II I i I l 146 229 THS THE SPECTROGRAPHEC SENSITIVITY OF THE LEAD SPECTRAL LINE 2833.1 A0 Thesis for Hm Dogma cf M. S. MICHIGAN STATE COLLEGE Shiriey Marie Evécksan 1948 This is to certify that the thesis entitled "The Spectrosrgphie Sensitivity of the , . _ . .- , Au head opeotral hlne 235).l A. presented by Shirley Marie Ericxson has been accepted towards fulfillment of the requirements for __£L._S,degree in Physical Chemistry A 74%,. Major professoJ M495 THE SPECTROGRAPHIC SflSITIVITY OF THE LEAD SPECTRAL LINE 2833.1 A° By Shirley maria Eridkson A THESIS Submitted. to the School of Graduate Studies of Michigan State College of Agriculture and Applied Science in partial fulfillment of the requirements for the degree of ILiASTER OF SCIENCE Department of Chemistry 1948 \l’zam ACKNOWLEDGMENT The author wishes to express her appreciation and thanks to Dr. D. T. Ewing, Professor of Physi- cal Chemistry, for his guidance and counsel during the course of this investigation. ******#* ****¥* *i‘iflk #* * 216977 TABLE OF CONTENTS IIJTRODUCTION...OOOOOOOOCOOOCOOOOOOOC.0...... APPARATUS...OOOOOOOOIOOOOOOOOOOIOO0.0.000... mpg-RIIMTALOOOOOOOOOOOOCOO...0.0.0....0.... TABIJE ICC...OOOOOOOOOOOOOOOOOOOOOO0.0.0.0... TABLE 11.0...OOCOOOCOOOOOOOOOOOIOOOOOI00.... TABLE IIIOOOIOOOOOOOOCOOOOOOOOOOO0.00.0.0... TABLE IVOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO TABIE v0.0.0.000.000000...OOOOOOOOOOOOOOIOOO TABLE'VI.................................... ST-n'fl‘fA-‘RYOOOO....0OOOOOOOOOOOOOOOOOOOC00...... REFRE‘ICESOOOOOOOOOOOOOOOOOOOIOOOOOOOOOOOOOC INTRODUCTION It was found possible by examination of very dilute solu- tions to detect spectrographically an amount of 209 milli- micrograms of lead. The factors influencing the sensitivity of lead will be discussed in this paper. The optimum working conditions were determined by observing the variables such as: (1)diameter of electrodes, (2) means of drying, (3) effect of acid on electrodes, (4) exposure time, (5) excitation voltage, and (6) development time. The work was done by drying the solutions on pure copper electrodes and passing a high voltage spark between the electrodes. Certain copper lines from.the electrodes were used as an internal standard. On all the spectroscopic plates referred to in this dis- cussion the inductance was 0.32 millihenriee and the capaci- tance 0.0074 microfarads. These remained constant throughout the investigation. Density has been defined as the Log I°/i where 1° is the incident light intensity in the photometering beam, and I is the light transmitted at the plate. The method employed concerns utilizing a definite amount of the element placed on the electrodes. Throughout this investigation the lead line referred to will be 2835.1 A° and the copper line 2882.9 A°. APPARATUS The condensed spark apparatus consisted of 110 volt A. C. source, variac, voltmeter, step up transformer consisting of a 110 volt primary producing 25,000 maximum secondary potential, capacitor, and inductance coil. The direct current are source was employed for an iron are in enulsion calibration. The source was composed of a 220 volt direct current generator, voltmeter, ammeter, potential divider, and series of resistors. The electrodes were composed of specially pure, hard copper rods, 0.25 inch in diameter. The ends were made filat by machine ing on a lathe. other than iron,copper is customarily used as a metallic electrode. It acts quite differently from.the iron and cannot be held steady, having a tendency to wander from place to place over the end of the electrodes. If small electrodes were used to prevent this wandering, they would become so hot that they would bend.