V O L U M E 25, NO. 6, J U N E 1 9 5 3 temporary organisms because their bituniina were obtained from surface beds ( 7 ) . The possibility of interference by simple nitrogen bases in the porphyrin det,ermination was investigated. The absorption of typical compounds of this kind (pyridine and quinoline) was found t o be negligible at the wave lengths used for porphj-rin determination : moreover! the characteristic absorption spectra of these hiws rould not be detected in any of the porphyrin solutions c~s:iniined. PRECISION
The following shows the precision to he expected. The sample is the same crude oil from which the porphyrins were isolated for 1)rc.paration of the standard transmittance curves. Duplicate s:Lniple8 of topped crude corresponding to 100 grams of crude oil sample 60 were digested with the reagent and the 7 7 0 hydrorliloric acid-extractable porphyrins were transferred to 100 ml. of c*hloroform. This crude oil has a very high porphyrin content, so, in order to bring the concentration within the desired range, t,hr chloroform solution was diluted sixteen fold before optical me:tsurements were carried out. The results are shown in Table 11. Since the porphyrins in 1 volume or 100 ml. of chloroform w r e extracted from 100 grams of crude oil, the porphyrin content ~ i this ‘ oil is 416 mg. per kilogram or 416 p.p.m. hj- weight. From the fi ures, it is seen that the final average results from duplicate runs farid I1 deviate by =!=4.5%from the over-all average value; I)ut taking into consideration the largest differences in results (from measurements made a t the two wave lengths which yielded :L maximum of 28.1 and a minimum of 23.9 mg. per liter in the dilute chloroform solution), the total experimental deviations inwy he taken to be i870 of the average. no more porphyrins cwuld be obtained hy re-treatment of the extracted oil, this figure may represent the expected accuracy.
94 1 ACKNOWLEDGMENT
The author is indebted to M.W. Tamele and A. E. Smith for advice and aid in matters pertaining to spectrophotometry, and to D. C. Crowell for technical assistance. LITERATURE CITED ( 1 ) Abderhalden, E., and Heyns, K., Biochem. Z . , 259, 320 (1933). (2) .Ischheim, S., and IIohln-eg, W., Deut. med. Wochschr., 1, 12 (1933). (3) Conant, J. B . , J . A m . Cham. Soc., 53, 3526 (1931). (4) Dunning, H. S . ,Moore, J. W., and Denekas, h l . O., paper presented a t 8 t h Southwest Regional Meeting of the AMERICAS CHEMICAL SOCIETY,Little Rock, Ark., Dec. 4-6, 1952. ( 5 ) Fikentscher, R.. 2002.A m . , 103, 289 (1933). (6)Gilman, H., “Organic Chemistry, An Advanced Treatise,” 2nd ed., Vol. 11, Xew l o r k , John Wiley & Sons, 1943. ( 7 ) Glebovskaya, E. A , , and Vol’kenshtein, PI. V., J . Gen. Chein. 1C.S.S.R.). , . 18. 1440 11948). ( 8 ) Ka’rrer, P., “Organic Chemistry,” 2nd ed., New T o r k , Elsevier Puhlishing Co., 1946. ( 9 ) Overberger. C. G.. and Danishefsky. I.. Polytechnic Inst. Brooklyn, Tech. RcBpt. 2, Technical Information Pilot, 6,4224 (1952). (10) Skinner, D. I d . Eng. Chem., 44, 1159 (1952). (11) Treibs, Alfred, Ann., 509, 103 (1934); 510, 4 2 (1934); 517,172 (1935); 520, 144 (1935). (12) Ibid., 510,62 (1934); 517, 191 (1935). (13) Ibid., 517, 175, 194 (1935). (14) Treibs, Alfred, a n d Steinmeti, H., Ibid., 506, 171 (1933). (15) Weigelt, J., Forsehungen u . Fortschr., 8 , 300, 357 (1932). (16) Weigelt., J., a n d Noack, K., .\'ana Acta, Neue Folge, 1, 87 (1932). I
~I
I -
RECEIVED for review ?‘;orember 7 , 1952. Accepted March 18, 19.53.
Sodium Carboxymethylcellulose Determination of Degree of Substitution Active Agent C.
