potassium. The maximum absorbance was obtained when equal concen- trations of potassium and crown ether were used (with an excess of counter ion). The absorbance remained constant at higher crown ether to potassium ratios. Hence a concentration of 2.7 x 10-3 M of crown ether was used. For a reproducible extraction, an excess of the counter ion is essential; however, a very large excess would lead to the blank being highly coloured and would introduce errors into the absorbance measurements. Hence 3 ml of a 0.04% BTB solution, diluted to 10 ml to obtain a BTB concentration of 1.9 X 10-4 M, were used.In order to avoid the formation of emulsions between the organic and aqueous phases, the BTB must be added after complexation of the K+ ion with the crown ether; the formation of emulsions is undesirable because the dye is then adsorbed and irreproducible values for the absorbance are obtained. For this reason a procedure consisting of two extraction steps was employed. The first step is performed in the absence of the counter ion and the second after adding BTB. Constant absorbances are obtained after shaking for 2 min in the first extraction step, and for 5 min in the second. Linearity, Sensitivity and Precision A linear relationship between absorbance and potassium concentration is obtained in the range 0.1-3.0 pg ml-l Foreign ion Tole r a ncei Pg Mg*+, Fe*+, Fe3+, Mn*t, Ni*t, Ag+, Hg*+, Pb*+, Zn*+, Cd2+ .. . . . . . . . . . . . . . . 1000 Ca2+ Co2+, Cu2+, Be2+ . . . . . . . . . . . . 500 Bi3+ . . . . . . . . . . . . . . . . . . 250 N a i , C s + . . . . . . . . . . . . . . . . . . 100 Sr*+, Ba*', T1+ . . . . . . . . . . . . . . 20 Rb', NH,+ 10 . . . . . . . . . . . . . . . . Table 2. Determination of potassium in fruits and beverages Potassium contenthequiv. per 100 g Sample Banana fruit . . Orangeflesh . . Lemonflesh . . Orange juice Lemon juice . . Applejuice . . Beer . . . . Low alcohol beer Proposed method . . . . 10.33 . . . . 3.69 . . . . 3.22 . . . . 3.91 . . . . 3.34 . . . . 2.12 . . . . 0.80 . . . . 0.52 Flame photometry 10.36 3.71 3.21 3.93 3.27 1.99 0.82 0.53 of potassium and the molar absorptivity is 1.8 X 104 1 mol-1 cm-1.The precision of the method was checked by analysing 11 samples as described under Recommended Procedure; a relative standard deviation of 2.3% (p = 0.05) was obtained. Effect of Foreign Ions The influence of alkali and alkaline earth metal ions and also other metal ions was investigated. An ion was considered to interfere if it caused a variation in the absorbance of more than twice the relative standard deviation obtained for the determi- nation of potassium alone. Table 1 shows the results obtained. The degree of interference for alkali metal ions is in the order Rb+ > Cs+ =: Na+. This is consistent with the order of the stability constants4 of the corresponding metal - crown ether complexes.The NH4+ ion produces a large interference but this can easily be removed by making the sample solution alkaline with lithium hydroxide and boiling. For some alkaline earth metal ions, e.g., Mg2+, and heavy metal ions, e.g. Agt , Hg2+ and Pb2+, the tolerance level is higher than might be expected from consideration of the stability constants of the corresponding metal - crown ether or ion-association com- plexes. This is due to the masking effect of EDTA in the buffer solution. Applications In order to ascertain the utility of the proposed method, the potassium content of some fruit juices and beverages (orange, apple and lemon juices and beer) was determined. The results are summarised in Table 2 and are compared with those obtained by flame photometry; there was good agreement between the two methods.Conclusion The sensitivity of the proposed method compares favourably with that of flame photometry, the latter being one of the most commonly used methods for the determination of potassium in food quality control. The tolerance level of the method towards transition metal ions and several heavy metals ions isANALYST. APRIL 1989, VOL. 114 535 very high; in addition, some of the alkali metal ions, e.g., Na+, which is normally present in many food samples, can be tolerated at high levels. The authors thank the Comision Asesora de Investigacion Cientifica y Tecnica del Ministerio de Educacion y Ciencia de Espaiia for supporting this study (PR 84-1024). 1. 2. 3. 4. 5. 6. 7. 8. 9. References Pedersen, C. J ., J. Am. Chem. SOC., 1967, 89,7017. Muroi, M.. Harnaguchi, A., and Sekido, E., Anal. Sci., 1986, 2, 351. Yoshio, M., and Noguchi, H., Anal. Lett., 1982, 15, 1197. Kolthoff, I. M., Anal. Chem., 1979, 51, 1R. Weber, E., Kontakte, 1984, 26. Shono, T., Bunseki Kagaku, 1984, 33, E449. Blasius, E . , and Janzen, K. P., Top. Curr. Chem., 1981, 98, 163. Antonovich, V. P., and Shelikkina, E. I.. Zh. Anal. Khim., 1980, 35, 992. Bitter, I., Toke, L., and Hell, Z . , FreJenius 2. Anal. Chem., 1985, 322, 157. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. Xi, Z . , Huang, S., Zhang, D., and Li, H., Fenxi Huaxue, 1986, 14, 102; Anal. Abstr., 1986, 48, 6598. Papadoyannis, J. N . , Anal. Lett., 1985, 18, 2013. Kimura, K., and Shano, T., J . Liq. Chromatogr., 1982, 5 , 223. Pacey, G. E., and Wu, Y. P., Talanta, 1984, 31, 165. Sanz Medel, A., Blanco, D., and Garcia Alvarez, J. R . , Talanta, 1981, 28, 425. Pacey, G . E., Wu, Y. P., and Bubnis, B. P.,Analyst, 1981,106, 636. Katayama, Y., Nita, K., Ueda, M., Nakarnura, H., Tagaki, M., and Ueno, K., Anal. Chim. Acta, 1985, 173. 193. Bubnis, B. P., and Pacey, G. E . , Talanta, 1984, 31, 1149. Shchori, E., and Grodzinski, J. J.. J. Am. Chem. Soc., 1972, 94, 7957. Nae, N. N., and Grodzinski, .I. J.,J. Am. Chem. Soc., 1977.99, 489. Paper 8102777C Received July I l t h , 1988 Accepted November I1 th, 1988

