ISSN:0003-2654    

DOI:10.1039/AN98308FX009

出版商:RSC    

年代:1983

数据来源: RSC

ISSN:0003-2654    

DOI:10.1039/AN98308BX011

出版商:RSC    

年代:1983

数据来源: RSC

ISSN:0003-2654    

DOI:10.1039/AN98308FP029

出版商:RSC    

年代:1983

数据来源: RSC

ISSN:0003-2654    

DOI:10.1039/AN98308BP035

出版商:RSC    

年代:1983

数据来源: RSC

摘要:

March 1983 The Analyst Vol. 108 No. 1284 Determination of Palladium in Nuclear-waste Samples by Inductively Coupled Plasma Emission - Fluorescence Spectrometry Paolo Cavalli Guglielmo Rossi and Nicolo Omenetto Commission of the European Communities Joint Reseavch Centre Chemistvy Division 21020 Ispva ( Vavese), Italy The determination of palladium in sample solutions of nuclear waste by in-ductively coupled plasma (ICP) optical emission spectrometry with a 0.5-m monochromator is hindered by severe spectral interference that occurs a t all the analytically useful wavelengths of palladium Interferences from argon, yttrium zirconium samarium and neodymium lines have been experienced with the palladium lines a t 363.47 324.27 340.45 and 360.95 nm. In order to overcome these interferences a spectrometer of high resolution is required.This precludes the use of a multi-channel spectrometer and indicates the application of a high-resolution scanning monochromator. In this paper we show that a simple and effective alternative approach to the problem is offered by combination of the ICP emission characteristics with the spectral selec-tivity of atomic-fluorescence spectrometry. Measurement of the palladium atomic fluorescence a t 363.47 nm from a sample atomised in an argon-shielded air - acetylene flame excited by the emission of a pure 5000 pg ml-l solution of palladium fed into the ICP torch allows for the precise and accurate determination of palladium with no problems due to scattering. In addition the palladium concentration in the samples is such that the ICP -resonance monochromator technique could be quickly and effectively used with no sample dilution provided that sufficient sample is available and that radioactivity is at a tolerable level.Keywords Palladium determination ; inductively coupled plasma ; atomic-jluorescence spectrometry ; nuclear materials Studies on the chemical separation processes of nuclear-waste solutions require analytical methods that are suitable for monitoring a series of key elements over a wide range of con-centration levels. The analytical characteristics of the inductively coupled plasma ( I C P y make it very attractive for this type of application. In particular the absence of self-absorption and self-reversal the marked freedom from chemical interferences and the very high detection power for a large number of elements represent the most desirable charac-teristics for the analysis of complex sample matrices.A typical composition of a nuclear-waste solution is presented in Table I. TABLE I APPROXIMATE COMPOSITION OF A TYPICAL SAMPLE OF NUCLEAR-WASTE SOLUTION Concentration interval/ pg ml-' Elements 0.1-10 Ag Al As Ge In Sb Tb 10-100 Cd Cr Cu Eu Gd Ni Rb Rh Se Sn Y 100-500 Ba La Pd Pr Ru Sn Sr Te 500-1 000 Ce Cs Mo Nd U Zr Although a multi-channel optical emission spectrometer equipped with an ICP (ICP-OES) source appears to be the first choice of combination to be investigated it must be stressed that with very complicated matrices (as for example the one under examination) the high detection power for a large number of elements can represent a serious limitation for the determination of some elements at the preselected wavelengths owing to the possibility of 297 > 1000 Fe N 298 CAVALLI et al.DETERMINATION OF PD IN NUCLEAR-WASTE Analyst Vol. 108 P Fig. 1. Experimental arrangement A ICP torch; F air - acetylene flame L quartz lenses; C chopper; P polychromator; SM scanning mono-chromator ; FM fluorescence monochromator ; and PM photomultiplier. spectral interferences. Further channels corresponding to particular elements may be missing from the spectrometer thus negating the determination of these elements. In these instances sequential-scanning spectrometers offer a greater flexibility a t the expense of the speed of analysis the most serious limitation to a multi-element analysis being represented by the size of sample available.The 30-channel ICP-optical emission spectrometer available in our laboratory does not include the element palladium whose determination is important in one of the several schemes available for the separation of the actinide^.^ Attempts to determine this element by coupling a medium-resolution scanning monochromator to the ICP source failed for reasons that will be discussed later. The aim of this paper is to describe the practical application of the combined use of the ICP and a separate atomiser (flame) for determining palladium in solutions of nuclear waste, either by conventional atomic fluorescence or by the resonance monochromator te~hnique.~-* TABLE I1 EXPERIMENTAL CONDITIONS Component ICP .. Nebuliser . . . . Emission monochromator and electronics . . . . Fluorescence monochromator and electronics . . . . . . Lenses . . . . Flame . . Details Emission Quantometer (ARL Lausanne Switzerland) Model 3400, and a 3000 PGT/27 HF generator (Henry Radio Los Angeles CA). Argon flow-rates 1 0.8 and 10.5 1 min-l for carrier internal and plasma gas respectively Concentric glass nebuliser T 2001 A4 (Meinhard Ass. Santa Anna, CA) Jarrell-Ash 0.5-in Ebert grating monochromator flS.6 a 30000-grooves per inch grating 25-pm matched slit widths. EM1 6256 PMT operated at 1300 V; Keithley Model 414 picoammeter; Perkin-Elmer Model 56 strip-chart recorder Jobin Yvon H-10 grating monochromator f / 3 . 5 1-mm slit widths.RCA 1 P28 PMT Model 382A chopper (Ithaco Ithaca NJ). Keithley 427 current to voltage converter and Dynatrac 391A lock-in amplifier (Ithaco Ithaca N J ) Quartz spherical lenses 3 cni diameter 12.5-cm focal length for emission work. Stoicheiometric argon sheathed air - acetylene flame No lenses were used for fluorescence wor March 1983 SAMPLES BY ICP EMISSION - FLUORESCENCE SPECTROMETRY 299 In the first instance the sample atomised in an air - acetylene flame is excited by the emission from a solution of pure palladium fed into the ICP torch and in the second approach, a solution of pure palladium atomised in the air - acetylene flame constitutes the resonance monochromator for the spectral frequenciesemitted by the sampleintroducedinto the ICP torch.The basic principles and theory underlying these two approaches their respective merits, analytical potentials and practical applications have been described in the literature5-* and will not be discussed further here. Experimental The ICP torch energised by a 3000 PGC/27HF generator (Henry Radio Los Angeles CA, USA) and fitted on a 30-channel 34000 ARL Quantometer (ARL Lausanne Switzerland), was used for the study of the spectral characteristics of palladium under medium resolution conditions. The torch was fed by a concentric glass nebuliser Model T 2OOL A4 (Meinhard Ass. St. Anna CA USA) and the plasma plume was focused on to the entrance slit of a 0.5-m Ebert monochromator (Jarrell-Ash Waltham MA USA). The same torch assembly was utilised for the fluorescence measurements by focusing the plasma plume on an argon-separated air - acetylene flame supported by a home-made five-slot circular burner.Fluorescence emission was monitored with a 0.1-m monochromator (Jobin Yvon Long-jumeau France). In considering the radioactive nature of the waste solutions the entire study was carried out using synthetic solutions made from analytical-reagent grade compounds (Merck, Darmstadt West Germany and Carlo Erba Milan Italy) closely matching the composition reported in Table 1. The experimental parameters chosen in the course of the study are given in Table 11. The experimental apparatus is represented schematically in Fig. 1. 360 350 340 330 3 Wavelengthh m 0 Fig. 2 Spcctral profile of the wavelerigth region 320-365 nni.(a) M’ater; (b) pure Pd solution 125 pg and (c) sample dilutcd 1 + 1 300 CAVALLI et al. DETERMINATION OF PD IN NUCLEAR-WASTE Analyst VoZ. 108 Results and Discussion The spectral lines of palladium emitted by an ICP source have been listed by Winge et aLg From this list it appears that a number of palladium lines should be suitable for analytical applications. From these the lines at 340.45 363.47 360.95 324.27 and 342.12 nm were considered to be the most promising. However whenever each of these lines was used for quantitative measurements of palladium in synthetic solutions using the medium-resolution monochromator concentration values significantly higher than the established ones were found in all instances. Examination of the spectrum obtained by scanning the wavelength region from 320.00 to 365.00 nm revealed the presence of a very complex structure which was likely to be the cause of spectral interferences.The wavelength region from 220.0 to 250.0nm appeared to be more attractive owing to the reduced number of intense lines in the spectrum. However none of the nine palladium lines that were identified in this region showed sufficient sensitivity for analytical application. The spectral emission profiles of the sample for these two wavelength intervals are presented in Figs. 2 and 3 respectively and are compared with the corresponding spectra recorded while aspirating distilled water and a solution of pure palladium into the torch. I t should be noted that the concentration of the palladium was chosen so as to correspond with that expected in the sample.A closer examination at the best obtainable resolution of the lines at 363.47 360.95 342.12 340.45 and 324.27 nm showed in all instances the occurrence of a strong spectral interference from a concomitant in the solution. 250 240 230 Wavelengthhm i '0 Fig. 3. Spectral profile of the wavelength region 220-(a) Water; (b) pure Pd solution 125 pg ml-I; and 250 nm. (c) sample diluted 1 + 1 . The comparison of the tracings obtained from a 125 pg ml-1 solution of palladium with those exhibited by the synthetic solution of nuclear waste (diluted 1 + 1) at these spectral frequencies is shown in Fig. 4. The nature of these interferences has been investigated further by comparing the spectral profiles of a pure solution of palladium at each of the above mentioned wavelengths with those of the same solution with one of the concomitants added.The chosen concomitant was suspected of interfering both because of its concentration level and because of its spectral signature. In all of the examples considered the palladium to concomitant concentration ratio was equal to that existing in the synthetic waste solution March 1983 SAMPLES BY ICP EMISSION - FLUORESCENCE SPECTROMETRY 301 365 3! 1 -l 1 342.5 337.5 326 323.5 Wavelengthhm Fig. 4. Spectral profiles a t indicated wavelengths as obtained with (a) pure Pd solution (125 pg ml-1) ; and (b) synthetic nuclear-waste solution sample (diluted 1 + 1 ) . As a result of these investigations the following conclusions were drawn (i) the yttrium line at 324.23 nm interferes strongly with the palladium line at 324.27 nm as is shown clearly by the spectral profiles in Fig.5; (ii) the use of the palladium line at 340.45 nm is hindered by the complex interference resulting from the concurrence of the iron (340.44 nm) neo-dymium (340.47 nm) samarium (340.48 nm) and zirconium (340.48 nm) lines while the palladium line at 342.12 nm is of no practical use owing to its low intensity under the selected experimental conditions as can be observed from the spectral tracing in Fig. 6; (iii) the argon line at 363.44 nm is almost coincident with the palladium line at 363.47 nm, thus prohibiting the use of this line for analytical applications; (iv) the palladium line at 360.95 nm is affected by a severe interference from the samarium and neodymium lines at the same wavelength (360.949 and 360.945 nm respectively) ; the spectral profiles related to these interferences are shown in Fig.7. Thus no useful lines for the direct determination of palladium in the sample by ICP-OES under the experimental conditions described could be identified apart from the line at 229.65 nm which is affected by a moderate background interference but its intensity is too low for practical purposes as is shown clearly in Fig. 8. The use of a monochromator having a higher resolving power such as those conventionally coupled to the ICP source (with a focal length of more than 1 m) is likely to make the majority of the palladium lines discussed useful for accurate determinations without any interferences.However it should be stressed that even when the necessary resolution is not available one can still take advantage of the ICP source through the simple instrumental approach offered by the fluorescence technique or by the resonance monochromator technique. In the analysis of samples of nuclear waste however only a limited amount (about 1-2 ml) of sample will be available; this fact and the radioactivity hazard suggest that the samples should be handled after a reasonable dilution. Therefore the ICP - resonance monochroma-tor technique would probably not be applicable to this matrix. Nevertheless it was con-sidered worthwhile to perform some measurements by this technique for comparative purposes taking into account its greater versatility with respect to conventional atomic fluorescence and the fact that scattering problems can be completely overcome.' Conventional atomic-fluorescence measurements have been performed by introducing a 5000pg ml-l solution of palladium into the ICP torch while the sample solution (dilute 302 CAVALLI et al.DETERMINATION OF PD IN NUCLEAR-WASTE AnaZyst VoZ. 108 1 + 9) was nebulised into the argon-shielded air - acetylene flame. A quartz lens was used to focus the plasma plume on to the flame. Conversely no collecting optics were used to monitor the fluorescence at 363.47 nm with the 0.1-m focal length monochromator whose entrance slit was located 5 cm away from the flame at right-angles to the main optical axis. 324.5 324.0 Wavelengthhm Fig. 5 . Spectral inter-ference of Y at 324.27 nm.(a) Pure Pd solution (5 pg.ml-l); ( b ) pure Y solution (1.5 pg ml-1); and ( G ) synthetic nuclear-waste solution sample (diluted 1 + 49). 342 341 340 339 Wavelengthlnm Fig. 6. Combined inter-ference of Fe Nd Sm and Zr at 340.46nm. (a) Water (b) pure Pd solution (1 pg ml-l) ; (c) synthetic nuclear-waste solution sample (diluted 1 + 199); and (d) Pd solution (1 pg rn!-l) + 3 pg ml-l Zr solution. Quantitation was achieved by aspirating standard palladium solutions into the flame at concentration levels above and below that of the sample. No significant contribution to the scattering of the measured signal was found. Almost coincident analytical results were obtained by the ICP - resonance monochromator technique. In this instance the sample (undiluted) was aspirated into the ICP torch the resulting emission being analysed by a resonance monochromator made by the air - acetylene flame fed with a 500 pg ml-l solution of palladium.The excellent matching of the analytical data from the two techniques constitutes a further indirect check of the negligible influence of the scattering with con-ventional atomic-fluorescence measurements. The analytical data as compared with atomic-absorption values are given in Table 111 March 1983 SAMPLES BY ICP EMISSION - FLUORESCENCE SPECTROMETRY 303 I 1 I 1 361.5 361.0 360.5 360.0 361.5 361.0 360.5 360.0 Wavelength/nrn Fig. i . Sm and Nd interference a t 360.95 nm. (a) Water; (b) pure Pd solution (5 pg ml-l) ; (c) pure Sm solution (3 pg ml-l); ( d ) pure Nd solution (15 pg ml-l) ; and (e) synthetic nuclear-waste solu-tion sample (diluted 1 + 49).( a ) , 230 229 Wavelength/nrn Fig. 8. Traces at 229.65 nm Pd wave-length. (a) Water; (b) pure Pd solution (250 pg ml-l); and (c) syn-thetic nuclear-waste solu-tion sample. Conclusions I t has been shown that with very complex matrices ICP-OES can suffer from severe problems arising from spectral interference which are likely to hinder or make impossible, analysis by simultaneous multi-channel spectrometers. In these circumstances scanning monochromators represent the obvious alternative way to solve the problem provided that adequate resolving power is available. With the determination of palladium in solutions of TABLE I11 ANALYTICAL RESULTS 'I'hc rcproducibility of the measurements \\.'as aln.ays of the orclcr of 2lYb.T'al latli urn conccn tration / Jlcthod of analysis pg ml-1 Analytical line/nm Expected (synthetic solutions) . . . . 260 ICP - excited fluorescence . . . . . . 250 1C1' - emission resonance monochromator . . 250 Flame atomic absorption . . . . 265 363.5 363.5 247. 304 CAVALLI ROSS1 AND OMENETTO nuclear waste a simpler approach to removing spectral interferences from concomitants in the solution is offered by the combination of the ICP source with the spectral selectivity of at omic-fluorescence spectrometry . The simplicity of the experimental set-up does not need to be stressed the general con-figuration of the ICP-emission spectrometer both simultaneous or sequential being in no way altered by the addition of a supplementary atomiser.As already discussed’ the use of an ICP to excite fluorescence in an external atomiser must not be regarded as a replacement for the conventional application of this source for analytical emission spectrometry. However by the techniques described the versatility and flexibility of the ICP can be further exploited and some troublesome analytical problems solved. 1. 2. 3. 4. 6. 6. 7. 8. 9. References Fassel V. A. Anal. Chem. 1979 51 1290A. Boumans P. W. J. M. and De Boer F. J. Spectrochim. Acta Part B 1975 30 309. Barnes R. M. Crit. Rev. Anal. Chem. 1978 7 203. Cecille L. Dworschak H. Girardi F. Hunt B. A, Mannone F. and Mousty F. in Navratil, J. D. and Schulz W. W. Editors “Actinide Separation,” ACS Symposium Series 117 American Chemical Society Washington DC 1980 p. 427. Epstein M. S. Nikdel S. Omenetto N. Reeves R. D. Bradshaw J . D. and Winefordner J. D., Anal. Chem. 1979 51 2071. Epstein M. S. Omenetto N. Nikdel S. Bradshaw J . D. and Winefordner J. D. Anal. Chem., 1980 52 284. Omenetto N. Cavalli P. and Rossi G. Rev. Anal. Chem. 1982 5 384. Cavalli P. Omenetto N. and Rossi G. At. Spectrosc. 1982 3 1. Winge R. K. Peterson V. J. and Fassel V. A. Appl. Spectrosc. 1979 33 206. Received May 17th 1982 Accepted September 2nd 198