V. FRANCIS, Wyandotte Chemicals Corp., Wyandotte, Mich.
The use of available methods of analysis for sodium carboxymethylcellulose for active agent content and degree of substitution has shown that no single method can be universally applied to all commercially available materials, too much time is required for routine control work, and some methods required complicated and expensive equipment not usually found in a control laboratory. .A search for a new method to correct these difficulties resulted in a procedure using the uranyl ion as a precipitating agent, forming insoluble uranyl earboxymethylcellulose. The use of this procedure on a variety of sodium carboxymethylcellulose samples has shown a minimum recovery of 98Yo sodium carboxymethylcellulose and a precision within 1 0 . 0 1 on the degree of substitution. Comparison of degree of substitution obtained by this method and other available methods has shown a maximum difference of 0.04. This method has been found particularly useful in routine control analysis, as a total time of only 2 to 4 hours is required, and no special equipment or experience is necessary.
S
ICVI.~RhT,methods have been proposed for the analysis of sodium carboxymethylcellulose for active agent (sodium carl~oxyr~iethylcellulosc) content and degree of substitution. These methods include the copper salt precipitation method of Conner and Eyler ( 1 ) and the three methods suggested earlier by Eyler, Klug, and Diephuis: an acid wash method, a conductometric method, and a colorimetric method ( 2 ) . .4n alcohol-insoluble method ifi also used in the industry, in which all material insoluble in a specified concentration of alcohol in water is called active agent. Through work in this laboratory on a wide variety of sodium c,arhoxymeth?-lcellulose samples, several objections were r;iised to the chemical methods mentioned above: The methods could not be universally applied t,o all types af materials, the time r,ecluired for analysis was too long for routine ‘control work, and iri some ciises considerable expensive equipment was required, which is tiot normally found in a control laboratory. Csing the
alcohol-insoluble method, various results are obtained b y different laboratories depending on the technique emploj ed, the type of sample, and concentration of alcohol. After unsuccessful attempts to improve existing methods, a new method \vas sought. It was believed that of the approaches tried by the various investigators, a salt precipitation method would be most likely to give the desired results. A study v a s made of the insoluble salts of carboxymethylcellulose, such as copper, zirconium, aluminum, and lead. The main difficulty encountered n a s to obtain a precipitate which, for all types of samples, could be easily filtered and nashed without extensive treatment and preliminary preparation. The uranyl salt appeared to answer these requisites best. Reid and Daul ( 3 ) have briefly investigated the uranyl salt of carboxymethylcellulose and reported that the amount of metal precipitated was higher than the theoretical. This may be due to the use of a 2y0sodium cubox y-
942
ANALYTICAL CHEMISTRY
methylcellulose solution and a 2% uranyl nitrate solution to produce the uranyl carboxymethylcellulose. In the proposed method, approximately 400 ml. of a 0.1% solution of the sodium carboxymethylcellulose is used, to which is added 1 gram of uranyl nitrate hexahydrate. The dilute solution for precipitation also avoids the formation of tough stringy fibers, which are most difficult to wash free of excess uranyl reagent and other salt impurities. REAGENTS AND EQUIPMENT
Uranyl nitrate reagent. Dissolve 40 grams of reagent grade uranyl nitrate hexahydrate in 800 ml. of distilled water and dilute to 1 liter. Alcohol, 95y0 ethanol or absolute methanol. Mechanical stirrer. Glass filtering crucible, Corning Grade C, 30 ml. Porcelain crucibles with cover. Drying oven. Muffle furnace. PROCEDURE
Sample weight is 0.250 to 0.500 gram. Transfer the weighed sample to a dry 600-ml. beaker and moisten the dry material with alcohol. Add approximately 100 ml. of distilled water and stir into solution with heating to approximately 50" to 70' C. After solution is complete, add 300 ml. of water and bring the temperature of the solution to 50" to 70' C. By means of a pipet, add 25 ml. of uranyl reagent, holding the tip of the pipet under the surface of the stirred solution. Remove the heat source and continue stirring for about 5 or 10 minutes. Remove the stirrer and allow the precipitate to settle. Decant the supernatant liquor through a tared glass filtering crucible, and wash the precipitate in the beaker with three 200ml. portions of water followed by two 100-ml. washes with alcohol. Transfer the precipitate to the crucible with alcohol. Remove as much liquor as possible from the precipitate by the vacuum filtering apparatus. D r in an oven a t 130' C. to a constant weight (usually about I gour is required), and weigh the precipitate. Record as UCMC found. Transfer the precipitate to a tared and covered porcelain crucible, removing as much precipitate as possible from the glass crucible. Reweigh the crucible and contents and record the weight of the transferred precipitate as UCMC used. Ignite in a muffle furnace a t 750' to 800' C. to the green uranium oxide, G308. Usually about 20 to 30 minutes are required. Cool the crucible and contents in a desiccator and weigh. Record the weight-of residue as USOS. CALCULATIONS
Uranyl fraction (UF) =
W't.
