Chromatographic Determination of Carboxyl Groups in Filter Paper A. J. ULTEE, JR.',
and
J. HARTEL
Vezelinstituut T.N.O., Delft, The Netherlands
A chromatographic method for determining the carboxyl groups in filter paper was developed. Experiments were carried out with several kinds of metal ions, making use of the strong bond of different metal ions to the carboxyl groups of the paper. Lead(I1) ions gave the most satisfactory results. The influence of ester and lactone groups on the carboxyl group determinations was studied. The method is rapid and reliable.
T
HE ion exchange properties of filter paper may invalidate the results of analytical procedures involving filtration through filter paper (12, 23)-for example, in the determination of the solubility of radium sulfate. On the other hand, Schute ( 2 4 ) has taken advantage of the ion exchange property of filter paper in the chromatography of alkaloids in aqueous media. While Schute used papers of ordinary varieties, others ( 1 4 , 31) have used paper especially enriched in carboxyl groups for chromatographic separations. Because of the wide use of such papers, a rapid method for the determination of carboxyl groups in filter paper is of considerable practical interest. Except for the determinations involving infrared spectroscopy ( 6 ) and decarboxylation (69), all previous carboxyl group determinations are based on ion exchange. The ions present are usually exchanged for hydrogen ions, which are determined by titration, preferably in the presence of electrolyte, in order to avoid difficulties arising from Donnan equilibria ( 1 8 ) . Neutral alkali salts are suitable for this purpose (9),although the end point s h o w considerable drift, owing to the presence of the cellulose. This can be avoided by the use of an excrss of alkali (18). It is supposed that any lactone groups present are opened by this procedure ( I O ) , but other reactions liberating carboxyl groups may also occur, especially when a large excess of alkali is used ( 2 2 ) . Another electrolyte often added is calcium acetate (15). In this case the buffering action of the salt and the strong affinity of the calcium ions for carboxyl groups cause the ion exchange to take place before titration, although the same buffering action makes the method lese reliable when the carboxyl content is low (32). A further method of determining the hydrogen ions is based upon iodometric titration (17). For the determination of carboxyl groups the paper can also be converted into the calcium form, whereupon the calcium can be determined after being exchanged for hydrogen ions ( 2 6 ) or by electrodialysis ( 2 5 ) . As this method is a matter of equilibrium reactions, there are advantages in carrying out this process chromatographically (20). Other methods for carboxyl determinations, involving the use of ions of heavy metals, are known for silver ( 2 7 ) , copper(I1) (23),tin(I1) (S), lead(I1) (8, 23), and uranyl(I1) ion (4). Often, use is made of ion exchange with methylene blue ( 1 , 28), although this method may involve some difficulties. Considerable uncertainty existed in most of the previously used methods for carboxyl determination. Although the ion exchange of filter paper is usually ascribed to the presence of carboxyl groups, it was believed that part of the ion exchanging groups might be present in the form of lactone or ester groups, which are easily opened (9, 10, 16). Hence, an attempt was made, with the aid of infrared spectroscopy, to determine whether
the presence of such groups might be responsible for some error in carboxyl group determinations. A chromatographic method of estimating the carboxyl content of filter paper has been outlined recently ( 2 4 ) . A measured quantity of hydrogen or alkaloid ions was used to saturate the available carboxyl groups in a certain area of the paper. After elution the spot was made visible by spraying, and its area was determined; this area should be inversely proportional to the carboxyl content of the paper. Similar investigations had been proceeding in the authors' laboratory for some time with the use of various metal ions to establish their suitability for carboxyl determinations. The best results were obtained with lead ions, which are strongly bound to the carboxyl groups and can be easily detected with hydrogen sulfide. Directions have been worked out for this case. EXPERIMEh-TAL
Modification of Filter Paper. Samples of Whatman KO. 1 filter paper and cellulose powder were oxidized with nitrogen dioxide gas ( 3 4 ) in the absence of air, with a view toward introducing carboxyl groups. The concentration was 0.5 gram of nitrogen dioxide per liter; the ratio nitrogen dioxide to cellulose was 1to 6 grams; the reaction period was 18 hours. The treated cellulose was thoroughly washed with water and dried. Under these conditions, filter paper is obtained with about 1.5% COOH, determined by titration with calcium acetate (34). The presence of lactone groups was investigated by spraying with hydroxylamine and iron chloride ( 3 0 ) . Samples of both untreated cellulose and oxidized cellulose were treated with a solution of diazomethane in ether for 18 hours a t a temperature below 5 " C. The free carboxyl groups are converted into methyl esters by this procedure. A part (1 gram) of the oxidized cellulose powder was treated with 160 ml. 0.2111 calcium acetate for 30 minutes, as is customary for the carboxyl group determination ( 9 4 ) . The calcium salt wa8 then filtered off and dried. Infrared Spectroscopy. Infrared spectra in the range of 5.5 to 6.5 microns were recorded for slurries of cellulose powder in paraffin oil (about 20 mg. of cellulose, 2iO-mesh, in 100 mg. of Table I.
