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MAY, 1968 THE ANALYST Vol. 93, No. I106 A General Graphical Method for Evaluating Experimental Results that Should Fit a Linear Equation BY H. M. N. H. IRVING (Department of Inorganic and Structural Chemistry, Th.e University, Leeds 2) When the results of an experiment should be representable by a linear equation of the general form y = fllx + c the errors inevitably associated with the values of xj and yj ( j = 1 to n >2) give rise to a set of n simultaneous equations that will be inconsistent. As an alternative to a least-squares computation, a graphical procedure is described for finding the best values of the constants m and c. The method is quite general and it is illustrated by worked examples of problems encountered in analytical chemistry, e.g., the potentiometric titration of a dibasic acid, the spectrophotometric deter- mination of the stability of a weak complex, the evaluation of redox potentials and the liquid -liquid extraction of a weak monobasic acid.WITH the increasing availability and use of computers, graphical methods of handling data are tending to drop out of favour. There are experiments, however, in which graphical procedures have advantages, even if only as a preliminary to more rigorous computational methods; sometimes the precision of the experimental data is such that conclusions from graphical methods are adequate. Many chemical problems yield experimental data in terms of sets of two variable quantities xj and yj that can be related by a linear equation which can be presented graphically as a straight line passing through the points (XI, yj).The problem is to determine the values of the constants m and c. Provided only two sets of observa- tions have been made ( j = 0 and 1) there will be a unique solution to the resulting pair of simultaneous equations, irrespective of the experimental errors made in the measurements. When, as in practice, there may be more than two sets of observations, each of which will be subject to experimental error, the corresponding linear equations will probably not be consistent, and the problem is now to find the “best” values for the constants m and c. This can be done graphically by drawing the “best straight line” through the sets of points (xj, yj) or by computing the slope and intercept of this line by the “least squares method.” It should be pointed out that in this procedure it is common to assume that all the random errors are associated with one of the observations (e.g., with measurements of xj), while measurements of the other variable, yj, are free from error.The object of the present paper is to present an alternative graphical procedure for the solution of sets of (possibly inconsistent) linear equations. No novelty is claimed for this procedure, which appears to have been suggested by Professor Finsler and has been used extensively by Schwarzenbach, Willi and Bach.l However, the method is not widely known and experience has shown that many research workers have not found the description in the German text easy to follow. I have therefore taken the opportunity of generalising the procedure and showing, by worked examples, how it can be applied in several different situations.BASIC PRINCIPLES Instead of plotting the data (xj, yl) as a series of points through which the “best straight line” is to be drawn, the basic principle is to use a co-ordinate system such that each associated pair of observations (xj andyj) is used to define a straight line; the various straight lines for all the observations are then to intersect in a common point whose co-ordinates are a measure of the desired constants m and c. yj = mxj + c .. .. .. .. * ’ (I), 0 SAC and the author. 273274 IRVING: A GENERAL GRAPHICAL METHOD FOR EVALUATING [AvtalySt, VOl. 93 Fig. 1. Plots of lines conforming to the general equation (i)K + ($)w = 1 Suppose a straight line is drawn to pass through the points (A,O) and (0,B) situated along the x-axis and y-axis, respectively, of a rectilinear co-ordinate system (Fig.1 ) . If this line also passes through the point (K,K') it is easy to show that its equation must be . . (2). ( ; ) K + ( ; ) K ' = . .. .. .. The graphical procedure now involves several stages- (i) The exact linear equation representing the process under investigation is written down in its appropriate symbols. (ii) The form of this equation is adjusted to conform exactly with equation (2), i.e., with the desired constants on the left-hand side, and only unity on the right. (iii) By direct comparison with equation (2), A is expressed in terms of the experi- mentally determinable quantities and the same procedure is carried out for B.The relationship of K and K' to the two desired constants is also written down. (iv) The points (A,O) and (0,B) are plotted with suitable scales and joined to give a straight line. (v) Similar straight lines are drawn for values of A and B calculated from all the other experimental results. (vi) The values of K and K' are determined from the point of intersection and those of the desired constants are deduced from them. A few examples will make the procedure clear. EXAMPLE 1- determining the values of the two acid-dissociation constants A dibasic acid, H2A, has been titrated potentiometrically with alkali, with the object of and [H+l [A2-] K2 = [HA-] 'May, 19681 EXPERIMENTAL RESULTS THAT SHOULD FIT A LINEAR EQUATION 275 If the total amount of acid is known, CA = [&,A] + [HA-] + [A2-] and, if observations are made of the pH after adding various amounts of alkali, we have, from considerations of electro-neutrality, where a is the degree of neutralisation.The last term on the right-hand side, therefore, refers to the concentration of univalent cation (e.g., K+) introduced during the titration. By elimination we arrive at the general equation [OH-] + [HA-] + 2[A'-] = [H+] + aCA Comparison with the standard equation (2) shows that 1 K2 = K , K , =I K' ' and that Table I (rows 1 to 3) gives experimental data for the potentiometric titration of 1 O O m l of about 103 M anthranilic acid-NN'-diacetic acid, o-HOOC.C,H,.N(CH~COOH)~, with car- bonate-free 0.1 M potassium hydr0xide.l TABLE I THE POTENTIOMETRIC TITRATION OF ANTHRANILIC ACID-NN'-DIACETIC ACID 10'C~ .. .. 1.031 1.029 1.026 1.023 1.021 1.018 1.016 1.013 a .. .. .. 0 0.26 0.60 0.76 1.00 1.26 1.60 1.76 p H . . .. . . 2.886 2.966 3.032 3.123 3.228 3.369 3.561 3.886 lOyH+] . . 1.301 1.110 0.929 0.763 0.692 0.428 0-276 0.130 lWA (calcuiited) . . 4.616 6.436 6.207 7.122 8.169 8.707 9.241 9.386 lO-aB (calculated) - 1.596 - 2.229 - 3.097 -4.344 - 6.200 - 9.379 - 15-83 - 36.97 12 AxlC 0 Fig. 2. Data, from Table I relating to the titration of anthranilic acid-NN'-diacetic wid. Calculation of Kl and K,276 IRVING: A GENERAL GRAPHICAL METHOD FOR EVALUATING [Afla&St, VOl. 93 The various straight lines are plotted in Fig. 2. Apart from that for a = 1.75, the convergence to a single point is quite satisfactory and leads to the values K = 10.4 x 10-4 and K’ = 2.0 x lo2, from which we deduce K , = 5.00 x and K , = 1-04 x 10-3. The more tedious treatment of these experimental data by least-squares computation leads to However, as Schwarzenbach, Willi and Bach point out,l values of these constants obtained from a completely independent titration may show an absolute error, which exceeds that calculated from the same titration curve.For example, in a second titration of anthranilic acid-NN’-diacetic acid the values K , = 4.80 x and K , = 1.01 x 10-3 were obtained graphically and the values K, = 4.25 (+O-25) x and K , = 1-05 (+0*02) x 10-3 by computation. Greater accuracy in the determination of K , and K , can only be achieved by paying much greater attention to points of experimental technique (e.g., the more exact measurement of the concentration of the titrant and the constancy of the potential of the reference electrode).In the present instance the graphical method suggests visually that the results for a = 1-75 are inconsistent with the rest, and this reading is automatically omitted when locating the point (K, K’). Calculation shows that a pH reading of 3.876 (ie., only one hundredth of a unit higher) would have given the “correct” result. Of course, in the least- squares calculation the less reliable data for a = 1.75 will have been included with the same weighting as all the others. EXAMPLE 2- to the equation can often be obtained from spectrophotometric measurements of the optical density, E, of mixtures containing Merent initial concentrations, CM and CL, of the components, provided the molecular extinction coefficients, E ~ , cL and eNLL, of the three species are known.Clearly, for a 1-cm cell length and Kl = 5.06 (+0*05) x and K , = 1-04 (+0.01) x 10-3. The stability constant, KML, governing the formation of a weak complex ML according M+L+ML .. .. .. .. (4), E = [MIEM + [L]EL + LML]Em = (cM - [ML1)EM + (CL - EMLI)€L + [MLIEML** (5) (cM - pL1) (c - LML1) = K M L w L l * .. . . (6). When Km is small it is often necessary to add a considerable excess of one component (e.g., L) to give appreciable amounts of ML, and with CL > [ML] we find, on eliminating terns in rMLl, that This readily leads to values of KML (which should be identical within the limits of experimental error) on inserting values of E appropriate to different initial concentrations CM and CL.When using l-cm cells we can replace CMEM by E&, the optical density when CL = 0, and CLeL by EL’, the optical density when CM = 0. We can also write E, = CMEML for the limiting case, in which the whole of the component M has been transformed into MI, by a large excess of L. In practice, the actual value of E, may not be determinable by TABLE I1 SPECTROPHOTOMETRIC STUDIES OF ADDUCT FORMATION 1 03cL 0 39-70 79-41 119.2 159.1 199.0 278.7 398.5 598-3 798.1 E 0.388 0.431 0.460 0-482 0-497 0.513 0.644 0.568 0.600 0.618 A (calculated) - -0.397 - 0.507 -0.611 - 0.726 -0.756 - 0.972 - 1.258 - 1.693 -2.145 B (calculated) 0.388 0.43 1 0-460 0.482 0-497 0.513 0.644 0.568 0-600 0.618May, 19681 EXPERIMENTAL RESULTS THAT SHOULD FIT A LINEAR EQUATION 277 o'2 t Wavelength, nm Fig.3. Absorption spectra (1- cm cells) for mixtures of 2-5 x 1 0 - 3 ~ copper bisacetylacetonate with varying amounts of isoquino- line in benzene. Curves 1 to 6 correspond to 0.0, 0.12, 0.20, 0.40, 0-60 and 0.80 M isoquinoline, respec- tively ly-axis 1 -1.4 -1.2 -1.0 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 x-axis Fig. 4. Data from Table I1 relating to adduct formation between copper bisacetylacetonate and isoquinoline in benzene. Calculation of K m and experiment, for this limiting value is only slowly approached asymptotically if the complex is weak. Indeed, the necessary large excess of the reagent L may so modify the nature of the solvent (specifically its dielectric constant and solvating power) as to yield spurious results.It now becomes necessary to treat both KML and cML as unknowns. Table I1 summarises data for mixtures of copper bisacetylacetonate, Cu(acac),, (=M) and quinoline (=L) in benzene when a weak 1 + 1 adduct, Cu(acac), . (quinoline), is formed.2 The absorption spectra of all the mixtures show an isosbestic point at 580 nm (Fig. 3), but the absorption caused by the 1 + 1 adduct and unchanged copper chelate has still not reached a constant value, even when the ratio of C, to CM is as high as 320: 1. Optical density measurements (1-cm cells) were made with a Unicam SP500 spectro- photometer at 670 mp, at which wavelength eL = 0, E& = 0.388, C, was always 2.5 x M and CL ranged from 0 to 0-8 M. By writing E~ = 0 in equation (7) and re-arranging we obtain and when this is compared with the standard form of the equation [equation (2)] we realise that KML = K , E, = K', and that the new variables A and B are to be calculated from A = ECL a n d B = E .. .... . . (9). @if - E) The calculated values of A and B are given in Table I1 and the corresponding lines are shown plotted in Fig. 4. The intersection leads to the values K = 0.27 f 0.01 and K' + 0-69, whence KML = 3-70 0.15 and E, = 0-690. The far more laborious method for handling such data is that suggested by Graddon and W a t t ~ n . ~ Here a trial value for E, is assumed and values for KML calculated for every experimental value of E. The average value of KML and its standard deviation is then calculated. The procedure is repeated for other assumed values of E,, and the approved value is taken as that for which the spread of values of K is least.The principle is illustrated by the calculations shown in Table 111.278 IRVING: A GENERAL GRAPHICAL METHOD FOR EVALUATING [hZa@!, VOl. 93 TABLE I11 CALCULATIONS OF THE STABILITY CONSTANT OF THE WEAK ADDUCT CU(ACAC)~. (QUINOLINE) E m .. . . . . 0.678 0.688 0.691 0.693 0.694 0-695 0.698 0-708 0.738 KML .. . . 4.200 3,870 3-810 3.760 3.714 3.700 3.630 3.400 3.860 Standard deviation 0-290 0-210 0.200 0.190 0.177 0.190 0.200 0-230 0.380 The close agreement between the graphical and the computed value KML = 3.71 0-18 is fortuitous in this instance. However, the graphical method quickly indicates a reasonable approximate value to use for E,.EXAMPLE 3- organic phase and water When a monobasic acid, HL, with acid-dissociation constant, Ke, partitions between an [HLI organic = [HL] + [L-] - Po [HL1orrranic , the partition coefficient for the undissociated species. where $0 = [HLI On re-arrangement, equation (10) gives ( $ - ) p o - ( & . . ) K a = l .. .. .. .. and comparison with the standard equation (2) shows that $0 = K , Ka = K’ and that we must set A = and B = [H+] as shown in Table IV, which summarises unpublished results for the partition of a weak acid between cyclohexane and buffer solutions adjusted to constant ionic strength (p = 0.1) with potassium chloride. TABLE IV PARTITION OF A WEAK BASE BETWEEN CYCLOHEXANE AND BUFFER (p = 0.1) pH .. .. . . 6.71 6.23 5.10 5-06 4.99 4.70 4.62 4-30 4.02 p ( = A ) ,.. . 0.360 0.745 0.880 0.940 1.01 1.32 1.48 1.60 1-80 1P [H+] (E B) . . 0.195 0.689 0.794 0.891 1.023 1.995 3.020 5.012 9.650 Fig. 5 shows the graphical solution, which leads to $0 = 1.93 & 0.03 and pKa = 5-02 & 0-02. Two points are especially noteworthy in these equations. Although the range of pH values covers only 1.7 units, [H+] varies 50-fold, and this makes it impossible to accommodate all the B-values along the ordinate axis without intolerably “crowding” the values for 0.2 < lOb[H+) < 2.0. Nevertheless, the results for values of B greater than 2 x lo4 can readily be incorporated by writing the equation to the line through the points (A,O) and (O,B), v ~ x . , y = (i) x + B, and calculating the value of x corresponding to the smallest accessible ordinate (in this example y = -2 x plotting this point and joining up to the point (A,O), as shown in Fig.5 for 106[H+] = 3.020, 5-012 and 99550. The same device has been used without explanation in Figs. 2 and 4. The second, and rather obvious, point is that this graphical procedure will break down if the partition coefficient $0 is more than an order of magnitude greater than the measured values of p. This imposes too lengthy an extrapolation to locate the point (K,K‘) with any accuracy. Indeed, it is just this condition which limits the value of the graphical procedure in the general case. The size of the area which, in practice, generally replaces the single unique point of intersection of all the lines through (A,O) and (0,B) gives an immediate indication of the quality of the experimental data and often shows whether the value of one or other of the constants K and K’ is particularly influenced by experimental error.May, 19681 EXPERIMENTAL RESULTS THAT SHOULD FIT A LINEAR EQUATION 279 Fig.5. Data from Table IV relating to the partition of a monobasic acid between cyclo- hexane and buffer solutions. Calculation of po and K, EXAMPLE A The stability of complex<s of EDTA and other complexones with iron(I1) and with iron(II1) ions can be determined from measurements of redox potential^.^ To take a simple example, the redox potential, EM, of the couple Fe(II1) - Fe(II), in the presence or absence of a complexone as desired, can be obtained from measurements of the potential E (relative to a standard hydrogen electrode) of a gold electrode dipping into V ml of a solution of an iron(I1) salt to which varying volumes, v, of a standardised oxidant such as iodine have been added.If Ve is the volume needed to oxidise the Fez+ completely we have V . . (12) .. .. .. RT E = EM + ( p) In (ve - V ) where the unknowns to be determined are the end-point volume, Ve, and the mid-point RT potential, EM. Writing (-) = s = 0*059517 at 25" C, and re-arranging we obtain Comparison with the standard equation (2) shows that Ve = K EM = S.lOg K', and that the variables A and B are to be calculated from A = v, and B = -loEls. Table V shows typical experimental data for the titration of 100 ml of about 8 X lo4 M iron(I1) sulphate containing 2 x 1 0 " ~ EDTA at a pH of 4.625 with a constant salt back- ground, p = 0.1, potassium chl~ride.~ The titrant was about 2.2 x M iodine.TABLE V TITRATION OF IRON(II) SULPHATE WITH IODINE IN THE PRESENCE OF EDTA E , mV .. . . 39.6 46.5 71.6 92.2 115.2 12443 v, ml .. .. 3-66 3-68 3.70 3-72 3.74 v, ml .. .. 1-40 1-70 2-60 3-20 3-52 3.60 lWP .. .. 4-671 6.109 15.02 36-19 88.59 128.7 E, mV .. . . 135.3 139.6 144-5 162-8 159.9 lWP .. . . 193.6 229.0 277.1 382.8 504.7280 IRVING The results are shown graphically in Fig. 6, which only displays the top right-hand portion of the whole large-scale graph. By inspection, V e = 3.8 and 10(EMls) = 7-5 whence EM = 0.0521. In this graph the precise location of the ordinate K’ is subject to considerable error and the uncertainty is about f0.002 volt, which is scarcely acceptable.More confidence could be attached to the result of plotting v-l against 10-EP for, as shown by equation (13), this gives a straight line of intercept vF1 and slope -v;llO(EM/s). Alternatively, a precise value of ve can be obtained by Gunnar Gran’s methoda; this involves plotting V.1017(k--E) against V (k is any arbitrary number such that 1017(k--E) forms a convenient range of positive numbers) and noting the values of v at which the resulting straight line cuts the x-axis. This value of ve can then be used in equation (12) to calculate the value of EM for all relevant values of E and v. Fig. 6. Data from Table V relaOing to the redox potentials of Fe(I1) - Fe(II1) in a buffer solution containing EDTA. Calculation of V , and EM In conclusion, I would again point out that the graphical procedures described above have their proper function. In some graphs difficulties of interpolation will not give results of acceptable precision, even when a large-scale graph is used; here more refined computational methods are essential. In others, the procedure will lead to numerical results entirely adequate for the precision of the calculations in train. There is little justification for using an elaborate programme and expensive computer time if the primary experimental results are insufficiently well defined, and the graphical procedure outlined above often provides a simple means of applying this criterion. REFERENCES 1. Schwarzenbach, G., Willi, A., and Bach, R. O., Heh. Ckim. Acta, 1947,30, 1303. 2. Al-Niaimi, N., D.Phi1. Thesis, Oxford, 1964. 3. Graddon, E. P., and Watton, E. C., J . Inorg. Nucl. Chem., 1961, 21, 4. 4. Schwarzenbach, G., and Heller, J., Heh. Chim. Acta, 1961, 34, 676. 5. Sharpe, K., Ph.D. Thesis, Leeds, 1968. 6. Gran, G., Analyst, 1952, 77, 661. Received October 27th, 1967

ISSN:0003-2654    

DOI:10.1039/AN9689300273

出版商:RSC    

年代:1968

数据来源: RSC

摘要:

Artai’yst, May, 1 9 6 8 , Vol. 93, +p. 281-285 28 1 Preparation of Microwave-excited Electrodeless Discharge Tubes for Titanium, Vanadium and Zirconium for Use as Spectral-line Sources BY R. M. DAGNALL, R. PRIBIL, JUN.* AND T. S. WEST (Chemistry Department, Imperial College, London, S . W.7) The preparation of microwave-excited electrodeless discharge tubes as spectral-line sources for the atomic-absorption and atomic-fluorescence spectroscopy of titanium, vanadium and zirconium is described. A long, cylindrical, resonant cavity has been found particularly useful for elements such as these. IN a previous communication,l a general method for the preparation of electrodeless discharge tubes for selenium and tellurium was described, and their use as spectral-line sources was evaluated for atomic-absorption and atomic-fluorescence spectroscopy.2 Since then, several other elements have been studied in detail, viz., antimonyJ3 bismuth,4 arsenics and tin.* Source tubes for many other elements have also been similarly prepared.However, there are several elements, e.g., titanium, vanadium and zirconium, and their compounds, which do not possess the vapour pressure requirements of about 1 mm of mercury at 200” to 300” C to fit into this general scheme. In such instances a different approach must be made to obtain a stable, intense and long-lived narrow-line spectral source. These elements also require special attention because of the large number of atomic lines in their spectra. A microwave-excitation cavity different from that normally used was also investigated in this study, and it was found to offer some advantages, both for these and some other elements.EXPERIMENTAL PREPARATION OF DISCHARGE TUBES- The tube vessels were prepared in essentially the same manner as that previously described.1 The principal differences, viz., materials used, their amount, tube length and operating conditions are given below for individual elements. SPECTRAL EVALUATION- A Hilger and Watts quartz spectrograph E742 was used for recording and assigning the radiation emitted from each tube. Records were obtained on Kodak B10 plates. A Unicam SPSOOA flame spectrometer, with an E.M.I. 9529B photomultiplier, was used for recording spectra and monitoring the stability at the principal resonance lines. DISCHARGE-TUBE EXCITATION- Excitation was achieved by using an Electro-Medical Supplies Limited “Microtron 200” high frequency generator of output 2450 25 MHz (up to 200 watts) connected to a resonant cavity.Cavity Model No. 214L-Obtained from Electro-Medical Supplies Limited. This cavity was used in all of our former studies and has been adequately described and illustrated elsewhere. This cavity is cylindrical in shape (about 5 cm in diameter and 13 cm long) , has an adjustable re-entrant gap, co-axial with the discharge tube, and a tuning probe offset, and parallel to the discharge tube (cf. Fig. 1). The cavity may be air-cooled and also possesses adequate viewing apertures, either at right angles to, or in line with, the discharge tube. The cavity can be used in any position and is readily interchangeable with the 214L cavity.Initiation was obtained with a “Tesla” vacuum tester. Cavity Model No. 21OL-Obtained from Electro-Medical Supplies Limited. * Present address : Jaroslav Heyrovskf Polarography Institute, C.S. A.V., Prague, Czechoslovakia. 0 SAC and the authors.282 DAGNALL, PRIBIL AND WEST : MICROWAVE-EXCITED ELECTRODELESS [A%W&St, VOl. 93 Type ‘C’ connector U I” Air inlet (Reproducsd by cwrtesy of Ekctro-Medical Supplies Limited, London.) Fig. 1. Gas-discharge cavity No. 210 L It was found that the discharge tubes could be operated in almost any position in this cavity and that the position of the tuning probe made little difference to the intensity of the discharges. Even when it was removed completely the tubes remained alight.This is in marked contrast to the critical nature of the tuning in the 214L cavity. In addition, the discharge tubes are well screened from draughts, which normally alter spectral characteristics. A further factor that adds to the usefulness of the 210L cavity, and which is absent in the 214L cavity, is the almost total “immersion” of the tube (up to about 7 cm in length) in the microwave field of excitation. Hence, a tube prepared from relatively involatile or very volatile materials is able to reach equilibrium conditions because, no matter how much movement of material takes place within the tube, it is always within the microwave field. In addition, the cylindrical cavity acts as an effective thermostat for the tube. The only disadvantage of the 210L cavity is that it is rather less efficient than the 214L cavity, and about 25 per cent.more power is required to initiate most tubes. In general, discharge tubes for most elements would only operate with the 210L cavity if they could be started at powers below about 30 to 40 watts with the 214L cavity. The intensities of the various discharges examined were similar in both cavities under optimum operating conditions. The best operating conditions for each element are given below. TITANIUM- Titanium discharge tubes were made by introducing about 5mg of titanium metal (as crushed sponge) and about 10 mg of iodine into a quartz tube about 7 to 8 cm in length. The tube was then filled with argon at atmospheric pressure from a cylinder, and the reaction between titanium and iodine was promoted by heating the tube gently with a bunsen burner, while keeping the top of the tube cool with moist asbestos string.This stage reduces the “running-in” period of the tube, and the very volatile titanium tetra-iodide (boiling-point 377.1” C) is deposited on the cool upper portions. The tube was then re-evacuated, flushed with argon and sealed under a pressure of argon of about 2 to 4 mm of mercury. These tubes still required a “running-in” period of between 1 and 2 hours when first prepared and only about 10 to 20 minutes afterwards. In most tubes a considerable amount of the less volatile black titanium &-iodide was observed after some time. We have not, as yet, established the lifetime of these tubes. The tubes thus prepared were examined in both types of cavity.The optimum excitation powers were about 35 watts when using the 214L cavity and about 50 watts when using the 210L cavity. Under these conditions, and in the absence of draughts, a stable, intense source showing no background emission from argon or iodine (except for the 206-2 nm line) was obtained. The stability when the 210L cavity was used showed less than +2 per cent. variation in response, while with the 214L cavity it was about +3 per cent. Also, the intensity of the discharge was slightly greater with the 210L cavity. The colour of the discharge was blue, and a spectrographic examination showed that it contained all of the expected atomic lines for titanium. The Unicam SPSOOA spectrometer is not capable of resolving all of the atomic lines, but the relative intensities of those linesMay, 19681 DISCHARGE TUBES FOR SPECTRAL-LINE SOURCES 283 which could be resolved were similar to those obtained in the arc, rather than the spark, spectrum.* Table I shows the relative intensities of the major lines observed when the Unicam SPSOOA flame spectrometer is used.TABLE I TITANIUM TUBE SPECTRUM Wavelength, nm 319.991- 334.19 336.461- 337.15 363.661- 364.277 366.361- 372-98 374.01 Relative intensity* (recorder reading) 16 16 15 25 50 70 73 60 66 66 50 396.63$ 90 396*29$ 396.43$ 85 398-25s 398.98 90 399.867 100 Tube operated at 50 watts in a 210L cavity; slit width, 0.007 mm; * Uncorrected for detector/monochromator response characteristics. t Spectral lines used for atomic-absorption studies.9 1 Unresolved lines with Unicam SPSOOA.gain, 2,O; and placed 25 cm from monochromator slit. VANADIUM- Attempts to prepare vanadium tubes in the way usually recommended failed and they could only be prepared by using commercially available vanadium trichloride. About 10 mg of vanadium trichloride were introduced into a quartz tube (about 6 to 7 cm in length) and, after flushing with argon, the tube was heated gently with a bunsen burner. When the first yellow fumes of free chlorine appeared, the heating was stopped, the tube was re-evacuated and then allowed to cool under vacuum. The tube was finally sealed under a pressure of argon of between 7 and 10mm of mercury. As usual, these tubes required to be “run-in” for about 1 hour when first prepared.Although most of the material remaining in the tube is vanadium trichloride, a small amount of vanadium dichloride (apple-green, boiling-point 1377” C) is also produced. The colour of the discharge was pink - violet, and the cylindrical 210L cavity is recom- mended for best operation at about 40 watts, without cooling. The success of the 210L cavity is once more thought to be because of its ability to act more efficiently as a thermostat for the tube than the 214L cavity, which yielded only an unstable discharge. Even with the 210L cavity, it is advisable to shield it from external draughts. Table I1 shows the principal lines observed with a Unicam SP9OOA spectrometer and their relative intensities. A spectrographic examination confirmed that the spectrum was primarily caused by atomic vanadium.Under these conditions a stable discharge was obtained. ZIRCONIUM- Zirconium tubes were prepared by using about 5mg of high purity zirconium metal and about 10 mg of iodine in a manner similar to that for titanium. In this instance, heating the metal and iodine under an atmosphere of argon to produce the moderately volatile zirconium tetra-iodide (vapour pressure 1 mm of mercury at 264’ C) was found to be essential because, otherwise, only a purple iodine discharge was obtained. The optimum pressure of argon as carrier gas corresponded to between 3 and 5 mm of mercury.284 DAGNALL, P ~ I B I L AND WEST : MICROWAVE-EXCITED ELECTRODELESS [Analyst, Vol. 93 TABLE I1 VANADIUM TUBE SPECTRUM Wavelength, Relative intensity * nm (recorder reading) 306.641- 16 100 26 20 26 40 66 45 3 18-34? $ 3 18*40t$ 318-64t 370.367 870.47t 370-60t 383*90t 386*64t$ 386*68t$ } 411.18 437.92 438-47t 439-00t 46 448.89 16 487.66 36 i Tube operated at 40 watts in 210L cavity; slit width, 0.012mm; * Uncorrected for detector/monochromator response characteristics.t Spectral lines used for atomic-absorption studies.* $ Unresolved lines with Unicam SP9OOA. gain, 2,O; and placed 25 cm from monochromator slit. The zirconium discharge was light blue in colour and was best obtained in the 214L cavity, at about 40 watts, without cooling. The tubes tended to overheat in the cylindrical cavity, with consequent instabiiity. The stability of these tubes at 40 watts was good, as is to be expected with an element or compound with a vapour pressure of 1 mm of mercury at about 200" to 300" C.In this instance the principal resonance lines at 318.34, 318-40 and 318.504 nm were not resolved by the Unicam SPSOOA spectrometer (Table 111), but no background emission was observed. TABLE 111 ZIBCONIUM TUBE SPECTRUM Wavelength, Relative intensity* nm (recorder readings) 208-64t 16 301.17t 36 302.967 20 339.20 30 360*98t 6 351*96? 3 364.77t 30 360-12t 100 362*39i 90 386.39t 40 389.03t 80 Tube operated a t 40 watts in 214L cavity; slit width, 0408mm; * Uncorrected for detector/monochromator response characteristics. t Spectral lines used for atomic-absorption studiese gain, 2,O; and placed 25 cm from monochromator slit. DISCUSSION No absolute intensity measurements or comparative measurements were made with hollow-cathode lamps, but we have no reason to suspect that these particular sources are any less intense than those previously described.For example, under operating conditions suitable for atomic absorption (i.e., operating powers of about 30 watts), we have found seleaium, antimony and arsenic electrodeless discharge tubes to be between 20 and 800 times more intense than conventional hollow-cathode lamps. Further, an increase in the operating powerMay, 19681 DISCHARGE TUBES FOR SPECTRAL-LINE SOURCES TABLE IV EFFECT OF POWER ON INTENSITY OF SOURCES Intensity (recorder reading) 285 I Power, * Titanium Vanadium? Zirconium watts (363-55nm) (318.4nm) (360.1 2nm) 20 15 0 0 30 25 18 2 40 32 28 5 50 65 36 32 60 > 100 68 50 70 > 100 83 82 Titanium tube with slit width, 0.005 mm and gain, 2,O; vanadium tube with slit width, 0.018 mm and gain, 2,O; zirconium tube with slit width, 0.004 mm and gain, 2,O.* Uncorrected for reflected power loss. t The 318.34 and 318-52 nm lines were unresolved from this line. also results in further increases in intensity. Table IV shows such a dependence for titanium, vanadium and zirconium at the lines normally used for atomic absorpti~n.~ Again, we have not established the lifetime of these sources, but many titanium, vanadium and zirconium sources have been prepared, and most of them have been run for up to about 50 hours without failing or markedly changing their operating conditions or intensity. Microwave-excited electrodeless discharge tubes are simple and inexpensive to prepare, and they do not require sophisticated or expensive operating equipment.The tubes, when correctly prepared, show no background-emission spectrum from the canier gas, but only the atomic spectrum of the metal concerned. The emission is normally as stable as that from a conventional hollow-cathode lamp and can be 2 to 3 orders of magnitude more intense. This is an important consideration in atomic-absorption spectroscopy because it overcomes many problems associated with the hollow-cathode lamp that has been used almost exclusively in this technique. In some instances, e.g., iron hollow-cathode lamps, a non-absorbing line is close to the resonance line, and the subsequent need for narrow slit widths results in a general loss in sensitivity and a prematurely curved calibration graph.This problem has been overcome by the use of a microwave-excited electrodeless discharge tube for iron.1° A similar situation also arises when an ionised metal or rare-gas line lies close to the resonance line, e.g., nickel and cobalt. In other instances, hollow-cathode lamps must sometimes be operated at low currents to avoid a loss in sensitivity caused by self-absorption effects. Yet again, some elements that can be detected in high temperature flames, such as nitrous oxide - acetylene, give only weak emissions in hollow-cathode lamps, e g . , silicon and boron. The use of resonance detectors also requires an intense source to eliminate noise at the amplifier output. While the recent introduction of high intensity hollow-cathode lamps is directed at solving these problems,ll their cost is high and little is known of their lifetime.Electrodeless discharge tubes prepared in this laboratory have been used following storage periods of more than 1 year, without any noticeable variation in output or the necessary operating conditions. These properties thus fulfil the essential requirements for spectral- line sources in both atomic-absorption and atomic-fluorescence spectroscopy. We are grateful to the Science Research Council for the award of a research grant in aid of this work, to I.M.I. Ltd. for the gft of pure titanium and zirconium metal, and to Electro-Medical Supplies Limited, London, for permission to reproduce Fig. 1. One of us (R.P.) also thanks the Czechoslovak Academy of Sciences, Prague, for study leave. 1. 2. 3. 4. 6. 6. 7. 8. 9. 10. 11. REFERENCES Dagnall, R. M., Thompson, K. C., and West, T. S., Talanta, 1967, 14, 551. 3 8 , Ibid., 1967, 14, 1151. --- , Ibid., 1967, 14, 1467. --- , Atomic Absorption Newslefter, 1967, 6, 117. We$, T. S:, Endeavour, 1967, 26, No. 97, p. 44. Brode, W. R., “Chemical Spectroscopy,” Second Edition, J. Wiley and.Sons Inc., New York, 1943. Amos, M. D., and Willis, J . B., Spectrochim. Acta, 1966, 22, 1325. Marshall, G., and West, T. S., Talanta, 1967, 14, 823. Sullivan, J. V., and Walsh, A., Spectrochim. Acta, 1965, 21, 721. Received October 12th, 1967 3 , Ibid., 1967, 14, 667. , I W . , in the press. --- --- --- ,

ISSN:0003-2654    

DOI:10.1039/AN9689300281

出版商:RSC    

年代:1968

数据来源: RSC

摘要:

286 Analyst, May, 1968, Vol. 93, +$. 286-288 Determination of Antimony in Rocks by Neutron-activation Analysis BY A. 0. BRUNFELT AND E. STEINNES (Mineralogical-Geological Museum, University of Oslo, Sarsgt. 1, Oslo 6, Norway) (Inslitutt for Atomenergi, Isotofie Laboratories, Kjeller, Nwway) Antimony has been determined in some geochemical standards (andesite AGV-1, diabase W-1, dunite DTS-1, granite GB and tonalite T-1) by neutron-activation analysis. A radiochemical procedure has been developed, in which antimony(V) is extracted into isopropyl ether and subsequently back-extracted after reduction to the tervalent state with tin(I1). The antimony activity is measured by y-spectrometry. Chemical-yield determina- tion is carried out by re-activation. The precision of the method is better than 5 per cent.for samples with antimony content exceeding 1 p.p.m. NEUTRON-ACTIVATION analysis can be used to advantage for the determination of antimony at low concentrations in geochemical samples. Antimony has been determined by this technique in rnete~rites,l*~*~ s4 tektites: silicate rock.~,~s~,6 and rnineral~.~ s5 To facilitate an efficient determination of micro amounts of this element, a specific radiochemical procedure is required before the radioactivity measurements are made. Tanner and Ehmann4 have used a radiochemical procedure based on multiple sulphide precipitations, followed by a reduction step to metallic antimony, while KiesP has used a procedure involving distillation, anion-exchange separation and sulphide precipitation. The procedure of Kiesl was part of a radiochemical separation scheme that also allowed for the simultaneous separation of other elements.The present paper presents a radiochemical procedure based on the extraction of antimony(V) into isopropyl ether. The antimony is back-extracted from the organic phase by reduction to antimony(II1) with tin(II), and subsequently precipitated as sulphide. The chemical-yield determination is carried out by re-activation. The silicate rocks analysed were some primary geochemical reference samples listed in Table I. EXPERIMENTAL APPARATUS- crystal was used. REAGENTS- A 400-channel y-spectrometer with a well-type, 3 x 3-inch, sodium iodide (thallium) in Reagents of analytical-reagent grade quality were used. Antimony standard solution-Prepare a stock solution by dissolving 25 mg of the metal a few millilitres of aqua regia and diluting with a solution of 0.1 M citric acid and M hydro- chloric acid to give a concentration of 50 pg of antimony per ml.Antimony carrier solution-Prepare a stock solution by dissolving antimony in con- centrated hydrochloric acid to give a solution containing 5 mg of antimony per ml. IRRADIATION- Finely crushed rock samples of about 100mg were accurately weighed into small polythene bags that were then heat-sealed. About 0.7 ml of the antimony standard solution was sealed in a quartz ampoule. The irradiation of the samples and standards was carried out in the reactor JEEP-1 (Kjeller, Norway) at a thermal-neutron flux of about 2*1012 neutrons per cm2 per second for 3 days.The irradiated samples were stored for 3 days to allow the short-lived activities to decay. 0 SAC and the authors.BRUNFELT AND STEINNES 287 RADIOCHEMICAL PROCEDURE- Open the polythene bag containing the sample and transfer it into a 250-ml polypropylene beaker containing 1.00ml of the antimony carrier solution. Add a mixture of 10ml of hydrofluoric acid - nitric acid (1 + 1). Heat the beaker on a water-bath, and stir with a polythene rod to ensure the complete dissolution of the rock powder. After evaporation to dryness, dissolve the residue in 10 ml of 9 M hydrochloric acid. Transfer the solution into a 100-ml glass beaker and heat with about 0-25 ml of bromine. Remove the excess of bromine by boiling. After cooling, transfer the solution into a 250-ml separating funnel and extract twice with 20 ml of di-isopropyl ether.Discard the aqueous phase, and wash the combined ether phases twice with 2 ml of 9 M hydrochloric acid. Back-extract antimony with 40 ml of a 3 M hydrochloric acid solution containing 50 mg of tin(I1) as tin(I1) chloride. Transfer the aqueous phase into a 100-ml glass beaker and precipitate antimony as antimony tn- sulphide with about 200mg of thioacetamide. Filter the precipitate on to a membrane filter, transfer it into a 50-ml glass beaker and dissolve in about 5.5 ml of concentrated hydro- chloric acid. With a pipette, withdraw 5.00 ml of the solution and transfer it into a polythene vial for y-activity measurements. Withdraw 0.500 ml of the standard solution from the quartz ampoule and dilute to 250 ml with concentrated hydrochloric acid.Transfer 5-00 ml of this solution into a counting vial. ACTIVITY MEASUREMENTS- The samples and standards were counted inside the well of the scintillation crystal for 5 to 20 minutes, depending on the activity level. The y-measurements were based on the 565-KeV photopeak of antimony-122 (half-life 2-75 days), which also contained a minute contribution of the 600-KeV y-ray of antimony-124. The area of the peak was evaluated according to the method of Covell.7 The radiochemical purity was checked by repeating the measurements after 3 to 4 days. DETERMINATION OF CHEMICAL YIELD- After measuring the y-activity, the samples were diluted to 100 ml with 0.4 M citric acid. About 1.2 ml of each solution were sealed in a polythene vial and activated for 3 hours, together with aliquots of the carrier solution diluted in the same way, at a thermal flux of about 2*1012 neutrons per cm2 per second.After the re-activation, the solutions were allowed to “cool” for 1 day. Aliquots of 1.00 ml were transferred into polythene vials for y-activity measurements. The y-counting was again based on the 565-KeV photopeak of antimony-122. The chemical yield was rather low, typically 30 to 50 per cent., but the re-activation technique renders precise chemical-yield determination possible, even if the yield is as low as a few per cent. RESULTS AND DISCUSSION The experimental results obtained by the present method for five different reference rock samples are presented in Table I. The relative standard deviation appears to be below 5 per cent. for silicate rocks with an antimony content higher than 1 p.p.m.At concentrations in the range 0.1 to 1 p.p.m., the precision seems to exceed 5 per cent. TABLE I RESULTS IN P.P.M. OBTAINED FOR ANTIMONY BY NEUTRON ACTIVATION OF STANDARD ROCKS Relative standard deviation Rock samples Experimental results Mean of single value, per cent. Andesite AGV-I* . . . . 4.33, 4.52, 4.27, 4.18, 4-44 4.35 3.1 Diabase W-l* . . . . 0.91, 0-87, 0.93, 0-92, 0.89 0.90 2.7 Dunite DTS-I* . . . . 0.53, 0.41, 0.51, 0.57, 0.49 0.50 11.6 GraniteGBt .. . . 0.21, 0.21, 0-25, 0.24, 0.24 0.23 8.1 Tonalite T-l$ . . . . 0.73, 0.68, 0.77, 0.76, 0.75 0.74 4.7 Rock suppliers : * U.S. Geological Society. t Carpatho-Balkan Geological Science. $ Geological Survey of Tanganyika.288 BRUNFELT AND STEINNES TABLE I1 ANTIMONY CONTENT IN P.P.M.OF U.S. GEOLOGICAL SURVEY STANDARD ROCKS Neutron-activation method Spectrophotometric Mass Pre'sent Rock sample method spectrometer Previous results results AGV-1 .. .. - - 5-42, 2.214, 4.76* 4.30 w-1 .. .. 1-28 0*809, 0*8'O, 0.3'1 0.9512, 0 ~ 1 4 ~ , 0.96, l*15t 0.90 DTS-1 .. .. - - 0.53, 0-404 0.60 * Relative determination to W-1 with assigned value of 0.90 p.p.m. t Results obtained with different bottles of W-1. In Table 11, the results are compared with those given in the available literature, which were obtained partly by neutron activation and partly by different analytical techniques. The present value of 0.90 p.p.m. for sample W-1 is in good agreement with that of other workers who used neutron-activation analysis, the only exception being the value of 0.14 p.p.m.reported by Tanner and Ehmann.4 The small differences may well be caused by significant differences in the antimony content of different bottles of W-1, as indicated by the results of Esson, Stevens and Vin~ent.~ The agreement with results obtained by the use of other techniques must also be considered as satisfactory.* y9 ,lo Serious disagreement with the results of Tanner and Ehmann4 has also occurred for sample AGV-1, and to a lesser extent for sample DTS-1. The present value for AGV-1, however, is supported by the work of Gorden, Randle, Goles, Corliss, Beeson and Oxley,6 who have determined the ratio of the amounts of antimony in AGV-1 and W-1 by using lithium-drifted germanium detectors in connection with instrumental activation analysis.The good agreement between other workers indicates that systematic errors yielding low results must be inherent in the results of Tanner and Ehmann. The presence of large systematic errors in the present method seems improbable. No y-emitting impurities were detected in the activity measurements. Possible interference from competing nuclear reactions, i.e. , uranium fission or (n,p) reaction in tellurium-122, is negligible, as the independent fission yield of the shielded nuclide antimony-122 is very low, and tellurium rarely occurs in silicate rocks. Neutron-shielding effects are also insignificant, because none of the major elements in the rocks is a strong neutron absorber, and the dilution of the standard was sufficient to avoid self-shielding caused by the large resonance integral of antimony-121.The accuracy of the present method is, therefore, in all probability about & 10 per cent. For samples with antimony content above 1 p.p.m., the accuracy is perhaps as good as + 5 per cent. The sensitivity of this method is adequate for the determination of antimony in silicate rocks, with sufficient precision and accuracy for general studies in geochemistry. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. REFERENCES Smales, A. A., Mapper, D., Morgan, I. W., Webster, R. K., and Wood, A. J., Int. Conf. Peaceful Hamaguchi, H., Nakai, T., and Endo, T., Nippon Kugakzt Zusshi, 1961, 82, 1485. Kiesl, W., 2. analyt. Chem., 1967, 227, 13. Tanner, J. T., and Ehmann, W. D., Geochim. Cosmochim. Acta, 1967, 31, 2007. Esson, I., Stevens, R. H., and Vincent, E. A., Min. Mug., Lond., 1965, 35, 88. Gorden, G. E., Randle, K., Goles, G. G., Corliss, J. B., Beeson, M. H., and Oxley, S. S., Geochim. Covell, D. F., Anulyt. Chem., 1959, 31, 1785. Ward, F. N., and Lakin, H. W., Ibid., 1954, 26, 1168. Taylor, S. R., Nature, 1965, 205, 34. Nicholls, G. D., Graham, A. L., Williams, E., and Wood, M., Analyt. Chem., 1967, 39, 584. Brown, R., and Wolstenholme, W. A., Nature, 1964, 201, 598. Hamaguchi, H., Kuroda, R., Tomura, K., Osava, M., Watanabe, K., Onuma, N., Yasunaga, T., Received December 18th, 1967 Uses Atom. Energy, Geneva, 1958.2, 242, paper 282. Cosmochim. Actu, 1967, in the press. Hosohara, K., and Endo, T., Geochim. Cosmochim. Acta, 1961, 23, 296.

ISSN:0003-2654    

DOI:10.1039/AN9689300286

出版商:RSC    

年代:1968

数据来源: RSC

摘要:

Analyst, May, 1968, Vol. 93, $9. 289-291 289 The Determination of Trace Amounts of Chromium Stable Isotope Dilution - Mass Spectrometry BY A. HEDLEY* (Bragg Laboratory, Naval Ordnance Irtspection Establishment, Shefield 9, Yorkshire) A simple chemical - mass-spectrometric method for the determination of chromium is described. The method has been applied to steels, copper-base and aluminium-base alloys. The conditions for the thermal ionisation of chromium are given, and the stable isotope-dilution technique is used for quantitative analysis over the range 0.003 to 0-2 per cent. The advantage of the isotope-dilution technique in not requiring quantitative extraction is clearly illustrated by the application of a single method to more than one type of alloy. A MASS-SPECTROMETRIC method for the determination of chromium at levels below 0.05 per cent. was evolved to check results obtained by chemical analysis for aluminium-base alloys.Further work showed that the same method could be applied satisfactorily to steels and copper-base alloys. It clearly illustrates one of the advantages of isotope dilution - mass spectrometry, as once isotope exchange has taken place there is no requirement for quantitative or “clean” separations. Blundyl reported on the efficiency of the extraction of chromium in the presence of smaller amounts of iron, nickel and copper than those used here. His results indicated that 100 per cent. extraction would not be achieved after one extraction under the conditions given in this paper. However, a second extraction could be performed if required.The mass spectrometer used was an A.E.I. MS-2-5 This is a 6-inch radius, 90” sector instrument fitted with a thermal-ionisation source for the analysis of solids. Ion detection is by a conventional plate collector, display being on a chart recorder. The techniques of thermal ionisation2v3s4 and isotope dilution3v4 have been adequately covered in earlier literature. The sample is dissolved in hydrochloric acid, oxidised with nitric acid and heated to fumes with sulphuric acid, and the chromium(II1) is then oxidised to chromium(V1) with cerium(1V) sulphate. The chromium(V1) is extracted into isobutyl methyl ketone in N hydrochloric acid and is then back-extracted into water. PREPARATION OF THE TRACER SOLUTION- Weigh about 2.5 mg of the oxide into a platinum crucible and fuse it with a 10-fold excess of a mixture of sodium carbonate and potassium nitrate (2 + 1).Leach the melt with de- ionised water and add, dropwise, a slight excess of lead nitrate solution (5 per cent w / ~ ) . Allow it to stand at room temperature for 30 minutes. Centrifuge the precipitate and wash it ten times with de-ionised water. Rinse the lead chromate out of the tube and dissolve it in nitric acid (sp.gr. 1.42). This solution when diluted to 50 ml has an approximate concen- tration of 1 ml equivalent to 30 pg of chromium-53. During the preparation there is the possibility that some enriched chromium may be lost and some natural chromium picked up. This would alter both the concentration and isotopic composition of the tracer solution. To determine these values, load the tracer solution on the source filament (described below) and measure sufficient beams to enable the com- position of the tracer solution to be calculated.Determine the strength of the solution by adding a known weight of natural chromium to a known volume of tracer solution and measure the isotopic ratio of peaks 53 : 52. The weight of artificially enriched chromium required to give the mixed isotopic composition can then be calculated by using the equation given below. The tracer, Cr,O, artificially enriched with chromium43 to a level of 97.5 per cent., was obtained from the Electromagnetic Separation Group, A.E.R.E., Harwell. EXPERIMENTAL *Address after June lst, 1968 : Admiralty Materials Laboratory, Holten Heath, Poole, Dorset. 0 SAC; Crown Copyright Reserved.290 HEDLEY: DETERMINATION OF TRACE AMOUNTS OF CHROMIUM [Analyst, vol.93 METHOD REAGENTS- Hydrochloric acid (Aristar, sp.gr. 1-18}. Hydrochloric acid, N. Nitric acid (Aristar, sp.gr. 1-42). Sulphuric acid, 50 per cent. v/v. Cerium(1V) sulphate solution, 10 per cent. wlv. Isobutyl methyl ketone. PROCEDURE- Weigh an appropriate amount of sample into a 125-ml conical beaker (Note l ) , add 0 6 m l of tracer solution, dissolve it in 1 O m l of hydrochloric acid (sp.gr. 1-18) and oxidise with a few drops of nitric acid (spgr. 1.42) (Note 2). Add 10 ml of sulphuric acid (50 per cent, v/v) and evaporate to fumes. Cool, dilute to about 50 ml, add 2 ml of cerium(1V) sulphate solution (10 per cent. w/v) and boil for 10 minutes.Cool the solution to room temperature and make it N in hydrochloric acid, before shaking it with 20 ml of isobutyl methyl ketone for 1 minute. Wash the organic layer with four 25-ml portions of N hydrochloric acid before back-extracting the chromium with two 10-ml portions of de-ionised water. Evaporate the aqueous layer to the smallest possible volume. NOTES- 1. An isotopic ratio of about 1 : 1 is preferred. If the approximate chromium content of the sample is known, a suitable sample weight can be calculated, keeping the amount of tracer used constant. 2. For copper alloys the addition of 5 ml of nitric acid (sp.gr. 1-42), after the addition of hydro- chloric acid, increases the rate of dissolution. MASS-SPECTROMETRIC PROCEDURE- Tests carried out with 2 pg of natural chromium indicated that the optimum filament was a triple filament assembly5 made of rhenium ribbon.Load the solution on to a side filament of the assembly by using a micro syringe, and dry the drops by passing a current through the filament. Place the source in the mass spectrometer and scan the mass range 51 to 54 with the centre filament at 6 amps and the side filament at 3 amps upwards. Once stable beams have been produced maintain these conditions and measure the isotopic ratio 53 : 52. A blank consisting of 0.1 g of the appropriate pure base metal, with 0-5 ml of tracer added, was carried through the full procedure. The blank had a value of about 5 p.p.m. when Aristar grade acids were used. CALCULATIOK- The two isotope peaks considered are chromium-52, the most abundant chromium isotope in nature, and chromium-53, purchased for use as a tracer.The ratio of the contents of chromium-52 and chromium-53 are measured. The chromium content can then be calculated from the following expression- E =- .-._.-. RO-R' R + l A t w - * x R ' - R RO+1 A0 s m where E = amount of chromium present in pep."., Ro = 53 : 52 ratio in the tracer material, R = 53 : 52 ratio in natural chromium, R' = 53 : 52 ratio in the sample - tracer mixture, A = atomic weight of natural chromium, A0 = atomic weight of the chromium in tracer form, t = atomic fraction of 52 and 63 in the chromium tracer, s = atomic fraction of 52 and 53 in natural chromium, w = volume of tracer added in millilitres, m = weight of sample taken in grams, and x = weight in pg per ml of chromium in the tracer solution.May, 19681 BY STABLE ISOTOPE DILUTION - MASS SPECTROMETRY 291 RESULTS Steels-Two B.C.S.standards, B.C.S. 322 and B.C.S. 271, were analysed, with the following results. B.C.S. 322 (0.039 per cent.) B.C.S. 271 (0.046 per cent.) 0.039, 0-039 0.044, 0.043 0.040, 0.039 0.043, 0.042 0.038, 0.039 0.043, 0.043 0.040 0.045, 0.043 Average 0.039 (1) Average 0.043 (3) Aluminium alloys-Three B.C.S. standards were analysed. B.C.S. 262 (0.06 per cent.) 0.061, 0.066 0.242 0.0029, 0-0027 0.062, 0.063 B.C.S. 263 (0.24 per cent.) B.C.S. 181/1 (0.01 per cent.) - 0.0031 Cofi+er alloys-No B.C.S. copper alloys containing a certified chromium figure are Therefore, to each 0-1 g of sample 35 pg of natural chromium were added, equivalent made.to 0.035 per cent. Three B.C.S. standards were used. B.C.S. 183/1 B.C.S. 207/1 B.C.S. 304 0.035 0.035 0-038 0-035 0.036 0.038 0.037 0.036 0.037 The high figures obtained for B.C.S. 304, an aluminium bronze, indicated that this alloy This was verified by analysing 1 g of the alloy in contained a small amount of chromium. duplicate, when the following figures were obtained. DISCUSSION The time taken for one analysis was between 14 and 2 hours but, as opposed to purely chemical methods in which the time taken for a batch does not increase greatly, the time taken with the mass spectrometer (30 to 45 minutes) is the same for each sample. This slight disadvantage is amply compensated for by the relatively simple method that can be applied to these three matrices.The method has no interference, as interferences have to be isobaric and no other elements have stable isotopes with masses 52 and 53. The parameters of the mass spectrometer preclude any doubly charged ions. B.C.S. 304: 0-0028, 0.0027 per cent. of chromium. CONCLUSION The results indicate that the method can be confidently applied to all three alloy types. There appears to be no objection to applying the method to other alloys that do not form insoluble sulphates or chlorides. The 3.53 per cent. of lead in B.C.S. 183/1 did not separate as sulphate with 0.1 g of sample. This paper is published with the permission of the Ministry of Defence (Navy Department). REFERENCES 1. 2. 3. Blundy, P. D., Analyst, 1958, 83, 566. Turnbull, A. H., “Surface Ionisation Techniques in Mass Spectrometry,” U.K. Atomic Energy Research Establishment Report R.4296, H.M. Stationery Office, London, 1963. Freegarde, M., “Mass Spectrometry-Applications of Isotope Dilution to the Analysis of Metals.” Paper presented at the Society for Applied Spectroscopy Conference, Cleveland, Ohio, October, 1964. Wilson, H. W., and Daly, N. R., J . Scient. Instrum., 1963, 40, 273. Inghram, M. G., and Chupka, W. A., Rev. Scient. Instrum., 1953, 24, 518. 4. 6. Received November loth, 1967

ISSN:0003-2654    

DOI:10.1039/AN9689300289

出版商:RSC    

年代:1968

数据来源: RSC

摘要:

292 Analysb, May, 1968, Vol. 93, Pp. 292-297 An Indirect Amplification Procedure for the Determination of Niobium by Atomic-absorption Spectroscopy BY G. F. KIRKBRIGHT, A. M. SMITH AND T. S. WEST (Chemisty Department, Imperial College, Londm, S. W.7) Niobium in the range 5 to 50pg is determined by an amplification procedure in which rnolybdoniobophosphoric acid is formed and extracted into butanol. The molybdophosphoric acid, which is also formed, is first selectively extracted away from the molybdoniobophosphoric acid into isobutyl acetate. The eleven rnolybdate ions associated with each niobium atom are determined by direct atomic-absorption spectroscopy in a nitrous oxide - acetylene flame at 313.2 nm. Of the twenty-eight other ions studied, only titanium causes appreciable interference, although its presence at the same concentration as.niobium can be tolerated. Large amounts of tantalum do not interfere. SEVERAL spectrophotometric methods have been reported for the determination of niobium, in which the coloured heteropoly complex formed between niobium , phosphate and molybdate in acidic solution is ~ s e d . ~ , ~ , ~ In these methods the molybdoniobophosphoric acid (MNPA) is reduced to “heteropoly blue,” after the selective decomposition of the excess of binary molybdophosphoric acid (MPA), by increasing the acidity of the solution, The methods reported are not sensitive, and strict adherence to the time of addition of acid and reducing agent, as well as measurement of the heteropoly-blue absorbance, must be observed.Babko and Shkaravskii4 have investigated the equilibria governing the formation of the molybdo- niobophosphoric acid, and its composition in aqueous solution. They report the formation, in an acid medium,. of a stable complex, in which the combining ratio of niobium - phosphorus - molybdenum is 1 : 1 : 11. The same authors also obsexved that, whereas molybdophosphoric acid is readily extracted into butyl acetate at pH 1, molybdoniobophosphoric acid is not extracted. ShkaravskiF has reported that tantalum does not form a ternary heteropoly complex with molybdenum a d phosphate. We have previously reported the sensitive indirect determination of silicon and phosphorus6 by atomic-absorption spectroscopy of the twelve molybdenum atoms associated with each atom of these elements in molybdosilicic and molybdophosphoric acids, after their selective extraction into an organic solvent.It seemed that a sensitive determination of niobium with high selectivity might similarly result from formation and extraction of the molybdoniobophosphoric acid, and the determination by atomic-absorption spectroscopy of the eleven molybdenum atoms associated with each niobium atom in the heteropoly complex. In the procedure reported here, MNPA is formed in 0.5 M hydrochloric acid by addition of molybdate and phosphate to the sample solution, and the excess of phosphomolybdic acid is extracted into isobutyl acetate. The MNPA in the residual aqueous phase is then extracted into butanol; the organic phase is washed with 0-5 M hydrochloric acid and the molybdenum present determined by atomic absorption in a nitrous oxide - acetylene flame at 313.2 nm.The high sensitivity of the method reported here for the determination of niobium results from the sensitivity obtainable for the determination of molybdenum in the nitrous oxide - acetylene flame ; the 1 1-fold amplification available from use of the molybdoniobophosphoric acid; the enhanced absorbance for molybdenum at 313-2 nm in butanol by virtue of efficient nebulisation of the solvent ; and the concentration of the molybdenum into a smaller volume of solution by extraction into butanol. The method is selective because few other elements form extractable heteropoly complexes under the conditions used. 0 SAC and the authors.KIRKBRIGHT, SMITH AND WEST 293 EXPERIMENTAL APPARATUS- Techtron AA4 flame spectrophotometer, fitted with a 5-cm nitrous oxide - acetylene burner and molybdenum high intensity hollow-cathode lamp.The instrument settings used for the determination of molybdenum were: slit width, 100 pm; wavelength, 313.2 nm; nitrous oxide pressure, 15 p.s.i. ; the acetylene flow-rate was adjusted to produce a flame with a “red-feather” of about 1 to 2 cm height. The burner height was adjusted so that as much as possible of the light from the hollow-cathode lamp passed through this red zone. REAGENTS- All reagents should be of analytical-reagent grade; we found that reagents conforming to the AnalaR specifications were suitable. Molybdate reagent solutio%-Dissolve 10.69 g of ammonium molybdate tetrahydrate, (NH,),Mo,0,,.4H20, in distilled water and dilute to exactly 1 litre.Phosphate reagent solzction-Dissolve 0.1098 g of potassium dihydrogen orthophosphate, KH2P0,, in distilled water and dilute to exactly 1 litre; 1 ml of solution contains 25 pg of phosphorus. Wash l i p i d for butanol phase-Saturate hydrochloric acid (0.5 M) with butanol, and store in polythene bottles. Isobutyl acetate and b.utamZ-Generd-purpose reagent grade. Niobium-Spectrographically standardised niobium powder (Johnson and Matthey Ltd.) . PREPARATION OF NIOBIUM STOCK SOLUTIONS- Silicon-free niobium stock solutions were prepared by the following procedure. Dissolve 0.1000 g of niobium powder in 10 ml of 40 per cent. hydrofluoric acid containing a few drops of concentrated nitric acid. Evaporate the solution almost to dryness in a platinum crucible.Dissolve the residue in 10 ml of warm 40 per cent. hydrofluoric acid. Transfer the solution to a polythene bottle and dilute to exactly 100 ml with distilled water. This solution contains 1 mg of niobium per ml. Transfer a 5-ml aliquot of this solution to a platinum crucible and evaporate to dryness. Dissolve the residue in 5 ml of 40 per cent. hydrofluoric acid, add a few drops of concentrated sulphuric acid, and evaporate the solution until no further evolution of white fumes occurs. Cool, re-dissolve the residue, then repeat the evaporation with hydro- fluoric and sulphuric acids. Make a final evaporation of the solution of the residue with 5 ml of 40 per cent. hydrofluoric acid without addition of sulphuric acid.Dissolve the residue in the minimum amount of hydrofluoric acid (about 2 ml) and dilute to exactly 100 ml with distilled water. The silicon-free niobium solution contains 50pg per ml of niobium. PREPARATION OF CALIBRATION GRAPH FOR NIOBIUM- To each of a series of six 100-ml separating funnels, add 10 ml of the molybdate reagent solution, 0, 0.2, 0.4, 0.6, 0.8 and 1.0 ml of the niobium solution (containing 50 pg of niobium per millilitre), 10 ml of the phosphate reagent and sufficient 6 M hydrochloric acid and water to make the final. solution 0.5 M with respect to hydrochloric acid. Mix the solutions, allow to stand for about 5 minutes, and proceed with each as follows. Extract the MPA into two 25-mI portions of isobutyl acetate by shaking each time for 1 minute and discarding the organic phase.Add 10 ml of butanol to the remaining aqueous phase and shake for 1 minute to extract the MNPA. Some free molybdate is extracted at this stage into the butanol, but it is readily removed by rapid successive shakings with three 10-ml aliquots of butanol- saturated 0.5 M hydrochloric acid. Spray the butanol phase directly into the nitrous oxide - acetylene flame and determine the molybdenum content by atomic-absorption spectroscopy. PREPARATION OF SAMPLE SOLUTIONS- Samples whose niobium content is to be determined should be dissolved in a mixture of hydrofluoric and nitric acids and treated further to remove silicon, as detailed in the instructions for the preparation of the niobium stock solution.294 KIRKBRIGHT, SMITH AND WEST: AN INDIRECT AMPLIFICATION [Analyst, Vol.93 RESULTS AND DISCUSSION FORMATION AND EXTRACTION OF MNPA- We have already reported the optimal conditions for the determination of molybdenum by atomic-absorption spectroscopy in a nitrous oxide - acetylene flame'; and the conditions were not, therefore, studied here. It is not possible to form MNPA in aqueous solution without the simultaneous formation of MPA. Consequently, throughout the studies undertaken to determine the optimal solution conditions for the formation and extraction of MNPA, the following general procedure was adopted to remove the MPA formed. Both MPA and MNPA were allowed to form in acidic solution, and then the MPA was extracted into two 25-ml aliquots of isobutyl acetate before the extraction of MNPA into 10ml of butanol.The molybdenum associated with the niobium in the MNPA was then determined by direct atomic-absorption spectroscopy in the washed butanol phase. Each solution was measured against a blank produced under identical conditions, but containing no niobium. EFFECT OF ACIDITY- The effect on absorbance of variation in the acidity of an initial aqueous solution, which was 2-7 x 10-2 M in molybdate, 3.6 x lo4 M in phosphate and contained 40 pg of niobium, is shown in Fig. 1. I I I I I I I 0 0.2 0.4 0 6 0.8 I .o I -2 Hydrochloric acid concentration (molarity) Fig. 1. Effect on absorbance for 40 pg of niobium of molarity of hydrochloric acid during formation of molyb- doniobophosphoric acid EFFECT OF MOLYBDATE AND PHOSPHATE CONCENTRATION- The effect on absorbance of variation of the phosphate concentration of the initial aqueous solution, which contained 30pg of niobium and was 2.7 x 1 0 - 2 ~ in molybdate and had an over-all acidity of 0.5 M, is shown in curve A of Fig.2. The effect of varying the molybdate concentration of the initial 3.6 x 10"' M aqueous phosphate solution at the same acidity, but containing 25 pg of niobium, is shown in curve B of Fig. 2. EXTRACTION OF MPA AND MNPA- When an over-all hydrochloric acid concentration of 0.5 M was used, the molybdate and phosphate concentrations in the initial aqueous phase were standardised at 2.7 x M and 3.6 x 1 0 4 ~ , respectively. Under these conditions it was shown, from determinations by atomic absorption of the molybdenum in the organic phase, that two extractions with 25-ml aliquots of isobutyl acetate quantitatively remove the excess of MPA from the aqueous phase.Radiotracer experiments with niobium-96 proved that no MNPA was extracted into isobutyl acetate under these conditions. After these isobutyl acetate extractions, treatment with a single 10-ml aliquot of butanol was shown to extract the MNPA quantitatively.May, 19681 PROCEDURE FOR THE DETERMINATION OF NIOBIUM 296 In our previous work on the determination of silicon by a similar amplification procedure, it was found that butanol extracts some of the excess of molybdate. Consequently, in all the present experiments, the butanol phase was washed with butanol saturated with dilute hydrochloric acid before determining its molybdenum content by atomic absorption.Curve C in Fig. 2 shows the effect of washing the final butanol phase with various concentrations of hydrochloric acid. From the results obtained it was decided that three rapid washes with 10-ml aliquots of butanol-saturated 0.5 M hydrochloric acid were sufficient. " A B C I I I I I 0 200 400 '600 800 loo0 pg of phosp )rus (A) 0 2 4 6 8 lox 1 0 , pg of molybdenum (8) 0 0.4 0.8 1.2 1.6 2.0M hydrochloric acid (C) Concentration Fig. 2. Curve A, effect seen on absorbance for 30 pg of niobium of variation in phosphate reagent concentration (solution 0-5 M in hydrochloric acid, 2.7 x 1 0 - e ~ in molybdate) : curve B, effect seen on absorbance for 25 pg of niobium of variation in molybdate reagent concentration (solution 0-5 M in hydrochloric acid, 3.6 x l o - 4 ~ in phosphate) ; curve C, effect seen on absorbance for 25 pg of niobium of variation in molarity of hydrochloric acid used to wash final butanol phase MOLYBDENUM-TO-NIOBIUM COMBINING RATIO IN MNPA- Babko and Shkaravskii4 have observed that the composition of the MNPA in solution depends on the acidity at its formation, and report that the molybdenum-to-niobium ratio is 11 : 1 at pH 0 to 1.0, 11 : 2 at pH 1.5 to 3.5 and 11 : 3 at pH 4-5 to 5.5.Thus the best amplification ratio is obtained by forming the complex at pH 0 to 1.0. An experiment was devised to establish whether the MNPA was formed and extracted stoicheiometrically as the 11 : 1 complex under the conditions used in our procedure. Different amounts of niobium were taken through the procedure, and the MNPA in the final butanol phase was decomposed and back-extracted into dilute ammonia solution and diluted to a known volume (25 ml) with distilled water. The molybdenum content of the aqueous solutions was determined by atomic-absorption spectroscopy in a nitrous oxide - acetylene flame.The solutions prepared for the calibration graph for molybdenum in aqueous solution were saturated with butanol and contained dilute ammonia solution. The results of these deter- minations gave a reproducible molybdenum-to-niobium ratio of 11.4 ( * 0-2) : 1. After correction for the small amounts of molybdenum not removed in the hydrochloric acid washing procedure, which constitutes the blank in the recommended procedure for niobium, a repro- ducible molybdenum-to-niobium ratio of 11.0 (k0.2) : 1 was obtained.Thus, under the recommended conditions, it is the 11: 1 MNPA that is formed and extracted quantitatively into butanol.296 KIRKBRIGHT, SMITH AND WEST : AN INDIRECT AMPLIFICATION [Analyst, Vol. 93 CALIBRATION GRAPH AND OPTIMUM CONCENTRATION RANGE- The calibration graph obtained when the recommended conditions are used is linear over the range 5 to 50pg of niobium. After subtraction of the reagent blank the graph passes through the origin, and the absorbances corresponding to these concentrations in the aqueous solution (0.22 to 2.2 p.p.m.) are 0.06 and 0-63. The blank, which results from the small amount of molybdate reagent not removed from the butanol phase by the washing procedure, is reproducible and may be subtracted from the absorbance produced by the standards taken through the procedure.This blank gives rise to an absorbance for molyb- denum in the flame of about 0.05 absorbance unit versus a butanol solvent blank. PRECISION- The replicate analysis of 11 samples, each with 23 ml of a solution containing 30 pg of niobium (1.30 p.p.m.), gave an average absorbance of 0.39, and the relative standard deviation was 0.009 absorbance unit or 2.4 per cent. EFFECT OF OTHER IONS- The effect of twenty-eight other ions on the absorbance produced in the determination of 30 pg of niobium by the recommended procedure has been investigated. An ion was con- sidered not to interfere when an error in the absorbance of less than twice the standard deviation of the determination of niobium alone (4.8 per cent.) was produced.The addition of 1 ml of 10-1 M solutions of the following ions in the determination of 30 pg of niobium caused no interference : aluminium, silver, bismuth, beryllium, calcium, cadmium, cobalt (11), copper, iron( 111) , nickel, magnesium, manganese( 11), antimony(V), zinc, sulphate, nitrate, fluoride and EDTA. In addition, the presence of 1 ml of 10-1 M solutions of the important refractory elements tantalum, tungsten and zirconium produced no interference when taken through the procedure. The addition of 1 ml of 10-1 M solutions of any of the above twenty-one ions corresponds to a range of excesses by weight over niobium from 30-fold to 700-fold. Of the elements that also form heteropoly acids under similar conditions, arsenic and germanium can be removed by volatilisation of their chlorides, and silicon is eliminated by volatilisation of fluorosilicic acid during the sample preparation procedure.Titanium, however, has been reported to form a molybdotitanophosphoric acids and, although the presence of large amounts causes serious interference, an equal amount of titanium (30pg) was found to be tolerable in the procedure. Attempts made to mask the interference of titanium were un- successful. Vanadium(V) and chromium(V1) are tolerable up to 3-fold and 45-fold excesses by weight, respectively. ACCURACY- samples. The results of these analyses are shown in Table I. Chemical analyses were performed for niobium in prepared solutions treated as unknown TABLE I DETERMINATION OF NIOBIUM IN PREPARED MIXTURES Niobium added to initial aqueous solution, pg per 25 ml 18 30 30 30 30 6 60 10 5 9 40 30 21 21 Other ions present, Pg Zr (3680) Cr (IV) ( 1350) W(V1) (1840) Co (2945) : Ni (2935) Cu (3175) : Zn (3270) Fe(II1) (2800) Ta (300) Zr (736) Ta (600) Ta (30,000) W(V1) (1840) - - - Niobium found, PQ 18 30 30.6 29.5; 30 6 49 10.3 6 8.9 40-2 30 24* 21 * Results high because of traces of niobium in the tantalum used.May, 19681 PROCEDURE FOR THE DETERMINATION OF NIOBIUM 297 CONCLUSION The method reported here for the indirect determination of niobium by atomic-absorption spectroscopy is much more sensitive than the direct method for niobium in the nitrous oxide - acetylene flame (1 per cent.absorption is given by 24 p.p.m. of niobium by the direct method, whereas by this method I per cent.absorption results with an initial aqueous niobium solution of 0-015 p.p.m.). Because of the selectivity with which molybdoniobophosphoric acid can be formed and extracted, the selectivity of the procedure compared with the direct method is good. Extraction of MNPA into butanol achieves a separation of the niobium from other major element components of samples. In the direct method, the presence of large amounts of other elements frequently suppresses the niobium absorbance because of the formation of oxide in the flame, so that solvent extraction may be required. Thus the use of a solvent- extraction procedure in this indirect method does not constitute a disadvantage compared with the direct atomic-absorption method. The method reported is precise and, after the dissolution of the sample, almost as rapid as the direct procedure. We are grateful to the Ministry of Technology for support of this work, and to the Courtauld Research Foundation for a grant for the purchase of the atomic-absorption equipment used in these studies. 1. 2. 3. 4. 5. 6. 7. 8. Davydov, A. A., Vaisberg, 2. M., and Burkur, L. E., Zav. Lab., 1947, 13, 1038. Norwitz, G., and Codell, M., Analyt. Chern., 1954, 26, 1238. Veitsman, R. M., Zav. Lab., 1954, 25, 552. Babko, A. K., and Shkaravskii, Y. F., Russ. J . Inorg. Chem., 1962, 7 , 809. Shkaravskii, Y. F., Ibid., 1963, 8, 1399. Kirkbright, G. F., Smith, A. M., and West, T. S., Analyst, 1967, 92, 411. , I , Ibid., 1966, 91, 700. Babko, A. K., and Shkaravskii, Y. F., Russ. J . Inorg. Chern., 1961, 6, 1068. --- Received November 29th, 1967

ISSN:0003-2654    

DOI:10.1039/AN9689300292

出版商:RSC    

年代:1968

数据来源: RSC

摘要:

298 A d y s t , May, 1968, Vol. 93, $$. 298-305 The Colorimetric Determination of Boron in Carbon and Stainless Steels BY D. BELL AND K. McARTHUR (Colville’s Ltd. Laboratory, Glengarnock Steel Works, Glengarnock, Ayrshive) A method proposed for the colorimetric determination of boron in carbon and alloy steels, and probably also in high-nickel alloys, is described. The procedure has been applied to several B.C.S. boron-containing steels with acceptable reproducibility and accuracy. A METHOD proposed for the colorimetric determination of boron in carbon and alloy steels is described. The colorimetric reagent used is a highly substituted hydroxyanthraquinone, l-hydroxy-4+toluidinoanthraquinone, which is more sensitive to boron than quinalizarin, and has the additional advantage of reacting in sulphuric acid solutions of lower concen- tration.Photo-electric measurement of optical densities is used to ensure maximum precision. The method has been applied to several boron-containing steels, with good results. Repro- ducibility in the boron range up to 0.003 per cent. is satisfactory at ~0.0002 per cent. for carbon steels. The procedure has been extended to include stainless steels. In the Rudolph and Flickingerl method for the colorimetric determination of boron in steel in the 0 to 0@06 per cent. range, a solution of quinalizarin in concentrated sulphuric acid is used as the boron colour reagent. The method has the attraction of great simplicity, because no preliminary separation of boron is required, and iron, in the iron(I1) state, does not interfere but, as it precipitates as sulphate in a very fine form, it obscures the reagent colour change for a lengthy period, and allowing the solution to stand overnight is usually prescribed to ensure satisfactory clarity.This investigation was primarily concerned with shortening the time required for the determination of boron in steel and obtaining better reproducibility by replacing visual assessment of the reagent colour change with photo-electric measurement in a suitable instrument. In the experimentd work that followed, it was found preferable to remove precipitated sulphates before adding the boron reagent, and the procedure adopted enables this to be done in a relatively short time. As the reaction between boron and the reagent used takes only a few minutes to complete, the total time required for the determination was reduced considerably.In the Rudolph and Flickinger procedure the optical density range is only 0.05 for 0.003 per cent. of boron, as measured in 1-cm cells with red filters. The low reagent concentration of 0*0005 per cent. was probably adopted to facilitate visual comparison against standards, as the reagent itself is strongly coloured. The optical density range can be improved by using a higher concentration of quinalizarin, a &fold increase about doubling it, but the resulting disproportionately large increase in optical density caused by excess of reagent prevents this procedure from being used. Trinder2 showed that 1-hydroxy-4-fi-toluidinoanthraquinone (HPTA) was superior to quinalizarin in sensitivity to boron and had the further advantage of reacting with boron in sulphuric acid solutions down to about 75 per cent.As the HPTA reagent reacts with boron in cold acidic solution, it appeared to have considerable advantages over quinalizarin, and was used in all subsequent experiments. The use of this anthraquinone derivative as a reagent for boron was first noted by RadleyS and investigated by Trinder.2 It is soluble in sulphuric acid solutions above about 65 per cent. v/v, giving a green solution that changes to blue in the presence of boron. The green colour deepens considerably with increasing sulphuric acid concentration, but boron sensitivity reaches a maximum at about 83 to 84 per cent. This is shown in Table I for a reagent concentration of 0-0025 per cent., which was the final concentration adopted for use 0 SAC and the authors.BELL AND MCARTHUR 299 in the proposed procedure.A Hilger photo-electric colorirneter, with tungsten lamp, 1 and 2-cm cells, heat-absorbing and Chance OY2 filters, was used throughout the investigation to measure optical densities. TABLE I EFFECT OF INCREASING SULPHURIC ACID CONCENTRATION ON OPTICAL DENSITY MEASUREMENTS Sulphuric acid concentration, Optical density of reagent Optical density of boron addi- per cent. v/v . . .. 65 70 76 80 82.6 86 87.6 90 95 (l-cm cell) . . .. . . 0.09 0.10 0-10 0.135 0.207 0.317 0.440 0.626 0.686 tion (0403per cent.) . . Nil 0.002 0.066 0.122 0.187 0.182 0.161 0-100 0-061 EXPERIMENTAL Because of the rapid increase in the optical density of the HPTA reagent with increasing acidity, small differences in the sulphuric acid content of ordinary supplies of concentrated sulphuric acid can result in appreciable variations between different batches of reagents prepared at different times, but when each series of tests and standards is processed with the same batch of reagents the accuracy of the boron determination is not affected.As Table I indicates, the change in optical density of the reagent between 82 and 85 per cent. acidity is about 0.09 for each 1 per cent. difference (with 2-cm cells and OY2 filters), while boron sensitivity is practically unaltered. As an example of the variations that can arise, several bottles of laboratory-grade concentrated sulphuric acid, taken at random, showed the following optical density blanks when added to aliquots of boron-free iron solution as pre- scribed in the adopted procedure: 0-603, 0.622, 0.402, 0-269, 0.344 and 0.454.As excessively high blanks are undesirable, selected batches of concentrated sulphuric acid can be advantageously reserved for use in the boron determination. Boron colour development, in the rather low concentration of less than 0.01 mg in a sample aliquot, is rapid and reaches a maximum in a few minutes, remaining stable thereafter for several hours, as shown in Table I1 (with 2-cm cells and OY2 filters). TABLE I1 RATE OF COLOUR DEVELOPMENT Optical densities for standing times of- r---- - -3 2 6 10 16 30 1 2 3 minutes minutes minutes minutes minutes hour hours hours Boron-free blank .. 0.424 0.423 0.420 0.418 0.418 0.421 0.419 0.422 With 0.003 per cent. 'Af boron added . . 0-751 0.766 0.764 0.763 0.765 0.766 0.763 0.768 Optical density bi boroh'addition 0.327 0.343 0.344 0.346 0.347 0.346 0.344 0.346 In the rather highly concentrated sulphuric acid medium required to keep certain anthraquinone derivatives in solution, many metal sulphates, especially those of iron(I1) and iron(III), are relatively insoluble and largely precipitate on raising the acidity to the prescribed level, but complete sedimentation may be rather prolonged. In the procedure adopted for use with the HPTA reagent, however, the precipitated sulphates separate fairly quickly and are removed before applying the boron colour test. As considerable heat is liberated when adding concentrated sulphuric acid to the sample aliquot, a protective glove should be worn during handling.Contraction on cooling should be allowed for. By the time the solution has cooled down to room temperature a slight cloudiness usually remains, but this can be removed completely by transferring some of the cloddy solution into a dry test-tube, warming it until the sulphates in suspension re-dissolve, then allowing it to cool again. Re-precipitation does not occur in the time required to complete the remainder of the procedure. To determine if any significant amount of boron was absorbed in the iron(I1) sulphate precipitate, the precipitates recovered from a boron calibration test were washed several times by stirring them in concentrated sulphuric acid and decanting off after settling; they300 BELL AND MCARTHUR : COLORIMETRIC DETERMINATION [~4,rtabSt, VOl.93 were then dissolved in 20 per cent. sulphuric acid and tested for boron by the proposed procedure. With the boron-free test as the standard of reference, the results given below show that none of the precipitates appears to have absorbed any measurable amount of boron. Optical densities were measured with 2-cm cells and OY2 filters. Original boron addition, per cent. . . Nil 0.001 0.002 0.003 0.004 0.006 0.006 Optical densities of sulphate precipitates 0.501 0.502 0.502 0.503 0602 0.603 0.603 The boron colour is developed by mixing 10 ml of the clear sample solution, after removal of the precipitated sulphates, with 10 ml of HPTA reagent in a stoppered test-tube or other suitable vessel, then measuring the optical density due to boron, as described in the procedure.A representative boron calibration, in which the Hilger photo-electric colorimeter was used, with 2-cm cells and OY2 filters, is given in Table 111. TABLE I11 CALIBRATION Optical densities r ~p Boron added, per cent. . . Nil O*OOP 0.002 0.003 0.004p’ As found .. .. . . 0-410 0.542 0.672 0-802 0.913 Less nil-boron blank . . - 0.132 0.262 0.392 0.503 The results given in Table IV show the reproducibility and accuracy of the proposed method, as applied to several B.C.S. standard steels. TABLE IV REPRODUCIBILITY OF RESULTS OBTAINED ON B.C.S. STANDARD STEELS AND COMPARISON WITH CERTIFICATE VALUES B.C.S. No. 273 277 326 327 328 329 330 Number of tests 14 9 23 26 23 6 6 Boron found, per cent.r 7 Range Average A 0.0024 to 0.0026 0.0025 0-0002 to 0.0004 0*0003 0*00106 to 0.0013 0.001 18 0*0029b to 0.0033 0.00306 0*00396 to 0.0042 0*00406 0.0081 to 0.0083 0-0082 0.0071 to 0.0073 0.0072 Boron, per cent. certificate value 0.0025 < 0.001 0.001 0.003 0.004 0.008 0.007 The above British Chemical Standard steels, which were supplied by the Bureau of Analysed Samples, Middlesbrough, are of the low alloy type, and have been accurately standardised for several elements, including boron. INTERFERENCES- None of the common residual elements, in the low concentrations normally occurring in carbon and low alloy steels, adversely affects the boron - HPTA colour reaction. Titanium interferes when present in appreciable amounts by altering the colour of the reagent, but this interference is negligible in samples containing less than 1 per cent.Elements that have coloured ions and are soluble in concentrated sulphuric acid solution, such as chromium, molybdenum and vanadium, increase the blank proportionately when present and would require appropriate compensation. Oxidising agents and nitrates, which either destroy the reagent or change its properties, should be absent. Reducing agents such as sulphites or iron(I1) sulphate do not interfere. Iron(I1) sulphate mostly precipitates in a dense form that settles out satisfactorily. Iron(II1) sulphate, on the other hand, separates in a voluminous form under the same conditions, so that only the minimum amount of iron(II1) should be present.The proposed method has been found to be applicable, even when considerable amounts of the more common alloying elements, in addition to iron, are present, provided compensation can be made for any increase in optical density by these elements. This is shown in Table V, all of the elements indicated being added in metallic form.May, 19681 OF BORON IN CARBON AND STAINLESS STEELS 301 TABLE V NET EFFECT OF LIMITED AMOUNTS OF CERTAIN ALLOYING ELEMENTS ON OPTICAL DENSITIES Optical densities Iron only + + + + + + + + + .. .. i.i,ofCi .. . . 20% of Cr . . .. 8yoofNi .. .. 0-5y0 of Ti . . .. 1% of Ti . . .. 1%of Mo . . .. 1%of v .. . . 1%of Nb .. .. l%of cu . . .. r Total 0-195 0.216 0.594 0.234 0.206 0.217 0.214 0.198 0-216 0.195 I Boron absent 1 Increase caused by added element - 0.021 0.399 0-039 0.01 1 0.022 0.019 0-003 0.02 1 Nil With 0.003% of boron addeci r Total 0.353 0.367 0-752 0-392 0-364 0-377 0.369 0.355 0-377 0.352 Net increase caused by added boron 0.168 0.151 0.158 0.158 0.158 0.160 0.155 0.167 0.161 0.157 Before the proposed method could be applied to alloy steels of unknown composition, it was necessary to find some way of obtaining a compensating blank, so that the net optical density due to the boron present could be obtained. Attempts to remove boron from the sample solution were either unsuccessful or inconvenient, but it was found that the presence of fluoride inhibited the boron colour reaction without affecting the optical density of the alloy solution.The addition of a soluble fluoride, before adding the HPTA reagent, therefore, allows a compensating optical density for the alloy components present to be obtained.Any pick-up of boron from the action of fluoride on the borosilicate glassware used is also inhibited. The optical density of the reagent is slightly altered by the fluoride addition and this varies to some extent between different batches of reagent but, as it can also be compensated for, the accuracy of the boron determination is not affected. The procedure adopted for obtaining a compensating blank for alloy samples is as follows. A 15-ml aliquot of the dissolved sample, after the sulphate precipitate has been removed, is transferred into a 50-ml test-tube containing 0-05g of sodium fluoride and heated, with occasional shaking, until. the sodium fluoride is dissolved.When cold, 10 ml of this fluoride- treated solution is mixed with 10ml of HPTA reagent solution, and the optical density measured under the same conditions as adopted for the boron colour test. The action of fluoride on the reagent is found by treating some of the nil-boron standard with sodium fluoride in a similar manner, and the difference in optical density before and after fluoride treatment applied as a correction to the compensating optical density. The application of this procedure to a stainless-steel sample is shown in Table VI, optical densities being measured in l-cm cells with OY2 filters. TABLE VI COMPARISON OF BORON CALIBRATIONS MADE IN PURE IRON AND IN STAINLESS-STEEL SOLUTIONS AFTER SODIUM FLUORIDE COMPENSATION Optical densities I h Boron added, yo .. . . No fluoride present . . . . Optical density due to boron addition . . .. .. After fluoride treatment . . Change in optical density of reagent after fluoride treat- ment .. .. . . Optical density due to boron after applying compensat- ing blank and reagent cor- rection . . .. .. Pure iron Stainless steei f A > r A -l Nil 0.001 0.002 0.003 Nil 0.001 0.002 0.003 0.230 0.300 0.368 0.436 0.645 0.714 0.784 0-854 - 0.070 0.138 0.206 - 0.069 0.139 0.209 0.276 0.276 0.277 0.277 0.690 0-692 0.691 0-692 + 0.046 + 0.045 - 0.070 0.137 0.206 - 0.067 0.138 0.207302 BELL AND MCARTHUR: COLORIMETRIC DETERMINATION [AutabSt, Vol. 93 The compensating optical density obtained for the stainless-steel sample in Table VI is 0.046 high because of the action of fluoride on the reagent but, as the same increase also occurs in the nil-boron standard simultaneously treated with fluoride, this correction is easily made.High-chromium steels are not readily soluble in dilute sulphuric acid and, in addition, the iron(I1) sulphate precipitate settles out very slowly so that the procedure, as applied to to these alloys, takes much longer to complete. High-nickel heat-resisting alloys may also contain boron and were included in the investigation, but as no actual samples were available synthetic metallic mixtures of equivalent composition were used instead. In these materials it was found that nickel sulphate, when in high concentration , does not separate satisfactorily, post-precipitation occurring on warming during fluoride treatment but, if when making the concentrated sulphuric acid addition to the sample aliquot the temperature is raised to between 120" and 130" C after half of the acid has been added, this difficulty is overcome.Alloys of this type are best processed on half-sample weight. In both high-chromium and high-nickel materials sulphate separation is rather slow, but filtration through a dry glass-fibre filter, after most of the precipitate has settled out, has been found effective in giving a clear solution in a reasonably short time. Table VII gives comparative calibrations for boron additions to pure iron, two B.C.S. stainless steels, two synthetic stainless steels and two synthetic high-nickel alloys. All of the tests were processed together with the same batch of reagents; optical densities were measured in l-cm cells with OY2 filters.TABLE VII COMPARATIVE BORON CALIBRATIONS IN A WIDE RANGE OF ALLOY COMPOSITIONS AFTER SODIUM FLUORIDE COMPENSATION Optical densities t \,, r L I Nil-boron blanks Boron added, yo A After fluoride Composition Direct* treatment? Difference# 0.001 0.002 0-003 B.C.S. No. 149/1 . . .. . . 0.192 0.230 +0.038 0.061 0.123 0.181 Cr, 18% + Ni, 8% + Fe, 74% . . 0.673 0.612 +0*039 0.068 0.116 0.176 Cr, 18% + Ni, 8% + Mo, 2.6% + Cu, 2% + Ti, 1% + Fe, 68.6%$ . . 0.661 0.693 +0*042 0.062 0.123 0.181 B.C.S. No. 236/2 (Cr, 18% + Ni, 8% + Ti, 3%) . . .. .. . . 0,635 0.673 +0*038 0.062 0.122 0.184 B.C.S. No. 261 (Cr, 17% + Ni, 13% + Nb, o-7y0) . . .. .. . . 0.718 0.759 +0*039 0-063 0-123 0.179 Ni, 76% + Cr, 20% + Ti, 2.6% (3 Ni- monic SOA)$II .. .. .. . . 0.382 0.425 +0*043 0.062 0.120 0.182 Ni, 66% + Cr, 20% + CQ, 20% + Ti, 2.6% (Nimonic 9O)JII. . .. . . 0.423 0.463 +0-040 0.058 0.118 0.178 Average boron calibration . . .. - - - 0.061 0.121 0.180 Average effect of fluoride on reagent . . - - +0.040 - - - * As obtained in the boron-free tests. ?As obtained in the sodium fluoride treated tests. $ Increase in optical density of reagent in the presence of fluoride. f All components added in metallic form. 11 Processed on half of the standard weight because of the high nickel and titanium contents, but received the same boron addition as the other tests. The boron calibrations obtained after applying the net compensating blanks are prac- tically the same in all of the above tests and confirm that the alloying constituents in the proportions indicated do not materially affect the determination of boron in complex nickel- chrome alloys by the proposed method.It is also apparent that when fluoride is used to obtain a compensating blank a boron reference calibration prepared from boron additions to pure iron is applicable to both carbon and alloy steels.May, 19681 OF BORON IN CARBON AND STAINLESS STEELS 303 As the four stainless-steel compositions quoted in Table VII show the same boron calibration, whether or not the component elements have been fused together, it is quite probable that the simulated Nimonic compositions will be the equivalent of the commercial alloys as far as the application of the proposed boron procedure is concerned.METHOD FOR THE COLORIMETRIC DETERMINATION OF BORON IN CARBON AND STAINLESS STEELS PRINCIPLE- After dissolution of the metal in dilute sulphuric acid, the acid concentration is increased to the prescribed level, and the precipitated sulphates are allowed to settle out. An aliquot of the cold clear solution is then mixed with an equal volume of the boron reagent solution and the optical density measured in a suitable photo-electric colorimeter. For alloy steels a compensating blank is obtained by treating a second aliquot with sodium fluoride to inhibit the boron colour reaction. RANGE- The range is 0 to 0*004 per cent. on the full sample weight. REPRODUCIBILITY- of +04002 per cent. APPLICATION- The method is applicable to all carbon steels and low alloy steels containing less than 1 per cent.of titanium. An extension of the method is applicable to highly alloyed steels of the stainless type and possibly also to heat-resisting high-nickel alloys. APPARATUS- any material absorption of boron occurring. 26-mm diameter test-tubes. A linear calibration graph is obtained up to 0-003 per cent., with a reproducibility Use preferably boron-free glassware, although borosilicate glassware can be used without Test-tubes-150 x 25-mm diameter nominal, marked at 10 and 15 ml, are suitable. Air condenser-About 60-cm lengths of glass tubing, with rubber stoppers to fit the Calibrated JEasks4O-ml capacity, with polythene stoppers. Specimen tubes-30-ml capacity, with leak-proof polythene caps, or any other suitable type of stoppered vessel.Photo-electric colorimeter-The Hilger “Spekker” instrument, with tungsten lamp, heat- resisting filters, 1 and 2-cm cells and Chance OY2 filters, or instruments of similar type, can be used. REAGENTS- Sulphuric acid solutions-2, 20, 50, 75 and 85 per cent. v/v and concentrated. Boron colour reagent-Prepare a 0@05 per cent. w/v solution of l-hydroxy+-toluidino- anthraquinone (HPTA) in 85 per cent. v/v sulphuric acid solution for the total-boron pro- cedure and in 75 per cent. v/v sulphuric acid for the acid-soluble boron procedure. Dissolve it in the cold, with shaking, and prepare freshly each day. Use the same batch of reagents with each group of tests and standards. It is made by several manufacturers; that made by I.C.I. Ltd., is sold under the trade name Waxoline purple A.l-Hydroxy-4-~-toluidinoanthraquinone is Solvent Violet 13 (Colour Index 60725). Ammonium persulphate solution-Prepare a 25 per cent. solution in distilled water. Iron(II) sulphate, analytical-reagent grade. Boron-free iron, B.C.S. 149/1 pure iron granules. Sodium carbonate, analytical-reagent grade, anhydrous. Sodium fluoride, analytical-reagent grade. Boric acid, analytical-reagent grade. Standard boron solutim A-Dissolve 0.0572g of boric acid in 1OOml of 20 per cent. sulphuric acid.304 BELL AND MCARTHUR : COLORIMETRIC DETERMINATION [Analyst, Vol. 93 Standard boron solution B-Dilute 10ml of standard boron solution A to 100ml with 20 per cent. sulphuric acid. 1 ml of solution contains 0~0o0010 g of boron. 1-5 ml of solution contains 0*001 per cent.on a 1.5-g sample weight. PROCEDURE FOR THE DETERMINATION OF TOTAL BORON CARBON AND LOW ALLOY STEELS- Preparation of sample solution-Transfer 1.5 g of drillings into a marked test-tube, add 13.5 ml of 20 per cent. sulphuric acid from a burette, fix the air condenser in position, then heat the tube gently until the drillings are dissolved. When dissolution is complete, add 0.25 ml of 25 per cent. ammonium persulphate solution to oxidise most of the carbonaceous matter, boil for a few minutes, then allow the solution to cool. Wash down the condenser with about 0 4 m l of distilled water, remove it from the test-tube, then make the volume of the solution up to the 15-ml mark and mix thoroughly. Filter through a dry No. 40 Whatman or similar filter-paper and collect it in a clry test-tube.Transfer a 10-ml aliquot to a 50-ml calibrated flask before iron(I1) salts begin to crystallise out. Now transfer all of the acid-insoluble matter on to the filter, wash it with 2 per cent. sulphuric acid, until free from iron salts, then with water until acid-free. Place 0.5g of sodium carbonate in the filter, transfer it into a platinum crucible, dry, ignite and fuse for 5 minutes. Dissolve the cold melt in 15 ml of 50 per cent. sulphuric acid containing 0.1 g of iron(I1) sulphate in solution to reduce chromates, etc., if present. Transfer 10 ml of this solution into the 50-ml calibrated flask containing the 10-ml aliquot of the main filtrate. Precipitation of iron(II) and other fairly insoluble sulphates-To the combined aliquots of the soluble and insoluble parts of the sample, representing 1-g sample weight, add concen- trated sulphuric acid, with occasional swirling, to the 50-ml mark, then add a further 2.5 to 3-0ml from a burette, depending on the temperature attained, to allow for contraction on cooling.Set aside to cool, by which time the precipitate should have settled out and the volume returned to the 50-ml mark. Decant off about 15 ml of the almost clear solution into a dry test-tube and warm it to re-dissolve any sulphate haze that may be present, then allow it to cool. Development of the boron colow-Transfer 10 ml of the clear sample solution into a 30-ml specimen tube or bottle, add 10 ml of the 0.005 per cent. HPTA reagent, replace the stopper or cap, mix the solution and allow it to stand for a few minutes for full colour development.Measure the optical density under standard conditions. Convert the optical densities thus obtained into percentages of boron by using a calibration graph prepared simultaneously with the tests. Preparation of a refeyence graph-Place 1.5 g of pure iron into five marked test-tubes, add in sequence, 0, 1.5, 3.0, 4.5 and 6-0ml of standard boron solution B, then make each solution up to exactly 13.5 ml with 20 per cent. sulphuric acid. These standards represent nil, 0-001, 0.002, 0.003 and 0.004 per cent. of boron, respectively. Carry this series through the prescribed procedure, together with the unknown sample. Measure the optical densities against water, with 2-cm cells and OY2 filters.Plot the optical densities obtained, after subtracting the boron-free blank reading, against the respective boron contents. The calibration graph is linear up to 0.003 per cent. For higher boron contents use a smaller sample weight and make up to 1*5g with pure iron. Stopper the flask and mix its contents thoroughly. HIGHLY ALLOYED STEELS- Use the same procedure as prescribed for carbon steels when the boron content is not more than 0.004 per cent. and the titanium content not more than 1 per cent. For higher boron and titanium contents use a reduced sample weight and make it up to 1.5 g with pure iron. Pass the sample solution, after most of the sulphate precipitate has settled out, through a dry glass-fibre filter to obtain a clear solution.To develop the boron colour add 10ml of HPTA reagent to a 10-ml aliquot of the prepared sample solution in a stoppered, glass test-tube or bottle, mix the solution and allow it to stand for a few minutes, then measure the optical density with 1-cm cells and OY2 filters.May, 19681 OF BORON IN CARBON AND STAINLESS STEELS 305 To obtain a compensating blank add 0.05 g of sodium fluoride to a 15-ml aliquot of the prepared sample solution, warm and shake it vigorously to assist dissolution, then allow to cool. Add 10ml of HPTA reagent to 10ml of this sodium fluoride treated solution, mix and measure the optical density, as for the boron colour. To obtain a correction for the action of sodium fluoride on the reagent, treat a 15-ml aliquot of the nil-boron calibration standard with sodium fluoride in exactly the same way, and simultaneously with the com- pensating blank, and apply the difference in optical density of the nil-boron standard, before and after fluoride 'treatment, as a correction to the compensating blank. Prepare a boron reference calibration graph in the same manner as for carbon steels. Refer the net optical density obtained, after deducting the corrected compensating blank, to the boron reference graph to obtain the amount of boron present in the alloy steel. HIGH-NICKEL HEAT-RESISTING ALLOYS (PROVISIONAL)- Treat as for highly alloyed steels, but use not more than half-sample weight because of the high nickel content. Make up to 1.5 g total weight with pure iron. When making the concentrated sulphuric acid addition, heat to between 120" and 130" C after half of the acid has been added to obtain a satisfactory separation of nickel sulphate. Continue thereafter as for highly alloyed steels. PROCEDURE FOR THE DETERMINATION OF ACID-SOLUBLE BORON- Use the same general procedure as described for carbon or highly alloyed steels, but discard the insoluble residue and omit the 10-ml addition of 50 per cent. sulphuric acid prescribed for dissolving the fused residue. Use a solution of the HPTA reagent in 75 per cent. sulphuric acid to balance the consequently higher acidity of the sample solution. REFERENCES 1. Rudolph, G. A., and Flickinger, L. C., A~zalyst, 1943, 68, 384. 2. Trinder, N., Ibid., 1948, 73, 494. 3. Radley, J. A., Ibid., 1944, 69, 47. First received June 24th, 1965 Amended May 9th, 1967