Analysis of Purified Sodium Carboxymethylcellulose Samples (100% sodium carboxymethylcellulose)
% Sodium Carboxymethylcellulose, Sample S o . Uranyl Pptn. 1 99.7 99.0 98.5 2 98.5 98.8 98.5 3 99.9 99.3 4 99.3 99.6 5 98.7 99.0 6 98.9 99.2 7 99.0 99.9 8 100.5 99.9 9 100.2 100.3 Average values obtained bv: a Acid methanol method ( 2 ) . b Copper precipitation method (I)
Degree of Substitution Uranyl pptn. Other methods 0.57 0.56a 0.56 0.56 0.66 0.M a v b 0.66 0.66
1.4 1.4 0.58 0.58 0.60
0.60 0.58 0.58 0.56 0.56 0.51 0.51 0.55
1.34.b 0.540
0.5Sa 0.570 0.57a
0.54arb
0.57atb
lulose remains slightly sticky and a little more difficult to transfer from the beaker. On drying, this material forms a hard cake which may be difficult to remove from the glass filtering crucibles. These difficulties are eliminated by washing with alcohol as specified. It is believed that most errors in this method are due to improper washing of the precipitate. The optimum pH conditions are in the range from pH 3.5 to 4.0 and are automatically provided by the uranyl nitrate reagent; no further adjustment is necessary. The pH is apparently not too critical, so long as the solution is acid enough to prevent precipitation of the uranium. The method of determining the uranium present in the uranium carboxymethylcellulose by direct ignition was chosen because very little handling of the sample, very little equipment, and less time are required than if titrimetric methods are used (6).
of UaOs X 0.961 UCMC used Table 11. Corn arison of Active Agent (Sodium Carboxymethylcellulose~ Values of Uranyl Precipitation and 80% Alcohol Wash Method
162 X UF Degree of substitution (DS) = 135 192 (UF)
-
% active agent (NaCMC)
Table I.
NaCMC = UCMC found X U02(CMC)2
Wt. of sample where KaCMC/U02(CMC)2 = 162. 80 (DS)/162 192 (DS) To calculate results on a dry basis, dry the sample in an oven for 2 hours a t 105" C. or calculate the dry sample weight from the moisture content.
+
+
DISCUSSION AND DATA
The sample weight and dilutions given above were chosen as optimum for all types of samples so far encountered to give a light, easily filtered precipitate. When the uranyl reagent is added, the precipitate should first develop as a turbidity. If larger particles or fibers are found a t this point, greater dilution is indicated. For extremely viscous samples, greater dilution is required; for material of very low viscosity, less dilution is necessary and a shorter filtering time is required. A turbidity present in the supernatant liquor usually indicates a need for additional stirring a t 50' to 70°, or in extreme cases, a t higher temperatures. For best results in filtering, the supernatant liquor should be clear, with perhaps a few small particles suspended in solution. If the final alcohol wash is omitted, the uranyl carboxymethylcel-
% Active Agent Sample No. 10 11 12 13 14 15 16 17
Uranyl pptn. 91.8 91.2 90.7 90.9 91.0 92.8 62.8 92.3
80% alcohol wash method 91.7 92.0 89.0 92.0 92.0 92.5 62.6 92.6
% Difference
+o. i
-0.8 +1.7 -1.1 -1.0 +0.3 +0.2 -0.3
Table 111. Comparison of Active Agent (Sodium Carboxymethylcellulose) Average Values of Uranyl Precipitation Method and Other Methods Sample No, Uranyl Pptn. Other Methods 91.2 90.2Q 11 89.2a 12 90.7 89.4' 13 90.9 89.6a 91.0 14 96.86 97.7 18 101.2b 99.5 19 101.8b 99.5 20 61. Oa 62.6 21 92.6b 92.2 22 Average values obtained b 0 Acid methanol mqthod'b'). b Copper precipitation method 1 ) .
% Difference +1.0 -1.5 +1.5 -1.4 +0.9 -1.7 -2.3 -1.6
-0.4
943
V O L U M E 25, N O . 6, J U N E 1 9 5 3 R o u t i n e Analyses of S o d i u m Carboxymethj-lcellulose
T a b l e IV.