ISSN:0003-2654    

DOI:10.1039/AN9830800297

出版商:RSC    

年代:1983

数据来源: RSC

摘要:

Ai?alyst March 1983 VoZ. 108 $9. 305-309 305 Determination of Tellurium by Atomic-absorption Spectroscopy with Elect rother ma1 Atom isat ion after Pre-concentration by Hydride Generation and Trapping William A. Maher" Departvnent of Oceanography University of Southampton Southampton SO9 5NH A procedure for the determination of tellurium a t sub-microgram levels bv atomic-absorption spectroscopy with electrothermal atomisation after the evolution and trapping of hydrogen telluride is described. Interferences are observed in the presence of silver(I) copper(II) mercury(I1) and selenium(1V) but can be overcome by suitable pre-treatment procedures. The detection limit (based on four times the standard deviation of six blank measurements) is 0.006 pg and the coefficient of variation is 4% at the 0.3-pg level.Keywords Tellurium ; Jlydride generation and trapping ; atornic-absorption spectroscopy ; electrothermal atomisation ; interferences Tellurium is used extensively in the electronics industry and is a potentially toxic environ-mental pollutant .l Hence sensitive methods of determination are required for monitoring tellurium concentrations in the environment and to allow the biochemical role and toxico-logical effects of tellurium to be assessed. Many techniques are available for the determination of tellurium.2-6 A widely reported technique has been hydride generation - atomic-absorption spectroscopy. The prior con-version of tellurium into hydrogen telluride is used to increase sensitivity and the hydride has been flushed directly into a flame'-9 and a variety of heated silica tubes.l0V1l At present, methods incorporating hydride generation have mainly been used to analyse standard solution^^-^^ with limited application to complex or environmental samples.8t11 In this paper the optimisation of a hydride generation and trapping system for the isolation and concentration of tellurium? prior to atomic-absorption spectroscopy with electrothermal atomisation is described.The advantage of using a trapping system is in the elimination of the effects of interferents causing variable rates of hydride evolution. Interferences have been investigated and procedures developed for the removal of severe interferences. Experimental Equipment The hydride generation and trapping system used is illustrated in Fig.1. Nitrogen was used to flush hydrogen telluride from the generator into the centrifuge tube. Sodium tetra-hydroborate(II1) solution was injected using a plastic syringe connected to a small length of narrow-bore plastic tubing leading to the bottom of the flask. All atomic-absorption measurements were made with a Varian Techtron AA5 background-corrected atomic-absorption spectrometer fitted with a Perkin-Elmer HGA 72 carbon furnace. The following spectrometer conditions were used throughout the work lamp current 8 mA ; wavelength? 214.3 nm; and spectral band pass 0.2 nm. Reagents and Glassware (2 + S ) rinsed with distilled water and dried before use. in 100 ml of 3 M hydrochloric acid. in 100 ml of 3 M hydrochloric acid. 5000 Australia.All chemicals were of analytical-reagent grade. Glassware was soaked in sulphuric acid TeZZurium(IV) standard solution 1000 pg ml-l. Dissolve 0.1264 g of tellurium(1V) oxide Tellurium( V I ) standard solution 1000 pg ml-l. Dissolve 0.1802 g of ammonium tellurate * Present address Department of Physical and Inorganic Chemistry University of Adelaide Adelaide 306 Analyst Vol. 108 Dissolve 2.5 g of sodium tetrahydro-borate(II1) in 25 ml of 0.1 M sodium hydroxide solution. This solution is filtered through a 0.4-pm membrane filter to remove inhomogeneities and increase solution stability to at least 5 h. Prepare a trapping solution by dissolving 0.8 g of potassium iodide and 0.5 g of iodine in 100 ml of distilled water. Dissolve 5 g of lanthanum(II1) chloride in 100 nil of distilled water.Dissolve 0.2 g of DAN in 100 ml of 0.1 M hydrochloric acid containing 0.5 g of hydroxylammonium chloride. This solution is purified after heating at 50 "C for 25 min by extraction with cyclohexane. EDTA - hydroxylamine solution 10% m/V. Prepare by dissolving 5 g of disodium ethylenediaminetetraacqtate (EDTA) and 5 g of hydroxylammonium chloride in 50 ml of distilled water . Dissolve 0.5 g of diphenylthiourea in 50 ml of chloro-form. MAHER DETERMINATION OF T E BY AAS WITH Sodium tetrahydroborate(III) solution 10% m/V. Potassium iodide (0.8% m/V) - iodine (0.5% m/V) solution. Lanthan.um(III) solution 5o/b m/V. 2,3-Diaminonaphthalene (DAN) solution 0.2% m/V. Diphenylthiouurea ureagent 1% m/V. Nz Ball-ioint Rubber 1 septum Syringe (1 rnl) Mod if i ed Drechsel head Pasteur pipette 100-ml flask-,) Centrifuge tube Fig.1. Hydride generation and trapping system. Procedure Solutions are initially diluted to 50 ml with hydrochloric acid (final concentration 6 M) and heated at 100 "C for 40 min to reduce any tellurium(V1) present to tellurium(1V). A hydrochloric acid solution is transferred into the hydride-generation flask and the apparatus assembled as in Fig. 1 with 2 ml of potassium iodide - iodine solution in the centrifuge tube. The nitrogen flow-rate is adjusted to 300 ml min-l 1 ml of sodium tetrahydroborate(II1) solution is injected and the hydrogen telluride that evolves is collected over a 4-min period. Aliquots (20 pl) of the potassium iodide - iodine solution are injected into the carbon furnace and the tellurium atomic absorption is measured using the optimum conditions established for the removal of the potassium iodide - iodine solution (Table I).TABLE I OPTIMUM CARBON FURNACE PROGRAMME FOR THE DETERMINATION OF TELLURIUM BY ATOMIC-ABSORPTION SPECTROSCOPY WITH ELECTROTHERMAL ATOMISATION Stage r 1 Parameter Dry Ash 1 Ash 2 Atomise* Temperature setting . . . . . . 18 35 90 600 Temperature/"C . . . . 39 98 370 2213 Time/s . . . . 40 60 10 5 * Atomisation temperatures quoted are manufacturer's temperatures March 2983 ELECTROTHERMAL ATOMISATION BY HYDRIDE GENERATION Results Optimisation of Hydride Generation and Trapping 307 To optimise the conditions for hydride generation and trapping the effects of sodium tetrahydroborate( 111) concentration hydrochloric acid concentration gas flow-rate and trapping-solution composition on the evolution and trapping of hydrogen telluride were investigated.Sample solutions containing 0.75 pg of tellurium(1V) in 50 ml of 5 M hydro-chloric acid and 2 ml of a 1% m/V potassium iodide - iodine solution were used for the optimisation of flow-rate and sodium tetrahydroborate( 111) concentration. The optimum gas flow-rate was 300 ml min-l and solutions containing 10% m/V sodium tetrahydroborate-(111) in 0.1 M sodium hydroxide quantitatively reduced up to 0.75 pg of tellurium to hydrogen telluride. Variation of the hydrochloric acid concentration was found to have a pronounced effect on hydride generation (Table 11) the optimum hydrochloric acid concentration being 6 M.Under these optimum conditions the collection of hydrogen telluride was complete within 4 min. A trapping solution containing 0.8% m/V of potassium iodide and 0.5% rn/V of iodine quantitatively trapped up to 0.75 pg of tellurium as the hydride. TABLE I1 EFFECT OF HYDROCHLORIC ACID CONCENTRATION ON HYDRIDE GENERATION AND TRAPPING The conditions were as follows trapping solution composition 1 yo m/ V potassium iodide 1 m/ V iodine ; flow-rate 300 ml min-l; collection time 10 min ; and all solutions contained 0.75 p g of tellurium(1V) and were injected with 1 ml of 10% m/V sodium tetrahydroborate(II1) solution. Hydrochloric acid concentrationlM . . . . 2.4 3.6 4.8 6.0 7.2 8.4 Tellurium recovered % . . . . . . . . 33 78 94 100 97 84 Preliminary experiments showed that only tellurium( IV) will form hydrogen telluride.Therefore any tellurium( VI) present initially in extracts or produced during preparation of extracts must be reduced to tellurium(1V). The method selected to reduce tellurium was to heat extracts with hydrochloric acid i . e . Te(V1) + 2C1- + Te(1V) + Cl,. The optimum heating time was 40 min at 100 "C when a hydrochloric acid concentration of 6 M was used (Table 111). H+ TABLE I11 EFFECT OF HEATING TIME ON THE REDUCTION OF TELLURIUM(VI) TO TELLURIUM(IV) All solutions contained 0.75 p g of tellurium(V1) in 50 ml of 6 M hydrochloric acid; a temperature of 100 "C ant1 optimised hydride generation trapping conditions were used. . . 10 20 30 40 50 60 lime of heating/min .. Reduction 7; . . . . . . 45 87 98 100 100 100 Precision and Detection Limit carried tlirougli the entire procedure. was 40/ (five determinations). deviation of the blank analyses was 0.006 pg (six determinations). The precision was estimated from replicate analyses of a 0.3-pg tellurium(V1) standard The relative standard deviation at this concentration The detection limit corresponding to four times the standard Interferences IdentiJicatiofz Possible interference by other elements was investigated by measuring the hydrogen telluride generated and trapped in the presence of elevated concentrations of other elements 308 MAHER DETERMINATION OF TE BY AAS WITH Analyst Vol. 108 The concentrations at which certain elements interfere are shown in Table IV.Various other elements [Al(III) B(III) Ca(II) Cr(VI) K(I) Li(I) Mg(II) Mn(II) Na(I) Pb(II), S2- Si(IV) Zn(II)] showed no significant interference up to the 5000 pg (100 pg ml-l) level. TABLE IV EFFECT OF INORGANIC IONS ON THE GENERATION AND TRAPPING OF HYDROGEN TELLURIDE All solutions contained 0.5 pg of telluriuni(1V) in 50 ml of 6 M hydrochloric acid and optimised hydride generation and trapping conditions were used. Species A m As(II1) Cd(I1) Co( 111) Cu(I1) Fe (I 11) Hg(I1) Mo(V1) Ni(I1) Sb (111) Se(IV) Sn(1V) V(V) Suppression and elimination Concentration/pg per 50 ml Tellurium recovered yo 10 0 1 100 100 52 50 100 1 000 100 2 500 75 1000 90 500 100 100 71 50 100 2 500 87 1000 93 500 100 10 0 1 100 500 67 250 105 100 100 1000 76 500 100 50 19 10 98 1 100 50 18 0.1 90 250 66 100 100 1000 100 Although several elements cause significant interference when present at the 1000 pg (20 pg ml-l) level only silver(I) copper(II) mercury(I1) and selenium(1V) are likely to be found at concentrations in environmental materials (excluding sediments) that will cause significant interference.Initially four complexing agents thiosemicarbazide l,l0-phenanthroline S-hydroxy-quinoline and disodium ethylenediaminetetraacetate were tested in an attempt to suppress interferences by complexation before generation of hydrogen telluride. These reagents were not effective in suppressing interferences.Interferences were removed by a combination of co-precipitation and sequential extraction. After reduction of tellurium(V1) to teliurium(1V) 1 ml of lanthanum(II1) chloride solution and one drop of phenolphthalein solution were added with stirring followed by the addition of 25% V/V ammonia solution until a pink colouration occurred (pH 9-10). The lanthanum precipitate containing tellurium but not copper( 11) and mercury(I1) was separated by centrifugation and washed twice with 20 ml of 3 M ammonia solution. The precipitated lanthanum hydroxide was dissolved in 10 ml of DAN solution 1 ml of EDTA - hydroxylamine solution was added and the mixture was heated in a water-bath at 50 "C for 50 min. The piazselenol formed was extracted into cyclohesane (2 x 10 ml) and discarded.The previous solution was extracted with 20 ml of diphenylthiourea reagent and the chloroform phase was discarded. Copper(l1) and mercury(l1). SeZenium(lV). Tellurium remained in the aqueous phase. SiZver(1) March 1983 ELECTROTHERMAL ATOMISATION BY HYDRIDE GENERATION 309 The efficiency of the co-precipitation and sequential extraction procedure to remove interferences was assessed by the analysis of solutions containing 0.5 pg of tellurium( IV) together with 1000 pg of copper(II1) and mercury(I1) and 10 pg of silver(1) and selenium(1V). The percentage deviation from interference-free determinations of tellurium was less than 7%. Average recoveries of 93 4% (five determinations) were achieved. Discussion and Conclusion A simple system for the generation and trapping of hydrogen telluride prior to the deter-mination of tellurium by atomic-absorption spectroscopy with electrothermal atomisation has been developed and optimised.Interferences from copper( 11) mercury( 11) silver( I) and selenium( IV) have been identified. Suppression of these interferences by complexing agents was unsuccessful probably owing to the instability of complexes in concentrated acid solution. However the use of a co-precipitation - sequential extraction procedure prior to hydride generation overcomes all identified severe interferences. The technique should allow the sensitive measurement of tellurium concentrations in extracts. Investigation of interferences to the method also demonstrated that the use of hydrogen telluride generation to isolate and concentrate tellurium from extracts is in general of limited use unless potential interfering elements are identified and removed. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. References Cerwenka E. A. and Cooper W. C. Arch. Environ. Health 1961 3 189. Corbett J . A. and Godbeer W. C . Anal. Chim. Acta 1977 91 211. Kapel M. and Komaitis M. E. Analyst 1979 104 124. Beaty R. D. A t . Absorpt. Newsl. 1974 13 38. Kraehenbuehl Ti. and Wegmueller F. Radiochem. Radioanal. Lett. 1978 36 31. Sighinolfi G. P. and Santos A. M. Talanta 1979 26 143. Fiorino J . A. Jones J. W. and Capar S. G. Anal. Chem. 1976 48 120. BCdard M. and Kerbyson J . D. Can. J . Spectrosc. 1976 21 64. Smith A. E. Analyst 1975 100 300. Thompson K. C. and Thomerson D. R. Analyst 1974 99 595. Greenland L. P. and Campbell E. Y . Anal. Chim. Acta 1976 87 323. Received July 27th 1982 Accepted September 6th 198

