1022
ANALYTICAL CHEMISTRY Table 111. RIolar -4bsorptivity ENOiG
Solvent Water
EhhQ
MW
hfr Reference 14,100 ( 2 6 5 ) Q 14,100 (267) 14,500 (265) 13,270 (267) 14,900 (269) 14,400 ( 2 6 5 ) Ethanol 15.300 (263) 15,010 (265) 14,680 (267) 15,153 ( 2 6 5 ) 14,500 (267) Methanol 15,200 (265) 14,400 (267) Water 14,000 (263) 16,700 ( 2 6 5 ) Wave length in mp in parentheses. b D a t a obtained in present investigation. Values b y Riegel were obtained b y a spectroscopic technique while all others in table were obtained b y spectrophotometric measurement: the absorbance coefficient is also derived uniquely by Riepel.
t o 5070 total guanidines. TVeighed amounts of each constituent were added to 0.25 gram of water-insoluble material for each sample. Each result is the average of duplicate determinations. An estimate of the precision and reliability of the method was obtained by preparing a large synthetic sample with approximately 10 to 1 ratio N02G/NAG for replication testing. The results (Table 11) indicate that the method has a precision, shown by a standard deviation obtained from ten values, of about I .7 parta per hundred for each constituent. There is considerable variance among molar absorptivity values reported for nitroguanidine and nitroaminoguanidine. The available values are summarized in Table 111. While absorption in alcohol was not directly required in the present investigation, it was determined in view of the discrepancy in the molar absorptivity of nitroaminoguanidine found here compai ed with previously reported values. In general, a notable effect on absorptivity occurs in going from the solvent alcohol to water, apparently a combined effect of solvent polarity and solute diesociation constants. The sample of nitroaminoguanidine which yielded E = 13,720 in water was dissolved in alcohol and c found to be 14,680, which is in substantial agreement with the value previously found by Van Dolah in these laboratories.
The det,ermination of molar absorptivity values in alcohol was subject to considerable variation, depending on the commercial alcohol used; the values always decreased a t least 10% over a period of several hours after the original reading. The use of carefully purified alcohol as solvent resulted in the values here reported; no change occurred in these latter solutions even upon standing for several days. (The commercial 95y0 alcohol was refluxed 8 hours over silver oxide, distilled onto calcium oside, then rrflused 1 hour, and distilled through a 12-inch column). I t is probable that much of the variability in previous1)- reported values was due t,o the presence of unknown impurities in the alcohols. Some impurities show slight absorption, resulting in high absorptivity; others react with nitroaminoguanidine and nitroguanidine, resulting in low absorptivity. The absorption curve in alcohol showed no appreciable change in shape after the decrease in absorption reading, KO conclusion could be reached as to reaction products. Molar absorptivity values were determined in methanol for added comparison. The values found are very nearly the same as those found in ethanol. LITERATURE CITED
;lyres, G. H., ANAL. CHEJI.,21, 652 (1949). Brode, W. R., J . O p t . SOC.Amer., 39, 1022 119493. Chatt.away, F., Ireland, S., and Walker, .%.. J . Chena. SOC.,127, 1851 (1925). Jones, R. X,, and Thorn, G. D., C O N .J . Research, B27, 828 (1949). Lappin, G. R.. and Clark, L. C . , d s a ~CHEM.. . 23,541 (1951). Lieber, E., Sherman, E., and Patinkin, S. H , J . A m . Chem. S u c . , 73, 2329 (1951). AIcKay, -4.F., Chem. Reus., 51, 301 (1952,. Riepel, E. R., and Buchwald, K. IT.. J . A w . Chem. Sm., 51,484 (1929). Schroeder,W. A., etal., ANAL.CHEM..23, 1740 (1951). Van Dolah, R. W., unpublished data. R L V E I V Efor D review March 6, 1853. Accepted . I p r i l 2 4 . 1833
