ANALYTICAL CHEMISTRY
1076 This counting system has been used extensively in identification of unknown emitters. For example, chemical tests indicated the presence of radioactive iron in a solution. An absorption
OF
K - X RAYS
CY particles when plotted on linear paper is a straight line whose intercepts are the range of the particles and the absolute 01 count. This makes possible very precise energy measurements of CY emitters. The- method is also applied to determining the proportion of two CY emitters in a mixture. These techniques are not infallible in identifying unknown emitters in a mixture, but they can be extremely useful when used in conjunction with chemical analysis and half-life studies.
A - GAMMA
8- OBSERVED CURVE MNUS GAMMA MINUS 046 MKV. COMPONENT IO 26 ME.’.! COMPONENT) C OBSERVED CURVE MINUS GAMMb 1046 ME,V. COMPONENT
D- OBSERVED CURVE
001-
0
,
,
20
40 60 80 100 I20 ABSORBER THICKNESS IN MG./CM!
IkO
Figure 9. Absorption curve of mixture of iron-55 and iron-59 study of the iron separation was made. Analysis of the curve shown in Figure 9 clearly shows the y and the 0.26- and 0.46m.e.v. p particles from iron-59 and the K-capture x-rays from iron-55. A half-life study confirmed the identification. The application of this system to CY counting has been described (6). It is shown that the absorption curve of monoenergetic
LITERATURE CITED
(1) Baker, TI-. H., “Counting Systems for Pulses of TVide Dynamic Range,” M o u n d Laboratory, Monsanto Chemical C o . , Miamisburg, Ohio, MLM-618 (Oct. 15, 1951). ( 2 ) Baker, W. H., “Sonlinear Pulse Amplifier of Wide Dynamic Range,” M o u n d Laboratory, JIonsanTo Chemical Co., Miamisburg, Ohio, MLM-851 (June 9, 1953). (3) Baker, W.H., Curtis, M .L . , Gnagey, L. B., Heyd, J. W., and S t a n t o n , J. S., .Vc~cZeonics, 13 (Yo. 2), 40-3 (1955). (4) Curtis, h l . L . , and Heyd, J. W.,“Absolute Alpha Counting. I. Determination of Back-Scattering Factors and Ranges,” M o u n d Laboratory, Monsanto Cheniical Co., Miamisburg, Ohio, MLM-834 (April 10, 1953). (5) Curtis, hl. L., and Heyd, J. IT., “Windowless Absorption Counter for Routine Energy Measurement of Soft Radiations,” Mound Laboratory, Monsanto Chemical Co., Xliamisburg, Ohio, MLM-842 ( d p r i l 10, 1953). (6) Curtis, M. L., H e y d , 3. IT.,Olt, R. G., and Eichelberger, J. F., Sucleonics, 13, h-0. 5. 39 (1955). (7) F e a t h e r , N., Proc. Cambridge P h i l . Soc., 34, 599 (1938). (8) Glendenin, L. E., Sucleonics, 2 (No. 11, 12 (1948). (9) Ibid.,p. 21. (10) Ibid.,p. 26. (11) Gnagey, L. B . , “Windowless Proportional Chamber for Absorption Measurements,” M o u n d Laboratory, Monsanto Chemical Co., Miamisburg, Ohio, MLM-857 ( M a y 15, 1953). (12) Stanton, J. S., and Heyd, J. W., “ T h e Preparation of Plastic a n d Metallic Absorbers,” M o u n d Laboratory, Monsanto Chemical Co., Miamisburg, Ohio, MLM-858 (June 17, 1953).
RECEIVED for review December 23, 1954. Accepted March 17, 1955. M o u n d Laboratory is operated by llonsanto Chemical Co. for the U. S. Atomic Energy Commission under Contract No. AT-33-1-GEN-53.
Schiff Reagent Its Preparation and Its Use in the Determination of Formaldehyde in Cellulose Acetate Formal DAVID E. KRAMM and CHARLES L. KOLB Celanere Corp. of America, Summit,
N. J,
This work was undertaken to provide a method for the determination of small amounts of combined formaldehyde in cellulose acetate formal samples. A Schiff reagent of controlled sensitivity and improved stability has been developed and utilized. Sensitivity has been correlated to sulfur dioxide concentrations and both optimum and reproducible response are shown to occur in the range 2.8 to 4.8 millimoles of sulfur dioxide per 100 ml. of reagent. The formaldehyde content of cellulose acetate formals has been determined colorimetrically using Schiff reagent. The method developed shows a standard deviation of 0.02170 of formaldehyde for samples of cellulose acetate formal film containing less than 0.8% of formaldehyde. The improved performance of Schiff reagent has resulted in’an analytical tool of increased versatility. Sufficient stability and reproducibility have been obtained to make daily calibration unnecessary.