ISSN:0003-2654    

DOI:10.1039/AN9830800305

出版商:RSC    

年代:1983

数据来源: RSC

摘要:

310 Analyst March 1983 Vol. 108 $9. 310-315 Determination of Trace Amounts of Molybdenum in Natural Waters by Solvent Extraction -Atomic-a bsorption Spectrometry After C helati ng I on -exc h a ng e Pre-co n cent rat i o n Miguel Ternero and lgnacio Gracia Department of Basic and Applied Chemistry E . T . S . I . I . University of Seville Avda. Reina Ilfercedes sln, Seville-12 Spain A method for the determination of molybdenum in natural waters in the micrograms per litre range is proposed. The method involves the pre-concentration of molybdenum on a Chelex- 100 chelating resin and subsequent elution with ammonia solution followed by extraction with a complexing reagent 1,4-dihydroxyphthalimide dithiosemicarbazone dissolved in NN-dimethylformamide - isoamyl alcohol (1 + 4) and a final direct determination by atomic-absorption spectrometry.The addition of ascorbic acid prior to extraction eliminates the interfering effect of several ions a t the concentra-tion levels normally found in natural waters. The sensitivity of the method is 0.3 pg 1-1 for 1% absorption. The method has been applied to the determin-ation of molybdenum in sea and surface waters. Keywords Molybdenum determination ; natural water analysis ; chelating ion-exchange separation ; atomic-absorption spectrometry ; 1,4-dihydroxy-phthalimide dithiosemicarbazone The determination of certain trace elements has become significant in studies of geochemical, biochemical and industrial processes in natural waters. An investigation of this problem is being carried out in our laboratories and this paper describes the development of a method for the determination of molybdenum in the micrograms per litre range.In order to detect the low levels of molybdenum that occur naturally1 (from less than 1 to 10 pg 1-1 and even larger amounts in sea water) pre-concentration methods are usually necessary. For this purpose c~precipitation,~-~ cocrystallisation,6~7 extraction,s-ll ion exchange12-15 and activated charcoaP have been used the determination being completed by either spectrophotometry or atomic-absorption spectrometry (AAS) or sometimes by other procedures (emission spectroscopy neutron activation analysis). In recent years many papers have described the direct determination of molybdenum by the use of modern tech-niques for example graphite furnace AAS,17 anodic-stripping voltamrnetry,l8 electron para-magnetic resonance spectrometrylg and oscillography.20 However such techniques are not available to all laboratories and may also introduce other problems in achieving the desired accuracy of analysis e.g.the prevalence of matrix interference effects in electrothermal atomisation AAS. This paper reports a sensitive and selective method based on pre-concentration of molyb-denum on a Chelex-100 chelating resin,21-22 followed by extraction with 1,4-dihydroxyphthali-mide dithiosemicarbazone (OH-PDT) in isoamyl alcohol and a final direct determination by AAS. The use of OH-PDT as a complexing reagent for molybdenum has been reported previously2s and applied to the determination of microamounts of molybdenum by an extrac-tion - spectrophotometric method.The proposed method in this paper with an AAS finish, gives a greater sensitivity and eliminates most of the interfering cations. In recent years several systems based on solvent extraction of molybdenum complexes with subsequent AAS determination in the organic phase have been used for enhancement of the sensitivity of molybdenum absorption and for concentrating the samples and eliminating interfering cations. Of these quinolin-8-01- isobutyl methyl ketone (IBMK) ,8 quinolin-8-01 -n-amyl methyl ketone,24 ammonium tetramethylene dithiocarbamate - IBMK,25 dithiol-IBMK26 and thiocyanate - IBMKll are generally used for the determination of molybdenum in waters usually with a preliminary concentration step.However limitations with regard to sensitivity simplicity and freedom from interferences (especially iron) are observed. The proposed method with pre-concentration and separation on Chelex-100 resin is relatively simple and sufficiently versatile for the analysis of sea and surface waters TERNERO AND GRACIA Experimental Reagents 311 All reagents and solvents were of analytical-reagent grade unless specified otherwise. Distilled de-ionised water was used. Chelating resin. Digest Chelex-100 (Rio-Rad Laboratories 100-200 mesh) with 2 N nitric acid and fill 2 cm diameter ion-exchange columns to a depth of 3 cm with it. Wash the columns with 20 ml of 2 N nitric acid and then with water until the pH of the eluate is 5-6. Prepare a 0.05% m/ V solution by dissolving 0.05 g of the reagent in 20 ml of NN-dimethylformamide and dilute to 100 ml with isoamyl alcohol.The synthesis of OH-PDT has been described previ~usly.~' Dissolve 1.500 g of molybdenum(V1) oxide in the minimum volume of 0.1 M sodium hydroxide solution dilute with water make slightly acidic (pH 3-4) with 0.1 M hydrochloric acid and dilute to 1 1 with water. Prepare a working solution containing 10 pg ml-l of molybdenum from this stock solution by appropriate dilu-t ion. Chloroacetic acid - sodium hydroxide bufler solution PH 2.6. Add 65 ml of 0.2 M sodium hydroxide solution to 300 ml of 0.2 M chloroacetic acid solution and dilute to 1 1 with water. Ascorbic acid solution 1% m/V. Dissolve 1 g of ascorbic acid in water and dilute to 100 ml with additional water.Nitric acid 0.1-4 N. Prepare from analytical-reagent grade concentrated nitric acid by appropriate dilution. 1,4-Dihydroxyphthalimide dithiosemicarbazone solution. This solution is stable for 1 week. Standard molybdenum solution 1.000 g 1-I. Apparatus A Perkin-Elmer 103 atomic-absorption spectrophotometer equipped with a dinitrogen oxide - acetylene burner head and a multi-element (cobalt copper iron, manganese molybdenum) hollow-cathode lamp was used. The operating conditions used are summarised in Table I. Digital p H meter. An Orion 701A instrument with glass - calomel electrodes was used for pH measurements. Spectrophotometev. TABLE I ATOMIC-ABSORPTION CONDITIONS FOR MOLYBDENUM DETERMINATION Wavelength . . Slit width . . . . Lamp current .. . . Acetylene pressure . . Acetylene flow-rate . . Dinitrogen oxide pressure Dinitrogen oxide flow-rate Aspiration rate . . . . Burner height . . . . 313.3 nm . . . . 0.7 nm . . . . 10mA . . . . 10 p.s.i.g. . . . . Setting 12 (approximately 8 1 min-l) . . . . 40 p.s.i.g. . . Setting 13 (approximately 16 1 min-') . . . . 3 ml min-' . . . . Adjust for optimum reading Procedure Filter the sample as soon as possible after collection through a 0.5-pm membrane filter. Take 1-5 1 of the filtered water and adjust its pH to 5-5.5 by cautious addition of 0.1 N nitric acid. Allow the sample to flow through the Chelex-100 column at a rate not exceeding 5 ml min-l. Wash the resin with 200 ml of water and elute molybdenum with 20 ml of 4 N ammonia solution.Collect the eluate in a 25-ml beaker and adjust its pH approximately to neutrality with appropriate dilute nitric acid (0.1-4 N). Transfer into a separating funnel add 5 nil of pH 2.6 buffer solution and 5 ml of ascorbic solution. After mixing add 10 ml of OH-PDT solution and shake vigorously for 1 min. Allow the phases to separate and draw off the aqueous layer. Transfer the organic phase into a glass-stoppered tube containing anhy-drous sodium sulphate and aspirate directly into the dinitrogen oxide - acetylene flame. Determine the absorbance at 313.3 nm using isoamyl alcohol as a blank under the speci-fied conditions. Prepare a calibration graph by using standard solutions of molybdenum(V1) treated in the same way 312 TERNERO AND GRACIA DETERMINATION OF Mo IN WATERS BY Analyst Vol.108 Results and Discussion Study of the Pre-concentration of Molybdenum on Chelex-100 Chelating Resin This effect was studied using a series of dilute standard solutions of molybdenum in the pH range 1-9. Quantitative retentions were observed in the pH range 5-6. A pH between 5 and 5.5 was selected for the analysis. These results are in agreement with those reported for retention of molybdenum from sea waters.14 The nature and concentration of the eluting agent was studied under the conditions described under Experimental using a 2 x 3 cm column of Chelex-100. Ammonia solution sodium hydroxide solution and nitric sulphuric and perchloric acids were investigated. Molybdenum was removed from resin only by ammonia solution and sodium hydroxide solution.Fig. 1 shows the elution diagrams at several concentrations. These diagrams were constructed by elution with successive 5-ml volumes of eluting agent. The recovery of molybdenum was assessed by the recommended procedure. A 20-ml volume of 4 N ammonia solution is recom-mended as a suitable amount of eluting agent. In order to establish the possibility of determining trace amounts of molybdenum in waters, the recovery from large volumes of sample was studied by the recommended procedure. Quantitative recoveries were obtained for sample volumes of 50 ml-5 1. The retention of molybdenum by Chelex-100 resin is dependent on pH. Eluate volurne/rnl Fig. 1. Elution diagrams of molybdenum from Chelex-100 resin with ammonia solution and sodium hydroxide solution A B C, D and E with 1 2 3 4 and 5 x ammonia solution respectively; F with 2 s sodium hydroxide solution ; amount of molybdenum added 50 pg; successive volumes of eluate collected 5 ml.Extraction and Atomic-absorption Spectrometry of Molybdenum When a solution of OH-PDT dissolved in NN-dimethylformamide - isoamyl alcohol is shaken with an aqueous acidic solution of molybdenum(VI) a yellow complex is formed immediately in the organic phase. This system has been used for the spectrophotometric determination of m0lybdenum.~3 However it is unsuitable for water analysis because of interferences from certain ions [iron(II) iron(ITI) copper(II) cobalt(I1) and vanadium(T’)] at the levels commonly found in natural waters. The extraction of molybdenum with subsequent AAS determination is dependent on pH.The most favourable pH range is 2-4 identical with that reported for the spectrophotometric determination. A chloroacetic acid - sodium hydroxide buffer solution is added for control of the pH of the extraction. The effect of OH-PDT concentration in A‘N-dimethylformamide - isoamyl alcohol (1 + 4) was investigated in the range 0.002-0.170 rn/V. A 0.006~0 solution was necessary in order to obtain maximum absorbance at 313.3 nm; the latter remained constant with increasing con-centration. The volume of the organic phase was kept constant at 10 nil varying the volume of the aqueous phase. When the phase-volume ratio was higher than 4 the absorbance increased because of A 0.05% solution is recommended as a suitable concentration of reagent.The influence of the phase-volume ratio (aqueous to organic phase) was studied March 1983 313 the appreciable solubility of the organic solvent in water. The absorbance remained constant when smaller ratios were employed. It is concluded that the volume of the aqueous phase should be smaller than 40 ml if a 10-ml volume of organic phase is utilised. The ionic strength of the aqueous phase does not affect the atomic absorption of the extracted complex. Salts such as sodium sulphate potassium perchlorate potassium chloride and potassium nitrate do not affect the absorbance signal even at a concentration of 2%. In order to establish the suitability of this system for the determination of molybdenum the results of a preliminary interference study with an AAS or spectrophotometric finish are reported in Table 11.I t is concluded that the selectivity with AAS is greater than that with spectrophotometry . SOLVENT EXTRACTION - AAS AND CHELATING ION EXCHANGE TABLE I1 TOLERANCE LIMITS FOR THE DETERMINATION OF MOLYBDENUM WITH THE OH-PDT - ISOAMYL ALCOHOL SYSTEM BY AAS AND BY SPECTROPHOTOMETRY Amount of molybdenum present 50 pg. I Ions added AI(lII) Ni(II) Mn(I1) . . Zn(II) Cd(II) Ti(1V) . . . . La(II1) . . . . . . . . . . Bi(III) Cr(II1). . . . . . W(V1) . . . . . . Pb(I1) . . . . . . Co(I1) . . . . . . . . Cu(II) Fe(II1) . . Fe(I1) . . . . . . Hg(II) ViV) . . . . Tolerance limit (mass excess relative to Mo) P Spectrophotometry AAS 15 > 100 15 50 10 15 1 50 2 15 <1 2 <1 2 <1 5 Determination of Molybdenum in Waters Calibration graph sensitivity and precision A calibration graph was prepared by using dilute standard solutions treated in the same way as the samples.A linear Calibration graph was obtained up to 12 mg 1-1 of molybdenum with respect to the organic phase and 24 pg 1-1 with respect to water samples when a 5-1 volume was utilised. The sensitivity was 0.15 nig 1-1 for 194 absorption in the organic phase and 0.3 pg 1-1 with respect to watcr samples wlien a 5-1 volume was utilised. The sensitivity obtained for the determination of molybdenum by AAS in tlie organic phase was about 3.3 times greater than that for aqueous solutions (0.50 mg 1-l). The coefficient of variation calculated from ten replicate analyses of dilute standard solutions containing 25 pg of molybdenum was 3.0%).Interference study The recommended procedure was used to analyse standard molybdenum solutions in the presence of the major constituents of natural waters and of several trace elements that interfere in AAS (tolerance limits smaller than 102 mass excess relative to molybdenum) (see Extraction and Atomic-absorption Spcctrometry of Alolybdenum and Table 11). Determinations in the presence of tlie major constituents were carried out at the levels normally present in sea water.‘ The results for tlie determination of 50 pg of molybdenum are shown in Table 111. From these results it is conclutled that the presence of the main constituents and of most of the trace elements did not affect tlie recovery of molybdenum at levels that occur naturally.The tolerance limits for hismuth(III) cobalt (II) copper( II) iron(II) mercury(II), chromium(II1) and leatl(I1) are greater than those obtained previously (Table 11) because of their smaller retention on the resin. Tungstate(V1) does not interfere in amounts up to a 20-fold excess. 1’anatlium( 1’) anti iron (I I I) depress the molybdenum absorption markedly probably be-cause of preferential extraction of their OH-PDT complexes or flame interferences.2s Th 314 TERNERO AND GRACIA DETERMINATION OF MO IN WATERS BY Analyst vd. 108 addition of ascorbic acid was found to prevent these interferences. When 5 ml of 1% ascorbic acid solution are added to the sample before extraction up to 5 mg of iron(II1) and 500 pg of vanadium(V) could be tolerated.The above limits are not likely to be exceeded in analyses of natural waters. TABLE I11 RECOVERY OF MOLYBDENUM IN THE PRESENCE OF THE MAJOR CONSTITUENTS OF WATER AND SEVERAL TRACE ELEMENTS THAT INTERFERE IN AAS Amount of molybdenum present 50 pg. Ions added Na(1) . . K(1) . . . . Ca(I1) . . . . . . . . s o p . . co,2- . . . . . . Cr(III) Pb(I1) . . . . . . W(V1) . . Fe(II1) . . . . . . V(V) . . . . . . . . . . ;p) - * Br- . . . . Bi(III) Co(II) Cu(II) Fe(II) Hg(I1) . . . . . . . . . . . . . . . . . . * . * . . . Mass excess relative Mo 2.1 x 105 7.6 x 103 8.0 x 103 2.7 x 104 3.8 x 105 1.7 x 104 1.3 x 103 5.6 x lo2 102 102 75 102 20 102 102* 102 10* Amount of Mo recovered/ p g 50.0 50.0 50.0 50.0 50.0 50.0 50.0 50.0 50.0 33.5 50.0 20.5 50.0 0.0 50.0 10.5 50.0 * With addition of 5 ml of 1% ascorbic acid solution before extraction.Analyses of natural waters The proposed method was applied successfully to the determination of trace amounts of molybdenum in sea and surface water samples (Table IV). The accuracy of the determinations was checked by carrying out replicate analyses of samples spiked with known amounts of molybdenum. The molybdenum recovery was calculated by comparing the results obtained before and after the addition of molybdenum standard solutions. The results showed that the recovery of molybdenum was satisfactory (Table IV).TABLE IV DETERMINATION OF MOLYBDENUM IN NATURAL WATERS Type Bottled mineral water . . . . Public water supply River water . . . . Dock's river water . . . . Sea water A . . . . Sea water B . . . I Estuary water? . . . . Location of sampling Granada Seville Guadalquivir river Seville Guadalquivir's dock Seville Atlantic Ocean, Huelva Atlantic Ocean, Huelva Huelva hIo found*/pg 1-' 7-Memi Range 0.3 0.2-0.3 0.9 0.8-1.0 2.7 2.7-2.8 6.3 6.2-6.4 7.5 7.3-7.6 7 . 2 7.1-7.4 9.9 9.8-10.0 Recovery (;,, 100.0 99.5 99.5 98.9 99.0 99.2 98.5 * Average of three separate determinations. t This water is affected directly by drainage of waste water from an industrial area, March 1983 SOLVENT EXTRACTION - AAS AND CHELATING ION EXCHANGE Conclusion 315 The suitability of the proposed method for determining small amounts of molybdenum in waters in the range 0.3-24 pg 1-1 has been demonstrated.The use of a chelating resin in a pre-concentration and separation step separates molybdenum from the major components and eliminates the matrix effect on the atomic-absorption signal. The combination of solvent extraction with AAS provides greater sensitivity and eliminates most interfering cations. Finally the method offers significant advantages with respect to relative rapidity simplicity and versatility. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 1 1 . 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26.27. 28. References Bond I<. G. and Straub C. P. “Handbook of Environmental Control Volume 111 Water Supply and Chan K. M. and Riley K. P. Anal. Chim. Acta 1966 36 220. Kim Y. S. and Zeitlin H. Anal. Chitn. Ada 1970 51 516. Kuznetsov V. I. and Loginova L. G. Z h . Anal. Khim. 1958 13 453. Korob I<. O. Cohen I. M. and Agatiello 0. E. J . Radioanal. Chem. 1976 34 329. Weiss H. V. and Lai M. G. Talanta 1961 8 72. Kulathilake A. I. and Chatt A. Anal. Chem. 1980 52 28. Chau Y. and Lum-Shue-Chan K. Anal. Chim. Acta 1969 48 205. Morgen E. A. Iiossins Kaya E. S. and Vlasov N. A. Zh. Anal. Khim. 1975 30 1384. McLeod C. W. Otsuki A Okanioto K. Haraguchi H. and Fuwa K. Analyst 1981 106 419. Kim C. H. Alexander P. W. and Smythe L. E. Talanta 1976 23 229. Kawabuchi K.and Kuroda R. Anal. Chim. Acta 1969 46 223. Kawabuchi K. and Kuroda I<. Anal. Chim. Acta 1968 40 479. Riley J. P. and Taylor D. Anal. Chim. Acta 1968 41 175. Korkish J . and Krivanec H. Anal. Chim. Acta 1976 85 111. Van der Sloot H. A. Wals G. D. and Das H. A. Anal. Chim. Acta 1977 90 193. Nakahara T. and Chakrabarti C. L. Anal. Chim. Acta 1979 104 99. Monien H. Bovenkork I<. Kringe K. P. and Rath D. Fresenius Z. Anal. Chem. 1980 300 363. Hanson G. Szabo A, and Chasteen N. D. Anal. Chem. 1977 49 461. Demkin A. M. Zh. Anal. Ichim. 1977 32 2389. Rosset I<. I3ull. Soc. Chim. Fr. 1964 2 1845. Kosset I<. Bull. lnf. Sci. Ttchnol. Comm. Energ. Atom. 1964 85 13. Ternero Rodriguez M. Analyst 1982 107 41. Butler L. I<. P. and Mathews P. M. Anal. Chim. Acta 1966 36 310. Mansell R. E . and Emniel H. W. At. Absorpt. Nemsl. 1965 4 365. Delaughter B. At. Absorpt. Newsl. 1965 4 273. Perez-Bendito D. Valcdrcel M. Ternero M. and Pino F. Anal. Chim. Acta 1977 94 405. Daud D. J. Anal. Chem. 1961 86 f30. Treatment,” Second Edition CRC Press Cleveland 1980 pp. 15-127. Received July 7th 1982 Accepted September 9th 198

ISSN:0003-2654    

DOI:10.1039/AN9830800310

出版商:RSC    

年代:1983

数据来源: RSC

摘要:

316 Analyst March 1983 Vol. 108 $$. 316-321 Effect of pH on the Response of Glassy Carbon Electrodes Hari Gunasingham" and Bernard Fleet? Imperial College of Science and Technology London SIV7 2A Z The use of glassy carbon as an electrode material engenders a number of practical problems owing to the presence of C-0 functionalities on its surface. One such problem is the susceptibility of the electrode t o pH changes. Highly surface-active glassy carbon electrodes having a high proportion of irreversible C-0 groups are particularly prone to variations in pH compared with ones having mainly quinoidal species This is reflected in the perform-ance of glassy carbon in the cyclic voltaninietry of hydroquinone. Keywords Glassy carbon electrode ; surface groups ; pH ; hydroquinone For routine analytical applications it is often desirable to have an electrode material that is relatively insensitive to the effects of pH.In practice however electrodes show a marked change in response. The pH response of electrodes can be traced to acid - base reactions taking place at the surface. For example the rest potentials of a number of metal and semiconductor electrodes have been reported to show a Nernstian response to pH with the rest potential changing by about 59 mV per pH Such behaviour has been attributed to electrochemically reversible redox reactions involving the surface oxides and H+(as.,. The effect of pH on carbon electrodes has been previously rep~rted.~-ll The effect has mainly been thought to be a consequence of surface C-0 functionalities in particular quinoidal groups formed on free valence carbon sites by the chemisorption of.oxygen. I t has been observed that the equilibrium potential of glassy carbon electrodes varied by about 59 m\.' per pH unit.1° The hypothesis put forward to explain this apparent Nernstian beliaviour is that the quinoidal redox couple is reversible with respect to reactions involving H+(aq.). An important consideration with respect to the effect of pH is its influence on electrode reactions. There is the direct effect on the species (undergoing electrolysis) itself; this has been the subject of considerable research. What is less clear is the indirect influence on elec-trode reactions as a result of changes in the electrode surface with pH. Change in pH could occur in the bulk solution or more subtly in the region in the immediate vicinity of the elec-trode where the actual electrode processes take place.In the latter instance depletion or enhancement of hydrogen ions (or hydroxyl species) could be the result of the electrode reaction itself. In a previous paper5 it was reported that glassy carbon showed varying surface character-istics depending on the degree of compactness of its bulk structure the more compact the structure the fewer the free valence carbon sites available on the surface and hence the fewer the C-0 functionalities formed. Here and in the previous work the glassy carbon used was of two types Tokai glassy carbon characterised by low surface activity (mainly quinoidal) ; and Plessy glassy carbon having a higher surface activity including irreversibly formed functionalities.This paper considers the effect of pH on the performance of glassy carbon electrodes in the pH range 0.3-8.4. At higher pH values a distinct difference in behaviour was observed. Differences in the electrochemical behaviour of glassy carbon at high and low pH have been noted by other workers.6-8 Our own findings in this respect will be the subject of a separate paper.B These reactions often involve surface oxides. Experimental Gold and platinum electrodes were similarly made using 3-mm discs encased in a Kel-I; (331 USA) body. The Plessy glassy carbons are classified as before namely GC1 and GC2. * Present address Department of Chemistry National University of Singapore Kent Ridge Singapore 051 1 .t Present address HSA Reactors Fesken Drive Rexdale Toronto Canada. The fabrication of glassy carbon electrodes has been described el~ewhere. GGNASINGHAM AKD FLEET 317 Glassy carbon electrodes were polished to a mirror finish with a 1 - p i diamond paste rinsed with ethanol and distilled water and then soaked overnight in distilled de-ionised water. After this treatment the clironopotentiometric and voltammetric experiments described below were performed with no further polishing. Electrodes were rinsed with distilled water prior to each analysis that required change of buffer solution. The major reason for not polishing the electrode between analyses was the likelihood of drastically changing the physi-cocheniical characteristics of the carbon surface which would have defeated the purpose of this study.Precautions were taken to keep potential limits at which electrodes were operated, to within the range -0.5 to + 1.5 V ~ ! E Y S U S S.C.E. which ensured that significant alteration of the carbon surface did not take place. Background cyclic voltammograms were routinely run in 0.5 ?tl sulphuric acid between experiments to check the state of the surface. From these voltammograms it appeared that both Plessy and Tokai glassy carbon surfaces remained reasonably constant throughout the entire course of the experiments. This conclusion was based on the background current as well as the background-peak potentials of the voltammo-grams. The former is indicative of surface area as well as the concentration of surface functionalities.I t should also be mentioned that no sign of adsorption was seen for the cyclic voltammetric studies of hydroquinone. Gold and platinum electrodes were cleaned with concentrated nitric acid polished with 1-pm diamond paste and then rinsed with ethanol and distilled de-ionised water. The electrodes were soaked overnight in de-ionised water. The following buffer solutions were used in this work sulphuric acid pH 0.3-0.8; citrate buffer (citric acid - sodium citrate) pH 2.2-5.5; and phosphate buffer (Na,HPO - NaH,PO,) pH 5 . 8 4 4 . Chrono-potentiometric studies were carried out with a Model PAR 173 potentiostat - galvanostat (Princeton Applied Research). Cyclic voltammograms were obtained with a Model PAR 174 polarograph. Purified nitrogen was used to de-aerate the solutions.Open-circuit potentials were measured with a Corning EEL Model 112 pH meter. Results were plotted on a Servoscribe plotter. Results and Discussion Open Circuit Potential uersus pH Typical cyclic voltammograms of the two carbons obtained for 0.5 M sulphuric acid given in Fig. 1 show the relative differences in surface activity. The cyclic voltammograms were obtained immediately prior to the open-As already mentioned GC1 is more compact than GC2. I 0.1 0.3 0.5 0.7 0.9 -0.1 +0.3 +0.7 +1.1 E N vs. S.C.E. Fig. 1. Background of (a) GC1 and (b) GC2 in 0.5 M sulphuric acid. Scan rate 20 mv s-1 318 GUNASINGHAM AND FLEET EFFECT OF pH Analyst "01. 108 circuit potential - pH measurements described below. The cyclic voltammogram of GC1 on the basis of the earlier reasoning shows the dominance of the quinoidal redox couple whereas GC2 shows evidence of irreversible functionalities.12 Meas-urements were made 2 min after immersion to ensure that the electrode had approached its equilibrium-potential value.As can be seen the graph for GC1 shows a near Nernstian be-haviour with a slope of about 60 mV per pH unit. This slope is consistent for a 2e/2H+ process which would be expected for the surface quinoidal redox couple; the slope for GC2 has a significantly lower value. The difference in the slopes could be explained on the basis that the acid- base redox reaction at the surface of GC2 is irreversible a consequence of the irreversible C-0 functionalities dominant on the surface of this carbon.Fig. 2 shows graphs of open-circuit potential versus pH obtained for GC1 and GC2. pH 8.4 pH 7.5 pH 6.7 pH 5.5 pH 4.1 pH 2.3 pH 0.8 ULL 600 71 0 2 4 6 8 PH Fig. 2. Open-circuit vmsus pH plots for (A) GC1 and (B) GC2. f cri E & +50 I 0 5 10 HCl/ml Fig. 3. Use of glassy carbon as an indicator electrode in acid - base titration: (a) GC1; and (b) GC2. Acid - Base Titration The use of carbon electrodes as indicators in acid - base titrations has been described and affords an interesting demonstration of the differing response of GC1 and GC2. Fig. 3 shows the titration of sodium hydroxide by hydrochloric acid as monitored by the two carbon elec-trodes. Each measurement was made 2 min after addition of the acid. As can be seen GC2 shows a poorer response at the end-point ; again this is consistent with the irreversible nature of the C-0 groups found on the surface of this carbon.Tokai glassy carbon previously oxidised at + 1.5 V showed a behaviour similar to GC1 with respect to the open-circuit potential veYsus pH graphs. This could be expected as the surface C-0 functionalities of this carbon are mainly of the quinoidal type. 1 .o 1 - I 2 min -Time -1.0 Fig 4. Effect of pH on cathodic charging curves of Plessy glassy carbon. Charging current = - 10 PA March 1983 ON THE RESPONSE OF GLASSY CARBON ELECTRODES 319 Chronopotentiometric Studies According to Vetter,13 the anodic and cathodic charging curves for platinum are the same regardless of pH and the only apparent change was a displacement of the charging curves by 59.2 mV per pH unit.This result is indicative of the reversible nature of the acid - base redox reactions involving adsorbed oxides on platinum surfaces. With glassy carbon the effect of pH on the charging curves is more complex. Fig. 4 shows the cathodic-charging curves ob-tained for GC2 between a pH of 0.8 and 8.4. It can be seen that as pH increases the charging curve becomes broader having less defined arrests. If corresponding points for each potential wwus time charging curve are plotted against pH interesting trends are found as shown in Fig. 5. Plot (A) representing corresponding points of the cathodic charging curves 5 min 0.6 , 4 0.4 uj 0.2 G o > > 0 2 4 6 8 PH Fig. 5. Corresponding potential uevsus pH plots (A) points taken 1 min after start of cathodic charging curve; and (B) points taken 5 min after start.after the start of each curve has a slope of about 60 mV per pH unit. This value reflects the response of the reversible quinoidal couple. A similar observation was reported by Evans and Kuwana,ll for oxygen plasma treated pyrolytic graphite though here the “surface quinone” potential was evaluated by cyclic voltammetry and differential pulse voltammetry. Plot (R), representing points 1 min after the start of the cathodic charging curves has a significantly lower slope that is close to 25 mV per pH unit. As the points are from the extreme negative region of the charging curves it is plausible to surmise that the small slope is the result of reactions involving irreversible C-0 functionalities and hydrogen adsorption.Hence, hydrogen adsorption appears to be an irreversible process on glassy carbon. Comparable trends were observed for anodic charging curves of GC2 as shown in Fig. 6. \Vith increase in pH arrests appeared to become broader and less well defined than with the cathodic charging curves. pH 4.1 I pH 6.7 pH 7.5 pHb.4 pH 2.3 pH 5.5 I‘ Time T;ig. 6. Effect of pH on anodic charging curve of Plessy glassy carbon. Charging current = - 10 u.1 320 GUNASINGHAM AND FLEET EFFECT OF pH Analyst Vol. 108 0.2 V vs. S.C.E. I Potential + Fig. 7. Cyclic voltammo-grams of hydroquinone for platinum electrode. pH 7.9 pH 6.8 - 0 . 4 2 pH 4.9 0.2 V vs. S.C.E. -0.2 Potential -b Fig. 8. Cyclic voltammograms of hydroquinone for gold electrode.Cyclic Voltammetry of Hydroquinone According to Adams,14 the cyclic voltammetry of hydroquinone on solid electrodes suggests a high degree of irreversibility. The over-all reaction involves a two-electron transfer and is highly sensitive to pH. Vetter15 showed that the reaction involved consecutive one-electron transfers. I t led to the conclusion that the reaction mechanism varies with pH; one at low pH and the other at high pH. Hydroquinone was chosen for our investigations on account of its well studied electrochemistry and because the response of the quinhydrone redox couple to pH should parallel that of surface quinoidal species on glassy carbon. Figs. 7-10 show cyclic voltammograms of 5 mM hydroquinone at different pH for platinuni, gold Tokai glassy carbon and GC2 electrodes.The scan rate for all voltammograms is 20 mV s-1. It can be seen that for the Tokai carbon platinum and gold electrodes as pH is increased the shape of the cyclic voltammogram does not change as significantly as it does with 0.2 V vs. S.C.E. -0.4 if-Potential __+ Fig. 9. Cyclic voltammograms hydroquinone for Tokai glassy carbon. of < ~ D H 2.2 I -0.3 / I \ I -0.i v Potential Fig. 10. Cyclic voltammograins of hydroquinonc for l'lcssy glassy carbon (GCB) March 1983 ON THE RESPONSE OF GLASSY CARBON ELECTRODES 32 1 GC2. Also the peak current decreases (as pH increases) most appreciably for GC2. Tokai glassy carbon in fact shows the least susceptibility to pH change in the way of peak shape as well as peak current.A plot of peak potential versus pH given in Fig. 11 shows that anodic and cathodic peak potentials become more negative with increase in pH. This has been described by Adams.14 The line drawn through the plotted points marks the average poten-tial versus pH change in the low pH range; the slope of this line for GC2 is significantly closer to the Nernstian value of 60 mV per unit than for the other electrodes. This is indicative of the greater reversibility of the hydroquinone electrode reaction in the GC2 electrode; a point further substantiated by the fact that the separation of the cathodic and anodic peak poten-tials as shown in the cyclic voltammograms of Fig. 10 are less for this carbon. The deviation at pH 6 for all the electrodes seen in Fig.11 could be ascribed to an anion effect caused as a result of changing from citrate to phosphate buffers. Another reason could be the difference in the quinhydrone redox process at high and low pH as mentioned before. 0.8 a d 2 0.4 s 0 0 4 8 0 4 8 PH Fig. 11. Variation of anodic (left) and cathodic (right) peak potentials with pH. Conclusion The results presented in this paper confirm the assertion previously made that the greater the surface activity of glassy carbon electrodes the greater the susceptibility to pH. Plessy glassy carbon of the GC2 type having a significantly greater proportion of irreversible C-0 functionalities at its surface appears to be more susceptible in this respect. It may therefore, be desirable from the analytical point of view to use a less surface active carbon such as the Tokai type in favour of a more active one such as GC2.The criterion would be electrocata-lytic performance (that is sensitivity) zlersuus reproducibility (in this example with change in pH). Moreover Tokai carbon affords some measure of predictability in regard to its response. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. References Trasatti S. Editor “Electrodes of Conductive Metallic Oxides Part A,” Elsevier Amsterdam 1981, Hoare J . P. Adv. Electrochem. Electrochem. Eng. 1967 6 202. Hoare J . P. J. Electrochem. Soc. 1962 109 858. Bockris J . 0. M. Conway B. E. and Yeager E. Editors “Comparative Treatise of Electrochemistry,” Gunasingham H. and Fleet B. Analyst 1982 107 896. Taylor R. J. and Humfray A. A. J. Electroanal. Chem. 1975 64 63. Taylor R. J. and Humfray A. A. J. Electroanal. Chem. 1975 64 85. Taylor R. J. and Humfray A. A. J. Electroanal. Chem. 1975 64 95. Gunasingham H. in preparation. Dodson A. and Jennings V. J. Anal. Chim. Ada 1974 72 205. Evans T. and Kuwana T. Anal. Chem. 1977 49 1632. Laser D. and Ariel M. J. Electroanal. Chem. 1974 52 291. Vetter K. J . “Electrochemical Kinetics,” Academic Press New York 1967. Adams K. N. “Electrochemistry at Solid Electrodes,” Marcel Dekker New York 1969. Vetter K. J. J. Electrochem. 1952 56 797. p. 333. Plenum Press New York 1980 p. 320. Received September 8th 1982 Accented Sehtenzher 27th. 198

ISSN:0003-2654    

DOI:10.1039/AN9830800316

出版商:RSC    

年代:1983

数据来源: RSC

摘要:

322 Analyst March 1983 Vol. 108 $9. 322-328 Determination of Polychloro=2-(chloromethyl-su1phonamido)diphenyI Ether Insectproofing Agents on Wool Textiles and in Textile Liquors by High-performance Liquid Chromatography Robert J. Mayfield and Ian M. Russell CSIRO Division of Textile Industry P.O. Box 21 Belmont Victoria 3216 Australia Polychloro-2-(chloromethylsulphonamido)diphenyl ether insectproofing agents were extracted from wool textiles with methanal- ammonia solution in sealed ampoules and determined by normal bonded-phase high-performance liquid chromatography. Liquor samples were extracted with dichloromethane and determined similarly. Satisfactory recoveries of the insectproofing agents were obtained from spiked liquor and wool samples. Accurate and repro-ducible analyses of the formulations were obtained down to concentrations of 0.05% m/m on wool textiles and 0.5mg1-1 in liquor samples.The short analysis time and simplicity of this method make it ideally suited for the routine determination of these insectproofing agents on wool textiles. Keywords Insectproofing agents; polychloro-2-(chloromethylsul~honamido)-daphenyl ethers ; wool textiles ; textile liquors ; high-performance liquid chro-matograp hy Polychloro-2-(chloromethylsulphonamido)diphenyl ethers (PCSDs) I are the main active constituents of several commercial insectproofing formulations used to impart durable insect resistance to wool and wool-blend textiles. Eulan WA New (Bayer) Eulan U33 (Bayer) and Mitin LP (Ciba-Geigy) are the major products now in use worldwide for industrial appli-cation to wool.The Eulan formulations are based entirely on PCSD1s2 and differ only in their concentration of active constituents. Mitin LP contains PCSDs as the major com-ponent in admixture with 4,4'-dichloro-3,3'-bis(trifluoromethyl)diphenylurea (flucofuron).3 Molantin P (Chemapol) is also based on PCSDs and is considered to be similar to Eulan U33.4 NHS02CH2CI n = 4-6 I Thin-layer chromatography and gas chromatography have been used to determine Eulan WA New in textile waste liquors.5 A standard method6 reported for determining PCSDs on wool textiles required Soxhlet extraction of the insectproofing agent over a 2-h period with 2-met hox yethanol followed by gas-chromat ographic determination. Another gas-chromatographic method has been described' for determining Eulan U33 on wool textiles in which the wool is first degraded with sodium hydroxide solution and the insectproofing agent is then extracted with diethyl ether.Wells2 has recently reported that PCSDs undergo thermal rearrangement at the injection port at temperatures exceeding 230 "C during gas chromatography. This places some doubt on the accuracy and reproducibility of gas-chromatographic methods for PCSD determinations. Normal-phase high-performance liquid chromatography (HPLC) has been used to deter-mine PCSDs on wool and in textile liquors.* Peak shape and resolution were better than those obtained by gas chromatography and analysis time was shorter. More recently Wells and Johnstone9 have described a method for extracting low levels of PCSDs from natural water with silicone oil coated polyurethane-foam plugs and determination by reversed-phas MAYFIELD AND RUSSELL 323 HPLC.Their work included a study of the effects of solvent composition pH column packing and detector wavelength on the HPLC determination of PCSDs but did not include the determination of PCSDs extracted from wool textiles. In our search for a suitable HPLC method for determining PCSDs extracted from wool and textile liquors the normal-phase mode was found to be superior to the reversed-phase mode. The use of a normal bonded-phase column was later found to provide additional benefits. We report here the normal bonded-phase HPLC analysis of PCSDs together with the simple and small-scale techniques developed for extracting them from wool textiles and textile liquors.Experimental Materials The wool used was a commercial woollen-spun 3-fold carpet yarn made from 33-pm wool and a soap-scoured plain-weave fabric of 135 g m-2 made from 22-pm Merino wool. The polyamide flocks (20 decitex) were T-6 (Allied Chemicals) and 6-6 (Du Pont). The insect-proofing agents used and their manufacturers were given earlier Albegal A (Ciba-Geigy) was used as a levelling agent where stated. PCSDs were isolated from Eulan WA New by treating a solution of the formulation (10 g) in water (200 ml) with 1 M hydrochloric acid (15 ml) and filtering the precipitate after thorough stirring. The collected solid was washed with several portions of water and dried. N-Benzoyl-4-butylaniline was prepared from benzoyl chloride and 4-but ylaniline (Aldrich) .The crude product was recrystallised three times from methanol. All solvents and chemicals were of analytical-reagent grade. Reagents 3 ml) to methanol (97 ml). methane (500 ml) add 2,2,4-trimethylpentane (500 ml) and mix thoroughly. Methanol - ammonia solution (3% V / V ) . Hydrochloric acid. Approximately 1 M. Internal standard solution. Dissolve N-benzoyl-4-butylaniline (0.040 g) in dichloro-Add concentrated ammonia solution (28-30y0, Apparatus The ampoules (10 ml capacity Australian Consolidated Industries) were made of Pyrex glass and were 130 mm in length (including the neck) and 17 mm in diameter. The neck was scored at the bottom and had a 13-mm opening which narrowed to 7 mm. A Techne SB-4 shaking water-bath was used for shaking the sealed ampoules.Dye-bath treatments were performed in an Ahiba Turbomat laboratory dyeing machine. The HPLC system was equipped with an Altex, Model 100 pump a Hitachi Model 100-10 variable-wavelength detector and an Altex 155-00 flow cell. Injections were made through a 30-pl sample loop attached to a Valco AH60 pneumatic valve and Varian 8055 Autosampler. A stainless-steel column (250 x 4.6 mm) packed with RSIL-CN (10 pm Alltech Associates) was used with a mobile phase of 50% V/V dichloromethane in 2,2,4-trimetliylpentane. The flow-rate was set at 1.5 ml min-l and the detector wavelength at 242 nm. Peak areas were determined by a Varian CDS IIIC data system. The 14-ml screw-cap vials were from Pierce. Method Extraction of textile satnples Cut the sample into pieces that can be introduced easily into the ampoule weigh (to the nearest milligram) about 0.2g of the samples place in ampoules and pipette in the methanol -ammonia solution (5 ml).Seal the ampoules at ambient temperature using a glassblowing torch and place in a shaking water-bath at 80 "C for 2 h. Condition the samples at 65 & 2% relative humidity and 20 & 2 "C for at least 4 h. Caution-Wear safety spectacles when entering or removing the ampoules from the water-bath in case an ampoule should explode. The water-bath should be fitted with a lid 324 MAYFIELD AND RUSSELL DETERMINATION OF Analyst Vol. 108 Remove the ampoules open them after cooling and transfer aliquots (2.5 ml) by pipette into screw-cap vials (14 ml) containing 1 M hydrochloric acid (7 ml) and the internal standard solution (2.5 ml).Cap the vials using PTI'E-lined septa as seals and shake thoroughly. Facilitate phase separation by centrifuging the vials for a few minutes. Introduce the organic phase (upper layer) into the sample loop of the high-performance liquid chromatograph. Extraction of liquors To 100 ml of the liquors in 250-ml conical flasks add anhydrous sodium sulphate (15 g), 1 M hydrochloric acid (2 ml) and dichloromethane (50 ml). Stopper the flask and stir vigorously on a magnetic stirrer for 1 h. Pour the contents into a separating funnel and collect the dichloromethane phase. Shake the aqueous layer in the funnel with fresh dichloromethane (25 ml) allow it to separate and then combine it with the first extract.Evaporate the extract to dryness on a rotary evaporator dissolve the residue in the internal standard solution (2.5 ml) and introduce this into the sample loop of the high-performance liquid chromatograph. Standards Prepare calibration standard solutions of the insectproofing agents in methanol in the concentration range 20-400 mg 1-l. Pipette aliquots (2.5 ml) of these standards into screw-cap vials containing 1 M hydrochloric acid (7 ml) and the internal standard solution (2.5 ml) and proceed as described for the textile samples. Include samples of fabric or carpet yarns (treated with known amounts of the appropriate insect-proofing agent by the dye-bath procedure described) in each set of analyses as standards to check on reproducibility and extraction efficiency.Calibration For determining the area of peak A the data system was programmed to project the base line a t the onset of peak A to the completion of peak €3 and to drop a perpendicular to the projected base line at the valley between these peaks. Determine the peak-area ratios (peak A to peak C Fig. 2) for the appropriate standard solutions and plot these against the concentrations to produce a linear calibration graph. Similarly determine the peak-area ratios for the unknown samples and obtain the concentra-tion of insectproofing agent from the calibration graph. Calculate the results as follows : Insectproofing agent (yo m/m) on a textile sample = C/2m Insectproofing agent (mg 1-l) in liquors = C/40 the where C is the concentration (in milligrams per litre) from the calibration graph and ?it is the mass (in milligrams) of sample.Application of Insectproofing Agents to Wool Dye-bath method The wool fabric (25 g) or carpet yarn (15 g) was pre-wetted in a 0.02yo m/V solution of a non-ionic surfactant in water rinsed and placed in the dye-bath (liquor to wool ratio 20 + 1 ) which was adjusted to 40 "C and contained ammonium sulphate (2 g 1-l) and formic acid (90% m/m 2 g 1-I). The liquor was circulated through the wool for 10 min and then the appropriate amount of insectproofing agent dissolved in water ( 1 0 ml) was added to the bath The temperature of the bath was raised to 100 "C at a rate of 2 "C min-l and main-tained at this temperature for 30 min. The fabric was removed from the hatli placed in cold water (500 ml) for 5 min hydroextracted and air dried for 48 h.Solvent application Aliquots (1 and 2 ml) were pipetted on to suspended wool fabric (0.2 g) and the acetone was removed by a stream of warm air to give applications of 0.5 and l.Oyo nz/m Solutions (1 g 1-l) of the insectproofing formulations in acetone were prepared March 1983 PCSDS OX WOOL AND IN TEXTILE LIQUORS BY HPLC Results and Discussion Extraction of Textiles 325 In normal practice insectproofing agents are applied to wool in an acidic dye-bath (pH 3-43) at or near the boil. Under these conditions they migrate into the swollen fibres to provide a treatment with good durabilitv. Efficient extraction of the insectproofing formulations used from wool treated in a dye-bath was acconiplished in sealed glass ampoules or scrcw-cap vials with 2-methoxyethanol, dimethylformamide or methanol - ammonia solution.However only nietlianol- ammonia solution proved satisfactory the other solvents giving rise to interfering peaks in subsequent normal-phase HPLC analysis of the extracted PCSDs. The optimum conditions for niethanol - ammonia solution extraction of the insectproofing agents from wool fabric and carpet yarn treated at the 0.6% m/nz level were found by vaq-ing the temperature (40-80 "C) and time (0.5-4 h) of extraction. Jlaximum recoveries from wool fabric were achieved after 1 h at A0 "C or after 0.5 h at 80 "C. The coarser carpet wool fibres required at least 1 11 at 80 "C. Prolonging the extraction time to 4 h at 80 "C slightly reduced the recoveries presumably owing to some chemical degradation of the PCSDs.An extraction time of 2 h at 80 "C was adopted for all types of wool textiles. Sealed glass ampoules were found to be more reliable than screw-cap vials for extraction of the wool. The high vapour pressure of the methanol - ammonia solution at 80 "C required good sealing to prevent leakages. No problems have been experienced with several thousand extractions that have now been performed in glass ampoules. However as a precautionary measure against injury in the event of an ampoule exploding the shaking water-bath should be fitted with a stainless-steel lid and safety glasses should be worn when entering or removing ampoules from the water-bath. Good recoveries (Table I) of PCSDs were obtained from wool fabric treated with known amounts of the different insectproofing agents applied from an organic solvent.An exact amount of formulation can be applied in this manner giving a surface deposit on the fibres that is easily extracted. TABLE I RECOVERY OF INSECTPROOFING AGENTS FROM WOOL BY EXTRACTION WITH METHANOL - AMMONIA SOLUTION AT 80 " c FOR 2 h Dye-bath application* Solvent application Amount applied, Formulation % mlm Eulan WA New . . 