ISSN:0003-2654    

DOI:10.1039/AN9891400533

出版商:RSC    

年代:1989

数据来源: RSC

摘要:

ANALYST. APRIL 1989, VOL. 114 537 BOOK REVIEWS Microcomputers and Laboratory Instrumentation. Second Edition David J. Malcolme-Lawes. Pp. xii + 272. Plenum Press. 1988. Price $39.50. ISBN 0 306 42903 9. This book aims to introduce the subject of microcomputers in the laboratory to scientists. After the introduction, the next four chapters discuss in detail the basic electronics associated with the handling and processing of analogue and digital signals from sensors and instrumentation. The means of generating output signals for control is covered. The text includes such topics as noise and interference, op-amps, TTL families and analogue to digital conversion, with both the theory and practical examples. The book continues by describing the elements of a microcomputer system in general and then specifically the EBM PC style of computer.Subsequent chapters address methods of interfacing computers including the main interfacing standards, and the book concludes with a chapter on design procedures and a case study. It is inevitable that a book which deals with microcomputers will be out of date as soon as it is published, such is the rate of developments in this area. It was unfortunate that the timing of the first edition of this useful and interesting book was in the early days of the IBM PC and before it was clear that this machine would set a de facto standard in the field of microcomputers. In this second edition, apart from having the text typeset, the author has completely revised the main sections discussing microcomputers and concentrated almost exclusively on the IBM PC and MSDOSiPCDOS environ- ment.Also, the sections on parallel, serial and GPIB interfaces have been expanded to advantage. The chapter on system design has been developed and there are numerous other small changes in the text to bring it nearer to date. The index is very comprehensive, but does not refer to the IBM PS/2 family or the micro-channel architecture used in some members of that family, although it is not clear that this will be such a standard as the earlier PC. Presumably the third edition will follow in due course. This is a very good book. It is written clearly in a friendly, encouraging, but realistic style with good explanations and descriptions. It covers the subject areas to a sensible depth and clearly fulfils the author’s objectives of providing scientists with an understanding of microcomputers and their inter- action with laboratory instrumentation.It may reflect the reviewer’s interests, but my major criticism is that the first half of the book is devoted to the basic electronics of signal handling, and the computers come second. Also, there is little discussion of the large range of interface cards and data acquisition software available for PCs, which would be an advantage to those unwilling to wield a soldering iron. This aside, I enjoyed the book and consider that it will be useful both as an introduction to the area and as a reference book to keep on the bookshelf. John Huddleston Chemical Sensor Technology, Volume 1 Edited by Tetsuro Seiyama.Pp. xvi + 250. Elsevier. 1988. Price $150; Df1285. ISBN 0 444 98901 3. This volume is the first of a new series of annual reviews of chemical sensor technology, which aims to chart the progress and innovations of investigators and engineers working in this field. It is, therefore, a multi-author compilation with 15 chapters on various aspects of sensors. The first short chapter, by the editor, discusses the technology of some current devices, their applications and the future outlook. Chapters 2-15 discuss specific classes of devices: physical and chemical aspects of oxidic semiconductor gas sensors, tin dioxide gas sensors, ceramic humidity sensors, limiting current type oxygen sensors, solid electrolyte sensors for S02/S03, indus- trial uses of zirconia sensors, room temperature solid-state gas sensors, ion sensors for micro-sampling, suspended gate field effect transistors, micromachining for chemical sensors, mic- rofabrication of biosensors, medical applications of the glucose sensor, a study of the artificial pancreas and optical chemical sensors.The chapters in multi-author volumes often vary in depth. quantity and quality; this book is no exception, and several chapters give