(1) A Bausch and lomb Littrow type quartz spectrograph was used in producing the photographic plates. Kodak Spectrum.Ana1ysis No. l_emu1sion type plates, 4 x 10 inches in size were used. These plates give a high gamma curve and result in good measure- ments over a limited concentration range. Kodak developer D-l9 and Kodak fixer were used in a developing tank that was agitated mechanically. A water thermostat regulated the constant temperature at 18° C. The Hilger microphotometer was used to measure the blacken- ing of the different lines on the photographic plates. The de- flection value of the line becomes the percent of light transmit- ted by the line if the clear plate reading is set at 100. A measurement such as this provides a correction for background, if present, as well as an indication for line density. Reference to the calibration curve (d/log I) of the negative will give the logarithm of intensity equivalent to this deflection. The differ- ence between the logarithm of intensity for the standard and the unknown will bear a linear relation to the logarithm.of percent of unknown element present.(2) In passing through any spectrograph, as through any optical instrument, light is lost through absorption in the lenses and prisms and thru reflection at each surface in the optics.(6) ~3- EXP ERIMEl-ITAL The solutions were prepared by adding 0.1599 grams of lead nitrate and diluting to 100 milliliters with 0.5% HCl (by volume). This gave a solution containing 0.1 gram of lead per 100 milli- liters of solution and was considered as the stock solution. From the stock solution.varying concentrations for the dilution series were made. The solutions were placed onto the electrodes by means of a measuring pipette graduated in hundredths of one milliliter. Two hundredths of a milliliter was used for each set of electrodes. During the initial part of the investigation the cathode (copper electrode) was machined on the lathe to produce a five degree convex surface while the anodes had a five degree concave surface. This procedure was discarded in favor of the flat end electrodes for no appreciable difference in sensitivity was obser- ved; the latter method also conserved time. The machined surface of the electrodes should be very smooth to prevent local concen- tration of the discharge.(4) The electrodes are resurfaced after sparking to remove the oxides present. It was found advantageous to discard the use of the more persistdnt lead line at 4057.1 A0 in favor of using the line at 2835.1 A0. This was done because in the first case duplication of the logarithmic ratio of the lead line to the background near the line was not constant for a given concentration. The varia- tion in some cases was greater than the readings themselves. The line at 4057.8 A0 has an arc and spark characteristic of 2000R and 300R respectively; the 2833.1 A° line has 500R and 80R arc and spark characteristics.(2) In an ideal procedure for quantitative spectroscopy there would exist a situation in.which all elements in the matrix enter the discharge, diffuse through it, and are excited to radia- tion at a uniform.relative rate, regardless of boiling points, atomic weights, vapor pressures, or excitation functions; or of variations in the discharge conditions; or of the time. Fortunate- ly it is not essential to have such an ideal or absolute source.(5) Carbon electrodes were arced with lead solutions but the cyanogen bands interfered with the lead lines in question; thus the copper electrodes were sparked. The sample solutions, 0.01 mililiter, were placed on the ends of each electrode; position'V on the spectrograph was uti- lized having a range of 2549 A0 - 3641.A°. The exposures were made for sixty seconds at a primary voltage of 50 volts. The slit width was taken as 42 microns (drum setting of 7). The weight used was 3 x 10-7 grams of lead on the electrodes in all cases where the weight was considered to be constant. The dia- meter of the electrodes was taken as 0.25"; the samples were dried in air for one hour, acid added and dried for one addi- tional hour. Table I shows that the sum of the deviations from the average values of the galvanometer deflections of the copper lines from copper electrodes less than 0.25" diametrically and two to three inches in length, was greater than the sum of the deviations for those electrodes with 0.25" diameter. TABLE I (Plate #27) DSVIATIONS OF GALVANOI‘dSTEiR DEFLECTIONS Diameter Galvanometer deflections deviations from mean Pb Cul Cu2 Cu3 Pb' Cul’ Cuz Cu3 (0.25" 20.8 22.5 18.9 15.7 < 0.25" 19.9 19.3 14.3 13.2 <:0.25" 20.3 '21.1 17.0 14.8 2.08 7.00 8.64 3.88 4<0.25" 21.4 18.2 13.2 13.7 <:o.25" 20.5 21.4 17.4 14.7 0.25" 21.0 