摘要:

790 Analyst, December] 1966, Vol. 91, $@. 790-794 The Proportion of 2-Methylbutanol and 3-Methylbutanol in Some Brandies and Whiskies as Determined by Direct Gas Chromatography BY D. D. SINGER (Laboratory of the Government Chemist, Ministry of Technology, Cornmall House, Stamford Strcet, London, S.E. 1) Stationary phases suitable for the separation of 2-methylbutanol (“active” pentanol) and 3-methylbutanol (isopentanol) are discussed. The most suitable for the determination of these alcohols in potable spirits by direct injection of samples are diethyl tartrate and polyethylene glycol 200. Poly- ethylene glycol 200 is preferred because other congeners can be determined a t the same time. With n-pentanol as an internal standard, 65 samples of cognac brandies, Scotch and other whiskies have been examined on one or other of these stationary phases. The sum of the two pentanol isomers determined separately agrces well with their determination as a single peak on polyethylene glycol 1500.The ratio of the concentrations of the isomers appears to be characteristic of the type of spirit. IN a previous paper1 it was demonstrated that the principal higher alcohols (n-propanol, isobutanol and “isopentanol”) in cognac brandies and Scotch whiskies occur in relative proportions that are, within a narrow range, characteristic of each type of spirit. It was suggested that determination of these proportions might be of use in identifying spirits analytically if sufficient results covering a wider range of spirituous products were available. The precise biochemical mechanism of formation of these alcohols and other congeners2 has been reviewed recently, and is still a matter for controversial discussion and further investi- gation.From a practical standpoint however, it is reasonable to suppose that under the precisely maintained conditions of fermentation of closely controlled starting materials and with the subsequent careful distillations that are carried out by producers of high quality spirituous beverages, many congeners will occur in consistent proportions to each other, according to the type of product. The actual amounts of the congeners may be expected to vary, for example, as the proportion of starch to protein varies in the wort or must, and according to the fractionation used during distillation.Consistency in any one type of spirit is aided by the judicious blending which tends to even out random changes. 60 45 30 Time, minutes Fig. 1. Chromatogram of a Scotch all-malt whisky on polycthylene glycol 200SINGER 791 The analyses reported previously did not distinguish between 2-methylbutanol and 3-methylbutanol. These isomers are often considered together as “isopentanol,” although this name is sometimes applied colloquially to the 3-methyl isomer to distinguish it from the 2-methyl isomer. The latter is sometimes referred to as “active” pentanol because of its asymmetric carbon atom. These isomers have close boiling-points, and are unlikely to be separated in the distillation of spirituous beverages. It was therefore thought of interest to investigate their presence individually in spirits of the type already examined.EXPERIMENTAL Stationary phases suitable for the separation of the isopentyl isomers have been dis- cussed by Dinsmoor and Webb3 with special reference to the analysis of sherry concentrates. Glycer01,~ “Tide’’5 and triethanolamine6 have also been used. These stationary phases had disadvantages. Efficient columns were seldom obtained, and packing the columns was sometimes difficult because of the stickiness of the prepared Celite. Even when efficient columns were obtained, long retention times were necessary for good separation and the base-line disturbance attributed to the water injected, and the large ethanol peak, both overlapped the pentanol peaks. All the stationary phases capable of separating the isomers are polar, and therefore several polar esters were investigated.Only partial separation was obtained on 6 foot x inch, 10 per cent. dibutyl tartrate and diethyl citrate columns, but excellent separation was obtained with a similar column of 10 per cent. diethyl tartrate at 55” C. As the column aged, the earlier peaks of n-propanol and isobutanol merged with the ethanol peak, but the separation of the pentanol isomer remained satisfactory over 400 hours of use. Since this work was started, Prabucki and Pfenninger’ have also described this use of diethyl tartrate for the study of extracts of spirits and beers. More recently in this laboratory in an investigation of the most volatile congeners, it was found that a 20 per cent. column of polyethylene glycol 200 gives excellent separation of the pentanol isomers at 70” C.The “bleed” of stationary phase is lower than with the diethyl tartrate column, and other congeners may be determined on the same chromatogram. The column lasts for more than 600 hours. Chromatograms on the two selected stationary phases are shown in Figs. 1 and 2, and the relative retention of a number of compounds on polyethylene glycol 200, as determined in solution in 40 per cent. v/v ethanol, are given in Table I. RELATIVE RETENTION Substance Methanol . . . . Ethanol . . . . Isopropanol . . s-Butanol . . .. Isobutanol . . . . n-Butanol . . . . 2-Methylbutanol . . 3-Methylbutanol . . n-Pentanol . . . . Acetaldehyde . . n-Propionaldehyde Isobutyraldehyde . . Isovaleraldehyde .. Acetal . . . . Acetone . . . . Ethyl formate . . Ethyl acetate . . Ethyl isobutyrate . . Ethyl isovalerate . . Ethyl hexanoate . . n-Propyl acetate . . Isobutyl acetate . . Isopentyl acetate . . TABLE I OF SOME COMMON COMPOUNDS ON POLYETHYLENE GLYCOL 200 .. .. . . . . .. . . . . . . . . . . . . .. . . . . . . , . . . . . . . .. . . .. . . . . .. . . . . .. . . . . . . . . . . . . . . . . . . .. . . . . .. .. . . .. . . .. Relative retention* - 0.366 0.446 0.434 0.702 1.000 1.481 1.98 2.12 2.70 0.078 0.154 0-262 0.89 0.169 0.150 0.121 0.172 0-26 0.47 1-23 0.29 0.36 0.66 * Isobutanol Obscured by ethanol Tends to tail as column ages Not separated from acetone Obscured by ethyl acetate Not separatcd from propionaldehyde Obscured by ethanol Obscured by methanol 1-00.792 SINGER: PROPORTION OF 2-METHYLBUTAKOL AND [AkXZZySt, VOl.91 METHOD This was similar to that previously described.l The samples, adjusted to exactly 40 per cent. by volume of ethanol by addition of water or pure ethanol, were mixed with one-tenth of their volume of pure 40 per cent. ethanol containing 500 mg of pure n-pentanol per ml as an internal standard. Columns were either a 6 foot x $-inch copper column of diethyl tartrate, 10 parts and Celite (80 to 100 mesh), 90 parts, or a 9 foot x Q-inch (0.08 i.d.) stainless- steel column of polyethylene glycol 200, 20 parts and Celite (100 to 120 mesh), 80 parts. Operating conditions for diethyl tartrate were: carrier gas, nitrogen at a flow-rate of 70 ml per minute at 55” C, and for polyethylene glycol 200, nitrogen at a flow-rate of approximately 18 in1 per minute at 70” C,.The polyethylene glycol 200 was obtained directly from Messrs. Union Carbide Ltd. (samples obtained from chemical wholesalers were not always satisfactory and sometimes had an opaque semi-solid appearance). For analysis, 2 or 5 pl of the sample mixture were used and the results obtained compared with standards prepared in 40 per cent. v/v ethanol. Time, minutes Chromatogram of a cognac brandy on diethyl tartrate Fig. 2 . RESULTS The results are shown in Table 11. The spirits are of a similar type to those previously analysed for the principal higher a1cohols.l The whiskies, type A, are blended Scotch whiskies, and are all popular blends consumed in Great Britain. The malt whiskies are types used for blends and are all “single” whiskies, i.e., the product of an individual “batch.” Some of TABLE I1 2-METHYLBUTANOL AND 3-METHYLBUTANOL IN BRANDY AND WHISKY 2-Methylbu tanol , parts per 100,000 of absolute ethanol 22 25 26 21 21 24 22 20 22 24 24 25 24 21 *A.Blended whiskies- 3-Mc thy1 bu tanol, parts per 100,000 of absolute ethanol 57 62 60 59 57 62 56 53 66 60 58 65 67 54 Sum 79 87 86 80 78 86 78 73 78 84 82 90 91 75 Sum, as dctermined on polyethylenc glpcol 1500 83 79 89 79 75 84 77 75 75 87 80 92 95 74 Ratio, 2-Methylbu tanol 3-Methylbu tanol 0.38 0.4 1 0.44 0.36 0.37 0.39 0.38 0.37 0.41 0.39 0.41 0-38 0-36 0.39December, 19661 3-METHYLBUTANOL I N SOME BRANDIES AND WHISKIES 2-Methylbutanol, parts per 100,000 of absolute ethanol 63 64 67 64 81 56 63 55 52 51 52 63 71 61 U.S.Bourbon 137 U.S. Bourbon 130 Canadian . . 22 Canadian . . 16 Dutch . . 10 Dutch . . 10 Dutch . . 12 B. 1Valt whiskies- C. Other whiskies- D. Cognac brandies, good quaZity- 15 37 45 38 40 35 42 43 39 34 58 34 15 38 33 29 37 26 32 36 E. Brandies, ipzferior quality- 32 34 28 34 36 1;. “Marc de Rourgogne” brandies- 67 58 62 53 60 TABLE II-continued 3-Methylbutanol, parts per 100,000 of absolute ethanol Sum 162 166 152 162 188 169 142 146 137 118 134 149 171 164 354 356 61 36 31 27 33 77 169 195 170 166 166 201 197 195 189 278 164 65 174 142 126 176 110 154 162 121 134 113 128 145 201 199 220 174 194 225 230 219 226 269 226 205 201 189 169 186 212 242 225 49 1 486 83 52 41 37 45 92 206 240 208 206 201 243 240 234 215 336 198 80 212 175 155 213 136 186 198 153 168 141 162 181 268 257 283 227 254 Sum, as determined on polyethylene glycol 1500 218 224 217 220 265 220 200 202 185 164 180 213 233 219 500 475 88 46 39 42 - 90 210 237 210 202 196 251 2 50 240 211 329 202 85 207 775 162 207 141 195 190 156 162 134 159 177 261 252 290 231 259 793 Ratio, 2-Methyl bu tan01 3-Rlethylbutanol -~ 0.39 0-39 0.44 0.39 0.43 0.33 0.44 0.38 0.38 0.43 0.39 0.42 0.41 0.37 0.39 0.3 7 0.36 0-44 0.32 0.37 0.36 0.20 0.22 0.23 0.22 0.24 0.2 1 0.2 1 0.22 0.20 0.19 0.2 1 0.2 1 0.23 0.22 0.23 0.23 0.2 1 0.24 0.21 0.22 0.26 0.25 0.25 0.24 0.25 0.33 0.29 0.29 0.30 0.3 1 the malt whiskies had been matured for 6 years in sherry casks at the time of analysis and some had been bottled almost immediately after distillation, a few months before analysis.Re-examination 18 months after bottling revealed no change in composition during this time. KO significant difference was found in the ratio of the pentanol isomers in the new and the old spirits, which are not therefore distinguished from each other here. The cognac brandies, “D,” bear a good commercial reputation and are blends of matured spirits. The cognac794 SINGER brandies, “E,” possess less commercial esteem, and, as reported previously,l contain appre- ciable proportions of s-butanol and a larger proportion of methanol than usually found in higher quality spirits. The grain whisky used for blending with Scotch malt whisky is the product of efficient fractional distillation, and contains a negligible amount of pentanols. As a result, there is little difference in the ratio of the pentanol isomers between the blends and the all-malt types.The whiskies produced outside Scotland are also the products of fermentation of unmalted grain, but have not been highly fractionated, and therefore contain pentanols. The ratio of the isomers in the few examples of these latter spirits examined falls within the range of that found for the Scotch whiskies and may be significant of a grain ferment, whether malted or not. The lowest proportion of the 2-methyl isomer is found in the good quality cognacs (0.19 to 0-24), and is significantly different from that of the inferior cognacs (0-24 to 0.26), and the “Marc de Bourgogne” (0.29 to 0.33). The author thanks the Government Chemist, Dr. D. T. Lewis, C.B., (Ministry of Tech- nology), for permission to publish this paper. REFERENCES 1. Singer, D. D., Axalyst, 1965, 90, 290. 2. Lawrence, W. C., Wallerstein Labs Cornmun., 1965, 26, 123 to 152A. 3. Webb, A. D., and ICepner, R. E., Arner. J . Enol. Vitic., 1961, 12, 61. 4. Van der Kloot, A. P., Tenney, R. I., and Bavissotto, V., Proc. Amer. SOC. Brew. Chern., 1958, 96. 5. Porcaro, P. J., and Johnston, V. D., Analyt. Chem., 1961, 33, 361. 6. Sihto, E., Nykanen, L., and Snomalainen, H., 1st International Symposium, “Les Methodes d’Analyse des Aliments,” Bordeaux 8-12th Oct., 1962, Bureau Internationale Permanent de Chimie Analytiq ue, Commission Internationale des Industries hgricoles, Groupement Inter- nationale de la Vigne et du Vin. 7. Prabucki, A. L., and Pfenninger, H., Helv. Chinz. Acta, 1961, 44, 1286. Received May 25th, 1966