the impression that they have been translated from a foreign language with varying degrees of success. The resulting text, however, is printed to a high standard with clear figures and provides a useful combination of articles discussing both the specific work of authors and more general descrip- tions of sensing technology. As a continuing series it makes no attempt to be exhaustive and the style chosen requires several volumes to provide a comprehensive picture of activity in the sensor field.In conclusion, this book provides a useful review of progress in several areas of sensor technology and will be particularly valuable to investigators who would like to learn more about fields related to their current work. J. M . Slater Nuclear Magnetic Resonance, Volume 17 Senior Reporter G. A. Webb. Specialist Periodical Report. Pp. xii + 484. Royal Society of Chemistry. 1988. Price fl10; $239. ISBN 0 85186 402 3. This is the seventeenth volume in a series dedicated to providing state-of-the-art reviews of the literature for the previous year. This volume covers June 1986-May 1987. The statistics of the book itself give some indication of its coverage and the enormous effort involved in producing it.Fifteen authors and one editor have produced 12 chapters and a collation of books and reviews contained in 472 pages. Of these pages, 130 contain only references, these being 4596 in number. Hence, there is available for the authors only about 0.07 of a page to deal with each reference. Under such constraints a reference by reference approach is impossible and most authors make use of tables of one sort or another. Even with tables, the coverage is necessarily less than comprehensive in some instances. For example, R. Dupree in his chapter on solid-state NMR has no space (and probably not the time) to cover metals, alloys, fast-ion conductors and low-temperature NMR.The formidable constraints of time, limited chapter length and vast numbers of references make the claim of the fly-sheet, that this and other volumes in the series offer “critical in-depth accounts of progress . . . ,” rather optimistic. To even mention all the relevant references is a major achievement in some areas. One or two authors are, however, blessed with subjects yielding sufficiently few references to allow some degree of critical reviewing: Cynthia Jameson’s chapter, on Theoretical and Physical Aspects of Nuclear Shielding, is one example. The chapter headings give an indication of the subject matter covered. Nuclear shielding, both the theory and the applications, is dealt with in two chapters; there are also chapters on theoretical aspects of spin - spin couplings, conformational analysis, oriented molecules, nuclear spin538 ANALYST, APRIL 1989, VOL.114 relaxation in liquids and multi-pulse NMR. Macromolecules are represented by two chapters covering synthetic and natural species. Biology is represented by a chapter on NMR in living systems. There are also two catch-all chapters covering heterogeneous systems and solid-state NMR. These two must have presented the authors with very considerable problems of choice and definition. While it is true that the range of chapters covers most of the NMR that a chemist is likely to be interested in, there is a certain degree of unevenness in the coverage. Solid-state NMK is a vast subject of enormous scientific and commercial importance. It is only accorded one chapter, giving it the same weight as theoretical and physical aspects of nuclear shielding.The latter chapter is useful to read and is of considerable scientific worth but there can be no doubt that solid-state NMR has much more direct and immediate relevance to many more chemists than do these aspects of nuclear shielding. This view is reflected in the number of references cited: 600 for solid-state NMR as against 147 for theoretical aspects of nuclear shielding. One would not want to see the contribution of such a distinguished author as Cynthia Jameson disappear, but there does seem to be an argument for scaling the chapter length to the number of references. Perhaps in order to lighten the load on the authors, subdivision of large subject areas would be useful.In particular, in the solid-state NMR area a division in to high resolution and relaxation time/wide line methods may be appropriate. Similarly one wonders if multi-pulse NMR is