21.5 17.5 13.5 0.25" 21.6 20.5 16.6 12.8 0.25" 19.9 19.8 15.7 12.0 2,§§_ 2.12 1.92 3.64 0.25" 21.4 20.8 16.5 12.5 0.25" 22.0 20.5_ 16.6 14.4 -6- It was found that the diameter of the copper electrodes at 0.25", as compared to those of less than 0.25", had no marked effect on the density of the lead line; the density of the copper line, which was used as an internal standard, was more constant and lower at a diameter of 0.25". The electrodes that were less than 0.25" were not of uniform diameter at the sparking ends due to machining the surface on the sides of the electrodes at vary- ing depths. The electrodes had no preliminary cleaning before sparking. Table II shows that a greater density for the lead and copper lines is obtained by reading the emulsion side of the plate on the densitometer as compared to the glass side in that the focal point is on the emulsion side causing the blackening to be more intense over a smaller area. The glass side covers a larger area for a particular line and results in a lower density value. This table also shows the consistency of the galvanometer deflec- tions for the uniform diameters of 0.25". -7- TABLE II (Plate #26) GAIVANOMETER DEFIECTIONS Diameter Emulsion side Glass side of Cu Pb Cu pr Dcu Pb Cu pr Dcu <.0.25" 21.4 11.5 .1881 .4578 23.4 16.6 .1079 .2570 <10.25" 23.8 20.9 .1419 .1984 25.0 22.9 .0792 .1173 ‘(0.25" 20.2 13.9 .2131 .3755 22.6 18.2 .1230 .2170 0.25" 24.2 19.6 .1347 .2262 25.1 21.8 .0774 .1386 0.25" 20.7 17.7 .2025 .2705 22.9 20.8 .1173 .1590 0.25" 21.3 18.7 .1901 .2467 23.2 21.3 .1116 .1487 A plate was made whereby half the electrodes, each pair con- taining 3 x 10-7 gram of lead in solution, were dried in the oven and the remaining half were dried in the air. The lead lines were absent and the copper lines were much lighter in those samples that were dried in the oven at 1000 C. for twenty minutes as com- pared to the samples that were dried in the air at room.temperature for one hour. The lead lines appeared and the copper lines were noticeably heavier in the latter case. The excitation conditions were identical. It appears that in the first case the lead nitrate combines with the moisture in the air forming a lead hydroxide and nitric acid; in the latter case the lead nitrate breaks down to lead dioxide and at 100° 0. the solid is volatilizad. When the solutions were left drying overnight or for a period of twenty- four hours, no lead lines or very faint lines appeared with no consistency. With the excitation conditions again remaining constant, a plate was made whereby half the samples had an additional 0.1‘ milliliter of 1% H01 (by volume) added to the end of each elec- trode. The additional H01 had no marked effect on the density of the lines; the lead samples were obtained in hydrochloric acid solutions which tend to increase the sensitivity of the lead. Sensitivity does not depend critically on the electrical characteristics of the spark source. Increase in the power leads to an increase in the initial intensity but increases the rate at which the sample is consumed and also increases the background intensity.(4) With the concentration and all other variables remaining constant, a plate was made to shOW'that the difference in excitation voltage had little effect on the sensitivity of the lead line. Excitation.voltages from twenty to sixty-five were used, and it was found that at a primary voltage of fifty a mini- mum galvanometer deflection resulted for the lead line in question; thus a maximum density resulted. Table III data is plotted to represent Fig. 1, which shows the relationship between primary voltage and the density ratio of copper to lead. A maximum den- sity ratio is obtained at 50 volts. TABLE III (Plate:%31) EFFECT OF PRIMARY VOLTAGE ON DENSITY RATIO Primary Galvanameter Deflection Density (log IOXE) Cu Voltage Pb Cu Pb Cu 55 20 27.3 24.5 .0409 .0879 .0470 25 27.3 24.8 .0409 .0826 .0417 30 25.2 22.2 .0757 .1307 .0550 35 27.2 26.3 .0425 .0571 .0146* 40 23.7 18.9 .1024 .2006 .0982 45 24.5 19.5- .0879 .1871 .0992: 50 21.1 14.2 .1528 .3248 .1720 55 20.6 15.5 .1632 .2868 .1236 60 22.0 18.4 .1347 .2123 .0776 65 22.5 19.1 .1249 .1961 .0712 the individual elements. * Not included because of incorrect timing. The rate at which a given element will come off varies wdth If another internal standard had been used besides copper, the maximum density ratio would have occurred at another point on the voltage scale. ‘With a conventional controlled spark source and a given capacitance across the secondary of the transformer there is a broad optimum.value for the inductance in the oscillating circuit.