ISSN:0003-2654    

DOI:10.1039/AN9669100790

出版商:RSC    

年代:1966

数据来源: RSC

摘要:

Analyst, December, 1966, Vol. 91, $9. 795-801 795 An Instrument for the Continuous Determination of Carbon Dioxide in High Purity Water* BY K. H. WALL (Central Electricity Generating Board, South Eastern Region, Cockfosters, Herts.) An instrument for the continuous determination of carbon dioxide in high purity water is described. The instrument consists essentially of a device for transferring the carbon dioxide from the water to a gas stream, which is then passed through an aqueous suspension of calcium carbonate. The pH of this suspension, which is proportional to the concentration of carbon dioxide in the gas stream and hence the original water, is recorded continuously. Precision tests a t lcvels of 20 and 60 pg per litre had a standard deviation of about 4 pg per litre.THE corrosive effect of carbon dioxide in boiler feed-waters is largely suppressed by the addition of volatile amines to produce a high pH. Under conditions of high temperature and pressure, however, the carbon dioxide could react with the protective oxide film on the metal surfaces of the feed system, increasing the transport of iron and copper to the boiler and accelerating high temperature corrosion. Manual methods of analysis for carbon dioxide of adequate precision and sensitivity are available,l 3 2 9 3 but few continuous methods have been described. Bartley and Moult4 proposed a method for the determination of carbon dioxide in steam by using an infrared gas analyser to determine the carbon dioxide present in the gases evolved from a conventional Straub de-gasser. Ehrenberg and Smit5 have described a method involving continuous acidification of the sample, followed by equilibration with carbon dioxide-free air which is subsequently equilibrated, in turn, with water.Conductivity measurements are then made on the water. Neither of these methods has been applied to boiler feed-water. The instrument described here is robust, reliable and does not require the continuous addition of reagents. DESCRIPTION OF THE INSTRVMENT The first part is based on a design proposed by Burdon6 for stripping a “selected compound” from a sample of water by boiling and sweeping it into a measuring device. Component parts of the glassware are shown in Figs. 2, 3, 4 and 5 . The sample is passed through a cation-exchange resin to remove ammonia, which would interfere.I t is then fed to the primary heating coil (145 kW) at a flow-rate of 220 ml per minute. This flow-rate is adjusted by altering the height of the constant head. The heated sample passes into the fractionating mlumn, which is vacuum jacketed and filled with glass Raschig rings, where it is scrubbed by steam produced by the secondary heating coil. The steam and carbon dioxide then pass into the stripping column, which is also vacuum jacketed and filled with Dixon gauze rings. Carbon dioxide-free air is sucked in through a non-return valve by a small pump, thus sweeping the carbon dioxide into the final stage. Toren and Heinrich7 and Lodge et al.8 have shown that the hydrogen-ion concentration of a suspension of calcium carbonate through which air is passing is proportional to the carbon dioxide content of the air.This system is used in the instrument, the pH being recorded continuously. The pH meter is a Pye Dynacap set to read from pH 8 to 10 ; the output of the meter is fed into a 500-pA current recorder, so that the effective chart width covers pH 8 to 9. The flow-rate of the sweep gas is controlled at 60 ml per minute by an automatic flow regulator. A diagram of the instrument is shown in Fig. 1. * Presented at a meeting of the Automatic Mcthods Group on Thursday, November 17th, 1966.796 WALL : INSTRUMEST FOR THE CONTINUOUS DETERMINATION OF [AK?Ut!ySt, VOl. 91 B A A = Pump J = Constant head B = Flow regulator K = Soda lime C = Silica gel L = Zeo-Karb 225 D = Calcium carbonate suspension M = Capillary tube E = Pressure equaliser N = Primary heating coil F,, F, F, = Flow-meters 0 = Fractionating column G = Stripping column P = Secondary heating coil H = Float switch Q = Non-return valve Fig.1. Diagram of the instrument Projections for Spherical ball joint BI 4 socket I I - 2 - I I : 16 Fig. 2. Primary heater (Vitreosil) and connecting piece (Pyrex), (dimen- sions in inches) Vitreosi I secondary heater ----- l o I: 6 B24 socket --Evacuated and silvered B24 cone Fig. 3. Details of the re-boiler (dimensions Fig. 4. Details of stripping column in inches) (dimensions in inches)December, 19661 CARBON DIOXIDE I N HIGH PURITY WATER 2.25- /,Spherical p ball socket Evacuated and silvered H . 797 Fig. 5. Details of fraction- ating column (dimensions in inches) In the event of loss of sample, the secondary heating coil will merely boil the water in the re-boiler under reflux.For this reason, a safety device, which consists of a float switch in the constant head, de-activates a relay, switching off the primary heater when the water level falls. The circuit diagram is shown in Fig. 6. The primary heating coil, however, will become red hot. 240V a.c. I I 24 0 Mains .-I I I I I I I 5 00 mA . J Fig. 6. Circuit diagram of the automatic cut-off safety device798 WALL: INSTRUMENT FOR THE CONTINUOUS DETERMINATION OF [Analyst, VOl. 91 DISCUSSION According to Henry’s law, the mass of gas absorbed by a fixed volume of liquid at a given temperature is proportional to the (partial) pressure. As the air above the liquid in the instrument is free from carbon dioxide and is continually being renewed, the carbon dioxide will be removed from the water and transferred to the sweep gas.Heating to boiling accel- erates this process. The reactions involved when carbon dioxide dissolves in water are well known- CO, + H,O = H2C03 = H+ + HCO,- HC0,- = H+ + LO,,- The equilibrium constants for these reactions are- Several workers have used a solution of sodium hydrogen carbonate to determine carbon dioxide in gas streams, e.g., Maxon and J o h n ~ o n , ~ and each group has found that the hydrogen-ion concentration is proportional to the carbon dioxide content. Assuming the activity coefficients to be unity and the hydrogen carbonate concentration to be high enough to be effectively constant, as K, is much smaller than K,- K (Hi) =cl (CO,) where K, and C are constants.Toren and Heinrich7 and Lodge et aZ.* also found a linear relationship by using a sus- pension of calcium carbonate in water, the hydrogen carbonate ion presumably being formed from the reactions- CaCO, = Ca2+ + CO,,- LO,,- + H,O = HCO,- + OH- OH- + CO, = HCO,- The advantage of the calcium carbonate suspension is that a decrease in the carbon dioxide content of the gas stream reduces the carbon dioxide content of the suspension to give a higher pH, whereas a sodium hydrogen carbonate solution does not readily lose carbon dioxide. calculated the solubility of calcium carbonate with decreasing carbon dioxide concentration, and concluded that the solubility decreases to a minimum, after which the carbonate begins to decompose to calcium hydroxide and the calcium-ion concentration increases again.The pH will, of course, rise rapidly when this occurs. Accord- ing to these authors, the minimuni occurs at a partial pressure of 4 x atmospheres of carbon dioxide. If this figure is calculated back to a water sample flowing through the instrument, the corresponding carbon dioxide concentration in the water is about 0.2 pg per litre. Below this concentration, therefore, the pH of the suspension can be expected to rise more rapidly. Johnson and EXPERIMENTAL The original Burdon design of the fractionating columns proposed blowing the sweep gas through to the measuring device, but it was found that the system rapidly became un- stable, the rather vigorous boiling of the water blowing the sample back out of the primary heater.A suction arrangement through a non-return valve with a rubber bag to act as as a pressure stabiliser proved satisfactory. I n early trials with the instrument a sample flow-rate of 220 ml per minute and a sweep gas flow-rate of 30 ml per minute were used. I t was necessary to have a vent to the atniosphere on starting to allow the gases expanded from the system to escape. Increasing the gas flow-rate to 60 ml per minute removed the necessity for a vent, but reduced sensitivity. However, the starting procedure is simplified. It was originally intended to obtain a zero by inserting a soda-lime tube in the gas stream immediately before the pH cell. When this was done, the reading obtained was much higher than expected.This was obviously caused by the effect predicted by Johnson and Williamson when the partial pressure of carbon dioxide fell below 4 x 10-7 atmospheres. An alternative method of establishing the zero is to remove carbon dioxide from the sample before it entersDecember, 19661 CARBON DIOXIDE I N HIGH PURITY WATER 799 the instrument. However, attempts to remove carbon dioxide from condensate with a small, mixed bed de-mineralisation column were not successful. A column, 40 cm high and 2.5 cm in diameter only removed about half of the carbon dioxide from water containing 70 pg per litre. Further tests with other resins showed that the best result, a reduction to less than 1 pg per litre, could be obtained by using two columns in series, the first filled with mixed bed and the second with De-Acidite FF.The zero of the instrument is therefore obtained by installing two such columns in the sample line. Zero tests have not been carried out at values higher than 70pg per litre. The effect of ambient temperature changes on the response of the instrument was not investigated in detail. However, variations from 15" to 25" C produced no noticeable change in the results obtained during tests. The automatic temperature compensation facility of the pH meter was used to correct for glass electrode temperature effects. CALIBRATION- The difficulties involved in making and storing large quantities of water of a known carbon dioxide content made a dynamic method of calibration preferable. The instrument was installed in a mixed bed de-mineralisation plant, the water produced by the plant being used as the dilution water for standard solutions of sodium carbonate that were introduced by a small pump.Volumes, ranging from 1 to 5 ml per minute, of 0.005, 0.002 and 0.001 N sodium carbonate solutions were added to de-mineralised water flowing at 300 ml per minute. To confirm that the sodium carbonate was satisfactorily converted into carbon dioxide by the cation-exchange resin, samples of the effluent from the instrument were analysed with a flame photometer. The calibration procedure was to obtain a steady reading with de-mineralised water as the sample, and then pump in standard sodium carbonate solutions in random order, noting the pH obtained at each level.Steady pH readings were normally obtained about 20 minutes after adjusting the flow-rate. The carbon dioxide content of the de-mineralised water was dete~~rrincd by a standard manual method,2 and this value subtracted as a blank. The results obtained (Table I) show a straight line relationship between carbon dioxide and hydrogen-ion concentration. A regression analysis gave the equation of the regression line as x = 82.26~ - 140.5, where x = pg of carbon dioxide per litre and y = Hf x The standard deviation about the regression line is 2 pg per litre, and the standard error of the regression coefficient is k0.9 pg per litre. No sodium was detected at any of the concentrations used. Carbon dioxide content of de-mineralised water, pg per litre 5 5 5 5 5 5 5 TABLE I CALIBRATION RESULTS Carbon dioxide added, pg per litre 152 285 50 183 73 146 102 PH 8.44 8.28 8-62 8.40 8.57 8.45 8.53 H+ x 10-9 3.63 5-25 2.40 3.98 2.69 3.55 2.95 PRECISION TESTS- A knowledge of the precision obtainable at the two main levels encountered in modern power stations was desirable, i.e., 20 pg per litre, a typical economiser inlet value and 60 pg per litre, a typical condensate value.Sodium carbonate solutions were added, as before, to a basic supply of de-mineralised water. Table I1 shows the results obtained, the standard deviations being 4.1 pg per litre at the 20 pg per litre level and 3.6 pg per litre at the 60 pg per litre level. Further tests were then carried out in a power station with water taken from the con- denser of a 120-mW generator.Samples were taken simultaneously for manual determinations by the standard method. The results, which are detailed in Table 111, have a standard deviation of 3.0 pg per litre. For this series, the zero was obtained by using the combined de-ionisation columns recommended.800 WALL INSTRUMENT FOR THE CONTINUOUS DETERMINATION OF [ArtdySt, VOl. 91 The standard deviation obtained with the instrument at the levels likely to be found in feed water is about & 4 pg per litre. This compares with a figure of better than 2 pg per litre for the manual method.2 However, the instrument requires little attention, and provides a continuous record of carbon dioxide concentrations. TABLE I1 PRECISION RESULTS IN LOGICAL ORDER Carbon dioxide content of de-mineralised water, pg per litre 5 3 2 2 2 3 2 2 2 2 Carbon dioxide added, p g per litre 23 23 24 20 20 52 57 55 53 53 Carbon dioxide found, p g per litre 23 30 22 22 16 56 60 52 60 56 Difference, p g per litre -5 + 4 -4 0 -6 +1 +1 -5 + 5 +1 TABLE I11 SIMULTANEOUS DETERMINATIONS ON CONDENSATE Manual determination, Instrument, Difference, p g per litre p g per litre pg per litre 22.6 24 + 1.4 25.4 28 + 2.6 18.7 20 + 1.3 25.0 24 - 1.0 28.8 24 - 4.8 OPERATION- The instrument is started by switching on the pump, pH meter and recorder, and opening clips A and B.The sample flow is adjusted to between 300 and 500 ml per minute and the heaters are switched on. When closing down, the heaters are switched off and clips A and B closed. It is convenient to leave the pump and pH meter switched on to keep the interior free from carbon dioxide and to reduce the response time on starting, It is possible to check for leaks in this way as the pH should rise above 9.2.Once started, the instrument needs no further attention, providing the sample flow exceeds 220ml per minute. Below this value the float switch operates to switch off the primary heater. If indicating soda lime is used for the guard-tubes the colour change will show when they should be replaced. The life of the cation-exchange resin will depend on the ammonia content of the water. Unusually low results are an indication that regeneration is required, but it is preferable to replace or regenerate the resin on a routine maintenance basis, the frequency being determined by the known ammonia content and the flow through the instrument. The calcium carbonate should be replaced about once a month as it becomes slimy, although no adverse results have been obtained.The drift of the instrument is governed by the stability of the pH meter. Variations of less than $-OW5 pH units over 2 hours have been obtained when making zero checks, but it is advisable to check the zero daily. APPLICATIONS AND PERFORMANCE The instrument can be used for the continuous determination of carbon dioxide in high purity waters of the type used for feeding boilers in power stations. I t is installed in a cabinet to prevent mechanical damage, and it has been used in power stations for about 2 years, proving to be robust and reliable in operation. The instrument has functioned satisfac- torily on samples varying in temperature from 15" to 32" C.I thank Mr. P. W. Polfreman for the design of the automatic cut-out safety device, and Mr. J. G. Whiteley for carrying out the manual carbon dioxide determinations. This paper is published by permission of Mr. H. J. Bennett, Regional Director, Central Electricity Generating Board.December, 19661 CARBON DIOXIDE IN HIGH PURITY WATER 801 Appendix CONSTRUCTIONAL DETAILS OF THE INSTRUMENT The framework of the instrument is made of aluminium angle and is about 5 feet high, 3 feet wide and 2 feet deep. Most of the internal parts are glass with the exception of the heaters, which are Vitreosil wound with nichrome wire and covered with aluminous cement. Flexible connections are made in neoprene. The dimensions of the heaters and columns are not thought to be critical.However, details are as follows. Primary heater (1.45 kW), length 16 inches, bore 13 mm nominal; secondary heater (132 W supplied by a 50-V transformer), length 4.5 inches, bore 13 mm nominal; re-boiler, height 12 inches, internal diameter 2 inches with B29 socket; fractionating column (vacuum jacketed), height 25 inches, internal diameter 1.5 inches with B29 cone and B24 socket; stripping column, height 10 inches, internal diameter 1 inch with B24 cone and socket. The pH cell consists of a sintered-glass crucible (35-ml capacity) containing 1 g of analytical- reagent grade calcium carbonate, and sufficient distilled water to cover the electrodes. The glass electrode is a screened general-purpose electrode, E.I.L., type GHS33. Other items are an Austen Dymax Mark 1 pump, a Platon Flostat Minor flow regulator, a Pye Dynacap pH meter, a Record 500-pA recorder and a Rotameter flow-meter. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. REFERENCES Jennings, P. P., and Osborn, E. M., Analyst, 1957, 82, 671. Sadler, M. A., “Improved Method for the Determination of Carbon Dioxide in Boiler Feed Water,” Central Electricity Generating Board,‘South West Region Research Report No. RD/SW/R32, 1966. Gaunt, H., and Shanks, C., Chem. G. Ind., 1964, 651. Bartley, W. B., and Moult, E., Engineer, 1958, 206, 484. Ehrenburg, J. P., and Smit, G. B., Analytica Chim. A d a , 1963, 29, 1. Burdon, M. C., and Central Electricity Generating Board, British Patent 846,498, 1960. Toren, P. E., and Heinrich, B. J., Analyt. Chem., 1957, 29, 1854. Lodge, J . P., Frank, E. K., and Ferguson, J., Ibzd., 1962, 34, 702. Maxon, W. D., and Johnson, M. J., I h i d . , 1954, 24, 1541. Johnston, J., and Williamson, E. D., J . Amer. Chem. Soc., 1916, 38, 975. Received March 171h, 1966