Reproducibility of Determinations Weight of Spots, Mg.(l
1. 58.95 9. 10. 2. 59.30 11. 3. 57.45 4. 59.90 12. 5 . 58.10 13. 6. 56.25 14. 7. 57.60 15. 16. 8. 58.05 .4verage Standard deviation a Obtained by applying 4.5 X 10-4 meq. Whatman No. 1.
58.25 58.05 59.40 57.25 55.55 56.50 58.00 55.70 57.77 mg. 2.16% of lead acetate on a strip of
Table 11. Determination of Error in Calculating Weights of spots --eight of Spots, hIg.=
40.07 11. 40.00 12. 40 50 13. ?. 40 90 14. 15. a . 40.50 6 . 40.30 16. 17. 7. 40.80 8. 39.80 18. 19. 9. 40.85 10. 40.45 Sverage Standard deviation One spot is copied and weighed 19 times. 1. 2.
3.
e
1 Present address, Benger Laboratory, E. I. d u Pont de Xemours 8: Go., Inc., Waynesboro, Va.
557
41.30 40 50 40 70 40.10 41.20 41.70 39 48 41.80 40.45 40.60 mg. 1.48%
,
558
ANALYTICAL CHEMISTRY
. _ ~ _ _ . .. ~ .
. . . . . . .
paraffin oil). Similar spectra of mo'"" ' cellulose, galacturonic acid, glum acid lactone, and calcium galactur, were recorded. Chromatographic Determination 01 boxgl Groups. P u o m n m n . By n of a micropipet 10 MI. of lead salt sol (acetate or nitrate) of known mnce tian (0.01 t o O.lM, depending or type of paper) is applied on a str paper, about 2 om. from the lower Immediately afterwards the stri suspended in boiled distilled water (1 and strip itre kept in an enclosed x in such a way that the bottom o strip is just in the water. If necei the paper is stretched by means of a hook. The water is then allowed t< to 8 height of a t least 10 em., v usually takes place within half an The lead spot is made visible by rea with hydrogen sulfide. In orde measure the area, it is traced , heavy type of siaed paper with thi 'SU.C 1. UpYLD " Y L a l ' l r " "J of carbon paper. The spat thus copied toncentration of U.U4, U.UI(, U.ZU, and U.4UM is cut out and weighed. If the weight per square centimeter of the types of Right. Duplicate spots paper is known, the area. of the spot and the carboxyl content of the paper oan he calculated. will shift only on the addition of complex-forming ions to the The same procedure hss been used with solutions of stannous elution also seems to .he .rechloride, copper sulfate, silver nitrate, mercuric acetate, and . agent . . (Si). . . Complex . . . formation . . . sponslble tor the fact that the method cannot be used rnth ferric nitrate. In the c u e of uranium salts, the spots were made visible by coating them with powdered potassium ferrocyanide, mercury(I1) and iron(II1) ions. Copper(I1) and tin(I1) ions, followed hv &amins. With methvlene blue the spots are visible on the other hand, produce very clear spots. However, these are larger than the spots obtained in the lead method (Tahle V); iCI hence it becomes evident that part of the carboxyl groups have ott-La a p 1 L ' a U b u t . ""',,"r, " I not reacted with copper(I1) or tin(I1) ions. . dht line is obtained for all Uranyl(I1) is one of the most firmly hound ions. [The detertypes of paper, which almost passes through the datum point mination of carboxyl groups in carboxymethylcellulose (6) is (Figures 1 and 2). actually carried ant at a p H as low as 4.1 The chromatographic With uniform types of paper the reproducibility of