0.5 1 .o Eulan 1333 . . . . . . 0.5 1 .o Mitin LP . . . . . . 0.5 1.0 Molaiitiii P . . . . . 0.5 1 .o Recovery, % 98 96 104 102 95 98 100 100 Yarn Amount applied Recovery, 0.6 90 1.2 91 0.6 92 0.6 85 1.2 88 0.7 87 1.0 85 % mlm ?o -Fabric r - - - - - - L 7 Amount applied Recovery, ?; tn/m /O 0.3 93 0.6 90 0.2 90 0.3 86 0.6 88 0.5 90 O/ -* These recoveries do not include small amounts of the insectproofing agents (2-4y0 of Eulan WA New, Lower recoveries of the PCSDs were found for wool fabric and carpet yarn treated with known amounts of the insectproofing agents in a dye-bath at 100 "C (Table I).This method of treatment allows migration of the insectproofing agent into the swollen fibre making its extraction more difficult. However a second methanol - ammonia solution extraction performed on the higher level treatments (1 .0-1.27" nz/m) failed to yield additional detectable amounts of PCSDs indicating that incomplete extraction was not the cause of the lower recoveries. Quantitative transfer of the insectproofing agent on to the wool from boiling dye-bath liquors is much more complex than by solvent application and some losses invari-Eulan 1333 and Mitin 1,P and 4-6% o f Molantiii P) which remained in the tlye-bath liquors 326 MAYFIELD AND RUSSELL DETERMINATION OF AnaLvst Vol.108 ably occur.1o For example the dye-bath liquors from the applications in Table I contained 2-4% of the applied amount of Eulan WA New Eulan U33 and Mitin LP and 4-6% of the applied amount of Molantin P. The determination of insectproofing agents on wool - polyamide blend carpets treated during blend dyeing is frequently required. PCSDs partition in favour of the polyamide by as much as 10 1 when applied to the blend in a dye-bath at or near 100 "C. Methanol -ammonia solution extraction of two types of polyamide used in carpets and treated with 0.6 and 1.8% m/m of Eulan WA New and Mitin LP in the dye-bath afforded recoveries of 92-94% indicating the extraction procedure to be applicable to both polyamide and wool.Extraction of Liquors Acidification to a pH of about 2 followed by a single extraction with dichloromethane was adequate for determining PCSDs in dye-bath liquors down to 0.5 mg 1-l. A 40-fold con-centration step was necessary for liquors containing less than 2 mg 1-1 of the formulations, and a 20-fold concentration sufficed for more concentrated liquor samples. Recoveries are given for the extraction of the insectproofing formulations from three typical dye-bath liquors (Table 11) spiked with a range of concentrations (0.5 1 5 and 20 mg 1-1) normally encountered in practice.The extraction efficiency was generally good with some variability occurring at the lowest concentration examined (0.5 mg 1-l) which is near the detection limit. The levelling agent Albegal A which is a surfactant did not hinder the extraction. TABLE I1 RECOVERY OF KNOWN CONCENTRATIONS OF INSECTPROOFING AGENTS FROM DYE-BATH LIQUORS Amount Added/ Dye-bath liquor mg 1-l Ammonium sulphate (2 g 1-l) + glacial acetic acid (0.25 g 1-1) . . . . 0.5 1.0 5.0 20.0 Ammonium sulphate (2 g 1-l) + formic acid (go% 1.25 g 1-l) . . . . 0.5 1 .o 5.0 20.0 Ammonium sulphate (2 g 1-l) + glacial acetic acid (0.25g1-l) + Albegal A (0.6 gl-l) . . . . . . . . 0.5 1 .o 5.0 20.0 Recovery of insectproofing agent "/o r - New Eulan U33 Mitin LP Molantin P Eulan WA 86 86 90 92 84 88 92 92 80 84 70 94 98 88 98 93 91 97 .- -80 74 60 87 98 86 98 97 91 97 - -90 90 68 90 88 90 96 90 101 92 94 90 96 - 87 -HPLC Analysis Reversed-phase HPLC was examined briefly for the determination of PCSDs extracted from wool but was found on some occasions to suffer from interfering peaks presumably from materials (dyes and textile auxiliaries) co-extracted with the PCSDs.These inter-ferences were not encountered with normal-phase HPLC and on this basis normal phase was selected as the preferred method of analysis. Silica particles initially used as the column packing gave good peak shapes and resolution but long equilibration periods were required following slight changes in the mobile phase to obtain reproducible retention times.This problem was overcome by using silica particles with a cyanopropyl bonded phase. Transfer of the PCSDs in the methanol - ammonia solution extract to a less polar solvent, as required for normal-phase HPLC was achieved by the addition of dilute hydrochloric acid to the extract and partitioning of the PCSDs into 2,2,4-trimethylpentane - dichloro March 1983 PCSDS ON WOOL AND IN TEXTILE LIQUORS BY HPLC 327 A I - 0 6 12 Time/m in Fig. 1. HPLC chromatogram of the PCSDs (40 mg 1-1 in 1 + 1 2,2,4-trimethylpentane - dichloromethanc) isolated from Eulan WA New. a) u 0 12 b' A Cl h A I c 0 12 0 12 d A C - 0 12 Time/min Fig. 2. HPLC chromatograms obtained from extracts of wool treated with (a) 0.6% m/m Eulan WA New; (b) 1.2% m/m Mitin LP; (c) 0.4% m/m Eulan U33; and (d) 0.4% m/m Molantin P.Peaks A and B are PCSDs and peak C the internal standard. methane. When using solutions of 400 200 and 100 mg 1-I of Eulan U33 in methanol -ammonia solution at least 98% of the PCSDs were found to partition into the 2,2,4-tri-methylpentane - dichloromethane phase in this step. The chromatogram (Fig. 1) obtained for PCSDs isolated from Eulan WA New contained two peaks (A and B) with capacity factors ( k ) of 1.69 and 2.19 respectively. Chromatograms (Fig. 2) obtained on analysis of wool treated with Eulan U33 and Mitin LP afforded values of k identical with those obtained for the PCSDs isolated from Eulan WA New.However Molantin P showed only one major peak (A) with a much smaller value of k (1.03) and clearly contained PCSDs which were of a different composition to that in the Eulan and Mitin formulations. Peak C in the chromatograms in Fig. 2 is due to N-benzoyl-4-buty1.aniline used as an internal standard. Some other internal standards found to be suitable were the benzoyl derivatives of 2,4-dimethylaniline and 9-toluidine but their retention times were longer. PCSDs exhibited an ultraviolet absorption maximum at 242 nm and this wavelength was used for detection to obtain the best sensitivity. With a 30-pl injection volume this enabled the formulations used to be determined down to o.05y0 m/m on wool textiles and 0.5 mg 1-' in spent textile liquors well below the concentrations normally encountered in practice.The peak-area ratio of peak A to peak C was used for quantification of the insectproofing agents. Calibration graphs of peak-area ratio rleysus concentration over the range 0-400 mg l-l for the formulations used were linear (correlation coefficients 0.999 1-1.0000). This concentration range corresponds to the treatment levels normally found on wool textiles. Standard fabric samples containing known amounts (0.3 and 0.6% m/m) of the insectproofing agent being determined are incorporated in each analytical run as a check on the extraction efficiency and reproducibility. Details of the repeatability (within a batch of analyses) and the reproducibility (between batches of analyses) of the method as applied to the determination of Eulan WA New on wool fabric carpet yarns and a dye-bath liquor are given in Table 111.The repeatability was very good (coefficient of variation 0.5-4.67;) for all samples except the industrial sample A. In this sample the poor repeatability was probably due to an unlevel application of insectproofing agent. The reproducibility of the analyses was very good in every instance (coefficient of variation 1.5-3.3%). The HPLC analysis time was 12min for each sample 328 MAYFIELD AND RUSSELL TABLE I11 REPEATABILITY AND REPRODUCIBILITY OF METHOD APPLIED TO THE DETERMINATION OF EULAN WA NEW Sample and treatment level Batch No.* Standard wool fabric (0.6% m/m) . . . . Overall . . . Standard wool carpet yarn (0.6% m/m) Overall . . . . Industrial carpet yarn A (application level unknown) .. . . Overall . . . . Industrial carpet yarn B (application level unknown) Overall . . . . Dye-bath liquor sample (spiked with 1 mg 1-l) . . * Each batch consisted of 5 replicate analyses. 1 2 3 1 2 3 1 2 3 I 2 3 1 Mean, 0.566 0.567 0.592 0.575 0.574 0.562 0.578 0.571 0.634 0.616 0.616 0.622 0.097 0.098 0.092 0.096 1 .oo % mlm Standard deviation, 0.006 0.004 0.003 0.015 0.007 0.007 0.003 0.008 0.053 0.094 0.109 0.010 0.003 0.003 0.003 0.003 0.046 % mlm Coefficient of variation yo 1.0 0.74 0.66 2.6 1.3 1.2 0.60 1.6 8.4 15 18 1.6 3.1 3.3 3.3 3.3 4.6 Conclusions Insectproofing agents based on PCSDs are extracted efficiently from wool and polyamide with methanol - ammonia solution and from spent dye-bath liquors with dichloromethane, and determined by normal bonded-phase HPLC.The limits of detection for the commercial formulations on textile samples and in dye-bath liquors were 0.050/ m/nz and 0.5 mg 1-l, respectively well below the levels normally encountered in practice. Recoveries obtained from textile samples and dye-bath liquors containing known amounts of the insectproofing formulations were very good as were the repeatability and reproducibility of the method. The simple extraction procedure and short analysis time make this method ideally suited to the routine analysis of textile samples for these insectproofing formulations. More than 3000 samples have already been determined in these laboratories by this method. The technical assistance of Mrs. Wendy Jackson is gratefully acknowledged. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. References Anliker R. Kauchle A . and Hefti H. Pvoc. I n t . Il'ool Tcxtalr Rcs. Con.f. 3achra 1975 5 . 161. Wells D. E. Anal. Chim. Ada 1979 104 253. Res. Discl 1979 No. 179 121. Mysicka %. and Hanousek V. Chem. Prum. 1976 26 420. Wrabetz I<. Scheiter H. and Meek D. Fresrnius Z. Anal. Chrrti. 1974 271 27%. British Standard BS2087 1971 Amendment Slip Xo. 2 1977 Appendix 1'. Kaniwa M. Kojima S. Nakamura A. and Sato \-. Eisei Iiagakzr 1979 25 80. Jackson W. Mayfield I<. J. and Iiussell I. hI. CSIIiO Rcport GL-12 CSlRO I)ivi.;ion of Textile Wells D. E. and Johnstone S. J. J. Chromatogv. Sci. 1981 19 137. Mayfield R. J. J. SOC. Dyers Colouv. 1983 98 6. Industry Belmont Australia 1980. Iicceived . I U ~ I P 181h 1982 ilcccptetl Septrinbcr. 9th. 198