T
HE development of a colorimetric method for the determina-
tion of formaldehyde in cellulose acetate formal falls naturally into two parts: the preparation of a sensitive Schiff reagent which will give reproducible results against known amounts of formaldehyde] and the achievement of sample hydrolysis in such a way that the formaldehyde is quantitatively obtained in a form suitable for measurement with Schiff reagent. STUDY OF SCHIFF REAGENT
Blaedel and Blacet ( 1 ) found that Schiff reagent reacts with formaldehyde in strong sulfuric acid to give a blue color which reaches a maximum intensity after 2 to 2.5 hours. While other aldehydes may also produce initial colors, these colors fade completely in the 2- to 2.5-hour period prescribed. This makes the test selective for formaldehyde. Blaedel and Blacet applied it to the determination of formaldehyde in the presence of other aldehydes. Hoffpauir, Buckaloo, and Guthrie ( 8 ) adapted the
V O L U M E 27, NO. 7, J U L Y 1 9 5 5 procedure of Blaedel and Blacet for use Tvith a photoelectric colorimeter, and obtained a reproducible curve for transmittance ( a t 550 to 555 mp) against milligrams of formaldehyde. This curve, however, is S shaped and does not obey the Beer-Lambert law. Several initial attempts to reproduce the n-ork of Hoffpauir and others xere unsuccessful. This was primarily due to the difficulties encountered in preparing a colorless Schiff reagent of the required sensitivity. Other workers, notably Segal ( 4 ) , haye encountered similar difficulties. In view of these difficulties, a quant,itative study x a s made of the following factors affecting Schiff reagent preparation and sensitivity: influence of rosaniline hydrochloride concentration, influence of sulfur dioxide concentration, and conditions for decolorizing xith act,ivate-l carbon. Apparatus. 1,umctrsn cpdlorinieter lIodel 402-E, Photovolt Corp. (or equivalent) 5 5 0 - m ~glass filter. ~Il)sorptioi~ wlls 0.5, 1, :ind 2 em. (Photovolt Corp.). Reagents. Rosaniline hydrochloride, llatheson, Colenian, ant1 Bell. Sodium mcta bisulfite, reagent grade (?;a$&:). Activ:ited c-:irbon, Such:ir-CS (West Virginia Pulp & Paper Co.). Sulfuric acid, 6 s . Staritlard iodine solution, 0,1.\. Starch *elution, 0.570. Formalin (40Y0 aqueous formaldehyde solution). llised acid reagent, volume composition 50% w t e r , 5% 10.1h>-drochloric acid, 4570 1 4 5 sulfuric acid. Aqueous hydrochloric acid, 1 O S . Aqueous sulfuric acid, 1LY. Schiff reagent prepared as designated below. Preliminary work with various batches of Schiff reagent, prepared according to the specifications of Hoffpauir et al. ( 2 ) and decolorized v i t h activated carbon as described by Segal (4) indicated that an optimum concentration of 3.0 millimoles of sulfur dioxide per 100 nil. of reagent gave greatest sensitivity. These reagents, as those of most previous investigators, contained 100 mg. of basic fuchsin per 100 ml. I n order to see whether any worth-while gain in sensitivity could be attained by increasing the dye concentration, several high dye reagents were prepared, with the sulfur dioside concentration controlled in accordance with the previous finding. Sensitivity was assessed by reacting each reagent with knoxvn amounts of formaldehyde and measuring the transmittmce after color development. Results are summarized in Table I. Table I. Influence of Dye Concentration on Schiff Reagent Performance HCHO,M g .
Dye. hIg./lOO
MI.