various determinations have shown, however, that with certain types of determinations is satisfactory. For Whatmrtn No. 1, for expaper, uranyl ions exhibit abnormal absorption phenomena. as a ample, the standard deviation from the average wa8 2.16% (Tahle result of which the spots obtained are too small. The uBe of I). The error in the determination of the size of the spots is silver ion leads to complications if reducing _ P_ ~ O U.D Sare nresent still smaller (Table 11). UBUally no differenceis found for elution in the paper (5, $8). Methylene blue produces very d e a i spots, periods varying between 20 minutes andI 24 hours, but with Borne hut in a weakly acid medium complete ion exchange does not t w e s of naner the water rises so slowl, r that the definite size of take place, owing to its position in the ionic series. 1 (Table 111). 1
Of
_I.I ....I..I .._.I ".."..ll.l"l." ".." ".".-".-.It cations for carboxyl groups varies. I n this connection it is possible to draw up B series (8, $3);
UO1++
P h + + > Sn+ > Cu++ > H + > methylene blue+ > Ba++> C a + + > Ag+ > TI+ > K f > N a + > Li+ > N(CH,),+
The most striking feature is the strong bonding of the hydrogen ion (23)and of Rome multivalent metals of the secondary groups. The lead ions are capable of displacing the hydrogen ions, so that the carhoxyl deterrainations are fairly independent of the pH. Consequently, pretreatment of the paper with acid does not affect the results (Tahle IV). It may be assumed that in this process all carboxyl groups react with the lead ions. The spot
Figure 2.
Earboxyl content
. I. . Methyl eat!:
of Whatrnsn No. 1
559
V O L U M E 2 7 , NO. 4, A P R I L 1 9 5 5 Table IV.
Influence of Pretreatment of Filter Paper on Carboxyl Determination
(Treated papers washed with dilute HC1 and water) Weight of Spot, Mg. Type of Paper Lead Acetate, Meq. Untreated Treated 9.7 x 10-4 115 111 Whatman N o . 1 Schleicherand Schull No. IlOlL 19.4 X 10-4 51 56 32 35 hlacherey, Nagel No. 613 19.4 X 10-4
In the case of galacturonic acid (Figure 3, I ) (see Figure 5 for the formula), a pronounced absorption peak is found a t 5.8 microns which is attributed to the stretching frequency of the C=O bond of the carboxyl group. With glucuronic acid lactone (Figure 3, II), the peak occurs a t 5.7 microns; with calcium galacturonate, on the other hand (Figure 3, III), the salt form maximum absorption occurs a t 6.25 microns.
Table V. Determination of Carboxyl Groups with Lead Acetate and Copper Sulfate on Whatman No. 1 Paper Weight of Spot, Mg. Copper sulfate Lead acetate 31.8 40.7 49.3 86.0 71.2 123.0
Salt Solution Used, l l e q . 1.94 X 10-4 3.88 x 10-4 5.82
x
10-4
The results obtained with the lead method for various types of paper have been summarized in Figure 2 and Table VII. The calcium acetate method usually produces higher values (Table VI). With a view ton-ard ascertaining whether this difference must be ascribed to the presence of easily opening lactone or ester groups, the authors recorded infrared spectra in the range 5.5 to 6.5 microns (Figures 3 and 4 ) . n
LooH
OH
H
OH
PLGlNlCACIO
Figure 5. Hexose derivatives, mentioned in text
1
I 5A
I
15
-
I
1
65
625
6.0
- P
Figure 3. I.
11. 111.
