Determination of 1,2-Propylene Glycol in Ethylene Glycol IRWIN M. BAUMEL' lnrtrument Facility,
U. S. N a v a l Engineering Experiment Station, Annapolis, Md.
A
from its absorbance a t 277 nip. One difficulty encountered in this scheme was the evolution of iodine during the distillation of the aldehydes. Iodine and iodine-containing acids formed by iodine and n-ater absorb strongly in the ultraviolet region and interfere with the acetaldehyde determination. Iodine probably results from an iodic acid reaction with propylene glycol to liberate hydriodic acid (7), which in turn reacts with iodic and periodic acid to yield iodine. Precipitation and reduction of the iodine followed by a second distillation failed to eliminate the problem. It was then found that the reaction must be run in a much more dilute solution than had been used, one which does not favor the iodic acid reaction. The addition of 300 ml. of ivater to the reaction mixture prevented the iodine formation and the aldehydes distilled over clear. The distillation of acetaldehyde n as expected to be quantitative Cannon and Jackson (1) showed that essentially complete transfpr of acetaldehyde occurs, while only a small fraction of the formaldehyde comes over. Small cuts taken after the first 40 ml of distillate showed no detectable acetaldehyde. -4working curve was prepared by ovidizing glycol mivturee of known concentration and plotting absorbance a t 277 mp us concentration of 1.2-propylene glycol or the theoretical yield of acetaldehyde. The working curve was checked from time t o time in the same manner. Synthetic aldehyde mixtures prepared to simulate the oxidized glycols Tvere not satisfactory, as they changed concentration on standing. Ultraviolet spectra of stored acetaldehyde and mixed acetaldehyde-formaldehyde solutions showed the development of absorption bands in the 220 t o 230 mp region which were absent in freshly prepared samples. It is believed that these bands are due to aldol and crossed Cannizarro condensation products, as fresh samples distilled with a small amount of sodium hydroside yielded the same absorption bands. I n the case of the stored samples, minute amounts of base leached from the glass container probably catalyze these condensations. The best results n'ere obtained by making absorbance readings on the samples as soon as they reached the temperature of the Beckman sample-cell compartmentj as those allon ed to stand several hours yielded poor results.
S ACCUR.4TE and routine method for the determination of
1,2-propylene glycol in antifreeze mixtures has been sought by the ilrmed Forces for quality control of antifreeze mixtures purchased under military specifications. These antifreeze mixtures also contain water, a dye. a corrosion inhibitor. and polyglycols. Polyglycols are alcoholic ethers of the types HO( CH$2H*O),H and HO(CHaCHCH?O),H. Existing methods do not yield the desired accuracy or reproducibility of results. L-ltraviolet analysis of the periodic acid oxidation product. seems t o be the answer to the problem. SLRVEY OF TIETHODS
Almost all of the previous n ork on this determination involved the oxidation of the vicinal glj-cols with peiiodic acid follon-ed by various methods of detecting the aldehydes. Karshowsky and Elving ( 8 ) and Cannon and J a c k o n ( 1 ) determined the aldehydes polarographically, but according to the latter authors their method is suited only for the determination of small amounts of l,2-propylene glycol. Dal Sogare, Sorris, and Mitchell ( e ) prepared the aldeh>-des by the periodate oxidation and then converted the acetaldehyde to iodoform. which was then determined colorimetrically in the visible range. Reinke and Luce ( 5 )flushed the aldehydes out of the periodate reaction niivture with an inert gas through scrubbing columns of glycine and sodium bisulfite, xith the glycine removing the formaldehyde and the bisulfite the acetaldehyde. This method yields consistrntly low results because glycine reacts with some of the acetaldehyde. although the calculations assume complete absorption by the bisulfite which is suhsequently titrated with iodine. There is also doubt as to m-hether the bisulfite quantitatively absorbs the acetaldehyde (3). Jordan and Hatch (4)used nitric acid to oxidize the propylene glycol to a form that nil1 yield iodoform on reaction with iodine and sodium hydroxide, this iodoform being determined volumetrically. In this reaction polypropylene glycol which frequently appears as an impurity n-ould cause an error. especially since one mole of polypropylene glycol yields tn-o moles of iodoform
APPARATUS DEVELOPMEST OF ULTRhVlOLET PROCEDURE
A Beckman Model DU ultraviolet spectrophotometer, hydrogen discharge lamp with appropriate p o w r supply, and 1-em. silica absorption cells n-ere used for the absorbance determinations. A 1-liter round-bottomed flask with a i 5 " adapter was connected to a water-cooled condenser. and a 105' condenser discharge adapter was connected t o a 10-inch length of 4 m m . glass tubing which dipped to the bottom of a 50-ml. Sessler tube.