ISSN:0003-2654    

DOI:10.1039/AN9669100795

出版商:RSC    

年代:1966

数据来源: RSC

摘要:

802 Analyst, December, 1966, Vol. 91, $9. 802-805 The Determination of Salt in Bacon by Using a Sodium-ion Responsive Glass Electrode BY J. H. HALLIDAY (T. Wall & Sons (Meat and Handy Foods) Ltd., Willesden) AND F. W. WOOD ( Unilever Research Laboratory, Colworth House, Sharnbrook, Bedford) Rapid determination of the salt content of cured meat products with a sodium-ion responsive electrode is described and discussed. The method enables the percentage of salt on water content to be measured directly on the meat in a few minutes. Many determinations can be made cheaply and accurately enough for purposes of routine factory control. INCREASING amounts of bacon are now being retailed, ready sliced, in vacuum packs. This bacon may be produced by automatic or semi-automatic production meth0ds.l To obtain a product that has a satisfactory shelf life and is organoleptically acceptable it is necessary to control the salt content of the bacon within close limits.This control is aided by rapid and accurate analysis soon after production. Existing chemical methods are fairlv slow and demand experience to reach the required accuracy. An electrochemical method for determining the sodium chloride concentration directlv in bacon would give a rapid result in terms of salt on water without weighing. A recent publication2 describes a method for the determination of the chloride content of cured meat products, but this method requires the weighing and dissolution of the sample. Sodium-ion responsive glass electrodes are now available commercially and have been used in many analytical applications.3 I t was considered worthwhile to attempt to determine the sodium-ion concentration in bacon by simple contact of the muscle with the electrode.This type of electrode in conjunction with a standard electrode has a potential, E , varying with the sodium ion activity, A,,, according to the equation- 2.3 RT log A,, F E = Constant + This potential can be determined in the same way as the potential of a hydrogen-ion sensitive glass electrode, by using a calomel reference electrode and a high impedance volt- meter. The salt content of lean bacon expressed as a percentage of the water content can vary from 2 to 10 per cent., and over this concentration range the sodium-ion activity coeffi- cient varies considerably.To use this electrode analytically, it is therefore necessary to use a calibration curve prepared from salt solutions of known concentration. Because of the temperature dependence of the potential, the calibration curve should be determined at the same temperature as the actual determination. The membrane of the type of glass electrode used, GEA33,* is made from B104 glass. This electrode is very specific for sodium ions, and can tolerate a 50-fold concentration of potassium ions without affecting the sodium ion response. The potential of this electrode is affected by a pH of less than 7, but at the concentration of sodium ions found in bacon, this effect is not significant. This paper reports the use of this electrode system for the determination of salt in back, half gammon and streaky bacon.APPARATUS AND CALIBRATION- EXPERIMENTAL Sodium-ion responsive glass electrode, tyee GEA33." Saturated calomel electrode, type GR J2.3." $H meter-A very stable pH meter is required, the No. 48R Hood pH meter* being A calibration curve was prepared by using solutions of analytical-reagent grade sodium * E.I.L. Ltd., Richmond, Surrey. suitable. chloride ranging in concentration from 1 to 10 g of sodium chloride per 100 g of water.HALLIDAY AKD WOOD 803 PREPARATION OF SAMPLE- The simplest method appeared to be to wrap portions of sliced bacon round the electrodes, but this proved to be too irreproducible for routine use. Mincing, macerating, or grinding the sample gave reproducible results, but was too time consuming for production control.Two methods of sample preparation were finally adopted for routine use after experience with many hundreds of determinations. ( a ) Two lateral holes were bored into the roll by No. 1 and No. 3 cork borers, and the electrodes inserted into the holes. A sample of macerated lean bacon was ready for analysis in half a minute, Two slices of bacon were placed together and rolled into a cylinder. This method will be referred to as the "roll method." (b) The sample was rapidly chopped with a multiblade knife (Fig. 1). Fig. 1. Diagram of a six-bladed cutter, corn- prising a + x +-inch M/S flat bar, six TY - Linker blades and a file handle PROCEDURES- Glass electrode method- When not in use the electrodes were kept immersed in a 6 per cent. salt solution, and before being inserted into a bacon sample they were lightly wiped with paper tissue but were not allowed to dry off.Repeated washing with distilled water prolonged the equilibration time and was avoided. After insertion into the sample, the electrodes were left until a steady millivolt or pH reading was obtained (usually 3 to 5 minutes), after which the electrodes were removed, wiped with paper tissue, and either inserted into another sample or replaced in the salt solution. The percentage of salt, based on the water content of the sample, was then read directly from the calibration curve. Chemical method- The results obtained by the glass electrode method were compared with those obtained on the same samples by the A.O.A.C. Volhard assay, as previously used in bacon analy~is.~ The published method, which gives the percentage of salt in bacon, was modified by adding sucrose to the reaction mixture after oxidising with the nitric acid and potassium permanganate and boiling until the solution was colourless.For comparison with the glass electrode method the results were converted to percentage salt on the moisture content of the bacon. The latter was determined by drying the sample overnight in an air-oven with a fan at 100" C 1" C.804 HALLIDAY AND WOOD: DETERMINATION OF SALT IN BACON [Aflat?’JSt, VOl. 91 RESULTS AND DISCUSSION Results obtained on macerated samples of the lean of back bacon are shown in Table I. TABLE I SALT DETERMINATIONS ON MACERATED LONGZSSZMI.S DORSZ MUSCLES OF BACK BACON Percentage of salt on water, w/w Time of Meter I- A \ reading, reading, Electrode Chemical Sample minutes mV method method 1 10 897-5 6.0 6.3 2 0- 6 896.0 6.6 6.8 2 895.0 5 895.0 10 894.6 0.5 2 5 10 0.5 2 5 10 0.5 2 5 10 0.6 2 6 907.0 907.0 907.6 907.0 9094 904.4 903.5 903.6 896.5 893.5 893-6 893.0 897.0 895.0 896.0 4.4 6-0 7.0 6.6 4.5 5-2 7-3 7-0 These results show a satisfactory correlation, although the percentage salt on water given The response time by the electrode is slightly lower than that given by the chemical method. of the electrode is seen to be about 3 minutes.Table TI shows the results obtained by the roll method of sample preparation. TABLE I1 SALT DETERMINATIONS ON VARIOUS TYPES OF BACON SAMPLES PREPARED BY USING THE ROLL METHOD OF PREPARATION Percentage of salt on water, w/w Type of sample Longissirnus dorsi., Half gammon lean Streaky .. .. Elektrode method 3.3 4.7 6.9 6.0 6.8 8.3 9.6 4-0 5.9 8.0 9.6 6- 7 6.3 7.0 8.2 9.8 10.6 4 Chemical rneihod 3.1 4-3 6.0 643 6.9 7- 8 8.1 4- 6 6-5 7.0 8-6 6.7 6.6 7-2 8.6 9.6 10.3 Reproducibility when using the roll method was not always satisfactory for the leaner Often a slight movement of the elec- It is, however, evident from Table I1 that The reason for this is not clear, samples of longissirnus dorsi muscle and half gammon. trodes caused fluctuations in the meter reading. streaky bacon can be analysed satisfactorily by this method. but is probably owing to the lower moisture content of this type of bacon.December, 19661 BY USING A SODIUM-ION RESPONSIVE GLASS ELECTRODE 805 Table I11 shows the regression of the values, y , determined by the chemical methods on those obtained by the electrode, x .The electrode method has been used for many thousands of analyses, To estimate the reliability of this method compared with the chemical method a statistical analysis has been performed; 50 samples each of lean and streaky bacon were used. TABLE I11 SUMMARY OF STATISTICAL ANALYSIS OF SALT DETERMINATIONS ON BACON BY CHEMICAL AND SODIUM ELECTRODE METHODS Longissimus dorsi and half gammon Streaky bacon (macerated sample) (roll method) Regression equation relating percentage of salt by chemical method (y) to electrode method ( x ) . . Confidence limits for slope (P = 0.95) . . .. 0.940, 1.062 0-852, 1.024 Residual standard deviation of individual points 0.42 0.46 y = 0.526 + 0.996 x y = 0.424 + 0.938 x For both methods the slope of the regression line did not differ significantly from 1.The regression equations show that the electrode gives a lower value than the chemical method. This can also be seen by inspection of the results shown in Table I. It is not serious for production control purposes, and is probably caused by the activity coefficient of the sodium ion in the aqueous environment of the sample being different from that in aqueous solution. We thank the Boards of T. Wall and Sons (Meat and Handy Foods) Ltd. and Unilever Ltd. for permission to publish this paper. REFERENCES 1. 2. 3. Barrett, J., Galbraith, C., Holmes, A. W,, and Herschdoerfer, S . M., “1st International Congress of Food Science and Technology,” London, 1962, “Abstracts of Papers,” Grp. D.9, Part IV, p. 113. Krzeminski, L. F., Bartal, A., and Landmann, W. A., J . Fd Scz., 1965, 30, 52. Mattock, G., in West, P. W., Macdonald, A. M. G., and West, T. S., Editors, “Analytical Chemistry 1962 : The Proceedings of the International Symposium held a t Birmingham University, 1962, ” Elsevier Publishing Co., London, 1963, p. 247. Horwitz, W., Editor, “Official Methods of Analysis of the Association of Official Agricultural Chemists, ” Tenth Edition,The Association of Official Agricultural Chemists, Washington, D.C., 1966, p. 346. Received A p i l 18th. 1966 4.