Determination of Magnesium Oxide by Hydrogen Flame Spectrophotometry PAUL CLOSE, WM. E. SMITH, . ~ N D31.4RIOS T. WATSON, J R . General Research Division, Owens-Illinois Glass Co., Toledo, Ohio
A
LTHOUGH many papers in the past decade have described the determination of the alkalies and calcium by flame spectrophotometry, few or no data have been presented on the determination of magnesium by flame techniques. No doubt, this has been due to the lack, until recently, of commercially available photometer and burner-atomizer equipment that would satisfactorily allow the determination of magnesium. The relative intensity of magnesium emission in the hydrogen flame is considerably superior to that in the acetylene or other fuel gas flames. The combination of the Beckman Model DU spectrophotometer with the KO.9200 flame photometry attachment and No. 9240 hydrogen-oxygen burner assembly, which was used in this work, permits magnesium to be measured satisfactorily ( 1 ) . The concentrations used are much higher than those ordinarily employed in flame spectrophotometry, but the use of a photomultiplier tube attachment would, no doubt, permit the employment of more dilute solutions. I n the analyses of materials such as portland cements, limestones, and cement mortars the determination of magnesium by conventional methods is time-consuming a t best and usually
follows the separation of silica. iron. alumina, and calcium. In the procedures described, silica, iron, and alumina are removed from the sample together, and magnesium is determined in the filtrate on the flame spectrophotometer At a wave length of 371 mr. The calcium, which is not removed, does not affect the magnesium flame emission itself, but, the background effect varies with changing calcium concentration. The calcium concentration is determined on the flame spectrophotometer at a wave length of 422.7 mp, so that a background correction can be made. S o noticeable effect of sodium and potassium in concentrations equivalent to 1% of each as osides could be detected. This quantity of alkali should exceed that ordinarily found in portland cement. I t n-as found, however, that the presence of sulfate as calcium sulfate, and manganese as manganous chloride, does affect the flame readings. Sulfate causes an error which may be either positive or negative in its net effect, depending upon the amounts of magnesium and sulfate present. The effect of sulfate was determined by comparing, against standards, solutions contain-
V O L U M E 25, NO. 7, J U L Y 1 9 5 3
1023
The magnesium oxide content of the mortar and its various components are frequently responsible in part for failures in masonry and plaster construction. An analytical method more rapid and direct than conventional procedures is desirable in estimating the total magnesium oxide contents of these materials. The use of the hydrogen flame spectrophotometer permits the direct determination of magnesium oxide on masonry materials. Results in the range of 0.5 to 6.0q0 magnesium oxide compare favorably (&O.lqo MgO) with the classical pyrophosphate method; magnesium oxide contents higher than 6.Oq0 are generally lower than the chemical results, but are still of practical value. The use of the flame technique for magnesium oxide permits a direct and rapid analytical procedure w-ith a minimum of sample preparation; a single determination can be made i n about a n hour.
ing equivalents to 1 and 5% sulfur trioxide and 1 and 5% magnesium oxide. The effect of manganese in amounts equivalent to 0.1 and 0.5% was similarly determined. In general, manganese causes a negative error. However, as its presence in amounts in excess of 0.1% is unlikely in cements, limestones, and mortars, the manganese error is not significant. These findings, based on an equivalent of a 1-gram sample,
Table I.
