E remains constant throughout the range of concentrations of eluent entering the column in the gradient elution. ACKNOWLEDGMENT
The authors express their gratitude to the Colgate-Palmolive Co. for financial assistance in this investigation. LITERATURE CITED
( 1 ) Alm, R. S., Williams, R. J. P., Tiselius, A., Acta Chem. Scand. 6, 826 (1952).
(2) Beukenkamp, J., Rieman, W., Lindenbaum. S.. ANAL. CHEM. 26. 505 (1954). ' (3) Bock, R. M., Ling, N. S., Zbid., 26, 1543 (1954). (4) Busch, H., Hurlbert. R. B.. Potter. V. R., J. Biol. Chem. 196, 717 (1952). (5) Drake, B., Arkiv. Kemi 8 , l (1955). (6) Freiling, E. G., J . Am. Chem. SOC. 77, 2067 (1955). (7) Gradde, T.' A.,' Beukenkamp, J,, ANAL.CHEM.28, 1497 (1956). (8) Lindenbaum, S., Peters, T. V., Rieman, W., Anal. Chim. Acta 11, 530 (1954).
Nervik, W. E., J . Phys. Chem. 59,690 (1955).
Palmer, J. K., Conn. Agr. Exptl. Sta., New Haven, Bull. 589, 1955. Peters, T. V., Rieman, W., Anal. Chim. Acta 14, 131 (1956).
Rieman, W., Lindenbaum, S., ANAL. CHEM.24, 1199 (1952). Sargent, R., Rieman, W., Anal. Chim. Acta 16, 144 (1957).
Sargent, R., Rieman, W., J . Phys. Chem. 60, 1370 (1956).
Schwab, H., doctor's thesis, Rutgers University, 1956. RECEIVED for review January 24, 1957. Accepted hlarch 4, 1957.
Determination of Melamine-FormaIde hyde Resins in Coatings M. H. SWANN and G. G. ESPOSITO Coating and Chemical laboratory, Aberdeen Proving Ground, Md.
b The insolubility of acid hydrolyzed melamine resins in dioxane provides a rapid gravimetric method for their determination in modified alkyds, epoxy and other coating resins.
A
resins used for baking finishes are frequently modified with 10 to 20% of a nitrogen resin such as urea- or melamine-formaldehyde. For some time, the extent of this modification was calculated from the value obtained by determining total nitrogen. An infrared spectrophotometric method ($), developed for determining relatire amounts of urea- and melamine-formaldehyde resins in alkyd blends, is rapid and applicable to mixtures of these two nitrogen resins, but has limited accuracy and is subject to interference from some other resins. Recently, urea resins (4) were determined from a calculation based on the measurement of ammonia evolved on high temperature saponification of the sample. The latter method appears to be applicable to coatings in general. The acid hydrolysis of the urea- and melamine-formaldehyde resins has been used by a number of investigators to measure the combined formaldehyde content of these resins. Hirt, King, and Schmitt ( 1 ) applied this hydrolysis to the determination of melamine resin content of certain wrapping papers, measuring the melamine by ultraviolet spectroscopy; this method is applicable to the analysis of the melamine-formaldehyde resin solutions but not to modified alkyds. I n recent investigations, the authors found that the products of acid hydrolysis of the urea and melamine LICYD
resins were insoluble in dioxane, which is a good solvent for coating resins in general. On this basis, a simple and
Table 1. Determination of Melamine in Melamine-Formaldehyde Solutions
Melamine - Present _ _ UV Total analy- nitrosis, gen, Resin Uformite hIhl-46 Undesignated Uformite 3.111-55 Melmac 243-3
Table II.
7 0 %
19 19 17 20
hlelamine Found ~ (Acid Hydrolysis),
1 19 5 2 20 1 5 16 2 0 19 1
70
19 19 16 18
5 7 6 8
rapid method of analyzing modified alkyds for melamine-formaldehyde resin was developed. Urea resins, which may appear separately or in mixture with the melamine resins, also give quantitative yields, but a specific method for determining the urea resins (4) provides a means of correction, thus allowing analysis of mixtures for both resins. Polyamide and triazine resins interfere and the method for melamine is not specific, but it is considered useful for the rapid analysis of coating resina known to be modified with melamine, or which can be qualitatively identified. The procedure can also be applied t o the analysis of coatings known to be modified only with triazine or urea
Analysis of Some Modified Alkyds and Epoxy Resins
Melamine. 9% Present Found I
Coating Type Alkyd, medium oil length (linseed)
Alkyd, long oil length (soybean) .4lkyd, short oil length (coconut) Alkyd, medium oil length, with urea-formaldehyde blended in amounts equal to melamine content
3.72 7.04 4.06 6.71 6.19 3.91 7.84 4.99
I
"
3.72 7.17 4 16 6 71 6.20 3.82 7.64
Calculated as Melamine-Formaldehvde Resin., 41, Present Found I -
11.1 21.0 12.1 20.0
11.1 21.4 12.4 20.0
5.05
3.54 2.07 12.00 11.67
3 66a 2 22a Epon 1004, melamine-formaldehyde blend 1 1 71 35 8 34 9 Epon 1007, melamine-formaldehyde blend 11 64 34.8 34 7 a Corrected for urea-formaldehyde present by analysis via saponification method (4).