100
200 300
$02,
Millimoles/ 100 MI. 3.01 3.04 2 84
0.046 0.077 0.13i 0.023 Per Cent Transmittance at 5.50 lip, 2-Cm.Cell 97.0 94.8 83.0 79,l 43:7 97 3 94.6 9z.3 93.3 74.8 35.5
It is apparent from Table I that worth-while g i n s in reagent response are achieved in going from dye concentrations of 100 mg. per 100 ml. to concentrations of 300 mg. per 100 ml. The colors obtained using reagents with dye concentrations greater than 300 mg. per 100 ml. appear t,o be dichroic, having purple to red hues instead of the usual blue color obtained with reagents of lower dye concentrations. Work with these reagents was therefore limited to this qualitative observation. In view of the above results it was decided to hase further work on a Schiff reagent containing 300 mg. of dye per 100 ml. Since the optimum sulfur dioside content previously established as 3.0 millimoles of sulfur dioside per 100 nil. of Schiff reagent applies t,o a reagent containing only 100 mg. of dye per 100 ml., t,his experiment \vas repeated to establish the sulfur dioxide concentration limits for optimum response of the high dye reagent,. These results are plotted i n FiguTe 1.
1077
Reference to Figure 1 indicates that in the range 2.8 to 4.8 millimoles of sulfur dioside per 100 ml., reagent response is essentially a maximum, and that above and below this range, reagent response rapidly deteriorates. I t is, thereforerproposed tc hold the sulfur dioside content within this optimum range. Trial and error esperimentation in the decolorization of Schiff reagent wit,h activated carbon has shown that, both the amount of carbon used and the reagent-carbon contact time esert important influences on the sensitivity of the reagent. I n general, the use of small amounts of carbon (200 to 800 mg. per 500 ml.) and relatively long contact periods (5 to 15 minutes) are not so effective as the use of larger amounts of carbon acting for shorter
A
E
TRANSMITTANCE IN PERCENT Figure 1.
Loci showing variation of Schiff reagent sensitivity with reagent sulfur dioxide content for fixed formaldehyde levels A. B.
0.250 m g . of HCHO 0.125 m g . of HCHO
C. 0.050 m g . of HCHO
Ordinates D a n d E enclose zone of o p t i u m reagent response
periods. Segal ( 4 ) recommends the use of 1 gram of carbon per 500 ml. of Schiff reagent and both Segal ( 4 ) and Tobie (6) use gravity filtration through filter paper to separate activated carbon, without specifving contact time. By employing a Buchner funnel and vacuum filtration, it has been found that much shorter reagent-carbon contact periods may be achieved. Presumably previous workers have avoided vacuum filtration in order not to lose sulfur dioxide. However, this fear is groundless once the optimum range for sulfur dioxide is known, for it is always possible to adjust the concentration after vacuum filtration, although experience has shown this to be rarely necessary. I n practice, therefore, a 45-second contact period has been empirically developed and used a t Segal’s recommended carbon concentration of 1 gram per 500 ml., followed by a vacuum filtration which requires about 2, and no more than 3, minutes for completion. Preparation of Schiff Reagent. Place 1500 ml. of distilled water in a 3-liter Erlenmeyer flask, add 4.500 zk 0.005 grams of rosaniline hydrochloride, and swirl to solution. Add 9.60 & 0.05 grams of sodium metabisulfite, mix and let stand 5 to 10 minutes, then add 40 ml. of 6 S sulfuric acid, mix well, stopper, and allow to stand overnight. Prepare a large Buchner funnel and 2-liter filter flask for a suction filtration through two sheets of No. 2 filter paper. Add 3.0 grams of activated carbon to the Schiff reagent, quickly mix by swirling, and time for a contact period of 15 seconds. After the lapse of the 45-second contact period, pour the Schiff reagent into the Ruchner funnel, and filter with suction ‘1s rapidly as possible. The total time required for filtration should be about 2 minutes and no longer than 3 minutes. The above time specifications provide that all of the Schiff reagent d l be in contact with the activated carbon a t least 45 seconds and that none of the Schiff reagent n-ill be in contact with the nctivated carbon longer than 225 seconds.
