Spectrophotometric Determination of Urea-Formaldehyde with Anthrone
SIR: A reddish uine-colored compound is formed when anthrone (9’10dihydro-9-ketoanthracene) reacts with urea-formaldehyde in acid solution. The color intensity follows Beers’ law. Anthrone has been used as the analytical reagent for the quantitative detection of carbohydrates (1-4). The conditions for its use as a quantitative reagent for determining urea-formaldehyde and Urea-formaldehyde in the presence of starch are described. EXPERIMENTAL
Apparatus. A Bausch a n d Lomb spectrophotometer equipped with 1inch cells is used for all absorbance measurements. Reagents. Reagent grade chemicals are used throug,hout, except for the urea-formaldehyde preparation. .INTHRONE. Dissolve 2.00 grams of anthrone in cool concentrated sulfuric acid and dilute to 1 liter with acid. Discard after 1 week. L-REA-FORMALDEHY DE. Accurately weigh out approximately 1 gram of ureaformaldehyde resin and dilute to l liter. Use dilutions of this solution to make standards. STARCH.Carefully oven-dry the starch at 105’ C. Immediately after cooling, weigh out 500 img. of O.D. starch. Heat approximately 500 cc. of distilled water to boiling and add weighed starch. After solution is obtained, cool and dilute to 1 liter. Use dilutions of this solution to make standards. Prepare a new concentrated standard each week. Procedure. T o a 1-inch cuvet, pipet 5.0 ml. of urea-formaldehyde solution containing 10 to 50 pg. of ureaformaldehyde and 10 ml. of anthrone reagent. Use a pipet with a large bore tip for the anthrone reagent and allow about 15 seconds drainage time. For improved standard curves, a 1-hour heating time at 80’ C may be necessary. Otherwise, the heat of acid dilution is used for color development. After cooling for 30 minutes measure with the spectrophotometer ai, 540 mp, using a reagent blank.
starch and urea-formaldehyde in the same solution. Absorbance spectra show no interference for starch determination. Conversely, both anthrone complexes absorb a t 540 mp. -\fter establishing the Beers’ law relationship for the anthrone-urea-formaldehyde complex, the additive absorbancies of starch and urea-formaldehyde were confirmed. Thus, for a starch-ureaformaldehyde mixture, measuring the starch a t 620 mp and subtracting its equivalent absorbance a t 540 mp, the difference in absorbance is the equivalent urea-formaldehyde present. Table I shows the results of known mixtures tested as de ribed. The method
Table I. Results from Known Mixtures of Starch and Urea-Formaldehyde
Starch, Crea-formaldehyde, mg. /li ter mg. /liter Known Found Known Found
does involve the preparation of three standard curves but only two sets of colorimetric standards-Le., starch and urea-formaldehyde.
0.4
0.3
0.2
0.I
w
0
z
$ 0.4
P
U
0.3
0.2
RESULTS A N D DISCUSSION
The absorption curve fer the anthrone - urea - formaldehyde complex was determined and compared to a similar curve prepared by substituting starch for the urea-formaldehyde. Figure 1 shows an anthrone-ureaformaldehyde maximum absorbance a t 540 mp and the usual anthrone-starch maximum a t 620 mp. The purpose of the investigation was the quantitative determination of both
0.I
1 SO0 Figure 1 . A. E.
70 0
600
WAVELENGTH,
mu
Absorption spectra
Anthrone-urea-formaldehyde, 26 mg./liter Anthrone-starch, 19 mg./liter VOL. 36, NO. 9, AUGUST 1964
1875
Work in this laboratory has shown that good can be Obtained with this procedure as it is applied to waste analysis. However, in mixtures containing amine substituted starches we have observed interference with the ureaformaldehyde determination. The results always tend to be high.
(2) Morris,
ACKNOWLEDGMENT
The author acknowledges permission of Weyerhaeuser c0,for publication, LITERATURE CITED
(1) Helbert, J. R., Brown, K. D., ANAL. CHEM.29,1464 (1957).
D. L., Science 107, 254 (1948). ( 3 ) Samsel, E. P., Aldrich, J. C., ANAL. CHEM.29,574 (1957). (4) Viles, F. J., Silverman, L., Ibid., 2 1 , 9 5 0 (1949). RAYG. WESTENHOUSE
Weyerhaeuser Co. Pulp and Paperboard Division Springfield, Ore.