VOL. 2 9 , NO. 9, SEPTEMBER 1957
1361
resins. I n the absence of all nitrogen resins other than the melamine resins, the advantage over total nitrogen as a method of analysis is esse of handling and the shorter time necessary to complete a determination in modified alkyds. An additional advantage of the new procedure is its value in separating nitrogen resins in coating blends to permit the analysis of other resins such as epoxy resins, which can then be analyzed by available methods (S), in the absence of nitrogen resins. Some analytical results appear in Tables I and 11. ANALYllCAL PROCEDURE
A sample of melamine formaldehyde resin representing 0.3 to 0.5 gram of nonvolatile material, or a sample of modified alkyd representing 0.125 to 0.3 gram of nitrogen resin, is nTeighed into a 250-ml. Erlenmeyer flask having a 24/40 ground-glass joint and is dissolved in 50 ml. of highest purity dioxane (Fisher Scientific Co. Catalog item D-53 has been found suitable).
From a buret, exactly 1.5 ml. of 6N hydrochloric acid is added with swirling of the sample. The sample is allowed to stand a t room temperature for 30 minutes and is then placed in a water bath a t 60" C., with air condenser attached. After 2 hours it is cooled to room temperature and filtered fhrough a weighed, fritted-glass crucible of medium porosity. The precipitate is transferred and washed with 75 to 100 ml. of dioxane. Air is drawn through the crucible for 5 minutes; then it is transferred to a vacuum oven and dried a t 50" C. to constant weight (approximately 2 hours), cooled, and weighed.
mine content of dioxane-insoluble mixtures of urea and melamine has not been entireIy satisfactory, I n the presence of urea resins, calculation is made a. follows, after the urea content on a separate sample has been determined by saponification:
The lveight of the precipitate can be calculated to melamine by the factor 0.540, or to melamine-formaldehyde resin by the factor 1.610. Factors were established after analyzing the resins shown in Table I by the ultraviolet and total nitrogen methods and basing the resin content on nonvolatile data supplied by the manufacturer for some of the samples. For unknown reasons, the determination liy ultra\-iolet of mela-
LITERATURE CITED
yo melamine
=
[a - ( b X c X
0.016l)l 0.54 X 100 b
weight of precipitate sample weight c = per cent of urea
where a b
= =
(1) Hirt, R. C., King, F. T., Schmitt, R. G., ANAL. CHEU. 26, 1273-4
(1954).
~
(2) Miller, C. D., Shreve, 0. D., Ibid., 28,200 (1956). (3) Swann, ?*I.H., Esposito, G. G., Ibid., 28. 1006-7 11956). (4) Ibid.; p. 1984.' '
RECEIVEDfor review January 16, 1957. Accepted April 17, 1957.
Quantitative Infrared Vapor Spectra R. A. FRIEDEL and J. A. QUEISER Cenfral Experiment Station, U. S. Bureau of Mines, Bruceton, Pa.
b The usefulness and limitations of infrared spectra of the vapor state are discussed. Quantitative introduction of volatile components into an evacuated infrared gas cell can b e achieved by discharging liquids from a selffilling micropipet through a sintered disk, Advantages of the method include applicability to aqueous solutions, production of fine structure, and elimination of solvent, interfering complexes, and some absorption-law deviations, Disadvantages include pressure-broadening and sorption of some vapors in the cell.
A
spectra are usually determined on chemical compounds in the state that they exhibit under standard conditions of temperature and pressure. The advantages of determining spectra in the vapor state have not been utilized, mainly because of the experimental difficulties involved in achieving quantitative results. When measurements in the vapor state are needed for theoretical or analytical purposes, volatile liquids are handled quantitatively by pressure measurements. For compounds having volatilities of a few millimeters a t room temperature, pressure measurements BSORPTION
1362
ANALYTICAL CHEMISTRY
are difficultand are customarily avoided. Sample and cell are usually heated to get sufficient vapor into the optical path; the temperature of the sample reservoir is sometimes given as a measure of vapor pressure. This method is reasonably accurate for a single component, but it is unsatisfactory for mixtures. These difficulties have been obviated by complete vaporization of precisely measured small volumes of liquid directly into an evacuated infrared cell. The technique is a modification of the self-filling micropipet method for introducing minute liquid samples into a mass spectrometer (6, 7 ) . The method permits accurate measurement of the amount of vapor in the cell and is applicable both to single components and to mixtures. Applications in ultraviolet spectrometry (3-5) and a method for obtaining infrared spectra of vapors by weighing liquids sealed in breakable ampoules have been described ( I S ) . Recently a catalog of infrared spectra of gases and of vapors from volatile compounds has been published (11). EXPERIMENTAL
Cell-Filling Technique. The technique for quantitatively vaporizing liquids into a vacuum has been de-
scribed in detail in connection with mass and ultraviolet spectrometry (4, '7). The absorption cell with mercury-covered sintered disk and a typical self-filling micropipet are shown in Figure 1. Mercury is poured into the barrel of the pipet containing the sample to seal the upper end; the pipet is touched to the sintered disk of the evacuated cell. and the rubber tubing is used as a squeeze-bulb to squirt the sample and part of the mercury into the sintered disk. If a valve or stopcock is not objectionable, more rapid evacuation is attained by placing the vacuum lead between the cell and the sintered disk (Figure 1). Spectral measurements were made on a Perkin-Elmer Model 21 doublebeam infrared spectrometer. DISCUSSION
OF RESULTS
Some advantages of the quantitative method of determining infrared vapor spectra are shown in Table I. Disadvantages include pressurebroadening and sorption of the vapors of some compounds in the cell. Sorption difficulties can be minimized by prior conditioning of the system with the sample. Qualitative Applications of Vapor Spectra ;Hydrogen-Bond Dissociation.