In the search for a better analytical method, variouP infrared and ultraviolet spectrophotometric approaches were tried. Direct infrared analysis was abandoned because the very st.rong absorption bands could not be resolved with cells of even the phortest path length available. h suitable solvent could not be found for dilution. The sandivich technique helped t o resolve the absorption bands but suffered from lack of reproducibility. rlnother problem encountered which discouraged further work on this approach was the large number of components in the average antifreeze mixture. Silver chloride cells were used in this part of the investigation. Infrared and ultraviolet analysis of various derivatives was attempted, but no suitable onts were found. Examination of published ultraviolet spectra showed acetaldehyde (6) to have a relatively strong absorption peak at 277 nip, whereas formaldehyde was virtually transparent in this ultraviolet region. This suggested that accurate results might be obtained by osidizing the vicinal glycols with periodic acid, distilling the resulting aldehydes, and determining acet,aldehyde Present address, Pyrotechnics Section, Picatinny Arsenal, Dover,
PROCEDURE
Accurately weigh about 5 grams of glycol mixture and dilute t o 250 ml. with distilled water. Pipet 50 ml. of this solution into the 1-liter flask. Add 300 ml. of water and 100 ml. of periodic acid solution (45 grams per liter) and a few glass beads and immediately connect the flask to the condenser adapter. Collect the distillate in the 50-ml. Nessler tube containing 10 ml. of water, the Sessler tube half immersed in an ice bath. Lower the tip of the 4-mm. distillate discharge tube below the surface of the water in the Sessler tube. Heat the flask and distill until the liquid in the Sessler tube is almost to the 50-ml. mark. Raise the tip above the surface of the distillate and allow it to come t o full volume. Insert a one-hole rubber stopper with a thermometer in the Sessler tube and allox the temperature of the sample to rise t o the temperature of the Beckman sample-cell compartment. Read absorbance at 277 mM.
N.J.
930
V O L U M E 2 6 , NO. 5, M A Y 1 9 5 4
931 tillation, eicept to ~ a i until t the proper temperature is reached. This entire determination should take about 1 hour to complete n ith results comparable to the best of the aforemeritionecd methods.
Table I. .4nalysis of SJnthetic 3Iixtures Containing Eth: lene Gl\col, 1,2-Propylene Glycol, and Borax I P - P r o p l lene Glycol,
i n samgle
5
round
Error, %
09 04 09 09
+o -0 +o
+o
01 04 01 01
' 95
10 10 10 07 10 00 10 00
i o +o +o +o
15 12 05 05
;o
14 70 14.80 14.60 14 90
+'ri.'lO - 0 10 +o 20
3 08
:4
8 3 3 3
.4CIiSOULEDG3IENT
The author is indebted to -4ndrew Davis and n'athan Ingher, \\.hose n o r k and ideas proved invaluable to the successful completion of this investigat,ion. LITERATURE C I T E D
(1) Cannon, IT.A , , and Jackson, L. C., .INAL. CHEM.,24, 1053 (1952). ( 2 ) Dal Sogare, S., Sorris, T. O., and Mitchell, J., Jr., I b i d , , 23,
1473 (1951). (3) Fuson, R . C., "Advanced Organic Chemistry," p. 378, Sew Tork, John Wiley & Sons, 1950. (4) Jordan, C . B., and Hatch, V. O.,ASAL. CHEM.,25, 636 (1953). (5) Reinke, R. C., and Luce, E. X., IND.ENG.CHEM.,ANAL.ED., 18,244 (1946). (6) Shell Development Co., U t r a r i o l e t Spectral D a t a , d.P.1. Project 44, S a t l . Bur. Standards, Serial 326, Sept. 30, 1949. (7) Shriner, R. L., and Fuson, R. C., "Identification of Organic Compounds," p. 105, Yea- Tork. John Wiley & Sons, 1948. (8) STarshoc\-sky,B., and Eli-ing, P. ,J., ISD. ESG. CHEX, ; ~ I C A L ED., . 18, 2-33 (1946).