(4) -10— g; Pb Density'ratio .18 .1 . / \ / \ °l £3 .081 / \ . ‘ / , / .QQI CL 20 25 30 35 Lo 45 50 55 60 Primary'voltage 65 volts Fig. 1.- Relation between primary'voltage ang,density ratio of Cu 2882.9 A to Pb 2833.1 A . The optimum.exposure time was obtained by reading the back- ground density and line density over a varying period of time produced by a given spectra. It was found that the density of the lead line varied directly with the time in seconds up to seventy-five and upon.further exposure the density of the line in question remained the same. .Another plate was made whereby the lead and copper line pair was observed. A maximum.of 60 seconds was obtained when the density ratio of lead to copper was plotted against the time. From Plate #43 the data for Table This shows the relation- IV was obtained and plotted on Fig. 2. ship between the exposure time and the density ratio of lead to copper. TABLE Iv (Plate #43) DATA.FOR DENSITY RATIOS Time Galvanometer Deflection DenSity Pb (Seconds) Pb' Cu Pb Cu 05' 15 24.2 29.2 .0933 .0117 .0816 30 19.0 28.2 .1983 .0269 .1714 45 13.3 24.8 .3532 .0826 .2706 60 13.3 27.4 .3532 .0393 .3139 75 4 13.7 26.8 .3404 .0490 .2914 90 16.0 26.8 .2730 .0490 .2240 -11.. £5; Density ratio .32 .30 .28 .26 .24 .20 .18 .16 .11; .12 .10 /\ / \ \ / 7 / / 1 0 10 20 30 LO 50 60 70 80 Fig. 2.- Relation between sure time and density ratio of Pb 2833.1 A to Cu 2882.9 A . 90 seconds It was observed that the green spark changed to a blue color at the end of 60 seconds indicating that the sample was all con- sumed at that time, for the blue color is due to the copper itself being sparked. Fast emulsions are used in order to minimize the exposure times. Very fast emulsions have poor storage qualities and poor reproducibility from.batch to batch, making them undesirable for quantitative work based on comparision.with standard plates con- taining known concentrations. It is submitted that the copper spark method in general offers higher absolute sensitivity with greater reproducibility and more complete coverage using one set of conditions.(4) It should be noted that on a very humid day in- consistent results were obtained. The background readings near the measured lead and copper lines were discarded, for the blackening was not noticeable to affect the densities of the lead and copper lines. Crane (3) investigated the developing process in order to in- crease the sensitivity; he found that with respect to the develop- ment time that there was no appreciable change in density of the line after two minutes with D-ll developer. The plates in this investigation were developed for three minutes in D-19 developer at 180 C., placed in acid stop for thirty seconds, and fixed in the acid fixing bath for ten minutes, rinsed in running water for ten minutes and finally dried for five minutes on the plate drier. -12- The visual methods of determining sensitivities give results of relative accuracy; this accuracy may be increased by densitome- try with an internal standard, with some loss in sensitivity, the deviation depending upon the specific buffer used. On each plate an intensity calibration was made by using a motor driven step sector, the steps being in a ratio of 131.5. Table V from Plate #41, contains data for Fig. 3, which is the calibration curve which represents the density plotted against the logarithm of the relative exposure. The reflecting prism.was always removed after sparking; the iron arc was exposed for sixty seconds utilizing a step sector necessary for emulsion calibration. The shutter was opened after the iron arc was struck and closed before the arc was broken. -13- TABIE v (Plate $41) CALIBRATION CURVE DATA (IRON ARC) Step Galvanometer Deflectién Density