A N A L Y T I C A L CHEMISTRY
1078 Pipet 10.0 ml. of the decolorized Schiff reagent into a 125-ml. Erlenmeyer flask, add 20 ml. of distilled mater and 5 ml. of starch, and titrate the free sulfur dioxide to a starch end point m-ith standard 0.1~Viodine solution. Calculate the free sulfur dioxide as fol1ow.s) 5 X milliliters of iodine X normality = millimoles of sulfur dioxide per 100 ml. of Schiff reagent. If the reagent sulfur dioxide content falls outside the optimum range of 2.8 t o 4.8 millimoles of sulfur dioxide per 100 ml. of reagent, adjust i t t o higher or lower levels until a value within this range is attained. Sulfur dioxide concentrations may be raised by adding a calculated amount of sodium metabisulfite, and lon ered by bubbling air through the reagent. I n general, if the above steps have been followed, the reagent sulfur dioxide content will fall within the optimum range. Standardization of Schiff Reagent. Prepare a dilute solution of formaldehyde containing ahout 8 mg. of formaldehyde per 100 ml. by adding 0.4 ml. of formalin to 2 liters of 0.05.Y sulfuric acid. This solution may be standardized by the gravimetric dimedon method of Yoe and Reid (6) or the modified bisulfite method employed by Nitschmann and Hadorn ( 3 ) : in the present work the bisulfite method Tvas employed. From the standard formaldehyde solution prepare by accurate dilution with 0.05-Y sulfuric acid a t least ten standard formaldehyde solutions containing from 0.15 to 4.0 mg. of formaldehyde per 100 ml. T o complete the standardization react 10 ml. of each formaldehyde solution with 20 ml. of Schiff reagent and 20 ml. of mixed acid reagent. After 2.0 t o 2.5 hours determine the transmittance, in per cent, a t 550 mp, with the colorimeter. The useful range of the curve can be extended by using a 2-em. cell for the lon formaldehyde range, a 1-cm. cell for the intermediate range, and a 0.5-em. cell for the high range, as indicated by Figure 2 . For these measurements the instrument is adjusted for 100% transmittance m-ith a blank containing 20 ml. of Schiff reagent, 20 ml. of mixed acid reagent, and 10 ml. of water. Plot the transmittance in per cent LIP. milligrams of fornialdehyde on regular graph paper. Typical graph is shom-n in Figure 2. The batch to batch reproducibility of Schiff reagent prepared as indicated is illustrated by the transmittance data of Table 11.
Table 11. Standardization Data for Tw-o Typical Batches of Schiff Reagent in Per Cent Transmittance a t 550 %I, Rlg.
HCHO 0.417 0.334 0.250 0.209 0.167 0.142 0.125 0.109 0,084 0,067 0.050 0.034 0.025 0.017
0.5-Cm. Cell Batch Batch A B 11.4 21.5 39.0 50.2
11.3 22.2 39.5 52.0
.. .. ..
..
,.
.. .. .. ..
..
.. ..
1-Cm. Cell Batch Batch A B
..
5.4 16.6 26.0 40.6 51.1 58,3 66.3 77.0 83.9 90.0
..
5.7 17.0 27.0 41.2 51.7 59.4 66.8 77.6 85.0 90.7
2-Cm. Cell
Batch
Batch
..
.. .. ..
A
.. .. .. ..
..
n
..
..
..
..
.. si:s
..
80:s 90.1 94.1 96.7
,.
90.7 94.7 97.5
Previous workers have employed a color development period of 2.0 to 2.5 hours for the Schiff reagent-formaldehyde reaction. The validity of this reaction time for the high dye reagent has been corroborated by determining transmittance as a function of time. Contrary to the experience of Hoffpauir et al. ( 2 ) , it has not been necessary to run a standard curve each time Schiff reagent is used. Standardization every 4 or 5 days is ample, provided the sulfur dioxide concentration is controlled n-ithin the optimum range. It is necessary, however, to run a standard curve each time a new lot of rosaniline hydrochloride is received or when the source of the dyestuff is changed. A change in source of dyestuff may produce minor changes in the shape and placement of the standard curve. The data of Table 111, collected over a period of 23 days for a single batch of Schiff reagent, shox the degree of stability that may be expected in reagent response. When the reagent was betn-een 13 and 1i days old, it m-as found that the sulfur dioxide concentration had fallen below the optimum range of 2.8 to 4.8 millimoles of sulfur dioxide per 100 ml. Therefore, it \vas adjusted upxvvard by the addition of
Table 111. Per Cent Transmittance Obtained for Schiff Reagent Aged 1 to 23 Days (1-Cm. Cell) Rlg.