ISSN:0003-2654    

DOI:10.1039/AN9830800322

出版商:RSC    

年代:1983

数据来源: RSC

摘要:

Analyst March 1983 VoZ. 108 $$. 329-334 329 Quantitative Determination of Carbonyl Compounds in Rendering Emissions by Reversed-phase High-performance Liquid Chromatography of the 2,4- Di nitrop henyl hyd razones Herman R. Van Langenhove Marc Van Acker and Niceas M. Schamp Laboratoviunz VOOY Ovganische Scheikundr Faculteit van de I_airdboitz~~zuetenscha~p~~~~ I~ijksiiItivevsiteit-Gent, Coupure L i n k s 653 B-9000 Gent Belgium A simple and rapid method for the determination of volatile carbonyl com-pounds in air has been developed. The method is applied to the quantitation of C,-C aldehydes and acetone in rendering emissions. Carbonyl compounds are sampled by absorption in a 2 x lW4 M 2,4-dinitrophenylhydrazine solution a t pH 1 and the resulting hydrazones are extracted with 2,2,4-trimetliylpentane concentrated and analysed by HPLC on a 10-pni RP-C, column with a water - acetonitrile gradient as the eluent.The hydrazones are then spectrophotonietrically detected a t 356 nni . The micro-scale conversion of carbonyls into 2,4-dinitrophenylhydrazones is investigated the separation of hydrazones is improved and the sampling conditions are tested in order to achieve quantitative sampling a t an air flow-rate of 1 1 min-l. Quantitation is possible for concentrations as low as 15 p.p.b. (formaldehyde) and 2 p.p.b. (nonanal). The over-all coefficient of variation (taken over sampling conversion and analyses) is less than loo/. Keywords Carbonyl quantitation ; 2,4-dinitropIienyllzydrazine derivatisntion ; reversed-phase HPLC analysis ; rendering plant enaissions The lower aliphatic aldehydes formaldehyde acetaldehyde and acrylaldehyde are well known in atmospheric pollution chemistry as important intermediates in photochemical smog forma-tion.Higher aldehydes on the other hand are more associated with flavour chemistry be-cause they are secondary oxidation products of fatty acids. Aliphatic aldehydes as a whole are emitted by animal rendering plants and these compounds together with lower aliphatic acids amines and sulphur compounds contribute to the odour nuisance commonly accompany-ing rendering activities In order to evaluate the relative importance of different groups of malodorants a method for the quantitation of aldehydes a t odour threshold levels (parts per lo9 p.p.b.) has been developed.The derivatisation of aldehydes into 2,4-dinitroplienylhydrazones followed by either gas chromatographic or high-performance liquid chromatographic (HPLC) analysis of the deriva-tives is a widely proposed method.1-6 Derivatives of isomeric carbonyl compounds have been separated by gas chromatography on capillary columns coated with OV-17,OV-101 and SF 96.' However double peaks due to syn- and anti-isomeric forms may hamper the determination and quantitation of compounds in unknown mixtures by altering the retention data.lV2 These workers summarised different normal and reversed-phase HPLC analyses of hydrazones that were in use up to 1979. They also reported the separation of 2,4-dinitrophenylhydrazones of carbonyls up to C6 by reversed-phase HPLC with a LiChrosorb RP-18 column and acetonitrile - water as the mobile phase.Other reversed-phase separations have been reported with either isocratic4 or linear solvent programming e l ~ t i o n . ~ The latter technique allows the separation of C,-C, linear aliphatic aldehydes within 10 min. The micro-scale conversion of propanal with 2,4-dinitrophenylhydrazine was investigated by Selini.6 According to this worker a two-phase system aqueous reagent -2,2,4-trimethylpentane was needed to achieve quantitative conversion. In this paper results of studying the micro-scale reactivity of C,-C9 carbonyls and 2,4-dinitrophenylhydrazine (2,4-DNPH) the trapping efficiency of aldehydes in 2,4-DNPH reagent and analyses of the derivatives obtained by HPLC are described. Results of the quantitation of carbonyl compounds in rendering emissons are also reported.Kuwata et aZ.3 reviewed the advantages of HPLC for hydrazone separation 330 Reagents The carbonyl compounds investigated were obtained from various commercial sources. Owing to trimer formation the purification of the aldehydes is essential if reliable results are to be obtained. Formaldehyde acetaldehyde and propanal were purified by distillation. Higher aldehydes were purified by preparative gas chromatography. The 2,4-dinitrophenyl-hydrazine reagent consists of 0.125 g of 2,4-DNPH in 100 ml of 6 N hydrochloric acid. The reagent was extracted twice with 50 ml of carbonyl-free 2,2,4-trirnethylpentane and the purified reagent was kept covered with a layer of the same solvent. The 2,2,4-trimethyl-pentane (1 1) was refluxed with 0.5 g of 2,4-DNPH and 50 ml of 6 N hydrochloric acid for 2 h and was then distilled from the reaction mixture.Hydrazone standards were prepared and purified by use of standard methods.' Apparatus and Chromatographic Conditions A Varian 8500 liquid chromatograph and a Varian spectrophotometer (UV-VIS Model 635) operating at a wavelength of 356 nm were used to perform the analyses. Samples were injected by use of an injection valve (Valco CV-6-UVPa N60) together with a 10-pl loop. The column used was a pre-packed 25 cm x 4 mm i.d. 10-pm LiChrosorb RP-18 column (E. Merck Darmstadt F.R. Germany). The column temperature was held at 40 "C with a water-jacket. The mobile phase was acetonitrile - water at a flow-rate of 1.5 nil min-l.Solvent concentrations are indicated on the chromatograms. Micro - scale Reaction The micro-scale conversion of C,-C9 linear aliphatic aldehydes into 2,4-dinitrophenyl hydra-zones was performed in an aqueous reagent (25 ml of distilled water and 0.8 ml of 2,4-DNPH reagent) and in a two-phase system (aqueous reagent and 15 ml of 2,2,4-trimethylpentane). The aldehyde concentrations ranged from 8.0 x M for nonanal. After being stirred for 1 h reaction mixtures were extracted with 2,2,4-triniethyl-pentane (2 x 15 ml). The solvent was then evaporated the hydrazones were re-dissolved in 1 ml of acetonitrile and analysed by HPLC. In a second experiment propanal hexanal and nonanal standards were diluted 1 + 2 1 + 4 and 1 + 9 and the reaction was carried out in the aqueous reagents.Sampling Efficiency In order to determine the sampling efficiency air concentrations of 0.36 p.p.m. (mol/mol) of formaldehyde 0.93 p.p.m. of propanal 0.56 p.p.m. of hexanal and 0.39 p.p.m. of nonanal were generated with a motor-driven syringe. Two bubblers containing different amounts of 2 x M 2,4-DNPH solution were connected in series and the polluted air was sampled at a rate of 1 1 min-l for 30 min. After sampling the reagent solutions were combined and stirred with a magnetic stirrer for 1 h. The hydrazones were next extracted with 50 ml of carbonyl-free 2,2,4-trimethylpentane while the bubblers were rinsed with a further 15 ml of carbonyl-free 2,2,4-trimethylpentane. The solvent fractions were then combined and the analysis was completed as described above.Rendering Emission Sampling Samples were taken in a Belgian rendering plant with an annual capacity of 10000 t of raw material. Gases and vapours released during cooking pass consecutively through a grease trap a surface condenser and two water scrubbers. The air sampling flow-rate was 1 1 min-l; samples were taken during 15-min sampling periods. VAN LANGENHOVE et a2. CARRONYL QUANTITATION Experimental A d y s t VoZ. 108 M for formaldehyde to 1.8 x The material is processed in batch cookers under vacuum. Samples were taken at the last scrubber outlet. Results and Discussion HPLC Separation and Calibration of the 2,4-Dinitrophenylhydrazones The separation of 2,4-dinitrophenylhydrazones of the linear aliphatic C,-C aldehydes 2-methylpropanal 2-methylbutanal 3-methylbutanal and acetone were investigated.Fig. 1 (a) and (b) show the separation obtained with 10- and 5-pm columns respectively. In both instances the derivatives of linear aliphatic aldehydes and acetone are completely separated March 1983 IN RENDERING EMISSIONS BY REVERSED-PHASE HPLC 33 1 i 100 a 2 7 5 1 50 25 I 2 5 /-.7 8 910 4 0 5 10 15 20 5 10 15 20 25 tlmin Fig. 1. Separation of 2,44nitrophenylhydrazones by reversed-phase HPLC using (a) a 10-pm and ( b ) a 5-pm RP-C, column. The water - acetonitrile gradient is indicated as percentage of acetonitrile. The compounds in the mixture are 2,4-dinitro-phenylhydrazones of 1 formaldehyde; 2 acetaldehyde; 3, acetone; 4 propanal; 5 butanal and 2-methylpropanal; 6 2-methylbutanal and 3-methylbutanal; 7 pentanal; 8 hexanal ; 9 heptanal; 10 octanal; and 11 nonanal.On the 10-pm column the same relative molecular mass derivatives of isomeric C and C carbonyl compounds overlapped. As is shown in Fig. 1 ( b ) partial separation of pentanal from 2-methyl-butanal and 3-methylbutanal could be achieved. Different solvent programmes with initial acetonitrile concentrations ranging from 40 to 60% were tested with no better result. On analysing standard hydrazone solutions of the different C and C aldehydes it was found that equal amounts (0.5 pg of derivative) of equal relative molecular mass derivatives gave equal peak heights the ratio of peak heights of derivatives of different aldehydes being as follows: 2-methylpropanal to butanal 1 .OO ; 2-methylbutanal to pentanal 1.02 ; 3-methylbutanal to pentanal 1.02.Therefore 2-methylpropanal and butanal were determined as the C aldehyde group 2-methylbutanal 3-methylbutanal and pentanal as the C aldehyde group. Deriva-tives of butanal and pentanal were the standards for the C and C aldehyde group. Calibration of the method was carried out by plotting peak heights (in millimetres) zwsus the amounts of aldehydes injected. Five-point calibration graphs ranging from 15 to 1.5 pg gave correlation coefficients greater than 0.999 for all of the aldehydes tested. Assuming an air sampling volume of 25 1 (at 25 "C) and 200 pl of acetonitrile in order to re-dissolve hydra-zones quantitation of aldehydes can be performed from as low as 15 p.p.b. (formaldehyde) to 2 p.p.b.