Infrared spectra
Galacturonic acid Glucuronic acid lactone Calcium galacturonate
The spectrum of untreated cellulose (Figure 4, 11) exhibits absorption only in the range of 6.1 microns, Fhich is ascribed to a bending frequency of absorbed water (21). In the case of oxidation with nitrogen dioxide (Figure 4, III), absorption appears a t 5.8 microns, which could indicate the presence of both acid and lactone. I n the case of treating the oxidized cellulose with diazomethane (Figure 4, IV), the peak is sharper and lies a t 5.75 microns. When oxidized cellulose is titrated according to the calcium acetate method, the infrared spectrum of the calcium 'salt formed (Figure 4, V) no longer shows any signs of absorption in t,he range of 5.75 microns. It must be assumed, therefore, that under these conditions the lactone ring is d i t oDen. The titration of alginic acid (16) is somewhat similar, since in a dry state its carboxyl groups are nearly all in the lactone form (11). During the titration of glucuronic acid lactone in the presence of calcium acetate considerable drift was found a t the end point. This indicates that the lactone ring opens, especially in a weakly alkaline medium. I n applying the lead method to the methyl esters of Whatman No. 1 and nitrogen dioxide-oxidized filter paper, it was invariably found that part of the carboxyl groups were still reacting (Figure 2 and Table VII). I n particular with esterified "celluronic acid," the wide variation in spot sizes is indicative of partial splitting of ester during the chromatography. Whatman No. 1 gave no visible reaction when spraykd with hydroxylamine and iron(II1) chloride; I
55
57 5
Figure 4.
825
60
Infrared spectra
I . Paraffin oil 11. Untreated cellulose 301-oxidized cellulose IV. Methyl ester of NOI-oxidized cellulose V. Calcium salt of NO*-oxidized cellulose
111.
65
-P
*
-
560
ANALYTICAL CHEMISTRY REFERWCES
Table VI.
Results Obtained with Calcium Acetate and Lead Method
Type of Paper Schleicher and Schiill No. llOlL Macherey, Nagel No. 613 Oxidized Whatman No. 1
Table VII.
Carboxyl Content, hleq./Gram Calcium acetate Lead acetate 0.08 0.046 0.10 0.65
0.064 0 420
Carboxyl Content of Some Filter Papers
Type of Paper Whatman N o . 1 Methylester of Whatman KO.1 Oxidized Whatman No. 1 Methylester of oxidized Whatman No. 1 Whatman No. 4
Carboxyl Content, Meq./Gram 0,008 0.002 0.420
0.017 0.007
0.007 0.035 0,046 0.064
Davidson, G. F., J . Teztile Inst., 39, T 6 5 (1948). Ibid., p. T87. Ibid., p. T93. Farrar, J., Neale, S. Ll., and Williamson, G. R., A’ature, 168, 566 (1951). Foreiati, F. H., Rowen, J. R., and Plyler, E. K., J . Research Nail. B u r . Standards, 4 6 , 4 (1950).
Francis, C. V.,ANAL. CHEM.,2 5 , 941 (1953). Geiger, E., and Kuneler, P., Helu. Chim. Acta, 28, 283 (1945). Haller, R., and Lorenz, F., Melliand Tertzlber., 14, 449 (1933); 1 2 , 2 5 7 (1931).
Heymann, E., and Rabinov, G., J . P h y s . Chem., 4 5 , 1 1 5 2 (1941). Hirsch, P., Rec. trav. chim., 71, 525 (1952). Kaye, 11.A. G., and Kent, P. W., J . Chem. SOC.,1953, 79. Kullgren, C., Svensk Papperstidn., 51, 47 (1948). Kunin, R., and Barry, R. E., I n d . Eng. Chem., 41, 1269 (1949). Lautsch, W.,llanecke, G., and Broser, W.,2. Saturforsch., 8b, 232 (1953).
Liidtke, M., Biochem. Z., 233, 25 (1931); 268, 372 (1934); 285, 78 (1936): Z . anuew. Chem.. 4 8 . 650 (1935).
nitrogen dioxide-oxidized paper showed a faint color and the methyl esters of these papers colored strongly. It is evident that oxidized cellulose contains a certain quantity of lactone groups which are readily split open. Such groups can also occur in native cellulose; therefore, no conclusions should be drawn regarding the acid value of the ionizable groups by extrapolation of titration curves (33). I n titrations with an excess of alkali the splitting of lactone is probably not the principal reaction involving the liberation of extra carboxyl groups. Carbonyl groups can, in an alkaline medium, be subject to conversions resulting in the formation of carboxyl groups. Furthermore, cellulose is very sensitive to oxidation a t a high p H value. Apart from difficulties arising a t very high lactone concentrations, the chromatographic determination of carboxyl groups carried out by means of lead ions seems to be a rapid and reliable method for determining the carboxyl content of filter paper. ACKNOWLEDGMENT
The authors express their sincere thanks to G. J. Schuringa for his encouragement, to J. R. H. van Nouhuys, director of the Vezelinstituut T.S.O.(Fiber Research Institute T.X.O.), for his permission to publish the results of this investigation, and t o R. C. Blume and G. S. Milford for discussing and-correcting the manuscript.