ISSN:0003-2654    

DOI:10.1039/AN9669100802

出版商:RSC    

年代:1966

数据来源: RSC

摘要:

806 SHORT PAPERS Analyst, December, 1966, Vol. 91 Mobile Laboratory Methods for the Determination of Pesticides in Air Part I. Phosphorothiolothionates BY G. A. LLOYD AND (2. J. BELL (Plant Pathology Laboratory, Hatching Green, Harpenden, Herts.) THE determination of pesticides in air affords a means of studying the effects on human exposure to these products when used in agriculture and horticulture. For such determinations, a mobile laboratory1 is used for collecting and analysing air samples. Although elaborate analytical instruments cannot be used in the field to make these analyses, colorimetric procedures are practicable as portable spectrophotometers are available commercially. Procedures are required that will determine the more toxic pesticides, chiefly the organo- phosphates, at concentrations in air of generally less than 0.2 mg per m3. Devices are used to sample the air, normally at 10 litres per minute, and the sampling period is adjusted com- mensurately with the sensitivity of the available colorimetric procedure.In general, these field methods should have few, brief manipulations, and should allow less than 10 p g to be determined normally in 20 ml of solution with an error of not more than 10 per cent. Contamination of samples by inorganic phosphates is likely on farms and in glasshouses and, therefore, well known procedures cannot be used to determine organophosphorus pesticides by decomposition to the phosphate ion. Hazardous or unstable reagents, lengthy refluxing and the use of complex apparatus should be avoided, but techniques requiring prolonged incubation a t less than 50" C, or boiling for short periods, are practicable in a mobile laboratory.Few published methods satisfy these requirements; suitable procedures are described in this paper and in ensuing papers. Disulfoton,2 diethyl S- [2- (ethylthio) ethyl] phosphorothiolothionate, and phorate,2 diethyl S(ethylthiomethy1) phosphorothiolothionate, are highly toxic insecticides and occupational hygiene studies required their determination to less than 0-1 mg per m3 in air. Published methods3 did not meet the requirements for use in the field. It was found, however, that certain phosphoro- thiolothionates or phosphorothiolates could be readily hydrolysed to yield thiols, which can be determined by a suitably modified colorimetric procedure of extremely high ~ensitivity.~ METHOD APPARATUS- flow of 10 litrcs per minute for vapour sampling.Spined glass bz~bbZers5-These are to contain 20 to 30 ml of solvent for operation a t an air Glass-fibre filters--T;l'hatman GF/A, 5.5 cm in diameter,6 for sampling dusts or droplets. Filter holders-These can be based on the design of the Ministry of Labour test-paper holder,' the intake orifice being 12 mm in diameter for operation a t an air flow of 10 litres per minute. Stoppered tubes-25-ml graduated, capacity, 40 ml to stopper. REAGENTS- Trapping solution-Dilute 1 volume of N aqueous sodium hydroxide containing 0.05 per cent. w/v of sodium cyanide to twice its volume with isopropanol. Sulphuric acid, 50 per cent. v/v and 1 per cent.v/v. Sodium nitrite stock solution-Dissolve 3.5 g of sodium nitrite and 0-5 g of sodium hydroxide Sodium nitrite working solution, 0-005 N-Dilute 1 volume of stock solution with 9 volumes Ammonium sulphamate, 10 per cent. w/v, aqueous. SuZphaniZamide-Prepare a 1.5 per cent. w/v solution in 6 N hydrochloric acid. N-1-Naphthylethylenediamine dihydrochloride-Prepare a 0.4 per cent, w/v solution in 6 N in 1 litre of water. of 1 per cent. v/v sulphuric acid. hydrochloric acid. Replace with a fresh solution after 1 week.SHORT PAPERS 807 Mercuric acetate-Prepare a 5 per cent. w/v solution in 75 per cent. v/v acetic acid. Chromogenic reugent-Prepare by mixing 8 volumes of sulphanilamide solution, 1 volume of Replace with N- l-naphthylethylenediamine solution and 1 volume of mercuric acetate solution.a fresh solution every hour. SAMPLING LAYOUT- Set up the sampling devices in the breathing zones of operators working with the pesticide and connect each device to a metered source of vacuum. Each filter holder must be placed with the opening pointing downwards to simulate, as far as is practicable, the mechanics of inhalation through a nostril. In our expcrience the exposure indicated agrees reasonably well with that whereby the operator himself provides the air flow.* Significant amounts of pesticides might be vaporised when applied in the form of a dust or spray, in which event, sample the air through a glass-fibre filter backed by a bubbler a t each sampling position. At the air sampling-rate of 10 litres per minute, a glass-fibre filter will normally trap a proportion of pesticide in vapour form, but this may be offset by evaporation of droplets or vaporisation from dust particles trapped on the filter.Hence, the amount found in the backing bubbler cannot reliably be used to calculate the vapour concentration in air. Normally, a precise separation of the two forms is not required for protection purposes and, to date, no air filter has been found that completely separates airborne particles and vapours. AIR SAMPLING- according to the intended period of sampling, as indicated below. (i) Vufiouvs-Charge each bubbler with 20 ml of trapping reagent and add more isopropanol, Intended sampling time, minutes . . 5 5 to 10 11 t o 15 16 to 21 22 to 26 27 to 32 32 to 36 36 to 40 Draw air through each bubbler a t 10 litres per minute, preferably for 10 to 30 minutes.Under these conditions the trapping efficiency is 80 per cent. for disulfoton and phorate; all results must be multiplied by the factor 5/4. Determine the collection efficiency for all pesticide vapours by connecting two or more charged bubblers in series. Draw air, a t normal temperature and humidity, over a sample of the pesticide a t 10 litres per minute for periods of 10 to 30 minutes. Repeat the test with different concentrations of pesticide in air, generally in the range 0.01 to 0.2 pg per litre; this can be done by varying the exposed surface area of pesticide. Transfer the bubbler contents to a graduated tube, adjust the volume to 20 ml with isopropanol and replace the stopper.Allow it to stand for 24 hours a t about 15" C to complete the hydrolysis of the phosphorothiolothionates to the corresponding thiols. (ii) Droplets or dusts-Draw air at 10 litres per minute through a glass-fibre filter. Transfer an exposed filter to a graduated tube containing 25 ml of the trapping reagent. Stopper the tube and shake it well to break up the filter. Allow it to stand for 24 hours a t about 15" C to complete the extraction and hydrolysis of the phosphorothiolothionate. Filter, if necessary (Whatman GF/A glass-fibre filter), transfer an aliquot (normally 20 ml) to a similar graduated tube and adjust the volume as required to 20 ml with the trapping reagent. The recovery of 5 to 50 pg of clisulfoton or phorate from a glass-fibre filter is better than 80 per cent., but for protection purposes i t is better to over-estimate the risk, and for this reason the amounts found should be multiplied by the factor 5/4.Added isopropanol, ml . . . . 2 4 5 7 8 9 10 11 PROCEDURE- Stopper the tube, mix the solution carefully by inversion and cool to about 16" C. Add 1.0 ml of 0.005 N sodium nitrite solution, mix and allow the solution to stand for 1 minute. Add 0.5 ml of ammonium sul- phamate solution and shake the solution vigorously for 1 minute, occasionally releasing the stopper; allow it to stand for a further 1 minute. Add 5.0 ml of chromogenic reagent. Mix well and allow i t to stand for 2 hours avoiding direct sunlight. Measure the absorbance of the solution a t 540 mp, with a light path of not less than 4 cm.Deduct the reagent or air blank reading and refer to a calibration graph prepared similarly from standard amounts (5 to 5 0 p g ) of toxicant in 20-ml volunies of trapping reagent. The accuracy of the colorimetric method is within 510 per cent. but the over-all accuracy with which airborne toxicants can be determined is limited partly by the accuracy with which the volumes of air samples are measured and controlled. Add 5.0 ml of 50 per cent. v/v sulphuric acid to 20 ml of hydrolysed extracts.808 SHORT PAPERS [Anahst, VOl. 91 Demeton-S-methyl, oxydemeton-methyl, dimethoate, mecarbam and morphothion2 have been successfully determined by this procedure and it is probable that demeton-S, thiometon, prothoate and vamidothion2 can be determined similarly. Phosphorothionates and 50-pg amounts of the following phosphorothiolothionates, azinphos- methyl, azinphos-ethyl, dioxathion, malathion and menazon2 give little or no reaction when analysed by this method. REFERENCES 1. 2 . “Recommended Common Names for Pesticides,” British Standard 1831 : 1965. 3. 4. 6. 6. 7. 8. Lloyd, G. A , , and Bell, G. J., Lab. Pract., 1965, 14, ( l l ) , 1292. Winnett, G., and Katz, S. E., J . Ass. 0-f. Agric. Chem., 1965, 48, 370. Saville, B., Analyst, 1958, 83, 670. Neale, E., and Perry, B. J., Ibid., 1959, 84, 226. Stevens, D. C., and Hounam, R. F., Ann. Occup. Hyg., 1961, 3, ( l ) , 58. Ministry of 1-abour, H.M. Factory Inspectorate, “Methods for the Detection of Toxic Substances Durham, W. F., and Wolfe, H. R., Bull. Wld Hltlz Org., 1962, 26, 75. in Air,” 1943, Booklet No. 1, H.M. Stationery Office, London. Received March l l t h , 1966