nisCussIoN
Representative (lata oil eynthetic antifreeze mixtures are s1ion.n in Table I. These mixtures contain 2.5% boraxu,which is used as a corrosion inhibitor. Its presence did not interfere with the determination. There can l w no interferences from po!ypropylene glycol with this method. :is only the vicinal glycols are oxidized by periodic acid and onl>- their osihtion products come over in the distillate. S Ofurther c~hemicalnianipulation is neceqeary after dip-
RECEIT-ED for reriew J u n e 12, 1$1.3. l c c e g t e d February 10, 1054. The oiinions expressed in this paper are those of the author a n d are not necessarily official opinions of t h p t-,S . Sal-a1 Esperiinent Station or the S a v y Deiiartnient.
Aluminum Powder as a Binder in Sample Preparation For X-Ray Spectrometry ISIDORE ADLER and 1. M. AXELROD U. S. Geological Survey, Washington 25, D.
C.
S
.4MPI,E preparation is an important, ever-present problem in x-ray fluorescence spectrometric analysis of powders. In particular, the density of packing, the surface smoothness, and the position of the sample may have a marked effect on the measured intensities. I t was felt that briquets or compacts, eompressed to the same extent, offered one obvious solution. This approach has been tried and found to be eminently satisfactory.
niobium in an iron oxide matrix, a briquet with a 1 to 1 dilution resulted in no more than a 5 to 10% loss of absolute intensity over the use of the sample powder alone. This is, of course, a favorable case because of the relatively short wave length of the niobium line. It is to be expected that the attenuation would be greater ior elements of low atomic numbers, but even here the use of the aluminum powder briquets offers advantages. Homogeneity of the specimens was also investigated. Five briquets n-ere prepared containing 57, each of niobic and molybdic oxides. The ratio of intensity of the molybdenum K a line to the niobium K a line was measured ten times for each briquet, using a multi-wave-length spectrometer built in this laboratory (1). One goniometer was set for the molybdenum K a line and the other was set for the niobium K a line. The briquets were changed after each measurement. Each side of each briquet was measured five times and the positioning was random. Be-
PROCEDURE
One half gram of minus 200-mesh sample or standard is intimately mixed with 0.5 gram of minus 270-mesh aluminum metal dust. The diist, obtained from commercial sources, required further sieving. A convenient method of mixing the powder and aluminum dust is to grind the mixture under ether, a technique commonly employed in some emission spectrographic laboratories. Enough ether to make a thin mud is added to the mixture, which is ground until the ether evaporates. This process repeated three or four times gives good mixing ( a well ventilated hood is required). The mixed sample is then compressed in a briquetting press with a mold 1 inch in diameter a t approximately 30,000 pounds per square inch. This results in a disk 1 Table I. inch in diameter and approximately 0.05 inch thick. These briquets have Briquet S o . the appearance of aluminum disks, are A Sidea ~ t r o n g and , can be handled and stored 1.35 with ease. 1.35 T E S T S FOR I N T E N S I T Y AND HOMOGENEITY
Lose of interlsity due to dilution by aluminum powder was investigated.
~~~
Comparison of the Ratio 1
2
-__
3IOKcP - for Five Briquets NbKa 3
4 5 B -4 B I B 1.36 L37 1.40 1.38 1.37 1.39 1.38 1.34 1.34 1.38 1.33 1.35 1.34 1.34 1.33 1.36 1.32 1.36 1.38 1.31 1.36 1.85 1.38 1.3H 1.36 1.37 1.37 1.33 1.32 1.36 1.38 1.33 1 34 1 34 1.35 1.33 1.32 1 31 1.32 1.33 1.32 1.34 1 34 1 28 1.30 1.30 1.34 1 28 dverage 1.344 1.348 1.352 1.364 1.356 1 . 3 3 8 1.346 1.348 1.338 1 . 3 2 4 Because a multi-ware-length spectrometer, featuring separate optics for each line. was used, there need not be 1 to 1 correspondence between ratios of concentrations and intensity ratios observed. X b K a count = 6400. b Labeling is random.
n
A
n
4