really a coherent subject; perhaps a division into two-dimensional methods and others might be an improvement. One must ask if all the Herculean effort involved in writing, editing and printing the book in such a short period is worthwhile. In my view it is. This volume together with its predecessors does give the reader a very useful snapshot of the current state-of-the-art and does offer a comprehensive literature guide to NMR. Its proper place is not in the library but on the office shelf. It is unfortunate that the ridiculously high price of &110 precludes this for all but the most richly endowed scientists.P. S. Belton Problem Solving With Microbeam Analysis K. Kiss. Studies in Analytical Chemistry 7. Pp. 409. Elsevier. 1987. Price $1 19.50; Df1245. ISBN 0 444 98949 8 (Volume); 0 444 41944 6 (Series). This hardback book is the seventh in a series of texts dealing with Studies in Analytical Chemistry. It is aimed at the industrial analyst whose field of expertise does not include microbeam analysis. Its justification stems from the techno- logical emphasis placed on the manufacturing methods of new products. The characterisation of the structures of such products, which involves studies on the micron or sub-micron scale, is often a prerequisite to understanding their perform- ance, in addition to guaranteeing their quality. This quest for knowledge, and the simultaneous develop- ment of computer technology, has resulted in the develop- ment of several sophisticated instruments which are expensive to purchase and require skilled operators.Dr. Kiss considers 17 such instruments/techniques which are classified under photon probes, electron probes or ion probes. As with almost all instruments, there are advantages in, and limitations to, their use. Through the information provided, Dr. Kiss seeks to direct the uninformed to the technique most appropriate for solving the problem in hand. However, the potential user is left to find the location where the technique, and relevant experience in operation, can be found. The book is divided into two sections. The first is headed “Theory and Techniques.” It has 11 chapters, covers 165 pages and has 590 references.The reader should not expect a comprehensive detailed discussion of each technique, e.g. , the chapter covering transmission electron microscopy and elec- tron diffraction covers eight pages of text and diagrams. The advantages/limitations of the technique are sometimes sum- marised at the end of the chapter, but Chapter 11 also does this and so compares the techniques. This chapter covers the strategy of technique selection and is probably the most informative section of the book. It is disappointing to find no mention of the use of selected area diffraction for establishing phase identity, and wavelength dispersive spectrometry included under scanning electron microscopy. By doing so Dr. Kiss fails to recognise that, under certain circumstances, analyses using wavelength dispersive methods can be faster than energy dispersive methods.Some of the 17 techniques introduced initially receive no further mention, except in Chapter 11. The second section of the book concerns applications of these techniques. The section covers a similar number of pages, and has a further 239 references. Case histories from many disciplines, but usually in the fields of polymers and microelectronics, are presented. Examples of applications to metallurgy, corrosion, glass, ceramics, fibres, food products, cosmetics and environmental problems are fewer, e.g., 16 metallurgical/corrosion applications fill 20 pages. The emphasis is on the chemical information that was obtained rather than the structural information, which is often dis- played in poor quality micrographs. The frequency of tech- nique mention suggests that some techniques, usually the older well developed ones, are much more applicable than those whose full potential has yet to be realised. This collection of relevant information obtained from these instrumentshechniques gives the potential user an unbiased opinion of their use. The alternative is a discussion with an experienced operator, who first has to be located, and who may not be familiar with the advantages or limitations of all other potentially useable techniques. D. J . Dyson

ISSN:0003-2654    

DOI:10.1039/AN9891400537

出版商:RSC    

年代:1989

数据来源: RSC