ISSN:0003-2654    

DOI:10.1039/AN9669100806

出版商:RSC    

年代:1966

数据来源: RSC

摘要:

808 SHORT PAPERS [Anahst, VOl. 91 Mobile Laboratory Methods for the Determination of Pesticides in Air Part II.* Thionazin BY G. A. LLOYD AND G. J. BELL (Plant Pathology Laboratory, Hatching Green, Harpenden, Herts.) THIONAZIN,~ diethyl 0-2-pyrazinyl phosphorothionate, is a highly toxic pesticide and, following its recent introduction into the United Kingdom,2 a study of the risks in its use to agricultural workers was required. In part, this involved its determination in the form of vapour or dust in air, a t concentrations of about 0.1 mg per m3. Thionazin can be determined spectrofluorimetrically3 but this is impracticable in the field. A colorimetric procedure is described which, in general, meets with the requirements of a field m e t h ~ d . ~ It involves hydrolysis of thionazin to hydroxypyrazine, which is then reacted with bromine to form a glutaconic aldehyde.Condensation of the latter with p-phenylenediamine hydrochloride yields a reddish brown polymethine dye that is soluble in a ~ e t o n e . ~ METHOD APPARATUS- Spined glass bubblers. GZass-fibre filters-Whatman, GF/A, 5.5 cm in diameter, and filter holders for air sampling. Stoppered tubes-Glass, 25-ml graduated, capacity, 40 ml to stoppers. Water-bath at 40" C. REAGENTS- isopropanol. Trapping solution-Dilute 1 volume of 0.2 N aqueous sodium hydroxide to 2 volumes with Acetic acid, glacial. Bromine water, saturated-Store over bromine. Phenol - bromide solution-Dissolve 2 g of phenol and 5 g of potassium bromide in 100 ml p-Yhenylenediamine hydrochloride-Dissolve 0.5 g in 100 ml of 2 per cent.v/v hydrochloric acid. Standard thionazin-Prepare a solution that contains 10 pg of thionazin per ml in isopropanol. A lternative standard-Prepare hydroxypyrazine from glycinamide and glyoxal,6 and dissolve * For details of Part I of this series, see reference list, p. 809. of water. it in isopropanol (4pg per ml = 10.5pg of thionazin per ml).December, 19661 SHORT PAPERS 809 AIR SAMPLING- Set up the sampling devices in the breathing zones of operators as described for the deter- mination of phosphorothiolonothionates in air.4 (i) Vupours-Charge each bubbler with 20 ml of the trapping reagent. Add more isopropanol according to the intended period of sampling4 and draw air through the solution a t about 10 litres per minute. At the end of the sampling period (10 to 30 minutes), transfer the contents of each bubbler to a graduated tube, adjust the volume to 20 ml with isopropanol, stopper and allow the solution to stand for 17 to 21 hours in a water-bath a t 40” C.Adjust the level of water in the bath so that it does not greatly exceed that of the solution in the tube, thus allowing the upper part of the tube to remain relatively cool. (ii) Droplets OY dusts-Draw air at 10 litres per minute through a glass-fibre filter. Transfer the exposed filter to a graduated tube containing 25 ml of the trapping reagent. Stopper and shake the tube well to break up the filter. Allow it to stand for 17 to 21 hours in a water-bath a t 40” C so that the upper part of the tube remains relatively cool. PROCEDURE- Cool the hydrolysed extract to about 15” C.Add isopropanol to replace any lost by evaporation and spin the extract in a centrifuge or filter it from the glass-fibre filter by passing it through a similar filter. Add 1.0 ml of acetic acid to 20 ml of the hydrolysed extract, mix well, and then add 1.0 ml of bromine water, stopper, mix and allow to stand for 1 minute. Add 0.5 ml of phenol - bromide solution, stopper, mix well, and allow to stand for 1 minute, ensuring that no free bromine remains around the stopper. Finally, add 1.0 ml of the p-phenylenediamine hydrochloride solution and 10 ml of acetone. Mix and allow the stoppered tube to stand in a water-bath a t 40” C for 30 minutes. Measure the absorbance of the solution a t 465 mp, with a light path of not less than 4 cm.Deduct the reagent or air blank reading and refer to a calibration graph prepared similarly from 10 to 200-pg amounts of thionazin and which has preferably been standardised against hydroxy- pyrazine by this method. Make the appropriate corrections when aliquots have been taken from the original extract and multiply the amount of thionazin found in a bubbler and on a glass-fibre filter by the factors 4/3 and 5/4, respectively, to allow for the collection efficiency of the bubbler (75 per cent.) and a minimum recovery of 80 per cent. from the glass-fibre filters. The accuracy of the over-all procedure is about 10 per cent., the measurement and control of air volumes being the major limiting factor. However, the accuracy of the colorimetric procedure is such that liquid formulations and their dilutions, as used in the field, can be analysed normally to within the limits of &lo per cent. by diluting suitable aliquots with the trapping solution. Formaldehyde, alkyl or aryl organomercury fungicides may be used with thionazin for horti- cultural purposes, but 1 00-pg amounts of these pesticides cause negligible interference when this method of analysis is used. REFERENCES 1. “Recommended Common Names for I’esticides,” British Standard 1831 : 1966. 2. Pest Technol., 1965, 7, (4), 26. 3. Kugemagi, U., and Terriere, L. C . , J . Agric. Fd Chem., 1963, 11, (4), 293. 4. Lloyd, G. A., and Bell, G. J., Analyst, 1966, 91, 806. 5. Feigl, F., “Spot Tests in Organic Analysis,” Elsevier Publishing Company, London and New York, 6. Jones, R. G., J . Amer. Chem. Soc., 1949, 71, 78. NOTE-Reference 4 is to Part I of this series. 1956, Fifth Edition, p. 280. Received March lltlz, 1966