6
1
13
17
20
23
HCHO
Day
Days
Days
Days
Days
Days
0 050 0.109 0.142 0.209
90.0 66.3 51.1 26.0
90.1 66.7 51.2 27.2
89.G 72.4 5-1.1 29 5
91.0 69.0 54.6 29.2
91.1 70.2 56.0 30 7
91.0 69.3 55.1 30.4
Table IV.
Solubility of Cellulose Acetate Formal in Hydrochloric Acid
Approximate Time Normality Required to Dissolve of 1 Gram C. A . Formal HC1 in 10 111. of Acid, IIin. 12 10 8 6
15 30 100
Insoluble
Color of HC1 Solution after 17 Hours Dark brown Light yellow Colorless Insoluble
Effect of Subsequent Dilution xith Distilled Water h-o precipitation No precipitation Polymer precipitates Polymer precipitates
sodium metabisulfite : thereafter the reagent response remained essentially constant from ages 17 to 23 days. The maximum error shon n by the preceding data, for standardizations no more than 6 days apart, i.q about 6% of the formaldehyde measured. It is felt that the degree of stability of reagent response demonstrated above is due piiniarily to control of sulfur dioxide concentrations nithin the optimum range. Freedom from the necessity of standardizing Schiff reagent daily provides a method of greater utility than that previously obtained. No special precautions n-ere taken to preserve the Schiff reagent used to collect the above data. The reagent was stored in a clear glass carboy under air nith a rubber stopper closure. ANALYSIS OF CELLULOSE ACETATE FORllAL
Hoffpauir et al. (a),in the determination of formaldehyde in cellulose formals, hydrolyzed the samples by an overnight treatment nith 1 2 s sulfuric acid a t room temperature. This procedure does not work in the case of cellulose acetate formals. Conditions n ere therefore varied by letting the sulfuric acid normalities range from 12 to 1 8 s and hi drolysis temperature, from room temperature up t o 50" C., nithout success. Strong hydrochloric acid, on the other hand, \vas found to be a rapid acting solutioning and hydrolyzing agent for cellulose acetate formal. The results of trials a t various hydrochloric acid normalities are shos n in Table IV. On the basis of the qualitative solubility behavior exhibited in Table IV, 1 0 s hydrochloric acid \vas selected for further mork. It mas thought that the Schiff reaction could be carried out in strong hydrochloric acid solution as well as in strong sulfuric acid solution; however, this is not the case. When 10,V hydrochloric acid is employed t o replace the 1 2 5 sulfuric acid used by Hoffpauir et al. ( 2 ) in standardizing Schiff reagent, yellow to orange colors are produced instead of blue. It appears, therefore, that hydrochloric acid provokes an interference reaction of some kind, and that the presence of sulfuric acid is essential. The high efficiency of hydrochloric acid as a sample hydrolyzing agent for cellulose acetate formal made its abandonment undesirable, consequently a means n as sought to eliminate hydrochloric acid interference effectively. To this end, mixed hydrochloric-sulfuric acid solute systems n ere investigated as color developing media for Schiff reagent. It was hoped that the ratio of hydrochloric to sulfuric could be controlled EO that the interference reaction mould be inhibited and the normal color reaction would proceed. These svstems are listed in Table T'. From the above n-ork, it appears that the hydrochloric acid normality, rather than hydrochloric-sulfuric ratio, is the factor controlling interference. Furthermore, in color developing media over 0 . 2 5 in hydiochloric acid, interfering reactions predominate. Solute system 4 has heen adopted as the basis for the analytical method for formaldehyde in cellulose acetate formal. Several
V O L U M E 27, NO. 7, J U L Y 1 9 5 5
145 HzSO4.
H20.
10.00
3.57
6 43
1.00
7.72
11 28
1 00
7 72
1.28
1 00
9.00
10 00
1 50
13.50
2 00
18 00
10s
HCI, MI.
0
111.
1\11,
IIgSO', Schiff HCHO Solution , Reagent, Std., 1\11, 1\11. MI.