(Various analysts, one sample; uranyl precipitation method) Detn. No. Degree of Substitution % ’ Active Agent 67.7 1 0.59 0.60 66.7 2 67.0 3 0.$8 66.0 4 0.59 68.0 0.58 5 68.0 6 0.57 68.1 0.57 7 67.3 0.57 8 Average 0.58 67.5
Cranium in the uranium carboxymethylcellulose has also been determined by two other methods: by determination of the excess uranium in the filtrate and wash water by the ammonia precipitation method ( 6 ) , and by a preliminary ignition and digestion of the uranium carboxymethylcellulose with acid followed by precipitation of uranium by ammonia ( 4 ) . Results obtained by these methods were identical with those obtained by the shorter direct ignition method. On alkaline samples where excess alkalinity is caused by sodium carbonate or sodium hydroxide, the solution should be neutralized with hydrochloric acid before addition of the uranyl reagent. Of the impurities so far encountered in sodium carboxymethylcellulose, sodium chloride, sodium glycolate, sodium carbonate and bicarbonate, and phosphates, only the phosphates interfere after neutralization of the sodium carboxymethylcellulose sample solution. A total time of 2 to 4 hours is required for duplicate samples, depending on the type of sodium carboxymethylcellulose. Table I gives examples of the results obtainable on 100% sodium carboxymethylcellulose samples with the uranyl precipitation method. Recovery of active agent on all samples is 98% or better of the active agent present. Table I1 compares results from the uranyl precipitation method and the alcohol-insoluble
method when, in the latter, 80% ethanol a t a temperature near the boiling point is used as a solvent. Table I11 compares active agent results by the uranyl precipitation method and other appropriate chemical methods. Table I\‘ gives results on one sample of a technical grade of sodium carboxymethylcellulose, obtained by various analysts using the uranyl precipitation method. These determinations were run in a routine manner by a simple following of directions. Neither temperature nor dilutions were closely controlled. A more careful analysis of this sample by the uranyl precipitation method and other methods gave an active agent content ranging from 66.7 to 67.5 and a degree of substitution from 0.56 to 0.58. CONCLUSIONS
The use of a uranyl salt as a precipitating agent for sodium carboxymethylcellulose provides a means of routine analysis for degree of substitution and active agent of sodium carboxymethylcellulose that can be completed in a short enough time to be useful for routine control work. The use of this procedure on a variety of sodium carboxymethylcellulose samples has shown a mininium recovery of 98% sodium carboxymethylcellulose, and a precision on the degree of substitution within ztO.01. Comparison of degree of substitution obtained by this method and other available methods has shown a maximum difference of 0.04. LITERATURE CITED (1) (2) (3) (4)
Conner, A. Z., and Eyler, R. W., ANAL.CHEM.,22, 1129 (1950). Eyler, R. W., Klug, E. D., and Diephuis, F., Ibid., 19, 24 (1947). Reid, J. D., and Daul, G. C., Teztile Research J.,17, 554 (1947). Samsel, E. P., Bush, S. H., and Warren, R. L., ANAL.CHEM.,20,
142 (1948). (5) Scott, W. W., “Standard Methods of Chemical Analysis,” 1‘01. I, p. 1027, New York, D. Van Nostrand Co., 1939. (6) Treadwell, F. P., and Hall, W. T., “Analytical Chemistry,” 5’01. 11, p. 166, New York, John Wiley & Sons, 1942. RECEIVED for review January 23, 1953. Accepted March 27, 1953.
Spectrochemical Analysis of Plant Material Using Spark Excitation W. T. MATHIS The Connecticut Agricultural Experiment Station, New Haven, Conn.
F”“
some time plant materials have been analyzed spectrographically a t the Connecticut Agricultural Experiment Station by a technique that differs from previously published methods and that the author believes is superior in a numher of respects. SCOPE
While the outlined details refer in particular to the analysis of plant materials, the procedure is essentially adaptable to analysis of almost any type of material that lends itself to wet preparation. In agricultural work this is a distinct advantage because many analyses are for so-called “available” constituents which necessarily involve solution or extraction preparation. Line intensities of nearly all of the plant elements, both major and minor, usually fall within a readable range on a single exposure, and the precision of the method is such that the average of duplicate exposures gives a very satisfactory analysis value.
the mixture is “sprayed” out by alternating current spark in making the exposure. Spark excitation offers the advantages of very short exposure time, elimination or minimizing of distillation differences, slight background and clear region for use of 4044 and 4017 potassium lines, and unusually good ratio reproducibility. APPARATUS
Excitation source, Applied Research Laboratories’ a x . spark source unit. Spectrograph, Applied Research Laboratories’ 1.5-meter spectrograph. Recording equipment, Kodak spectrum analysis KO.1 film. Microphotometer, Applied Research Laboratories’ comparatordensitometer. Developing equipment, Applied Research Laboratories’ develop ing and drying equipment. Calculating equipment, Applied Research Laboratories’ calculating board.
OUTLINE OF METHOD
PROCEDURE
Cratered electrodes are packed with the graphite removed in drilling, impregnated with the solution to be analyzed, dried, and
Standardization. Analysis of a single type of plant material, i n which the major elements potassium, calcium, magnesium, and