ISSN:0003-2654    

DOI:10.1039/AN9669100808

出版商:RSC    

年代:1966

数据来源: RSC

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December, 19661 SHORT PAPERS 809 Determination of Thiourea in Sewage and Industrial Effluents BY DENIS DICKINSON (City Laboratories Service, Shortley Road, Coventvy) THE determination of thiourea in industrial sewage and effluents is important because of the strong inhibitory power of thiourea on the biological oxidation of nitrogen. There is some doubt about the concentration of thiourea that would be damaging to a purification plant, but it is desirable to be able to determine the compound in concentrations of about 1 p.p.m., and to detect it at a much lower level.810 SHORT PAPERS [Analyst, Vol. 91 Methods have been described for detecting and determining thiourea in certain fruits.l These methods involve the use of Grote's reagent in some modification, the preparation of which is cxtremely tedious.For detection of thiourea in low concentrations the A.O.A.C. recommends the use of pentacyano-ammonio ferroate. It has now been found that a 0.1 per cent. solution of this compound reacts quantitatively and reproducibly with thiourea in slightly acid solution (pH up to 4.5) to give a clear blue colour that can be used to detect 0.07 mg of thiourea and to determine 0.02 to 0.7 mg in 50 ml of solution (see second paragraph of Standardisation). METHOD REPARATION OF PENTACYANO-AMMONIO FERROATE- Dissolve 2 g of sodium nitroprusside in 8 ml of 0.88 ammonia solution and allow the solution to stand in a refrigerator a t about 0" C for 24 hours. Bring the mixture to room temperature, add about 1 ml of distilled water, mix and filter.To the filtrate add absolute ethanol until no further precipitate (yellow) forms. Filter with suction, wash with ethanol to remove ammonia, and dry the solid in a vacuum desiccator. Reduce to powder and store over calcium chloride in a desiccator in the dark. I t is necessary to expose this solution to daylight for it to become sensitive; it is sufficient to prepare the solution in the morning when it becomes satisfactory for use after about 4 hours. I t remains usable for a t least 2 days thereafter, if stored in the dark. The mass may thcn appear solid. For use, prepare a 0.1 per cent. solution in water. STANDARDISATION- Prepare standards containing up to 0.75 mg of thiourea in 50 ml. Add 0.1 ml of dilute acetic acid (10 per cent. v/v) and 3 ml of the pentacyano-ammonio ferroate reagent.Mix the solutions. Allow 30 minutes for the blue colour to develop. Measure the absorption a t 610 mp with a l-cm or a 4-cm cell depending upon the sensitivity desired. The range may be extended upwards by using more reagent. The colour develops rapidly after about 10 minutes and is stable between 20 and 40 minutes after mixing. The plot of absorptiometer reading against thiourea concentration is a straight line, provided the amount of thiourea present does not exceed 0.7 mg. If the concentration expected is below 2 p.p.m. (0.1 mg) it is advisable to use 4-cm cells. TABLE I DETERMINATION OF THIOUREA IN MIXED SOLUTIONS Thiourea found, mg Composition of mixture, mg pcr 50 ml Ammonium Sodium thiocyanate thiosulphate Thiourea I A > 1.0 0 0.27 0.5 0 0.54 1.0 0 0.54 0.5 1.5 0.27 1.0 3.0 0.27 0.5 1.5 0-54 1.0 3.0 0-54 0 3.0 0.27 1.0 3.0 0 0 0 0.22 Total 0.315 0.515 0.585 0.35 0.36 0.655 0.60 0.34 0.07 0.22 Correction for ammonium thioc yanate 0-07 0.05 0.07 0.05 0.07 0.05 0-07 0 0.07 0 1 Net 0.245 0.49 0.515 0.30 0.29 0.605 0.53 0.34 0 0.22 Recovery, per cent.91 91 95 111 107 112 98 126 100 - The above determinations were made with an E.E.L. Spectra instrument fitted with a l-cm cell. Fearon2 investigated the reactions of pentacyano-ammonio ferroate with many compounds and laid the foundation for the present method. He concluded that the only substances capable of producing stable blue colours in acid solution are the thioureas and relatcd sulphur compounds. These include ammonium thiocyanate and the thiosulphate ion.Under the conditions now des- cribed it requires about ten times the amount of ammonium thiocyanate to give a blue colour comparable with that given by thiourea. Provided that ammonium thiocyanate is not present in very much greater concentration it is therefore practical to determine both compounds in a mixture. The thiocyanate is determincd by the pyridine - pyrazolone method3 and the equivalent absorption deducted from the total to obtain a net value due to thiourea. The reaction withDecember, 19661 SHORT PAPERS 81 1 thiosulphate is much less sensitive and is probably different in its mechanism; 1.5 mg gave the same absorption as 0.02 mg of thiourea. Consequently, thiosulphate must be present in amounts that can be determined by titration before it is likely to interfere, and a correction can then be made. Recovery tests with mixtures of thiourea, ammonium thiocyanate and sodium thiosulphate were carried out. The results in Table I were obtained. REFERENCES 1. Horwitz, W., Editor, “Official Methods of Analysis of the Association of Official Agricultural Chemists,” Ninth Edition, Association of Official Agricultural Chemists, Washington, D.C., 1960, p. 401. 2. 3. Fearon, W. R., Analyst, 1946, 71, 562. Epstein, J., Analyt. Chew., 1947, 19, 272. Received June 21st, 196G

ISSN:0003-2654    

DOI:10.1039/AN9669100809

出版商:RSC    

年代:1966

数据来源: RSC

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December, 19661 SHORT PAPERS 81 1 Absorptiometric Determination of Fenitrothion Residues in Cocoa Beans BY S. H. YUEN (Imperial Chemical Industries Ltd., 14gricultural Division, Jealott's Hill Research Station, Bracknell, Berkshire) FENITROTHION, dimethyl 3-methyl-4-nitrophenyl phosphorothionate, the active ingrcdient of the commercial formulation, Sumithion, has a low mammalian toxicity, viz., acute oral LD,, to rats, 673 mg per kg, and is effective against a wide range of insects.l It has shown promise for the control of cocoa capsids, Didantiella theobvorna, and there was a need for a method for determining residues of the insecticide in treated cocoa beans at harvest. Dawson, Donegan and Thain2 des- cribed a gas - liquid chromatographic method for determining residues of fenitrothion and related compounds in cocoa beans, after extracting them into benzene and purifying by solvent partitioning.Kovac and Sohler3 extracted fenitrothion residues from fruits and vegetables with light petroleum and separated them by thin-layer chromatography, with subsequent ultraviolet absorptiometry of the hydrolysed product, 3-methyl-4-nitrophenolate. Similar methods were used for determining traces of fenitrothion in milk,* bananas6 and cocoa beans6 The colorimetric method, developed by Averell and Norris' for determining residues of para- thion (diethyl 4-nitrophenyl phosphorothionate) , may be adapted for determining fenitrothion. The method depends on reduction of the insecticide to the corresponding aromatic amine and the formation of a coloured compound by diazotisation and coupling with N- 1 -naphthylethylene- diamine. When applied to cocoa beans, it suffers from interference by plant pigments and fat, which comprise about 50 per cent.of the bean.8 To overcome these difficulties, the clean-up procedure and the effect of several variables on the development of the colour were investigated. In the method described below, the insecticide is extracted into chloroform. The extract is decolorised with activated charcoal, and the f a t removed from the hot reduced solution by adding paraffin which collects the oily substance and the zinc powder as a solid mass on cooling. The final colour is developed in a hydrochloric acid - isopropanol solution, and reaches the approxi- mate maximum intensity 1 hour after adding the coupling reagent.METHOD APPARATUS- able from Townson and Mercer, was used. Macerator-A top-drive macerator with adaptors for fitting a 200-ml macerator flask, obtain- Spectrophotometer-A Unicam SP600. REAGENTS- Hyflo Super-cel-Obtainable from Johns-Manville Co. Ltd. Activated charcoal-For decolorising purposes. Obtainable from British Drug Houses Ltd. Hydrochloric acid, 0.5 N - isopropanol, 60 per cent. solution-Dilute 45 ml of concentrated hydrochloric acid (sp.gr. 1.18) and 600 ml of isopropanol to 1 litre with water.812 SHORT PAPERS [Analyst, VOl. 91 Zinc powder. Parafin wax, congealing fioint about 60’ C. Sodium nitrite solution, 0.25 per cent. w/v-Prepare a fresh solution daily. Ammonium sulphamate solution, 2.5 per cent. w/v-Prepare a fresh solution weekly.N- 1-Nuphthylethylenediamine solution, 1 per cent. w/v-Dissolve 0.5 g of N- 1-naphthylethylene- diamine dihydrochloride in 50 ml of hydrochloric acid - isopropanol solution; prepare a fresh solution every 3 days. STANDARD SOLUTIONS OF FENITROTHION- (i) Stock solution-Dissolve 0-050 g of pure fenitrothion in chloroform, and dilute to 250 ml with chloroform. 1 ml of fenitrothion E 200 pg of fenitrothion. (ii) Working solution-Dilute 10.0 ml of stock solution to 200 ml with chloroform, 1 ml of solution = 10 pg of fenitrothion. PROCEDURE- Pvepavalion of calibration graph-Transfer 0, 2.0, 4.0, 6.0, 8.0 and 10.0 ml of working standard solution, equivalent to 0, 20, 40, 60, 80 and 1OOpg of fenitrothion, respectively, to six 250-ml round-bottomed flasks with €324 1-inch necks.Half immerse the flasks in turn in a water-bath a t about 60” C, and evaporate off the chloroform under reduced pressure. Add to each flask 25 nil of hydrochloric acid - isopropanol solution and 1 g of zinc powder, and boil under reflux for 15 minutes on a heating mantle. Add 2 g of paraffin wax, and boil for a further Q minutc. Filter the cooled contents through a cotton-wool pledget in a 2-inch diameter funnel into a 50-ml Cali- brated flask. Wash the reaction flask and filter twice with 10-ml portions of hydrochloric acid - isopropanol solution, and collect the washings in the calibrated flask. Add to the calibrated flask 1 ml of sodium nitrite solution, mix, and set aside for 10 minutes. Add 1 ml of ammonium sulphamate solution, mix, and set aside for 10 minutes. Add 1 ml of N- 1-naphthylethylenediamine solution, make up to the mark with hydrochloric acid - isopropanol solution, mix, and set aside for 1 hour.Filter the solution through a fluted Whatman No. 5 filter-paper, discard the first few millilitres of filtrate, and measure the optical density of a further 10 ml a t 550 mp in a 2-cm optical cell, with water in the reference cell. Draw the calibration graph relating optical densities of the standards to concentrations of fenitrothion in micrograms. The graph was linear, and optical densities of 0.04 and 0.22 were obtained by the reagent blank and 20 pg of fenitrothion, respectively. Detevnzination-Take 250 g of cocoa beans at random from the sample provided, and grind to coarse particles.Weigh 50 g of the ground sample into a macerator flask, add 100 ml of chloroform, and macerate for 3 minutes. Prepare a Hyflo Super-cel filter as follows : moisten a Whatman No. 5 filter-paper with water in a 7-cm Buchner funnel supported on a 500-ml filter flask, and suck it dry. By using a 1-inch rubber bung, gently press 5 g of Hyflo Super-cel to form a pad on the Buchner funnel, wash it with a small amount of chloroform under suction, and discard the filtrate. Filter the macerated material through the prepared filter. Wash the macerator flask with 100ml of chloroform, and pass the washings through the same filter into the filter flask. Transfer the filtrate to a 200-ml calibrated flask, dilute to the mark with chloroform, and mix. Transfer 100 ml of the filtrate (equivalent to 25 g of sample) to a 250-ml conical flask, add 1 g of activated charcoal, and mix.Filter the contents through a Whatman No. 40 filter-paper into a 250-1111 round-bottomed flask with a B24 1-inch neck. Wash the conical flask with a small amount of chloroform, and pass this through the same filter into the round-bottomed flask. Complete the reduction of fenitrothion, and the development and measurement of the colour as directed in the “Preparation of calibration graph,” commencing from “Add to each flask 25 ml of hydrochloric acid - isopropanol solution . . .”; read off from the calibration graph the fenitrothion content of the sample solution in micrograms. Conduct a similar determination with 50g of untreated cocoa beans, as described above.Evaporate off the chloroform under reduced pressure a t 60’ C . Y 100 25 Recovery, per cent. where Y = the weight of fenitrothion found (corrected for the blank), pg. Fenitrothion content, p.p.m. = - x -December, 19661 SHORT PAPERS 813 RESULTS AND DISCUSSION Recoveries by the proposed method were determined by analysing untreated cocoa beans, to which 0.4 to 3 p.p.m. of fenitrothion had been added. Results are shown in Table I. TABLE I RECOVERY EXPERIMENTS ON UNTREATED COCOA BEANS 0.8 Fenitrothion added, Fenitrothion found, p.p.m. p.p.m. 0-4 0.30 0.53 0.60 0.52 0.52 0.65 0.53 0.47 0-56 0.89 1.18 0.94 1.16 1.06 t 0.94 1.45 f c ;1 I I I I c I 1.6 1.42 2.0 { 1.28 1.34 2.73 2.38 r I 1-98 3.0 Recovery, per cent. 76 66 75 65 65 81 66 59 70 56 74 5!) 72 66 59 72 71 64 G7 91 79 66 The percentage recoveries ranged from 56 to 91 with a mean of 69 (standard deviation, &ts.O).The average apparent fenitrothion content obtained on 12 samples was 0-22 p.p.m., with a standard deviation of k0.12 p.p.m., on which basis the limit of detection for the method is consideredlo to be 0.2 p.p.m. During 1962, field trials were conducted in Tafo and Bunso, Ghana, by Plant Protection Limited with the co-operation of the National Research Council of Ghana, for the control of cocoa capsids. In these trials each acre was treated with 5 gallons of 0.5 per cent. fenitrothion in water. Thirteen samples of cocoa beans that were harvested 1 to 30 days after applying the treatment were analysed for fenitrothion residues. No residue was detected in any of the samples treated.With minor modifications, the method has been satisfactorily applied to tomatoes grown on soils drenched with fenitrothion for controlling nematodes. The low dry matter content of tomatoes permits a 100-g sample to be taken for each determination, and its insignificant content of fatty materials renders the paraffin-wax treatment unnecessary. However, more colour from plant pigments appears in the chloroform extract, and rather more activated charcoal, i.e., 4 g, is required to decolorise the extract. The modified method is simpler, has the limit of detection of 0.1 p.p.m., and is considered to be generally applicable to various fruit and vegetable crops. REFERENCES 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. “Sumithion Technical Manual,” Sumitomo Chemical Co. Ltcl., Osaka, Japan, 1963. Dawson, J. A, Donegan, L., and Thain, E. M., Analyst, 1064, 89, 495. Kovac, J., and Sohler, E., 2. analyt. Chem., 1966, 208, 201. Franz, J., and ICovac, J., Ibid., 1965, 210, 354. Miyamoto, J., Kawaguchi, Y., and Sato, Y., Botyu-Kucgaku, 1965, 30, 9. Miyamoto, J., Sato, Y., and Fujikawa, K., Ibid., 1965, 30, 49. Averell, P. R., and Norris, M. V., Analyt. Chem., 1948, 20, 753. Thorpe, J. F., and Whiteley, M. A., “Thorpe’s Dictionary of Applied Chemistry,” Fourth Edition, Volume 111, Longmans, Green and Co., Idondon, 1946, p. 233. Wilson, C, W., Baier, R., Genung, D., and Mullowney, J., Analyt. Chem., 1951, 23, 1487. Wilson, A. I,., Analyst, 1961, 86, 72. Received November 15th, 1965