Effect of Sulfate on Flame Readings
Effect on Flame
Net Effect, % hIgO
Present, 0 05 gram AIgO, 0.05 gram SO1 per 100 ml. Background reading a t 371 rnp lowered 0.9 to.09 Calcium reading a t 422.7 mplowered 2.0 +o. 20 Rlagnesium reading a t 371 mp lowered 4.6 -0.46 S e t effect as error -0.17 Present, 0.01 gram RIgO, 0.0; gram 908 per 100 ml. Background reading a t 371 m p lowered 0.9 +o. 09 Calcium reading a t 422.7 m p lowered 2.2 10.22 hlagnesium reading a t 371 rnp l o d r e d 1.2 -0.12 h-et effect a,- error +o. 19
with 0.64 gram of calcium oude per 100 ml. present, are summarized in Tables I and 11. PROCEDURE
Standard Solutions. T u o stock solutions of calcium n-ere prepared starting v, ith analytical reagent calcium chloride dihydrate. The first solution was prepared equivalent to 80.0 grams of calcium oxide per liter by dissolving 209.7 grams of calcium chloride dihydrate in water, filtering, and diluting to 1 litrr. The second of the two solutions, equivalent to 64.0 grams of calcium oxide per liter, was prepared by precipitating the calcium as oxalate, igniting it to carbonate, and subsequently dissolving 114.2 grams of the carbonate in sufficient 1 to 1 hydrochloric acid, filtering, and diluting to 1 liter. The precipitation x a s made by the dropwise addition of a cal(*iumchloride solution to a hot splution of oxalic acid-ammonium oxalate M ith continuous stirring. The purpose of preparing the sevond qolution was to test the calc.ium chloride for the presence of a sipnificnnt quantity of magnesium. As no difference between the two solutions in background readings could be detected it was concluded that the calcium chloride dihydrate u a s of sufficient purity for calibrating the standard curves. The solutions were not standardized because of their relative high concentration and the small effect of a moderate change in calcium on the harkground correction.
Present, 0.05 gram N g O , 0.01 gram SOXper 100 ml. Background reading a t 371 rnp lowered 0 2 +o. 02 Calcium reading a t 422.7 mp lowered 0.5 +o. 05 Magnesium reading a t 371 m p l o w r e d 1 6 -0.16 S e t effect as error -0.09 Present, 0.01 gram hIgO, 0.01 gram SO3 per 100 ml. Background reading a t 371 mp lowered 0.2 +o. 02 Calcium reading a t 422.7 mp lowered 0.7 + O . 07 hIagnesium reading a t 371 mp lowered 0.3 -0.03 ?it-t effect as error + O . 06
Table 11. Effect of Manganese on Flame Readings Effect on Flame
Net Effect, % MgO
Present, 0.05 gram MgO, 0.005 gram 3 I n O per 100 ml Background reading a t 371 mp raised 0.8 -0.08 Calcium reading a t 422.7 mp lowered 0.2 +o. 02 Magnesium reading a t 371 mp lowered 1.1 -0.11 Ket effect as error -0.17 Present, 0.01 gram MgO, 0.005 gram 3InO per 100 ml. Background reading a t 371 mp raised 0.8 -0.08 Calcium reading a t 422.7 mp 0 0.00 hlagnesium reading a t 371 m p raised 1.1 +o. 11 Ket effect as error $0.03 Present, 0.05 gram h l g 0 , 0.001 gram . \ I n 0 per 100 ml, Background reading a t 371 mp 0 0.00 Calcium reading a t 422.7 mp lowered 0.5 +0.05 Magnesium reading a t 371 mp lowered 1.1 -0.11 Net effect as error -0.06 Present, 0.01 gram MgO, 0.001 gram 3In0 per 100 ml. Background reading a t 371 mp 0 0.00 Calcium reading a t 422.7 mp 0 0.00 hfagnesium reading a t 371 mp 0 0.00 ?iet effect as error 0 00
0.01 GRAM
0.03
0.05
MAGNESIUM
0.07
0.09
O X I D E P E R 100
ML.
Figure 1. Per Cent Transmittance Reading of Magnesium Flame Emission
The magnesium stock solution was prepared from analytical reagent magnesium chloride hexahydrate by dissolving 50.4 grams in water, filtering, and diluting to 1 liter. I t was standardized by precipitating with 8-quinolinol and igniting to magnesium oxide; and by precipitating with ammonium phosphate and igniting to MgtP20,. Aliquots equivalent to 0.1000 gram gave values of 0.1013 and 0.1010 gram, respectively. The standard magnesium curve, Figure 1, was corrected accordingly. A standard sam le solution, comparable to a prepared portland cement sampfe, was prepared from the stock solutions to check the instrument settings. This solution contained 0.05 gram of magnesium oxide per 100 ml. and 0.64 gram of calcium oxide per 100 ml. (5% MgO and 64y0CaO).