Sector n log 1.5 E31 :52 F53 Pea. Fe2 Re3 l .176 25.6 27.6 ~—-- .0689 .0362 ---- 2 .352 23.3 25.5 ---- .1097 .0706 ---- 3 .528 20.1 22.5 27.5 .1739 .1249 .0305 4 .704 17.6 19.45 24.9 .2316 .1882 .0736 5 .880 15.3 17.3 22.2 .2924 .2391 .1234 6 1.056 14.1 15.3 19.7 .3279 .2924 .1753 7 1.232 12.4 13.5 17.6 .3837 .3468 .2243 Eel : 2813.3 A° Reg = 2869.3 A0 The highest line to background ratio occurs at the beginning of the exposure, so that the more the exposure is prolonged for a given set of conditions the Poorer will be the sensitivity. There is no advantage in long exposures from the standpoint of precision, since little sample light is being contributed at the end, in con- trast to the usual situation in the analysis of metal electrodes in which conditions are adjusted to give as nearly constant inten- (4) sity as possible. There has been much controversy as to whether (7) the arc or spark source has a greater sensitivity. McBurney -14... Density .40 .35 .30 .25 .20 .15 .10 .05 o‘q Fig. 3.- Plate calibration curve. 29/ .2 .h .6 .8 1.0 1.2 1.h Log E states that the high potential spark is best adapted to the quan- titative analysis of metals and alloys, such as Al, Zn, and steel, where the sample is of the proper size and shape to be machined or ground to a smooth, even surface on one side; it forms one electrode while carbon is the other. There greater sensitivity is desired, the arc is better in a given.set of conditions. For the determination of lead a working curve is shown in Fig. 4, obtained from Table VI; the data was taken from Plate #41. TABLE VI (Plate #41) WORKING CURVE DATA FOR LEAD BY SPARK METHOD 7W1. of Galvanometer deflection Density A Log intensity lead _8 T8'2833:18? Cu 2882.9A° (Log Ii/I) g x 10 25 Cu Pb Cu Pb/tu 20.9 29.0 23.7 .0074 .1024 0 .46 -.46 41.8 25.3 27.0 .0667 .0457 .33 .22 .11 62.7 24.9 26.8 .0736 .0510 .37 .25 .12 83.6 21.5‘ 26.1 . .1374 .0605 .58 .31 .27 104.5 19.5 26.2 .1798 .0588 .70 .30 .40 125.4 17.6 26.6 .2243 .0522 .84 .26 .58 146.3 20.4 26.8 .1602 .0490 .64 .25 .39 167.2 16.9 27.2 .2419 .0425 .89 .21 .68 * Conditions irregular -15- HO‘ Cu 2882. Log Pb 28 .7 .5 .h .3 .2 .1 -.1 -.2 -03 ”oh f (D 9’ p / 1/ p // j E 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0 2.1 2.2 Log lead weight - 8. Fig. h.-‘Working curve for lead by spark method. 2.3 Various samples of water were taken to examine for lead content; a raw composition sample from the Lansing Conditioning Plant, a tap sample from the laboratory, a tap sample from an East Lansing home, and a sample from the Red Cedar River were spectrographically examined and the Pb 2833.1 4° did not appear; the concentration must have been less than 209g x 10"9 gm Pb/.02 m1., if there were lead in the water samples. -16.. l. 2. 3. 4. SUMMARY The spectrographic sensitivity of lead by an alternating spark excitation has been fmund. Electrodes of uniform diameter tend to produce a more con- stant copper line when copper used as an internal standard from the electrode. The blackening of the lead and copper lines produced on the plate varied with the humidity; on a very damp day the lines were fainter. A working curve for low concentrations of lead has been derived. -17.. 1. 2. 3. 4. 5. 6. 7. REFERENCES Bausch and Lomb, "Quartz Spectrograph", Bausch and Tomb Optical Company, Rochester, N. Y., p. 29. Brode, W} R., “Chemical Spectroscopy“, 2nd Ed., John'Wiley and Sons, Inc., New York, N. Y., 1943, p. 121, 512. Crane, J. A., "The Spectrographic Sensitivities of Mangan- ese, Cobalt and Magnesium", M. S. Thesis, M.S.C., East Lansing, Mich., 1946, p. 6. Fred, M., Nachtried, N. 8., and Tomkins, F. S., J. Optical SOC. Aim, i, 281, 282, (1947). Proceedings of the 6th, Summer Conferences on Spectroscopy and its Applications, New York, John'Wiley and Sons, 1938, p. 54. Sawyer, R. A., "Experimental Spectroscopy", Prentice-Hall, 1110., .New York, N. Y., 1944, P0 109. McBurney, T. C., ‘Jestern Metals 4, No. J, 32-5 (1946) c. A. Aug. 10 (4262) (1946). -18- 1.03 a e .44— III ‘11. I... ...v‘ 411- .161.j.,0. | " 1 11V. 0 v u . 1‘ I ._ P4fl1.....§.411.. 1.1.11.1; .41.»... 3.... .. if : ._ MD}... ‘51)... .11)....1- _ L x . 1’. .0 .v. .... - 53...... run lei: LTJ.‘ \a.