ISSN:0003-2654    

DOI:10.1039/AN9669100811

出版商:RSC    

年代:1966

数据来源: RSC

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814 SHORT PAPERS [Analyst, VOl. 91 Spectrophotometric Determination of Complexed Dibenzoylmethane BY S. INCITTI AND A. LA GINESTRA (Comitato Nazionale per L'Enevgia h'ucleare, Laboratory F. Giordaizi, Department of Chemistry, Urziversity of Rome, Italy) IT is useful when studying metal P-diketonates to have a rapid method for determining the /3-diketone bound to the central ion. Ronner and Thornel have described an absorptiometric method for determining acetylacetone that is based on the formation of a complex with the iron(1 IT) ion. To aid our investigation of some dibenzoylmethides, we have developed a similar method for determining dibenzoylmethane. EXPERIMENTAL INFLUENCE O F VA4RIOUS FACTORS ON THE ABSORPTION SPECTRUM OF THE IRON(II1) - DIBENZOYL- METH.INE COMPLEX-- If a solution of ammonium iron(II1) sulphate in 0.1 N sulphuric acid is added to an equal volume of a solution of dibenzoylmethane in ethanol, a red - violet coloured complex is obtained, whose absorption spectrum in the range 400 to 700 mp is shown in Fig.1. The absorption maximum lies a t 518 mp, and the extinction coefficient a t this wavelength is 1085 litres per mole per cm. A 1 + 1 water - ethanol mixture proved to be a good solvent for dibenzoylmethane, its iron(lI1) complexes and also for iron(II1) alum. This solvent has, therefore, been used for our tests in preference to other possible solvents. The concentration of the sulphuric acid influences the wavelength and optical density a t the absorption maximum of the iron(II1) complex, as shown in Fig. 2.I t is necessary, therefore, to fix a value for the sulphuric acid concentration. We found that 0.1 x sulphuric acid is excellent Wavelength, mp I 500 600 Wavelength, rnp Fig. 1. Absorption spectrum of the Fig. 2. Influence of the sulphuric iron(m) - dibcnzoylmethane complex in acid concentration on the iron(Ir1) - di- ethanol - 0.1 N sulphuric acid mixture benzoylmethane complex absorption for this purpose, that is, for hydrolysing most of the metal dibenzoylmethides. The colour intensity obtained changes with time, but not markedly; the greatest intensity is observed 40 minutes after adding the iron(II1) alum. The absorption was measured with a Beckman DK2 spectrophotometer, with 1-cm quartz cells. As acetone reduces the molar extinction coefficient of iron(II1) dibenzoylmethide, it is necessary to use the same amount of acetone in the calibration solutions.There is no interference from the metal ions obtained from the dibenzoylmethides hydrolysed, a t least when present in amounts up to that of the dibenzoylmethane determined. The method has been applied to the dibenzoylmethides of iron(III), chromium(III), cobalt(III), copper(II), nickcl(I1) , titanium(lV), zirconiurn(IV), cobalt(II), tin(1V) and uranium(V1). Good results were obtained for all of the complexes, except for the chromium(II1) and cobalt(II1) derivatives. These complexes are not hydrolysed by the 0.2 N sulphuric acid added to their ethanol - acetone solutions. It is necessary to use acetone to dissolve some dibenzoylmethides.December, 19661 SHORT PAPERS 815 Probably the high stability of the p-diketonates of d, and d, ions, as found by Collman2 for chromium, cobalt and rhodium acetylacetonates, may be the reason for the inapplicability of this method to these complexes.Perhaps they could be more easily hydrolysed after previous reduction of the ions. The following procedure is suggested. PROCEDURE- Dissolve the dibenzoylmethide in acetone, or preferably in ethanol, and place a volume ( A ) of the solution, which should contain a t most 7 mg of dibenzoylmethane, in a 25-ml calibrated flask and add (12.5 - A ) ml of ethanol and 5 ml of 0-1 N sulphuric acid. After shaking the mixture, add 5 ml of iron(II1) alum (8.2 per cent. w/v in 0.1 N sulphuric acid) and then make up the volume with 0.1 N sulphuric acid.Read the absorption a t 518 mp, 40 minutes after adding the iron(II1) alum, against a blank containing the same volumes of solvents as were used for the sample solution. Time, minutes Fig. 3. Absorption variation at different times for a solution containing 3 mg of dibenzoylmethane per 26 in1 Inorganic anions that could precipitate or give complex ions with iron(III), such as phosphate, molybdate, fluoride and citrate, must be eliminated because of their interference in the deter- mination. The presence of chlorides and sulphates in concentrations higher than that of the iron(II1) added could interfere. It is, therefore, evident that the calibration graph must be made with solutions containing the same amounts of these salts, in the same way as separate calibration is required for different amounts of acetone.TABLE I DETERMINATION OF DIBENZOYLMETHANE I N DIBENZOYLMETHIDES Theoretical percentage Dibenzoylmethane of dibenzoylmethane found, per cent. Ti (dibenzoylmethane) &I, Zr(dibenzoylmethane),Cl Sn (dibenzoylmethane) ,C1, Ni(dibenzoy1methane) Cu (dibenzoylmethane) , Fe(dibenzoy1methane) , Co(dibenzoy1methane) UO,(dibenzoylmethane) . . . . .. . . .. . . .. .. . . .. .. .. . . .. .. . . 79.0 84.1 70.1 88.3 87.5 92.3 88.4 62.5 79.6 84-0 69.5 88.5 88.1 92.5 88.3 62.1 Dibenzoylmethane. mg Fig. 4. Calibration graph for the iron(m) - dibenzoylmethane complex816 SHORT PAPERS [Anazyst, V O l . 91 All other 19-diketones must be absent or separated beforehand. With the above procedure, and over a range of concentration (0.1 to 7 mg of dibenzoylmethane per 25 ml) we obtained a straight-line graph (Fig. 4) passing through the origin, according to the relationship- where d is the optical density, 1 is the cell width, and c is the molar concentration of dibenzoyl- methane. The results obtained in the determination of dibenzoylmethane in some dibenzoylmethides are given in Table I. d = 1 0 8 5 1 ~ REFERENCES 1. Bonner, T. G., and Thorne, M., Analyst, 1954, 70, 759. 2. Collman, J. P., Angew. Chem., Tnternat. Edn, 1965, 4, 132. Received November Sth, 1965