ANALYTICAL CHEMISTRY
1024 Spectrophotometer Settings and Calibration of Standard Curves. The instrument settings used for measuring the magnepium flame emission were as follows: Wave length Sensitivity control Selector switch Phototube resistor Slit Hydrogen Oxygen
371 mp 2 , 5 turns from clockwise unit 0.1 10,000 megohms 0 . 4 nim. 5 pounds per sq. inch 20 pounds per sq. inch
Under these conditions the magnesium curve is a straight line from 0.005 to 0.08 gram of magnesium oxide per 100 ml. (Figure 1). Response of the instrument to magnesium is practically 10% on the per cent transmittance scale for each 0.01 gram of magnesium oxide, or 1% ' for each 0.1 yomagnesium oxide on a 1-gram sample basis. The magnesium curve (Figure 1) was established by preparing 100-ml. solutions from the stock solutions, each containing 0.64 gram of calcium oxide and varying the magnesium oxide concentration in 0.01-gram steps from 0.01 to 0.08 gram. I
W
-I
4: U
*
40
10
z
0.3 GRAM
Figure 2. A. B.
0.5
0.4
CALCIUM
0.6 OXIDE
0.7 PER
0.8 100 M L .
Per Cent Transmittance Keading of Calciuni Flame Emission .4t c a l c i u m wave l e n g t h of 422.7
mp
Background at m a g n e s i u m wave l e n g t h of 371
mp
-4scalcium is not removed from the samples, the background effect, which varies with calcium concentration, must be measured and the magnesium readings corrected. The background correction (curve B, Figure 2) was obtained by measuring the magnesium flame background with solutions varying in calcium concentration from 0.40 to 0.80 gram of calcium oxide per 100 ml. in steps of 0.08 gram. The actual calcium concentration of the samples (Curve A , Figure 2) was determined with the following instrument settings: 4 2 2 . 7 nip
2 turns from clockwise limit I
tween solutions or samplcs the atomizer is flushed with water to avoid salt iucrustations 011 the burlier tip. Thc reproducibility of readings was satisfactory. JVhcti the selected switch is set at 0.1 for magnesium, t'he readings are easily duplicated to ~ k 0 . 2 7transmittance. ~ However, when the selector switch is set a t 1 for calcium, the meter needle fluctuates somewhat more. Nevertheless, the averages were satisfactory, probably contributing to an error of not more than i 0 . 0 5 ~ o magnesium oxide. Frequent flushing of the atomizer is conducive to reproducibility of readings. In the authors' experience, the use of two separate sample cups of water for flushing is the best practice; the atomizer is flushed tnice after each reading of a sample solution. An example of the reproducibility of background readings (0.64 gram of calcium oxide per 100 ml.) a t the 422.7 mw caalcium line is as follows: 32.9, 32.9, 33.0, 32.8, 32.9, and 32.8; a t the 371 mp magnesium line: 20.2, 20.1, 20.4, 20.3, 20.1, and 20.3; and an example of the reproducibility of magnesium readings (0.005 gram of magnesium oxide and 0.64 gram of calcium oxide per 100 ml.) is: 69.8, 69.8, 69.8, 69.6, 69.6, and 69.8. Preparation of Samples. I n general, the treatment of the materials analyzed was the same, but ~ i t hsome slight differences. Both the limestones and mortars contained some organic matter; this was removed by ignition over a gas burner for 5 to 10 minutes. It was found advisable for complete recovcry of magnesium to digest the limestones and mortars with a small quantity of dilute hydrochloric acid after evaporation and prior to dilution and neutralization. The calcium carbonate used in the precipitation of iron and :tlumina \vas a reagent grade prepared for J. L. Smith fusions in the determinations of alkali. Flame tests indicated a small magnesium blank equivalent to 0.01 to 0.03% magnesium oxide. l b o u t 0.5 to 1.0 gram of the dry reagent is added to the sample solution. Flame background tests indicate 0.1 to 0.15 gram disrolves in the cement samples. The acid used to digest the limestone and mortar samples was adjusted so that the resulting filtrates would contain 0.5 to 0.7'gram of calcium oxide per 100 ml.