(nonanal). TABLE I CONVERSION OF LINEAR ALIPHATIC ALDEHYDES INTO 2,4-DINITROPHENYLHYDKAZONES Conversion efficiency is expressed as a percentage relative to standards ($1 = 5 ) . In j cc ted / illdch yde nmol Formaldehyde . . . . 20.9 ilcetcldehydc . . . . 14.25 Propanal . . . . 11.12 Butanal . . 9.1 Pen tanal . . 7.6 Hexanal . . . . 6.7 Heptanal . . . . 6.0 Octanal . . . . 5.1 Nonanal . . . . 4.7 One- phase system 70.95 & 2.6 101 & 3.5 101 * 4.9 93 * 6.1 89 * 4.7 104 f 2.8 96 & 3.6 94 3.5 101 f 2.5 Two-phase system 74.7 j 7.6 99 * 4.2 105 5.2 102 f 2.4 95 f 3.6 93 f 3.7 55 f. 2.8 32 f. 6.2 6 f 5. 332 Analyst VoZ. 108 Micro-scale Conversion of Aldehydes Into 2,4-Dinitrophenylhydrazones Table I shows that a quantitative conversion of linear C,-C aldehydes is obtained in the one-phase system.Formaldehyde shows a conversion of 75%. In the two-phase system heptanal and higher aldehydes show a decreasing conversion due to the hydrophobic character of these compounds. Table I1 shows that no decrease in conversion efficiency is ascertained by lower-ing aldehyde concentrations. From this it can be concluded that C,-C9 aldehydes can be quantitatively converted in the aqueous reagent system. The efficiency of conversion for formaldehyde is 75%. VAN LANGENHOVE et aZ. CARBONYL QUANTITATION TABLE I1 CONVERSION OF PROPANAL HEXANAL AND NONANAL INTO THEIR 2,4-DINITROPHENYLHYDRA-ZONES AT LOWER ALDEHYDE CONCENTRATIONS Conversion efficiency is expressed as percentage relative to Conversion (%) at dilution Initial aldehyde A > standards.Aldehyde concentration/M 1 + 2 1 + 4 1 + 9 Hexanal . . 26.5 x 100 111 104 Nonanal . . . . 18.6 x 105 103 110 Propanal . . 44 x 10-6 100 103 90 Sampling Efficiency The sampling efficiency of formaldehyde propanal hexanal and nonanal in the 2,4-dinitro-phenylhydrazine solution was tested using increasing amounts of reagent. Table 111 shows the best sampling results. It can be seen that a sampling unit of two bubblers containing 100 ml of reagent each was efficient for formaldehyde propanal and hexanal ; nonanal however was not quantitatively sampled Quantitative sampling of all four aldehydes was achieved by using two bubblers containing 200 ml of reagent each. Therefore the latter conditions were used during rendering emission sampling.TABLE I11 HYDRAZINE REAGENT AT A SAMPLING FLOW-RATE OF 1 1 min-1 SAMPLING EFFICIENCY OF PROPANAL HEXANAL AND NOSANAL IN THE 2,4-DINITROPHEXYL-Conversion efficiency is expressed as percentage relative to standards ( 1 2 = 5). Sampling efficiency using two bubblers containing n r v Aldehyde 100 nil of reagent each 200 nil of reagent each Formaldehyde . . . . 97 f 6.4 104 f 5.4 Hexanal . . . . 103 f 2.S 104 7.0 Nonanal . . 90 f 2.3 103 f 7.5 Propanal . . 100 f 5.4 100 .& 8.7 Quantitation c3f Carbonyls in Rendering Emissions Table IV shows the results of the quantitative determination of aldehydes in rendering emissions taking iI.to account the 75% efficiency of conversion of formaldehyde.Fig. 2 shows a typical chromatog;s,;. Samples were taken on 1 3 . 2 . 1 9 8 1 between 4 p.m. and 8 p m . The sampling time w~~ 15 min and it took another 15 min to prepare for sampling. During sampling 10 cookcis were in use. Each cooker contains 1500-3000 kg of raw material which is heated for 1- C h. Malodorants are liberated by the thermal breakdown of cell structures and the chemkal decomposition of animal matter. Amounts of malodorants vary during the heating proczss and depend on the nature and freshness of the raw material which results in a typical emission pattern for each batch process. The normal activity of the plant involves processing different materials at the same tinie. Therefore the concentrations mentioned in Table IV do not show the evolution of amounts of carbonyls emitted during the processing o March 1983 I N RENDERING EMISSIONS BY REVERSED-PHASE HPLC 333 100 50 25 I I I L 0 5 10 15 2C tlmin Fig.2. Chromatograxn of the analyses of 2,4-dinitrophenylhych-a-zones of carbonyl compounds samplecl a t the rendering plant. The water - acetonitrile gradient is indicated as percentage of aceto-nitrile. Compounds are 2,4-dinitro-phenylhydrazones of 1 formalde-hyde; 2 acetaldehyde; 3 acetone; 4 propanal; 5 C,-aldehydes; 6, C,-aldehydes ; 7 hexanal ; 8 hep-tanal; 9 octanal; 10 nonanal. one material. The variations in the carbonyl concentrations of the rendering emissions shown in Table IV are caused by the coincidence of malodorant producing stages in the different batches.This may explain the relatively large concentration differences between different samples. In order to find out if there is some relationship between the individual carbonyl concentra-tions the Spearman rank correlation coefficients8 for all aldehydes except formaldehyde which shows little variation were calculated. Hexanal heptanal The results are shown in Table V. TABLE IV QUANTITATIVE DETERMINATION OF CARBONYL COMPOUNDS IN RENDERING EMISSION Concentrations are in p.p.m. Sample number Aldehyde Formaldehyde Acetaldehyde Acetone . . Propanal C,-aldeh ydes C,-aldehydes Hexanal . . Heptanal Octanal . . Nonanal . . I 1 1 2 3 4 5 6 7 . . 0.2 0.2 0.19 0.19 0.21 0.19 0.19 2 1.87 2 2.27 3.8 2.13 1.92 0.16 0.16 0.14 0.08 0.22 0.2 0.13 0.21 0.25 0.16 0.22 0.35 0.24 0.29 .. 0.53 0.96 0.90 1.22 1.45 0.82 0.64 0.94 1.79 1.75 2.3 2.7 1.49 1.28 . . 0.44 0.48 0.34 0.56 0.69 0.57 0.34 . . 0.19 0.21 0.16 0.25 0.30 0.32 0.16 . . 0.17 0.21 0.16 0.23 0.27 0.36 0.14 . . 0.28 0.38 0.33 0.41 0.48 0.44 0.2 334 VAN LANGENHOVE VAN ACKER AND SCHAMP octanal and nonanal correlate significantly at the 1% level. At the 5% level these aldehydes, also correlate with propanal. The C,-aldehyde group correlates with the C,-aldehyde group at the 1% level. Neither the C,- nor the C,:group correlate with propanal hexanal heptanal or octanal. An explanation for the correlations may possibly be found in the reactions that lead to aldehyde formation. Linear aliphatic aldehydes are formed by the dismutation of fatty acid hydroperoxides with or without migration of double bonds.g During the hating of animal matter amino acids may react with a-dicarbonyl compounds to form an aldehyde having one carbon atom less than the original amino acid.This reaction called Strecker degradation, will give rise to the branched aldehydes 2-methylpropanal 2-methylbutanal and 3-methyl-butanal from valine isoleucine and leucine respectively.1° TABLE V SPEARMAN RANK CORRELATION COEFFICIENTS BETWEEN THE DIFFERENT CARBONYL CONCENTRATIONS 1 Acetaldehyde; 2 acetone; 3 propanal ; 4 C,-aldehydes ; 5 C,-aldehydes ; 6 hexanal 7 heptanal ; 8 octanal; 9 nonanal. 2 3 4 5 6 7 8 0.210 0.331 0.501 0.501 0.690 0.610 0.690 0.652 0.104 0.104 0.580 0.540 0.576 1.0003. 0.595 0.444 0.500 0.595 0.444 0.500 0.607 0.607 0.879* 0.803* 0.786* 0.9603.0.9543. 0.9923. 9 0.828t 0.557 0.786* 0.750* 0.750* 0.9493. 0.8983. 0.929t * Significant at 5% level (n = 7). t Significant at 1% level ( n = 7). Taking into account these two reactions generating aldehydes the Spearman correlation coefficients seem to indicate that the C,- and C,-aldehyde groups mainly consist of branched aldehydes otherwise a correlation of these groups with aldehydes formed by fatty acid oxida-tion would be expected. The literature results for odour detection values of individual aldehydes are not very con-sistentll in that the thresholds for aldehydes seem to vary between 1 and 50 p.p.b.l0?l2 In contrast the reported threshhold for acetone varies between 20 and 32 Comparing these data with the concentrations found in rendering emissions it can be concluded that acetone does not contribute to the odour problem.All of the aldehydes that were determined are present in supra-threshold concentrations. Therefore these compounds are at least partially responsible for the rendering odours. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. References Hoshika Y. and Takata Y. J. Chromatogr. 1976 120 379. Smith R. A. and Drummond I. Analyst 1979 104 875. Kuwata K. Uebori M. and Yamasaki Y. J . Chvomatogr. S c i . 1970 17 264. Fung K. and Grosjean D. Anal. Chem. 1981 53 168. Demko P. It. J . Chromatogr. 1979 179 361. Selim S. J . Chromatogr. 1977 136 271. Wild F. “Characterization of Organic Compounds,” Second Edition Cambridge l’niversity Press, Siegel S. “Nonparametric Statistics for the Behavioral Sciences,” McGraw-Hill New York 1956, Badings H. T. Neth. Milk Dairy J . 1970 24 147. Amoore J . E. Forrester L.J. and Pelosi P. Chem. Senses Flavor 1976 2 17. Fazzalari F. A. Editor “Compilation of Odor and Taste Threshold Values Data,” American Society Quadagni D. G. Buttery R. G. and Okono S. J . Sci. Food Agvic. 1963 14 761. Davis J . C. Chem. Eng. 1973 86. Kittel G. and Wendelstein P. G. J. Arch. Klin. Exp. Ohren-Nasen- Kehlkopfheilk 1971 199 683. Cambridge 1962 p. 112. p. 202. for Testing and Materials Baltimore MD 1978. Received January 4th 1982 Accepted September 23rd 198

ISSN:0003-2654    

DOI:10.1039/AN9830800329

出版商:RSC    

年代:1983

数据来源: RSC