ISSN:0003-2654    

DOI:10.1039/AN9669100814

出版商:RSC    

年代:1966

数据来源: RSC

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816 SHORT PAPERS [Anazyst, V O l . 91 Detection of Some 21-Hydroxy and 2,-Methoxy Estrogens and Other Phenolic Compounds by a Modified Folin - Ciocalteu Test BY R. L. RISACHER AND A. M. GAWIENOWSKI (DeFartment of Chemistry, University of Massachusetts, A mherst, Massachusetts) IN the routine determination of estrogen metabolites on paper-chromatographic strips with the Folin - Ciocalteu reagent to locate the compounds,' it was found that some compounds gave the characteristic blue colour before the addition of a base. As King2 had speculated that such an anomalous compound might be 2-hydroxyestriol, i t was decided that an investigation of the specificity of the phenomenon might prove of value. The compounds tested included a variety of substituted phenols and related compounds These compounds were dissolved in a suitable solvent and spotted on Whatman No.1 paper strips. The Folin - Ciocalteu reagent3 diluted (1 + 2) with water was applied by putting about 10 ml in a watch-glass and passing the strip through it. Ammonia solution was applied by the same method, whether or not a reaction was noticed after dipping the paper in the reagent. Care was taken to exclude ammonia fumes from the working area during the application of the reagent. RESULTS- The results of the Folin - Ciocalteu test on phenolic compounds are given in Table I. TABLE I RESULTS OF FOLIN - CIOCALTEU TEST ON PHENOLIC COMPOUNDS Compound Catechol . . . . Coumarin . . . . Diethylstilbestrol . . 2,%Dimethoxyestrone L-Epinephrine bitartrate Estradiol . . . . Estradiol diacetate .. Estriol . . . . Estronc . . . . Gallic acid . . . . Guaiacol . . . . 2-H ydrox yestradiol 6-Ketoestradiol . . 16-Ketoestradiol . . 2-Mcthoxyestradiol . . 2-Methoxyestrone . . Phenol . . . . Vanillin . . .. Veratraldehyde . . Veratrole . . . . Epinephrine . . . . Piperonal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . .. . . . . .. .. .. .. . . .. . . . . Bcfore application After application of ammonia solution of ammonia solution + + + + + (violet) + - + + + + + + + + 4- +December, 19661 SHORT PAPERS 817 Of all the compounds tested, vanillin was the only o-hydroxy or o-methoxy phenol that failed to give a positive reaction before the addition of ammonia solution, while diethylstilbestrol was the only compound other than o-hydroxy or o-methoxy phenols that did give such a reaction.Each time a reaction occurred before the addition of ammonia solution, its subsequent addition resulted in a more intense blue colour. I t was also noted that o-hydroxy phenols gave a stronger reaction than a-methoxy phenols. 2,3-Dimethoxyestrone and veratrole ( 1,Z-dimethoxybenzene) gave no reactions a t all. With 2-methoxyestrone the sensitivity of the reaction was approximately 2 pg per cm2; for 2-hydroxyestradiol the sensitivity was 1 pg per cm2. A commercial preparation of the reagent gave identical results. These observations should be of use in the preliminary classification of estrogen metabolites. This work was supported by the USPHS Training Grant IT1 GM 1301. REFERENCES 1. Mitchell, F. L., Nature, 1952, 170, 621. 2. 3. King, R. J. B., Biochem. J . , 1961, 79, 355. Folin, O., and Ciocalteu, V., J . Biol. Chem., 1927, 73, 627. Received May loth, 1966

ISSN:0003-2654    

DOI:10.1039/AN9669100816

出版商:RSC    

年代:1966

数据来源: RSC

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December, 19661 SHORT PAPERS 817 A Rapid Infrared Spectrophotometric Method for the Analysis of pp‘-DDT in Formulations of Technical DDT BY D. J , HAMILTON AND T. J. BECKMANN (Agricultural Chemical Laboratory, Defiartment of Primary Industries, Brisbane, Queensland, A ustralia) ROUTINE analysis of dichlorodiphenyltrichloroethane (DDT) formulations demands a rapid and reliable method for determining the insecticidally active constituent. The insecticidal properties of the material depend on the concentrations of the pp’-isomer present. The principal difficulty to overcome is that of determining pp’-DDT in the presence of related compounds, particularly the op’-isomer. Infrared spectrophotometry has been used by many analysts to determine DDT in pesticide formulations. Most w0rkersl9~9~ have used the band centred on 1015 cm-l.This band is also present in the spectrum of op’-DDT and, therefore, its intensity is related to the total amount of DDT present. McDonald and Watson2 overcame the effect of op’-DDT by using a compensating solution in the reference beam of a double-beam spectrophotometer. Downing, Freed, Walker and Patterson4 obtained @’-DL)T concentrations by difference, after determining the impurities at other wavenumbers. A comparison of spectra of op’-DDT and pp’-DDT suggested that the pp‘-isomer peak a t 808 cm-l would be relatively free from interference from the OF’-isomer. Subsequently, our attention was drawn to a paper by Henry, Colas and Prat4 in which this peak (808 cni-l) was used for determining DlIT. These workers, however, applied their method only to the analysis of technical DDT.EXPERIMENTAL APPARATUS- prism, was used. flow-rate of solvent. used. Double-beam infrared spectrophotometer-A Unicam SP100, fitted with a sodium chloride Chromatografihy tubes, 30 cm x 1.6 cm i.d.-The tubes incorporate stopcocks to control the Spectrophotometer cells-1-mm path length potassium bromide or sodium chloride cells were REAGENTS- Florid, 60 to 100 mesh-In the batch used no heat treatment was found to be necessary. Carbon disulphide, analytical-reagent grade. Light petroleum - diethyl ether developing solution-Mix 6 volumes of diethyl ether (peroxide Acetone, laboratory-reagent grade. free) with 94 volumes of light petroleum (b.p. 60” to 7 O O C ) .818 SHORT PAPERS [Analyst, VOl.91 Sodium sulphate, anhydrous crystalline analytical-reagent grade. pp’-DDT, m.p. 108.5” to 109°C-Recrystallise from 7 5 per cent. ethanol, then from light op’-DDT, m.p. 77.5’ to 77.6” C. petroleum. PROCEDURE- By sucking solvent up through the column, air bubbles are easily removed. When the Florisil has settled, place a 1-5-cm layer of anhydrous sodium sulphate on top of the adsorbent. Allow the solvent to flow until it is level with the top of the sodium sulphate. Make an appropriate dilution of the sample of DDT formulation in acetone so that about 0.1 g of @’-DDT is contained in a volume of less than 5 ml of solution. Transfer this volume quantitatively to the top of the column. When the sample solution has just entered the column, add the ether - light petroleum (6 + 94) solution to the tube, and develop the chromatogram with this solvent.Adjust the flow-rate to 2 to 3 drops per second. The next 20 ml should contain all of the DDT. Transfer this fraction to a 50-ml Erlenmeyer flask and evaporate the solution to dryness on a steam-bath under a stream of dry nitrogen. Continue this evaporation for a period of 13 minutes, after visible traces of volatile substances have disappeared. Take up the residue in carbon disulphide, transfer the solution quantitatively to a 10-ml calibrated flask and dilute to volume. Dry the solution with a small amount of anhydrous sodium sulphate. Determine the absorbance of the solution in a 1-mm cell in the wavenumber region from 750cm-l to 830cm-l, with carbon disulphide in the 1-mm reference cell.Draw a horizontal base-line from the trough a t 798 em-l and, from this line, measure the absorbance of the peak at 808 cm-l. Determine the concentration of pp’-DDT in the solution from a standard curve of concentration against absorbance. The standard curve can be prepared by measuring the absorbance of pp’-DDT in carbon di- sulphide in the concentration range of 2 to 20 mg per ml. The resulting relationship between concentration and absorbance is linear, but there is a small positive intercept (absorbance 0.01) on the absorbance axis when the line is extrapolated back to zero concentration. [NOTE-The batch of Florisil should be checked to determine at what volume the DDT leaves the column.] Pack a chromatographic column with Florisil, slurried in hexane, to a height of 9 cm. Begin collecting the eluate from the time of introducing the sample to the column. Discard the first 10 ml of eluate as containing no DDT (see Note).RESULTS AND DISCUSSION PREPARATION OF SAMPLE- DDT dusts containing only insecticide and inert fillers require only extraction with carbon disulphide and filtration before measurement. The presence of surface-active agents and solvents in formulations precludes direct deter- mination on the sample after simple dilution in carbon disulphide, as it has been found that the surface-active agents and the solvents present in most concentrates interfere. The surface-active agents may be removed by a chromatographic step while the solvents may be evaporated. Acetone is used for dilution of the sample before chromatography.This solvent will dissolve both formulations based on organic solvents as well as the aqueous “mayonnaise” types. Further, no non-volatile contaminant in laboratory-reagent grade acetone interferes with the subsequent infrared determination. RETENTION VOLUME ON THE COLUMN- Technical DDT was applied to the column and the non-volatile residue, after evaporation, weighed for each 5 ml of eluate collected. The peak of the DDT eluted from the column occurred in the fourth 6-ml fraction, when the conditions of the chromatography were those described under “Procedure.” By discarding the first 10ml of eluate and collecting the next 20m1, all of the DDT is recovered from the sample. LOSS OF DDT DURING HEATING ON THE STEAM-BATH- On heating 0-0375 g of DDT in a 50-ml Erlenmeyer flask on the steam-bath under a stream of dry nitrogen, the weight of the DDT decreased by 0.15 per cent, per minute.The DDT wasDecember, 19661 SHORT PAPERS 819 weighed at intervals of 5 minutes for a total time of 25 minutes. Thus, under the conditions of the analysis, heating for 1 to 2 minutes has little effect on the recovery of the DDT. PRECISION OF THE METHOD- formulation, the same volume of the formulation being taken each time. Eight determinations, as described in the procedure, were made on a commercial DDT The results provide the following values- Mean absorbance . . .. . . 0.293 Standard deviation . . .. . . 0-00316 Coefficient of variation . . . . 1-1 per cent. It should be noted here that these determinations were made with the one column of adsorbent.It is this that makes determinations rapid, as only one column need be packed for eight to ten determinations. RECOVERIES OF @’-DDT- Various amounts of pp’-DDT were weighed and 4 ml of an acetone solution of a commercial DDT sample were added to each. The absorbances a t 808 cm-l were measured and the corresponding p$’-DDT concentrations were read from the standard curve. As the solutions had been diluted to 101111 with carbon disulphide, the amount of @’-DDT present in the solutions was found by multiplying the con- centration by ten. The resulting fortified solutions were analysed. The last column then shows the percentage recovery. These results are shown in Table I. Solution 1 2 3 4 5 6 7 8 PP’-DDT added, g 0 0 0.0188 0.0295 0.0465 0.0612 0.0568 0.0889 TABLE I RECOVERY OF pp’-DDT pp‘-DDT found, Pp’-DDT recovered Absorbance from standard (Pp’-DDT a t curve, found, less 808 cm-l g 0.099 €9, g 0.296 0.0990 0 0.298 0.0990 0 0-357 0.1190 0.0200 0.386 0.1290 0.0300 0.432 0.1455 0.0465 0.446 0.1606 0.05 16 0.453 0.1530 0.0540 0.551 0.1870 0.0880 EFFECT OF Op’-DDT O N THE PEAK AT 808CM-’- Recovery, per cent.- - 106 102 100 100 95 99 A similar experiment to the recovery of pp’-DDT was carried out with various weights A constant volumc of an acetone solution of a technical DDT formulation containing 0- of-DDT instead of pp’-DDT. of g of @’-DDT was added to the column for each run. To this volume amounts of op’-DDT, from 0 to 0.07 g, were added. Calculation of a coefficient of variation for thc five figures obtained gives a value of 1.1 per cent. This figure, on comparison with the precision of the analysis, indicates that op’-DDT has little effect on the peak a t 808cm-l. We thank Mr. W. J. Roulston, CSIRO, Veterinary Parasitology Laboratory, Brisbane, for helpful criticism, and the Director-General, Department of Primary Industries, Queensland, for permission to publish this paper. REFERENCES 1. 2. 3. 4. Downing, J. R., Freed, W. V., Walker, I. F., and Patterson, G. D., Ind. Engng Chem. Analyt. Edn, Mcdonald, I. R. C., and Watson, C . C., Analyt. Chem., 1957, 29, 339. Austin, H. C., Bonner. F. L., and Epps, E., J . Ass. 0-ff. Agric. Chem., 1957, 40, 286. Henry, L., Colas, A., and Prat, J., Chim. Ind., 1964, 71, 919. 1946, 18, 461. Received April 26th, 1965

ISSN:0003-2654    

DOI:10.1039/AN9669100817

出版商:RSC    

年代:1966

数据来源: RSC