PORTLASD CEMENT.Transfer 1 gram of sample to a suitable evaporating dish or beaker, add 25 ml. of 1 to 4 hydrochloric acid, warm, and stir until in complete solution. Evaporate to apparent dryness or until the odor of acid cannot be detected. Take up the residue in 50 ml. of hot water, heat to boiling, add magnesium-free calcium carbonate and methyl red indicator, :md continue boiling until the solution is distinctly alkaline.
Table 111. Comparison between Cheniical and Flame Analysis (Each column represents separate sample taken for analysis) % MgO, Chem. .inalysis % 31g0, Flame Analysis Poitland Cement 1 4.05 4 02 4.09 4.09 2 3.57 3.52 3.59 3.61 3 2.47 2.44 2.54 2.59 4 0 74 0.68 0.74
10,000 megohms 0 . 2 mm. 5 pounds per sq. inch 20 pounds per sq. inch
The same calcium solutions used for background effect were wed to establish the calcium curve. In establishing the standard curves, duplicate solutions were prepared and the usual four separate flame readings taken and averaged. The standard 0.05 gram of magnesium oxide per 100 ml. sample solution was used as the primary standard for magnesium, and a solution of 0.64 gram of calcium oxide per 100 ml. for the calcium and background curves. The procedure is to make the instrument settings, atomize the standard into the flame, and make final adjustment with the sensitivity control so that the same reading is always obtained with the standard, During a set of runs, the flame is checked occasionally with the standard. and always at the end. Be-
Liiiieqtone
Cement llortar
IO'.88
10.50a 10.54 8.26 8.070 8.08 4.60 4.55 4.69 6.02 6.07 6.00 3.48 5 3.31 3.35 0 Diluted t o 0.5 gram per 100-nil. voluine. CaCli added t o bring CaO concentration t o approximately 0.60 gram per 100 ml. b Chemical analysis by precipitating with 8-quinolinol, igniting, and weighing a$ U g O . 1
2
3 4
V O L U M E 2 5 , NO. 7, J U L Y 1 9 5 3 Add paper pulp and filter through a rapid filter into a 100-ml. volumetric flask. Wash with warm water until the volume of the solution is near the mark of the flask; cool and dilute to the mark. LIMESTONE.Transfer 1 gram of sample to a platinum crucible or dish and ignite to remove organic matter if this is necessary. Then transfer to a suitable evaporating dish, cover, add 10 ml. of 1 to 1 hydrochloric acid, heat to boiling, and boil until the sample is decomposed. Rinse cover and sides of dish and evaporate until the odor of acid has disappeared. Add 1 ml. of 1 t o 3 hydrochloric acid and 4 ml. of hot water and digest for a few minutes. Add 45 ml. of hot water and continue the sample treatment as for portland cement. CEMENTM O R T ~ R STreat . the ignited sample as for limestone, but add 20 ml. of 1 to 1 hydrochloric acid and boil for 5 minutes hefore evaporation. Take up the evaporated residue with 10 nil. of 1 to 9 hydrochloric acid, heat for 5 minutes near boiling, dilute with 40 ml. of hot water, and continue the sample trentmmt as for limestone. RESULTS
Table I11 she)! s a comparison between the chemical and flame analyses of %vera1 cements, stones, and mortars. The chemical analyses with one exception were obtained following the usual dehvdration of silica with hydrochloric acid, precipitation of iron and alumina with ammonia, double precipitation of calcium witli owlate, and double precipitation of magnesium with am-
1025
monium phosphate, and final ignition and weighing as Mg21’,0i. The chemical values for magnesium oxide of the portland cements were also corrected for manganous oside found in the pyrophosphate. The data show an excellent agreement between the chemical and flame analyses. Only the higher magnesium oxide contents (over 6%) show deviations much in excess of 0.1%. However. even these results are acceptable for most purposes. The determination of magnesium in these materials can bc made in about 1 hour; a single operator can carry out twelvca determinations in the usual working day. ACKNOWLEDGMEh-T
The authors wish to thank W. C. Taylor, chief, Chemical Section, General Repearch Division, Owens-Illinois Glass Co., foi encouragement and helpful criticism received in this work. LITERATURE CITED
(1)
Beckman Instruments, Inc., South Pasadena, Calif., “Instructions for the Hecknisn Spectrophotometer,”Bull. 259 (Septernber 1951).