ISSN:0003-2654    

DOI:10.1039/AN9689300298

出版商:RSC    

年代:1968

数据来源: RSC

摘要:

306 Arcalyst, May, 1968, Vol. 93, +$. 306-310 The Determination of Magnesium in Silicate and Carbonate Rocks by the Titan Yellow Spectrophotometric Method BY W. H. EVANS (Ministry of Technology, Laboratory of the Government Chemist, Cornwall House, Stamford Street, London, S.E.l) A method is proposed involving an initial separation of ammonia group elements by means of a succinate precipitation, followed by a spectrophoto- metric determination of magnesium with Titan yellow reagent; calcium interference is minimal. Satisfactory agreement with the pyrophosphate gravimetric method is obtained for a wide range of magnesium values in silicate and carbonate rocks. THE existing pyrophosphate gravimetric method of determining magnesium in silicate and carbonate rocks is time consuming and tedious; the need exists for a more rapid method also applicable over a wide range of values of magnesium.The possibilities are complexo- metric titration, involving the difference between two titrations and giving rise to large errors at the lower end of the scale ; atomic-absorption photometry that requires expensive equipment for precise results; and spectrophotometric methods. The majority of methods proposed for the latter are based on the deposition of a dyestuff on magnesium hydroxide to form a strongly coloured lake in alkali-metal hydroxide solution; they are subject to many interferences, in particular from ammonia group elements. Of these reagents the triazole dye, Titan yellow, has been used most often. In its recent applications to the determination of magnesium in silicates ,l *2 s3 masking reagents to overcome interference from ammonia group elements are used, and buffering to high concentrations is recommended to overcome inter- ference from aluminium and calcium.These additions tend to affect the stability of the lake and impair the reproducibility of results. A procedure is described wherein the ammonia group elements are removed by a double succinate precipitation, and in the spectrophoto metric method described calcium interference is largely nullified. EXPERIMENTAL SPECTROPHOTOMETRIC DETERMINATION- Of many colloids examined as stabilisers for the Titan yellow lake, poly(viny1 alcohol) , or sodium polyacrylate, in conjunction with glycerol has proved superior.* The spectrophoto- metric procedure described by Bradfield: in which a 0-001 per cent.solution of Titan yellow, 0.01 per cent. poly(viny1 alcohol) and 10 per cent. glycerol final concentration are used, provided a suitable basis and, with modification, gave excellent reproducibility. It was found desirable to keep the alkali strength as low as possible as poly(viny1 alcohol) reacts with alkali to give a complex absorbing at 490 mp. A final volume of 50 ml was used to decrease interference from other elements. Under these conditions, and measuring at 540mp, a smooth calibration graph could be drawn between 5 and 60pg of magnesium that was substantially linear between 10 and 50 pg. Several authors396 have examined the variation in the composition of the Titan yellow dyestuff in detail recently, while subsequent to their work King, Pruden and Janess recom- mended a procedure for the preparation of a refined Titan yellow reagent.A commercial 0 SAC; Crown Copyright Reserved.EVANS 307 product, Titan Yellow C.I. 19546 (Clayton yellow) reagent for magnesium, supplied by Hopkin and Williams Ltd., was used for this investigation and proved satisfactory at a 0*001 per cent. final concentration. INTERFERENCES- The effect of low level concentrations of interfering elements on the spectrophotometric measurement, referred to above, is shown by the results summarised in Table I; at higher levels interference increases rapidly. TABLE I EFFECT OF LOW LEVEL CONCENTRATIONS OF INTERFERING ELEMENTS ON MAGNESIUM DETERMINATIONS Magnesium concentration , p.p.m. 0.3 0.6 0.9 0.3 0.6 0.9 0.3 0.6 0.9 0-6 0.6 0.8 0-6 Error at varying concentrations of interfering elements, per cent.A r \ Interfering element 0.1 p.p.m. 0.2 p.p.m. 0-4 p.p.m. 1.0 p.p.m. 2.0 p.p.m. (as oxide) + 1.2 Nil Nil + 1.2 + 2.0 + 0.4 Nil + 1.2 Nil Nil Nil Nil Nil Nil - 1.0 - 2.2 + 1.3 - 0.4 - 0.4 + 1.2 + 2.0 + 0.4 - 0.7 Nil Nil Nil - 1.2 - 2.0 - 2.6 - 2.6 - 4.6 - 1.3 + 6.4 + 4.6 + 2.1 - 1.3 + 1.2 - 0.4 - 2.7 - - Fe - - Fe - Fe - - Al - - Al - - Al - - Mn - - Mn - - Mn - - Ti + 0.7 Nil Ba - - 1.4 Sr -0.7 - 1.2 P(as PsO,) + 1 mg of CaO The spectrophotometric measurement is sensitive to ammonium salts, hence an am- monium hydroxide precipitation of ammonia group elements followed by oxalate removal of calcium cannot be considered without subsequent removal of all ammonium salts.Willard and Tang7 precipitated aluminium quantitatively by means of a succinate precipitation under carefully controlled conditions. These involved the gradual hydrolysis of urea to ammonia to give a final pH of 4-4; calcium, magnesium and the greater part of the manganese did not interfere. It has now been found that 99 per cent. separation of both calcium and magnesium is possible by a single rapid precipitation of ammonia group elements by using sodium succinate and a final pH of 6.0; this separation becomes quantitative, for both synthetic mixtures and rock solutions, with a second precipitation. The quantity of succinate has little effect on the result of the spectrophotometric determination, except for a slight blank not exceeding 3 pg of magnesium per gram of succinate, and has the added advantage of controlling the initial pH of the solution used for spectrophotometric measurement.The levels of iron and titanium in the resulting solution are negligible. Fluoride interferes seriously in the separation of aluminium, giving rise to levels in excess of the limits imposed by the results shown in Table I. All but the last traces of fluoride could be removed after wet decomposition of samples, by evaporating to fumes once with a small volume of concen- trated sulphuric acid before applying the succinate precipitation to the final perchloric acid solution. If this condition was fulfilled, aluminium levels (as alumina) in all samples did not exceed 0.16 p.p.m. Manganese, as manganese oxide, enhanced the magnesium figure for concentrations greater than 0.2 p.p.m.; the incompletely separated manganese after a succinate precipitation is at a level not exceeding this concentration. Similarly phosphate, in the presence of calcium, and barium and strontium, are seldom present in silicate and carbonate rocks at levels sufficient to cause interference in the spectrophotometric deter- mination (Table I); the effect of the remaining commonly occurring trace elements could be disregarded. The effect of different concentrations of calcium varies with the amounts of magnesium present (Fig. 1); a level of calcium equivalent to 110 p.p.m. of calcium oxide could not be exceeded by this method. Attempts to diminish this effect with altered alkali conditions or by using differential solubilities or complex formation of the calcium and magnesium salts as carbonates, borates, tungstates, hydroxy acids or dibasic acids were unsuccessful.Inter- ference could be lessened by increased glycerol concentration but this was impractical because308 EVANS: DETERMINATION OF MAGNESIUM IN SILICATE AND CARBONATE [Ana(ySt, VOl. 93 of the difficulty in handling solutions of high viscosity. Sucrose, at a 0.3 to 0.4 per cent. concentration, however, was effective and had no detrimental effect on the spectrophotometric determination. Fig. 1 indicates this to be so for the concentrations of calcium most likely to be encountered in rock analysis. Calcium oxide concentration, p.p.m. (log scale) Fig. 1 Effect of different concentrations of calcium (as oxide) on known magnesium content: 0, with sucrose; x, without sucrose METHOD REAGENTS- Reagents should be of analytical-reagent grade.HydroJuoric acid, 40 per cent. vlv. Perchloric acid, 60 per cent. v/v. Sodium succinate solution, 0-05 per cent. Glycerol. Sucrose. Sodizlm hydroxide solution, 8 per cent. w/v. Titan yellow solution, 0.2 per cent. w/v-Dissolve, with boiling, 50 mg of poly(viny1 alcohol) in 20 or 30 ml of distilled water, add 100 mg of a suitable sample of Titan yellow and dilute to 50 ml. Titan yellow reagent-Dissolve, with boiling, 100 mg of poly(viny1 alcohol) in 20 or 30 ml of distilled water. Decant the solution into a 200-ml flask, add 5 ml of the 0.2 per cent. Titan yellow solution, 4 g of sucrose and 100 ml of glycerol. Magnesium standard soldion-Dissolve 0.603 g of clean magnesium ribbon in 10 ml of perchloric acid and dilute to 1 litre.This solution contains the equivalent of 1 mg of mag- nesium oxide per ml. Dilute this solution to give a working solution containing 5 pg of magnesium oxide per ml, and adjust to pH 6 with 0.05 per cent. sodium succinate solution. A Hilger Uvispek spectrophotometer or equivalent instrument is suitable for the measurement of optical densities. PROCEDURE- Decompose 1 g of silicate or carbonate rock with 20 ml of hydrofluoric acid by digestion overnight in a platinum or PTFE basin. Add 5 ml of perchloric acid and evaporate to dryness on an air-bath. Repeat the evaporation, until no further fumes are evolved, with three further separate 5-ml portions of perchloric acid, to the first of which are added 2ml of sulphuric acid (1 + 1).Finally dissolve the residue in 5 to 10 ml of perchloric acid and dilute to 200 ml. This solution retains its activity for some months. Dilute to 200 ml.day, 19681 ROCKS BY THE TITAN YELLOW SPECTROPHOTOMETRIC METHOD 309 Dilute 20 ml of this solution (equivalent to 100 mg of rock) to 40 ml and adjust to pH 2 with the aid of a pH meter by adding 8 per cent. sodium hydroxide solution. Add 2 g of sodium succinate and a Whatman accelerator, boil for 2 to 3 minutes and allow to settle. Filter the solution through a Whatman No. 40 filter-paper into a 200-ml graduated flask, washing the precipitate with a 0.05 per cent. sodium succinate solution. Re-dissolve the precipitate with 1 ml of perchloric acid, re-precipitate as above, and make the solution up to 200 ml.Withdraw a suitable aliquot (1 to 20 ml) of the solution containing 10 to 50 pg of magnesium, and dilute to 30 ml in a 50-ml flask (pre-washed with acid). Add by pipette, successively, 10ml of the Titan yellow reagent and 5ml of 8 per cent. sodium hydroxide solution, shaking the solution after each addition; dilute to 50 ml. After 1 hour measure the optical density in 2-cm cells at 540 mp. Prepare a series of standards containing from 0 to 50 pg of magnesium at the same time, and plot a curve of the optical density, corrected for the blank value, against magnesium present. A blank determination for the entire procedure should be carried out concurrently; this should not exceed the equivalent of 0-2 pg of mag- nesium per mg of rock.RESULTS TABLE I1 RECOVERY OF MAGNESIUM ADDED TO ROCKS OF LOW MAGNESIUM CONTENT Magnesium as mg of magnesium oxide present 0.16 0.19 0.17 0.38 0-25 0.25 Magnesium as mg of magnesium oxide added 0.20 0.20 1.00 1.00 5.00 15.0 Magnesium as mg of magnesium oxide recovered 0.37 1.20 1.38 5-28, 6-22 15-26, 15.23 0.38, 0.39 Recoveries obtained for the entire procedure for synthetic mixtures containing magnesium at the 0.50, 1.00, 5.0 and 15.0-mg levels, together with iron, aluminium, titanium and calcium, average 99.9 per cent., with a relative standard deviation of 0.016. Recoveries of magnesium added to rock material low in magnesium content are shown in Table 11. In this case the mean value of recovery is 100.3 per cent., with a relative standard deviation of 0.015.TABLE I11 COMPARISON OF MAGNESIUM VALUES OF SOME SILICATE AND CARBONATE ROCKS Magnesium oxide, Magnesium oxide, per cent. (Titan yellow) 0.39, 0.38 1.89, 1-85, 1-86 6-74, 6.67 per cent. (gravimetric) Granite G.I . . .. .. 0.38, 0.39. 0-37 0.41,* 0.35T Tonalite T.l . . .. .. 1-84, 1.86, 1.86 1.89 Diabase W.l . . .. .. 6.67, 6-62, 6-63 6.62,* 6.52t Granite . . .. * . .. 0.15 0-17 Olivine-basalt . . .. .. 4.70 4.74 Olivine-basalt . . .. .. 10.2 10.2 Tremolite-schist . . .. .. 19.1 19.1 Limestone . . .. .. 0.23 0.20 Limestone . . .. .. 4-73 4.70 Limestone . . .. .. 7.06 7-08 Dolomite. . .. .. .. 14.7 14.8 Porphyritic granophyre . . 0.78 0.80 All values recorded are averages of duplicate determinations. * Preferred value.* T Preferred value.s This method has been applied to some eighty silicate and carbonate rocks, and the values within the range 0-2 to 20.0 per cent.of magnesium oxide compared with results obtained by the gravimetric pyrophosphate procedure. The maximum differences from the gravimetric values were -0.20 and +0.27 per cent. The correlation coefficient was calculated as 0.998,310 EVANS with a relative standard deviation of 0.014. Comparative figures for a few rocks are shown in Table 111. The solution obtained after succinate precipitation of ammonia group elements is also a suitable medium for the complexometric determination of calcium. This paper is published by permission of the Government Chemist and the Director, Institute of Geological Sciences. 1. 2. 3. 4. 6. 6. 7. 8. 9. REFERENCES Shapiro, L., Chemist Analyst, 1969, 48, 73. Meyrowitz, R., Amer. Miner, 1964, 49, 769. King, H. G. C., and Pruden, G., Analyst. 1967, 92, 83. Bradfield, J., Analytica Chim. Ada, 1962, 27, 262. Hall, R. J., Gray, G. A., and Flynn, L. R., Analyst, 1966, 91, 102. King, H. G. C., Pruden, G., and Janes, N. F., Ibid., 1967, 92, 696. Willard, H. H., and Tang, N. K., Ind. Engng Chem. Anatyt. Edn, 1937,9, 367. Fleischer, M., and Stevens, R. E., Geodim. Cosmodim. Ada, 1962, 26, 626. Ingamells, C. O., and Suhr, N. H., Ibid., 1963, 27, 897. Received June 20th, 1967

ISSN:0003-2654    

DOI:10.1039/AN9689300306

出版商:RSC    

年代:1968

数据来源: RSC

摘要:

Adyst, May, 1968, Vol. 93, pp. 311-318 311 Origanum Oils and their Investigation by Gas-chromatographic and Infrared Spectroscopic Analysis BY C. CALZOLARI, B. STANCHER AND G. PERTOLDI MARLETTA (Istituto di Merceologia, UniwersitG di Trieste) A gas-chromatographic study of the essential oil of origanum has been carried out with both capillary and packed columns. Furthermore, some new components of the essential oil of origanum were found by coupling preparative gas-chromatographic analysis and infrared spectroscopy. WE have frequently observed that spices of various geographic origin have different organo- leptic characteristics, indicating that the environmental conditions of the plant growth influence the composition of aromatic components of the spice. To determine the possible variations we examined the essential oil that is extracted from the plant.The present paper deals with the examination of oil of origanum obtained from samples of different origin and its characterisation by gas-chromatographic analysis. The composition of the essential oil of origanum has already been partially studied,lJ,* and the presence of some of the main components recorded. In order to define accurately the aromatic properties of the essential oil of origanum, it was examined by gas-chromatographic methods, and the substances separated were identified by infrared spectroscopy. By this procedure almost all of the constituents of the essential oil that were present in amounts greater than 0.1 per cent. were identified. The examination was carried out on five samples of commercial essential oil of origanum and four samples distilled in our laboratory from origanum grown in Greece (var.Heraclaeotium), Turkey (var. Onites), Spain (var. floribundum Munby) and Italy (Sicily) (var. Gracile). Gas-chromatographic analysis of the oils was carried out with packed columns and capillary columns of different diameters. SAMPLE PREPARATION- The essential oil of origanum was extracted by steam-distillation according to the A.0.A.C.4 method. The commercial samples were supplied by the following firms: Bertrand Freres, Grasse, France (stated Lebanese origin) ; Dragoco, Milano, Italy; Esperis, Milano, Italy (stated Italian origin) ; Valerio, Milano, Italy (stated Italian origin) ; Viansino, Milano, APPARATUS- Analytical and preparative gas chromatograph-Wilkens Instrument and Research Inc., Aerograph Moduline, Model 1521-1, dual column, equipped with a dual thermal conductivity detector, two flame-ionisation detectors and linear temperature programmer. Gas chromatogra$h-C. Erba (Milano, Italy), Fractovap, Model D, dual column, equipped with linear temperature programmer, flame-ionisation detector, constant flow of pressure and completely modular. Spectrophotometer-Perkin-Elmer, Infracord, Model 137, double beam. GAS-CHROMATOGRAPHIC ANALYSIS- The following columns were used. (A) Stainless-steel column, 2 metres long, 0.d. 4 inch, packed with 10 per cent. Carbowax 20M on silanised Chromosorb (80 to 100 mesh); carrier gas nitrogen. The Wilkens gas chromatograph was used with flame-ionisation detector. (B) Stainless-steel column, 7 metres long, i.d.1 mm, packed with 2 per cent. Carbowax 20M on silanised Chromosorb (100 to 120 mesh) ; carrier gas nitrogen. The Erba gas chroma- tograph was used with flame-ionisation detector. EXPERIMENTAL Italy. 0 SAC and the authors.312 CALZOLARI et al. : ORIGANUM OILS AND THEIR INVESTIGATION BY [Analyst, Vol. 93 (C) Stainless-steel column, 30 metres long, id. 0.25mm, coated with Carbowax 20M (C. Erba's capillary column); carrier gas nitrogen. The Erba gas chromatograph was used with flame-ionisation detector. (D) Stainless-steel column, 50 metres long, i.d. 0*25mm, coated with Carbowax 20M (C. Erba's capillary column); carrier gas nitrogen. The Erba gas chromatograph was used with flame-ionisation detector.(E) Aluminium preparative column, 2 metres long, 0.d. 4 inch, packed with 20 per cent. Carbowax 20M on Chromosorb AW (60 to 80 mesh); carrier gas helium. The Wilkens gas chromatograph was used with thermal conductivity detector. (F) Aluminium preparative column, 10 metres long, 0.d. Q inch, packed with 20 per cent. Carbowax 20M on Chromosorb AW (60 to 80 mesh); carrier gas helium. The Wilkens gas chromatograph was used with thermal conductivity detector. PROCEDURE- The preparative gas-chromatographic analysis of the essential oil of origanum was carried out by first fractionating on a 2-metre fractionating column that separated the oil into five main fractions. Thus the main component, carvacrol, which is present in amounts up to a possible maximum of 83 per cent., was eliminated.Each of the fractions then underwent preparative gas chromatography on a 10-metre column (2500 theoretical plates), which allowed a better separation. The best conditions for analysis were chosen for each fraction and the separated compounds were collected on dry ice - acetone at -70" C. The samples were then analysed by infrared spectroscopy.K RESULTS AND DISCUSSION For the qualitative and quantitative determination of the essential oil, the Kovats Indexes6 (Table I) and the areas for each of the peaks were calculated as percentages. Table I1 shows a more accurate percentage composition for the results previously reported (see Note I in Calzolari, Pertoldi Marletta and Stancher' and Note I1 in Pertoldi Marletta and Stancher*), which had been obtained with a shorter column. To compare the results obtained by the various columns, the peaks were numbered by reference to the number of peaks separated by capillary column (D).The 2-metre 10 per cent. Carbowax 20M column was used for these determinations, as less satisfactory results had been obtained with other stationary phases previously tried (Apiezon L, Apiezon M, methylsilicon polymer SE30, butanediol succinate, LAC3 R-728, polydiethyleneglycol succinate, LAC2 R-446, polydiethyleneglycol adipate) . As an example, Fig. 1 shows the chromatogram obtained from the essential oil extracted from Greek origanum. 3 In I Fig. 1. Greek origanum on column A, sample 0.2p1, programme temperature 65 to 220" C (rate 4" C per minute), nitrogen flow 9 ml per minute, injector temperature 270" C, detector temperature 230" C, sensitivity = 4 x 10Peak number 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 29b (Spain) 29b (Esfieris) TABLE I KOVATS INDEXES CALCULATED FOR EACH COLUMN Columns A + > + + + + + + + + + + > + + + + + + + + -t- + + + + + + + + + + + + + + May, 19681 GAS-CHROMATOGRAPHIC AND INFRARED SPECTROSCOPIC ANALYSIS Mark + indicates the resolved peaks in each column examined.B + > + + + + + + + + + 3- + + + + -4- + + + + + + + + + + + + { + -t + + + + + + + + + + + + + + C + > + + + + + + + + + + + + + + + + + + + + + { + + { + + ( + + + + + + + + + + + + + + i- + -1- + + + + + D + + + + + + + + + + + + + + + + + + + + + + + -+ { + + { + + -I- + + + + + + + 4- + + + 3- + + + + + + + + + + + Kovats Index A 1025 } 1042 1090 1135 1156 1175 1196 1212 1233 1268 1296 ) 1370 1438 1470 1534 1558 1570 1621 1645 1694 1715 1750 1763 1773 1836 1870 1946 1984 2021 2118 2152 2181 2264 1630 1645 Kovats Index D 1010 1023 1030 1072 1113 1129 1153 1162 1172 1178 1200 1212 1225 1239 1251 1281 1291 1338 1389 1437 1450 1466 1495 1538 - ) 1548 1564 { 1595 1610 1634 1647 1674 1692 1701 1715 1726 1741 1759 1771 1834 1867 1894 1929 1972 1985 2094 2118 2126 2137 2171 2252 1595 1595 313 Table I1 shows that both the commercial origanum oils and the oils we extracted contained the same components, although in different amounts.314 CALZOLARI et al.: ORIGANUM OILS AND THEIR INVESTIGATION BY [Analyst, Vol.93 TABLE I1 RESULTS OF THE QUANTITATIVE ANALYSIS FOR THE LABORATORY-EXTRACTED AND COMMERCIAL OILS OF ORIGANUM Laboratory-extracted oils Commercial oils f A A \ r > Greece Turkey Spain Italy Bertrand Dragoco Esperis Valerio Viansino per cent. per cent. per cent. per cent. per cent. Peak Areas, Areas, Areas, Areas, Areas, Areas, Areas, Areas, Areas, number per cent. per cent. per cent. per cent. 1 v 4 6 8 9 10 11 12 ;: } ;; } 2 } 16 16 21 22 25 26 27 28a 28b* 29a 29bi 32 36 37 39 40 41 42 43 44 E } 2 } 47 0.03 0-96 0.14 0.10 0.93 traces 0.86 0.11 0.22 traces 3-67 6.90 0.04 0.22 0-13 traces 0.19 0.10 traces 0.85 1.05 traces 0-50 0.74 1.53 traces 0.10 0.1 1 0.08 traces traces 0.24 0-12 - - 0.02 0.31 0.28 0.03 0.4 1 traces 0.47 0.17 0.23 traces 1.90 2-27 traces 0.16 traces traces 0.39 0.04 traces 1-44 0.82 traces 0.1 1 3.15 2.46 traces 0-36 0.27 0.03 traces traces 0.36 0.37 - - 0.03 1.69 0.30 0.32 2.13 traces 2.22 0.26 0.36 6.50 23.00 12.64 0.19 0.2 1 0.04 traces 0.93 0.58 traces 13.30 3.32 traces 0.09 1.42 4-63 traces 0.43 0.14 traces traces traces 0.78 1-56 - - traces 1.13 0.03 0.10 1.31 traces 1.66 0.1 1 0.77 7.82 6.01 0.02 0.26 0.30 traces 2.60 0.12 4-87 0-67 - - - - traces 0.61 0.77 1.60 traces 0.66 - - 0-23 0.14 - - 0.03 2.00 0-12 0.21 2-20 traces 2-22 0.32 0.20 traces 6.68 9.60 0.63 0.89 0.7 1 0.02 0-17 0.20 traces 0.63 2-41 traces 0-03 0.51 0.17 traces 0.09 0.12 0.03 traces 0.02 0.53 traces - - traces 1.86 0.24 0.27 1-36 traces 0.91 0.26 0.72 traces 1-66 14-12 0.01 0.30 0.33 traces 2.64 0.08 traces 1-35 3.46 traces 0.76 1.33 0.68 0.09 0.14 0.16 0.04 - - - - 0.64 - traces 0.66 0.04 0.08 0.28 traces 0.23 0.06 0.32 traces 0.46 2.14 0.04 0.14 0.06 0.47 0.38 0.02 0.40 1-64 13.64 traces 0.51 0.07 traces 0.06 0.04 0.02 - - - - - 0.06 - 0.04 1.94 0.10 0 21 2.16 traces 2.04 0.26 0.21 traces 6.03 8.59 0-46 0.76 0.7 1 traces 0.19 0.10 traces 0.80 2.26 traces traces 0.56 0.03 0.09 0.04 0.10 0-08 traces traces 0.14 traces - - 0.04 1-64 1-16 0.20 1.91 traces 2.06 0.36 0.45 traces 4.68 7.75 0.26 0.63 0.40 0.01 0.82 0.03 1.03 2-75 traces 0.02 1-62 0-23 0.19 0.23 0.04 traces traces 0-60 - - - - - 60 6-19 0.86 18.34 69.90 31.28 1.60 1-24 18-83 21.21 61 74-90 83.10 4-66 9.33 38.67 66.21 76-08 63-29 49.08 62 traces traces traces traces traces 0.22 0.08 traces 0.70 * Peak 28b is present only in the Spanish essential oil and was identified with No.17 (Spanish) (see Note I11 in Stancher and Pertoldi Marlettas). t Peak 29b is present only in the essential oil, Esperis, and was identified with No. 18 bis (see Note I11 in Stancher and Pertoldi Marlettab). of Table I11 lists the constituents we identified and the methods we used for the identification each comDonent. PreparGive gas chromatography was used in the analysis of all nine available essential oils in order to ascertain whether the same components were always present. Only in the essential oil of origanum, Esperis, was the component, peak number 28b, and in the Spanish essential oil the presence of the component, peak number 29b, found (Table 111). The possibility of changes in composition of the terpene compounds during gas-chromato- graphic analysis had previously been ~uggested,~ but pure terpene compounds that we subjected to successive preparative gas-chromatographic analysis and infrared analysis showed no alteration.1°May, 19681 GAS-CHROMATOGRAPHIC AND INFRARED SPECTROSCOPIC ANALYSIS TABLE I11 IDENTIFICATION OF COMPONENTS IN ESSENTIAL OIL OF ORIGANUM 315 Identification methods A I t Peak number 2 3 4 6 8 10 11 12 13 16 16 19 21 22 23 26 26 28a 28b 29a 29b 32 36 37 39 40 46 60 61 62 To Compound Bicyclic or tricyclic terpene .. .. Camphene .. .. .. .. 8-Pinene .. .. .. .. Myrcene . . .. .. .. .. a-Terpinene . . .. .. .. Limonene .. .. .. .. 1.8-Cineole . . .. .. .. Pentyl alcohol . . .. . . . . y-Terpinene .. .... .. p-C ymene .. .. .. Primary alcohol. . .. .. .. a-Pinene . . .. . . . . .. Most likely aliphatic secondary alcohol Secondary or tertiary terpene alcohol Chain-branched aliphatic alcohol . . Linalol . . .. .. .. .. Primary unsaturated alcohol . . . . Aromatic ether . . .. .. .. Secondary alcohol . . . . . . Borneo1 . . .. .. .. .. Carvone .. .. .. .. .. Secondary terpene alcohol . . .. Caryophyllene . . .. .. .. Sesquiterpene? . . .. .. .. Sesquiterpene . . .. .. .. Aromatic compound . . .. .. Polyterpene hydrocarbon . . .. Thymol .. .. .. .. .. Phenolic compound . . .. .. Carvacrol .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. Infrared spectra + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + Elemental analysis + + + + + + + + + + + + + + Me1 ting- nh0 point + + + + + + + + + + + + + + + + + + ascertain the relationship between the chromatographic resolution and the number of plates used, we carried out a gas-chromatographic analysis of a sample of essential oil of origanum with columns of different diameter each packed with Carbowax 20M.Columns B, C and D were used for this purpose and Table IV shows the number of plates and the standard effective peak number11 of all analytical columns used so far. TABLE IV COMPARISON OF EFFICIENCIES OF THE PACKED AND CAPILLARY COLUMNS Theoretical plates Standard effective Column number peak number A 2700 4-8 B 6600 7.1 C 9000 8 D 14,600 9 The standard effective peak number of a column is the effective peak number calculated for the consecutive alkanes, which are eluted at retardation ratios of about 5-0.11 Figs.2, 3 and 4 show the chromatograms obtained on columns B, C and D. The resolution obtained on our capillary columns did not improve the separation, especially for column B . Some new peaks of minor constituents were noted, and in some instances the separation between adjacent peaks improved. Moreover, it is interesting to note that this did not occur with peaks Nos. 28 and 29, which overlapped in the capillary column.316 CALZOLARI et al. : ORIGANUM OILS AND THEIR INVESTIGATION BY [Autalyst, Vol. 93 _1 Fig. 2. Greek origanum on column B, sample 0 . 2 4 , programme temperature 65 to 220" C (rate 4.5" C per minute), nitrogen flow 2.6 ml per minute, by-pass 26 ml per minute, injector temperature 270" C, detector temperature 230" C, sensitivity = 4 x 10 51 tli W 50 Fig.3. Greek origanum on column C, sample 0 . 1 ~ 1 , programme temperature 65 to 220" C (rate 4.5" C per minute), nitrogen flow 1 ml per minute, by-pass 45 ml per minute, injector temperature 270" C, detector temperature, 230" C, sensitivity = 4 x 1 2f 37 I 36 35 29 16 N m X Fig. 4. Greek origanum on column D, sample O-lpl, programme temperature 65 to 220" C (rate 4.5" C per minute), nitrogen flow 1 ml per minute, by-pass 50 ml per minute, injector temperature 270" C, detector temperature 230" C, sensitivity = 4 x 1May, 19681 GAS-CHROMATOGRAPHIC AND INFRARED SPECTROSCOPIC ANALYSIS 317 However, the 50-metre column gave the best resolution and Table I shows the new Kovats Indexes of the single peaks. CONCLUSIONS In the gas-chromatographic analysis of essential oil of origanum we used various columns of different diameters and lengths to study the relationship between the numbers of plates used and the resolution obtained.For this investigation we used two packed columns: (A), 2 metres long, 0.d. Q inch; and (B), 7 metres long, i.d. 1 mm, and two capillary columns, 30 and 50 metres long. In the four kinds of columns examined we retained Carbowax 20M as the stationary phase because previous results had shown it to be the best. The percentage areas were calculated only for packed column (A), as in the other three gas-chromatographic columns the use of a by-pass was necessary to inject a minimum amount of sample into the column.This by-pass can sometimes lead to the components injected into the column being selected according to their volatility and consequently to an erroneous quantitative evaluation. The chromatograms obtained with the packed column B were particularly satisfactory, as the resolution obtained with this column could be compared with the resolution with the capillary column. This study has shown that it is unnecessary to use capillary columns to obtain a good definition of the components of the essential oils, as a long packed column of small diameter containing a small percentage of stationary liquid phase on a silanised support can often yield satisfactory results. Thus the disadvantages of the capillary columns, vix., high cost, short life and difficulty of coating in the laboratory are eliminated.The preparative gas-chromatographic analysis of nine different kinds of essential oils of origanum (five commercial oils and four laboratory-extracted oils) increased our knowledge of the components of this oil and established the presence of nine constituents not previously identified in essential oil of origanum. Furthermore, we obtained the infrared spectra of fourteen other substances that are contained in this essential oil. These substances were only partially identified, as direct comparison with the pure compounds was not made and this alone could give more accurate information about them. However, the fourteen compounds were classified with satisfactory accuracy, and, whenever possible, the refractive index was determined and elemental analysis carried out, although frequently the amount available was only sufficient for an infrared spectrum to be obtained. Of the fourteen partially identified components, two belonged to different oils, vix., No.28b was present only in the Spanish origanum essential oil and No. 29b in the origanum essential oil, Esperis. Thirty components were totally or partially identified, and the presence confirmed of seven other components that had not been previously described in the literature. The possibility of isomerisation or changes in composition of the terpene compounds during the preparative gas chromatography was studied by analysing various pure terpenes, first by preparative gas-chromatographic analysis and then by infrared spectroscopy. This control did not show any alteration in our experimental conditions. The quantitative composition of the origanum oils examined varied according to their place of origin.Therefore, the quantitative area-percentage results obtained from chromato- grams could supply sufficient indication to establish the origin of the spice, although examination of a series of samples of the same origin would be necessary to form a more complete picture. The results obtained demonstrate the advantages of coupling preparative gas-chromato- graphic analysis and infrared spectroscopy for the isolation and identification of the com- ponents of mixtures such as essential oils. Results are more accurate by this method than by the method of comparison of retention times with those of known compounds, which is inaccurate when carried out on high-resolution capillary columns. REFERENCES 1. 2. 3. 4. Fenaroli, G., Sostanze aromatiche naturali,. 1963, I, 796. Blake, M. I., Analyt. Chem., 1958, 30, 400. Ikeda, R. M., Stanley, W. L., Vannier, S . H., and Spliter, E. M., Fd Res., 1962, 27, 455. 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., 1965, p. 472.318 6. 6. 7. 8. 9. 10. 11. CALZOLARI, STANCHER AND MARLETTA Stancher, B., and Pertoldi Marletta, G., Ann. Facoltb di Economia e Commercio, Universita Messina, Italy, Atti del V Convegno della Qualitb, 10-12 Settembre 1966, Anno IV, N. 2, p. 663. Kovats, E., Helv. Chim. Ada, 1968, 41, 1916. Calzolari, C., Pertoldi Marletta, G., and Stancher, B., Universitb degli Studi di Trieste, Facolta di Economia e Commercio, Istituto di Merceologia, Pubbl. N. 28, 1966, p. 1. Pertoldi Marletta. G., and Stancher, B., Universitb degli Studi di Trieste, Facoltb di Economiae Commercio, Istituto di Merceologia, Pubbl. N. 29, 1966, p. 1. Zubyk, W. J., and Conner, A. Z., Analyt. Chem., 1960, 32, 912. Stancher, B., and Pertoldi Marletta, G., Rass. Chim., 1967, 3, 99. Perry, S. G., and Hurrell, R. A., J. Gas Chromat., 1966, 3, 2. Received Azsgust lst, 1967

ISSN:0003-2654    

DOI:10.1039/AN9689300311

出版商:RSC    

年代:1968

数据来源: RSC

摘要:

Analyst, May, 1968, Vol. 93, $$. 319-322 319 The Determination of Trace Amounts of Methallibure in Pig Meals BY H. E. HUDSON AND B. PEARSON (Imperial Chemical Industries Limited, Pharmaceuticals Division, Hurdsjield Industrial Estate, Maccksjield, Cheshire) A method has been developed for determining trace amounts of methal- libure in pig meals. Because of the difficulties to be overcome in developing a method for this purpose, it was first necessary to isolate the methallibure from the meal constituents, by using column partition chromatography, and to determine its concentration by monitoring the eluent fractions spectro- photometrically. The solvent partition system used also resolves the active agent from its decomposition product, and the method is, therefore, applicable to stability studies.METHALLIBURE (1-cc-methylallyl-6-methyldithiobiurea), I, is a veterinary drug used to synchronise oestrus in pigs; it is marketed for this purpose as a pre-mix (I.C.I. Ltd., “Aimax”), which is subsequently diluted with pig meal. C&= CH.CH.NH.C.NH.NH.C.NH.CH, II S LH, S II I It is readily soluble in methanol and shows an absorption maximum at 250 mp (E:2m = 1250) ; this property can be used for its determination in pre-mixes containing inorganic diluents. The detemination of methallibure in pig meals is more difficult for the following reasons. (1) Simple solvent extraction to remove the active agent from the meal also removes meal constituents and hence produces a high level of background absorption in the ultraviolet spectrum. (2) Methallibure has been shown to oxidise in meals to give 2-a-methylallylamino- 5-methylamino-l,3,4-thiadiazole, 11.I1 This compound has an absorption maximum in methanol at 273 mp (EiZ = 489) and exerts appreciable absorption at 250 mp, the absorption maximum of methallibure itself (see Fig. 1). (3) It has been observed that methallibure is unstable in methanol extracts of meals. This instability is attributed to incompatibility with some methanol-soluble component of the meal, as yet unidentified. Therefore, the present work was undertaken with the object of developing a method of assay specific for methallibure and applicable to a wide range of meals containing an active agent content of between 50 and 100 p.p.m. 0 SAC and the authors.320 0.7 0.6- E m 0.5- v x 2 0'4- aJ U 8 0.3- n U .- - - U 0 0.2- 0.1 HUDSON AND PEARSON: DETERMINATION OF TRACE [ArtfZ&St, VOl.93 - - 'I Wavelength, mp Ultraviolet spectra for : A, meth- allibure; and B, the decomposition product of methallibure in methanol Fig. 1. EXPERIMENTAL For reasons already stated, it is advisable to separate the drug from any degradation product and to remove, or minimise, contamination from solvent-soluble meal constituents. Column-partition chromatography has been used for this purpose, and it has been shown that the active agent can be isolated by direct application of the medicated meal to the column, followed by elution in the normal way. Under these conditions, the bulk of the eluent-soluble meal constituents leave the column in the first three fractions, but trace amounts influence the first absorption minimum of the methallibure chromatogram (see Calculation of results).There is no indication that methallibure is unstable in the partition - solvent system used. By using the procedure described below, evidence was obtained for the isolation of the methallibure from its oxidation product and is presented in Fig. 2, which shows the characteristic chromatogram for the active agent obtained from a sample of methallibure to which has been added 50 per cent. of its oxidation product. Confirmation of the presence of methallibure was obtained from the ultraviolet spectrum of the eluent in fractions 32, 34 and 42 (Fig. 3). I I I I l l I 10 20 30 40 50 Fraction number Wavelength, mp Fig. 2. Evidence for the isolation of methallibure from its oxidation product Fig.3. Methallibure contaminated with 50 per cent. of its decomposition product: A, fraction 34; B, fraction 32; and C, fraction 42 METHOD APPARATUS- fitted with a sintered disc and tap, was used. Chyomatographic column-A column of 700-mm length and 20 to 23-mm internal diameter,May, 19681 AMOUNTS OF METHALLIBURE IN PIG MEALS 321 REAGENTS- Acid-washed Celite-Transfer 500 g of Celite 545" into a 3-litre beaker and add 2 litres of concentrated hydrochloric acid. Stir the mixture to an even paste and allow it to stand, with periodical stirring, during 12 hours. Decant the bulk of the acid and suspend the residue in 1 litre of water. Filter through a Buchner funnel and wash the residue with water until free from acid.Continue the washing with 500 ml of methanol, and finally wash with 1 litre of a mixture of equal parts of analytical-reagent grade methanol and ethyl acetate. Dry the residue at about 100" C until free from solvent odour. Hexalze-The optical density of the hexane, when read in a 1-cm cell at 254 mp against a 1-cm cell air blank, must not exceed 0.7. If the optical density reading is greater than 0.7 the hexane must be purified as described below. Transfer 10 litres of hexane and 100ml of oleum (20 per cent. sulphur trioxide) into a suitable container and stir rapidly with a stainless-steel stirrer for 30 minutes. Separate the oleum and add an excess of crushed ice. Wash the hexane successively with two 1-litre volumes of water, two 1-litre volumes of 5 per cent.sodium hydrogen carbonate solution and two 5-litre volumes of water. Dry the washed hexane over anhydrous calcium chloride and distil it, collecting the fraction boiling between 65" and 68" C. SOLVENT SYSTEM- purpose reagent grade formamide and 100 ml of hexane. 5 minutes and allow it to stand for 45 minutes before use. phase and the lower layer the eluent phase. Transfer into a 2-litre separating funnel 900 ml of chloroform B.P., 100 ml of general- Shake the mixture vigorously for The upper layer is the stationary PREPARATION OF STANDARD- Accurately weigh about 30 mg of pure standard methallibure and dissolve it in 100 ml of stationary phase. Add 2.0ml of this solution to 4 g of acid-washed Celite, contained in a 100-ml beaker, and mix well. PREPARATION OF SAMPLE- transfer it into a 100-ml beaker containing 4 g of acid-washed Celite and mix well.Accurately weigh sufficient meal to contain about 0-25 to 0.5mg of active agent and PREPARATION OF CHROMATOGRAPHIC COLUMN AND SUBSEQUENT TREATMENT- Transfer 25 g of acid-washed Celite into a 250-ml beaker and add 12.5 ml of stationary phase with a 20-ml straight-sided pipette. Thoroughly mix the stationary phase with the Celite and lightly pack the mixture into the column, adding the mixture in portions of about 3g, and packing down with a tamper after each addition. Add the dry sample mixture reserved from Preparation of sample to the top of the stationary phase in the column, taking care to carry out this latter operation quantitatively. Open the tap at the bottom of the column and carefully add eluent phase to a depth of about 12 inches above the packing.Continue the development with eluent phase and collect successive 10-ml volumes of eluate in 6 x 1-inch stoppered test-tubes. Collect sixty-two fractions and add to each fraction 3 - O m l of analytical-reagent grade methanol and mix well. Measure the optical density of each fraction in a 1-cm cell on a suitable spectrophotometer at 253 mp (the absorption maxima for methallibure in the eluent phase) against a reference solution consisting of 10 ml of eluent phase and 3.0 ml of analytical-reagent methanol. Repeat the above procedure by using the standard mixture reserved from Preparation of standard in place of the sample. The recommended time for a 10-ml fraction is 12 to 2 minutes.CALCULATION OF RESULTS Methallibure in pig meal produces a non-symmetrical chromatogram (Fig. 4) caused by trace contamination with eluent-soluble meal excipients. The residual absorption is determined by drawing a line to strike the minima of the chromatogram tangentially, and * Johns-Manville Co. Ltd., 20, Albert Embankment, London, S.E.l.322 HUDSON AND PEARSON I I I I 10 20 30 40 50 Fraction number Fraction number Fig. 4. Methallibure in pig meal Fig. 6. Methallibure the absorption minima are read. The average of these two values gives the residual absorp- tion. Then, 2 Optical densities between minima of sample peak - (residual absorption x number of fractions) X Optical densities between minima of standard peak - (residual absorption x number of fractions) x 100 Weight of standard (mg) Weight of sample (mg) = Percentage w/w of methallibure content. RESULTS AND DISCUSSION Samples were chosen to cover a wide variation of meal composition and analysed by the proposed method, after fortification with known amounts of methallibure. Figs. 4 and 6 show typical chromatograms for a medicated meal and for methallibure; the results shown in Table I illustrate quantitative recovery of methallibure. The proposed method gives results well within the accuracy usually considered acceptable for products of this type. TABLE I RECOVERY EXPERIMENTS ON DIFFERENT PIG MEALS FORTIFIED WITH ADDED METHALLIBURE Methallibure initially present, p.p.m. 100 100 100 100 100 880 880 880 880 Methallibure recovered, p.p.m. 104 100 100 97 97 860 870 840 860 Received November 13th, 1967

ISSN:0003-2654    

DOI:10.1039/AN9689300319

出版商:RSC    

年代:1968

数据来源: RSC

摘要:

Analyst, May, 1968, Vol. 93, f+. 323-325 323 Efficiency of Extraction of Metabolically Incorporated HEOD (Carbon-14) from Pheasant Tissues, Eggs and Faeces BY YVONNE GREICHUS, DONALD LAMB AND CLIFFORD GARRETT (Experiment Station Biochemistry De#artment, South Dakota State University, Brookings, South Dakota 67006, U.S.A.) Acetonitrile partitioning and Florisil column procedures were examined for efficiency of extraction and purification of HEOD (carbon-14) residues. Fat, liver, eggs and faeces from pheasant hens fed with 1.5mg of HEOD (carbon-14) were used. Gas - liquid chromatographic analysis of HEOD- fortified controls gave results similar to those obtained by liquid scintillation counting when samples were extracted and purified with a Florisil column. Analysis by liquid scintillation counting showed that recoveries of HEOD (carbon- 14) from fortified controls compared favourably with recoveries of HEOD (carbon-14) that had been metabolically incorporated into the tissue for both the partitioning and Florisil column procedures.It was concluded that gas - liquid chromatographic analysis of a fortified control sample gave an accurate measurement of the recovery of HEOD from tissues in which the HEOD was metabolically incorporated within the range of concentrations studied. SAMPLE fortification, or "spiking," is commonly used to determine the efficiency of extraction and isolation of pesticide residues from biological tissues. By using this method, McCully and McKinley1 recovered 73 to 112 per cent. of thirteen pesticides added to mutton and beef fat.Similarly, Parker, Dewey, DeVries and Lau2 obtained 29.4 to 103 per cent. recovery of twelve chlorinated organic insecticides added to human fat. With this method it is assumed that pesticides that have been metabolically incorporated into tissue are extracted with the same efficiency as pesticides added to the tissue just before analysis. The validity of this assumption has been investigated by using liquid scintillation counting and gas - liquid chromatography to analyse various samples from pheasants fed with carbon-14 labelled HEOD (1 ,2,3,4,10,10-hexach1oro-6,7-epoxy-1,4,4a,5,6,7,8,8a-octa- hydro-exo-lJ4-e~do-5 ,8-dimethanonaphthalene). METHODS REAGENTS- Hexane. Light petroleum, boiling range 30" to 60" C . A cetonitrile. Dichloromethane.These reagents used in this work were of Nanograde quality, obtainable from Mallinck- rodt Chemical Works, St. Louis. The maximum interfering gas - liquid chromatographic peaks are no greater than that produced by 10 ng per litre of heptachlor epoxide or 100 ng per litre of parathion: solvents of equal purity can be used. Sodium sulfihate, anhydrous , granular. Florid, 60 to 100 mesh, activated at 650" C-Prepare for use by heating for 12 to 14 hours at 140" C, adding 3 per cent. of distilled water, and storing in an air-tight container. Scintillation jZuid-Dissolve 100 mg of lJ4-bis-2- (5-phenyloxazolyl) benzene , scintillation grade, and 3 g of 2,5-diphenyloxazole. HEOD (carbon-14) , specijc activity 4 millicuries per millimole-This was checked for purity by gas - liquid and thin-layer chromatography and found to be radiochemically more than 99 per cent. pure HEOD.PROCEDURE- Fatty tissue, liver, eggs and faeces of pheasant hens that were fed with 1.6 mg of HEOD (carbon-14) by capsule and sacrificed within 1 week were used in this study. Similar samples 0 SAC and the authors.324 GREICHUS et aZ. : EFFICIENCY OF EXTRACTION OF [Arcalyst, Vol. 93 were also taken from pheasant hens that had received the capsule alone without any HEOD. The extraction and purification by acetonitrile partitioning and by Florisil column treatment were examined. Acetonitrile $artitioning-Samples for acetonitrile partitioning consisted of 2 g of fatty tissue from the pheasants fed with HEOD (carbon-14) and 2-g samples of fatty tissue from the pheasants not fed with HEOD.Similar samples of the latter tissue were used for both the blank and fortification with 0.002 mg (0-0066 microcurie) of HEOD (carbon-14) for testing the extraction procedures. Each sample was placed in 40 ml of hexane and homo- genised in a VirTis “45” homogeniser. One half of this homogenised sample was brought to dryness by using a Rinco rotating vacuum evaporator and reconstituted in 16 ml of scin- tillation fluid. To determine the amount of HEOD (carbon-14) before partitioning, this half was counted in a Packard Tri Carb, Series 3000, Liquid Scintillation Spectrometer. Scintillation samples were adjusted for quenching by comparison of counts, with and without an internal standard. The other half of each sample was partitioned with acetonitrile, as described elsewhere.a Each sample was placed in a 250-ml separating funnel and the HEOD partitioned into four 25-ml portions of hexane-saturated acetonitrile.The acetonitrile phase was combined with 500 ml of distilled water and the HEOD extracted with two 100-ml portions of light petroleum. The combined light petroleum extracts were washed twice with 100ml of distilled water, and the excess of water was removed by pouring the light petroleum through anhydrous sodium sulphate. After evaporating the light petroleum extracts to a small volume, it was analysed by liquid scintillation counting to determine the amount of HEOD (carbon-14) remaining after partitioning. FZorisiZ coZumn treatment-A Florisil column was used for the extraction and purification of fatty tissue, liver, eggs and faeces.The samples were taken from the same sources as those used in the acetonitrile partitioning. The entire content of each egg was homogenised before sampling. The faeces were dried in a forced-draught oven at 60” C to a constant weight and then finally ground with a mortar and pestle before sampling. Two-gram samples of fat, liver, egg and faeces from HEOD-fed pheasants were thoroughly mixed with 10 g of Florisil. These mixtures were then divided into two equal parts by weight. One part was used to determine the carbon-14 activity before it entered the Florisil column. To reduce quenching, this half was placed on 20 g of anhydrous sodium sulphate in a small column and eluted with 125 ml of a mixture of dichloromethane and light petroleum (1 + 1 v/v).The sample was brought to dryness, dissolved in 16 ml of scintillation fluid and counted. An internal standard was then used to determine the amount of any remaining quenching. Internal standards are not reliable if the quenching is too great, and this pro- cedure effectively reduced quenching. Losses of carbon-14 activity on the sodium sulphate column were determined by scintillation counting of the column material and found to range from 1 to 5 per cent. The carbon-14 activity values before entering the Florisil column were adjusted to take these losses into consideration. The second half of each mixture was extracted and purified by using the Florid-column method of Stemp, Liska, Langlois and Stadelman.4 The mixture was placed on top of 40 g of Florisil in a 20 x 400-mm column, and the HEOD eluted with 750 ml of 20 per cent.v/v dichloromethane in light petroleum. The eluates were then reduced to a small volume by using the rotating vacuum evaporator and made up to 10 ml. One 5-ml portion was counted and the other 5-ml portion analysed by gas - liquid chromatography. A 2-g sample of fatty tissue, liver, egg and faeces was also taken from pheasants that had received no HEOD. This was fortified with an amount of HEOD (carbon-14) similar to that metabolically incorporated in the treated pheasants. The fortified samples were treated by the same procedures for the determination of carbon-14 activity, before and after the Florisil column, and for gas - liquid chromatographic analysis as the metabolically incorporated HEOD (carbon-14) samples. The instrument used for gas - liquid chromatography was a Wilkens Aerograph HY-FI, model 600, equipped with an electron-capture detector cell that has a 250-millicurie tritium source.The &inch 0.d. x 5-fOOt Pyrex column was packed with 5 per cent. Dow-11 silicone on 60 to 80-mesh, HMDS-treated Chromosorb W and operated at 185” C, with a nitrogen carrier gas flow-rate of about 44 ml per minute.May, 19681 METABOLICALLY INCORPORATED HEOD (CARBON-14) 325 RESULTS The percentage recovery by acetonitrile partitioning was 89.9 and 79.4 for the meta- bolically incorporated HEOD (carbon-14), and 89.9 and 81.3 for the samples with added HEOD (carbon-14). Samples from pheasants that had received no HEOD (carbon-14) had counts similar to the background count.A comparison of the recoveries of metabolically incorporated and of added HEOD (cabon-14) from samples of fatty tissue, liver, eggs and faeces is shown in Table I for the Florisil column procedure. The samples contained from 0-4 to 40 p.p.m. of HEOD. Un- fortified samples gave the same count as background. The samples were checked for meta- bolites by gas - liquid chromatographic analysis with the Dow-11 column and on a similar column packed with 2 per cent. QF-1 silicone (fluoro) on 60 to 80-mesh, HMDS-treated Chromosorb W. Samples analysed by thin-layer chromatography revealed no radioactivity on the plate, except for the HEOD spot. The presence of undetected carbon-14 metabolites would lower the amount of carbon-14 recovered after extraction and purification of the HEOD.This did not appear to be a serious problem in this study because recovery of carbon-14 from fortified samples was similar to that of the metabolically incorporated HEOD (carbon-14) samples. TABLE I PERCENTAGE RECOVERY OF HEOD (CARBON-14) FROM FLORISIL COLUMN HEOD-fortified tissues Metabolically incorporated HEOD : r A \ scintillation counting Gas - liquid f A \ Scintillation chromatographic Sample Bird 1 Bird 2 Bird 3 Average counting analysis Fatty tissue . . 99 103 94 99 98 94 Liver .. .. 93 92 87 91 92 95 Eggs .. .. 90 91 88 90 91 94 Faeces . . . . 95 80 84 86 84 96 The results show that the recoveries of HEOD from the Florisil column are similar for the metabolically incorporated and the added insecticide and that the results by gas - liquid chromatographic analysis are similar to those obtained by scintillation counting. It is concluded that metabolically incorporated HEOD is efficiently extracted from several pheasant tissues by the techniques used. This paper is published with the approval of the Director of the South Dakota Agricul- tural Experiment Station as publication No. 790 of the Journal series. REFERENCES 1. 2. 3. 4. McCully, K. A., and McKinley, W. P., J . Ass. 08. Agric. Chew., 1964, 47, 652. Parker, K. D., Dewey, M. L., DeVries, D. M., and Lau, S. C., Toxic. Appl. Pharmac., 1965, 7 , 719. U.S. Public Health Service, 1965, “Pesticide Residue Analysis of Foods,” Training Course Manual, Stemp, A. R., Liska, B. J., Langlois, B. E., and Stadelman, W. J., Poult. Sci., 1964, 43, 273. Robert A. Taft Sanitary Engineering Centre, Cincinnati, Ohio L-2-1. Received September 4th, 1967

ISSN:0003-2654    

DOI:10.1039/AN9689300323

出版商:RSC    

年代:1968

数据来源: RSC