Extraction of Iron(ll1) from Concentrated Phosphoric Acid SIR: The presence of iron(II1) as an impurity in phosphoric acid made by the wet process has led to a study of the removal of this cation from phosphoric acid solutions 5.1, 7 . 7 , 8.7, and 12.1M in phosphoric acid. The presence of hydrochloric acid significantly affects the extraction of iron from phosphoric acid solution. Previous work ( 1 , 5 ) indicated an increase in the per cent of iron extracted with increasing iron concentration whereas the results of this research show a decrease in the per cent iron extracted with increasing iron concentration. Dodson, Forney, and Swift (1) reported that isopropyl ether is a good extractant for the removal of iron from aqueous solutions of hydrochloric acid. Thus in the present work concentrated hydrochloric acid has been added to solutions of iron(II1) in phosphoric acid and the tetrachloroferrate(II1) produced has been extracted into isopropyl ether.
f 0.2' C. for 45 minutes with occasional mixing to ensure that equilibrium was reached. I n all cases, phase separation was established quickly. Analyses for iron(III), phosphate, and chloride were performed only on the aqueous phase and the concentrations of species in the organic phase were determined by difference. The concentration of iron was learned by reducing Fe(II1) to Fe(I1) with stannous chloride and titrating this solution with 0.05N potassium dichromate. The amount of P20sin the aqueous phase was found spectrophotometrically using the molybdovanadate method ( 2 ) . The chloride ion concentration was determined by the Volhard method. RESULTS A N D DISCUSSION
As in previous studies of the separation of iron(II1) from hydrochloric acid solution (1, 3, 4, the concentration of HC1 was found to play a most important part in the extraction process. I n the present investigation,
EXPERIMENTAL
lOOr
All chemicals were reagent grade and no attempts were made at further purification. The solutions of iron in phosphoric acid were prepared by dissolving ferric phosphate in concentrated (85%) phosphoric acid and diluting with water to the desired concentration. The procedure for extraction involved shaking the ferric phosphate solutions with 25 ml. of isopropyl ether and varying amounts of 1 2 . 3 s hydrochloric acid. The flasks were shaken and immersed in a constant temperature bath a t 25"
Table I.
HCI = 4 X ) M
\HsPO,
5.1 7.7 8.7 12.1
HCI
301
Effect of Acid Concentration on Extraction of Iron
[H,PO,] Moles/liter
1876
'q P 0 , = 7.7 M
5
5.1M
= 4.OM
20
Molar concn. of HC1 necessary to initiate extraction
maximum extraction
3.5 2.5 1.0 0
-5.7 5.3 5.2 4.7
Molar
concn. of HC1 at
ANALYTICAL CHEMISTRY
'Ot -
0 0
0.1
0.2
0.3 0.4 0.5 Iron Taken, m q l m l .
0.6
Figure 1 . Effect of iron concentration on extraction of iron from phosphoric acid
there is a limiting hydrochloric acid concentration below which there is no extraction of iron into the ether phase (Table I ) . Depending upon the HCl concentration, there is a maximum per cent iron extracted which shifts to higher concentrations of HCl with decreasing concentration in the system (Table I). The per cent phosphate extracted from phosphoric acid solutions 5.1, 7 . 7 , and 8.7M increased with increasing hydrochloric acid concentration. For these three solutions, there was a lower limit below which no phosphate was extracted into the ether phase (Table 11). For 12.1M H3P04,however, the per cent of phosphate extracted increased with decreasing HCl concentration, 45y0 of the phosphate being extracted a t 0 molar HCl. At constant phosphoric acid and hydrochloric acid concentrations, there is a decrease in the proportion of iron transferred to the organic phase with increasing ferric concentration. This is in contrast to previous investigations (1, 5 ) which showed that during the extraction of ferric ion from concentrated HC1 solutions, the per cent of iron extracted increases with increasing iron concentration. This deviation from the Sernst distribution law was attributed to polymerization of the FeC14- species and enhanced extraction of the polymer. However, it was later found (3,6)that the deviation from the distribution law is caused by dissociation of HFeC14 in the organic phase. This dissociation results in an increase in the per cent iron extracted by decreasing the activity of the undissociated HFeC14 in the organic phase. Thus, in the present study, the extraction and subsequent dissociation of H B P Oin ~ the organic phase causes a repression of the ionization of HFeC14 and the system more closely obeys the Kernst law. I t is interesting to note t h a t the decrease in the per cent iron extracted with increasing iron concentration is evident in the more concentrated phosphoric acid solutions while the concentration of iron present appears to