RFCEIVED for review h-ovember 4,1952.
Accepted April 22, 1953
Comparison of Infrared Absorption Spectra of Steroids Obtained on Solid Films and Mulls and in Solutions HiRRIS ROSEXKRANTZ AND LEONARD ZABLOW ?’he Worcester Foundation for Experimental Biology, Shrewsbury, Mass., and the National Institute of Mental Health Cooperative Research Station at the Worcester Foundation, Public H e u l t h Serrire, Federal Security .4gency, Worcester, Mass. The variability of infrared spectra obtained on the same steroid in different states has not previously been evaluated. Cross comparisons could be made among spectra obtained on steroids prepared as solid films, as mulls, or in carbon disulfide solutions when tendency for hydrogen bonding was not profound. Where bonding occurred, significant absorption changes were observed between 9 and 10 microns. Despite these changes, the major portion of the fingerprint region (8 to 9, and 10 to 13 microns) suggested identity among the spectra. Hydrogen bonding occurred in solid films and mulls
I
N R E C E S T J ears the infrared absorption spectra of many steroids and structurally related compounds have appeared in the literature (I, 8, 6-8). Infrared analysis has been a fundamental technique in the elucidation and identification of the structures of steroidal hormones and their metabolites ( 2 , 6). I t has become increasingly desirable that infrared curves obtained on these biologically important compounds be easily comparable despite the variation in instrumentation and film preparation The early 1% ork of Furchgott, Rosenkrantx, and Shorr (1 ) contained absorption curvee which were recorded on a manually operated spectrophotometer, the compounds being studied as melted or deposited films. The published spectra of Jones and Dobriner (6) primarily are of the fingerprint region of compounds observed in carbon disulfide solutions. Recently, a group of isosteroids was studied by Josien, Fuson, and Cary ( 7 ) and the infrared spectra that were obtained m-we represented as lines of dif-
and no structural alteration was seen in nielted films of steroids that had relatively low melting points and contained less than four oxygen atoms. Spectra may be compared to a significant extent, irrespective of the preparative method employed. This could avoid unnecessary duplication of curves, especially for workers who are not in a position to compile an extensive catalog of spectra. Use of published curves may lead to identification of an unknown compound where no more pure steroid is available for study in a manner identical to that used in studying the unknown.
ferent lengths appearing at particular frequencies. The samples were prepared as Kujol mulls or in solutions of carbon disulfide and hexachlorobutadiene. More recently, Rosenkrantz, Milhorat, and Farber (8) have obtained the infrared absorption curvec: of compounds in the ergostane and cholestane series, the materials being examined in the solid state. In none of the above investigations, where the same compound was studied by different workers. are the infrared spectra superimposable in all respects. -4lthough there is good agreement between the early curves of Furchgott, Rosenkrantz, and Shorr arid those of Jones and Dobriner, several discrepancies exist, some of which may be assigned to the different instruments used. Hoa-ever, no evaluation has been made of the variations in the absorption spectra obtained when a steroid was studied in the solid or solution state. The present study has attempted to clarify this issue. I t is hoped that the data will demonstrate the sperific ad-