AIcGee, P.’A., Fowler, W.F., Jr.; and‘Kenyon, W.O., J . A m . Chem. SOC.,6 9 , 3 4 7 (1947).
Kabar, G. hl., and Padmanabhan, C. V., Proc. Indaan Bcad. Sci., 31.4,371 (1950).
Neale, S . >I., and Stringfellow, W. A.. Trans. Faradav S O C . 31, , 1718 (1936);33,881 (1937).
Nevell, T. P., J . TertiZeInst., 42, T91 (1951). Roudier, A . , Assoc. tech. i n d . papetihre, Bull., 4 , 118 (1953). Rowen, J. W., and Plyler, E. K., J . Research NatZ. B u r . Standards, 4 4 , 3 1 3 (1950).
Sarkar, P. B., Chatterjee, H.. hIaeundar, A. K., and Pal, K. B., J . SOC.Dyers Colourists, 63, 229 (1947).
Schdnfeld, T., and Broda, E., Mikrochemie aer. Mikrochini. Acta, 3 6 / 3 7 . 5 3 7 (1951).
Schute, J. B.; thesis, University Leiden, p. 90, 1953; S a t u r e , 171,839 (1953).
Sookne, -4.AI., Fugitt, C. H.. and Steinhardt, J., J . Research S a t l . B u r . Standards, 2 5 , 61 (1940).
Sookne, A. >I., and Harris, AI., Ibid., 25, 47 (1940). Ibid., 2 6 , 2 0 5 (1941). Weber, 0. H., 2. prakt. Chem., (K.F.),158, 33 (1941). Whistler, R. L., llartin, -4.R., and Harris, M.,J . Rescarch S a t l . B u r . Standards, 2 4 , 13 (1940). Whittaker, V. P., and Wijesundera, S., Biochem. J . , 51, 348 (1952).
Wieland, Th., and Berg, A , , Angew. Chem., 6 4 , 4 1 8 (1952). Wilson, K., Srensk Papperstzdn., 5 1 , 4 5 (1948). Rijk, A. J. A. van der, and Studer, ll.,Helv. Chim. Acta, 32, 1698 (1949).
Yackel, E. C., and Kenyon, W. O., J . A m . Chem. S O C . ,64, 121 (1942).
RECEIVED for review April 28, 1954. .4ccepted October 25,
1954.
Rapid Determination of Water in Silicate Rocks LEONARD SHAPIRO and W. W. BRANNOCK
U. S.
Geological Survey, Agricultural Research Center, Beltsv;lle,
A rapid and simple method for the determination of total water in silicate rocks has been developed by modifying the Penfield procedure. In this method, the time required for a single determination has been reduced to less than 10 minutes. Comparison of the data obtained by this modification and the Penfield method indicates the same degree of accuracy.
T
H E value obtained for total water in a rock analysis includes water of crystallization, water held uncombined in the grains or on their surfaces, and water formed, as the result of heating, from hydrogen or hydroxyl groups present in regular atomic arrangement in molecular or crystal structure. The determination of water in rocks invariably involves initial
Md.
ignition of the powdered sample, either by itself or with a flux, and subsequent measurement of the expelled water. The expelled water can be measured in several ways. It can be absorbed in a desiccant in a preweighed tube (I), condensed and determined by measurement of volume (S), or measured as in the method of Penfield ( 4 ) , which is more widely used than any other method. In the Penfield method the upper part of the glass tube, containing the condensed water expelled from the sample powder, is separated by fusion from the lower part of the glass tube, containing the powder. The part containing the water must be allowed t o reach thermal and moisture equilibrium with the laboratory air before weighing. A second time-consuming heating and equilibration step is necessary in getting the final or “dry tube” weight to subtract from the initial weight to obtain the amount of water in the sample. Because of these time-consuming steps, the