Ratio CI/SOi
0
20.00
10 00
4.12
0
20 00
10 00
0.24
20 00
10.00
0.16
0
20 00
10.00
0.16
5 00
0
20 00
10,oo
0.16
0
n
20 00
10 00
10 00
samples were allowed to react n-ith 1 0 s hydrochloric acid at room temperatures for time periods ranging from 17 to 67 hours. -4 constant maximum formaldehyde yield is obtained after 17 hours; a t shorter time periods incomplete sample breakdown is achieved. ilbout 5% of the ssniplea encountered are incompletely broken don-n after 17 hours at roqm temperature. For these samples, a subsequent 2-hour low temperature heat treatment at 35' to 30" C. efiectively completes sample decomposition. T o establish uniform sample-to-sample degradation conditions, this heat treatment x a s adopted for all samples. Tse of temperatures higher than 33" t o 40" C. result in the formation of prohibitive amounts of extraneous color (bromi to black).
\\
-I%!
IO'
0 Figure 2.
I
1
I
I
I
I
I
I
I
-
0.10 0.20 0.30 0.40 MILLIGRAMS OF FORMALDEHYDE Standardization of Schiff reagent against known amounts of fornialdeh>de A. B. C.
Comments Unsatisfactory orange-yellow colors develoD
PROCEDURE FOR ANALYSIS SAMPLES.Accurately weigh into a tared 125-1111, glassstoppered Erlenmeyer flask a sample of cellulose acetate formal of amropriate size. If, as is general& the case, there is initially no knoBledge of the formaldehyde level, choose an arbitrary sample size of 1.0 to 1.3 grams and carry out the procedure described below. I n the event that the transmittance fails to fall within the range of 10 to 95%, consider the determination to be a pilot determination and adjust sample size t o a satisfactory level in accordance with the indications of the pilot determination. I n case the use of the arbitrary sample size provides a transmittance within the range 10 to 95%, accept the determination as a valid one. To the weighed sample accurately add 10.00 ml. of 10N hydrochloric acid, stopper the flask, and swirl vigorously. During the first 2 hours, occasionally swirl the flask vigorously, then allow to stand overnight a t room temperature (17 to 20 hours). Securely stopper the flask and heat for 2 hours at 35" to 40" C., cool to room temperature, then add from a 100-ml. buret, 90.00 ml. of 1 4 s sulfuric acid and mix. Pipet a 10-ml. aliquot of the mixed acid hydrolyzate into a 125-ml. glass-stoppered Erlenmeyer flask containing 20.00 ml. of distilled xater. I n the event that this 10-ml. aliquot provides a prohibitively low transmittance (due t o high formaldehyde content), a smaller aliquot may be employed instead. Optional aliquot sizes t o meet this contingency, together with accompanying changes in color developing media composition, are indicated in Table VI. Add by automatic pipet 20.0 ml. of Schiff reagent, mix, and let stand for 2 hours. (Caution. The use of suction in pipetting Schiff reagent will result in undesirable loss of reagent sulfur dioside.) Measure the transmittance in per cent of the colored solution a t 550 mp n-ith a colorimeter. Adjust the instrument for 100% transmittance mith a blank containing 20 ml. of Schiff reagent, 20 ml. of mixed acid reagent, and 10 ml. of distilled v.-ater. From the transmittance obtained, determine the milligrams of formaldehyde by reference to the standard curve. Calculate the formaldehyde content of the sample as folloxs: milligram. of HCHO from curve X 10 %HCHO = aliquot si7e in milliliters X sample v. t. in grams The use of an aliquot greater than 10 ml will result in an interference reaction involving hx-drochloric acid.
Cnsatisfactory orange-yellom colors develop 0 16 Unsatisfactory orange-yellow colors develop
080 grams per liter 1\lgSO$.
w
b e e n s h o w n experimentally that the standard curves with and xithout hydrolyzed cellulose acetate are identical and, therefore, the omission of acid hydrolyzed cellulose acetate from the standardization solute system is a valid shortcut.
Various Solute Systems as Color Developing .Media for Schiff Reagent
Table V. 'Slitem No.
1079
2.0-cm. cell 1.0-cm. cell 0.5-cm. cell
OF
Table YI. Composition of Color Developing 3ledia for Yarious Size Aliquots Aliquot SlZ? 111. 10.00 5 00 3 00
Mixed Acid Reaeent, 311.
H?O.
Schiff Reagent,
20.00 1.5.00 1 3 00
20.00 20.00 20 00
nii.
1\11.
Total Volume Colored Solution, 111.
hnalysis is accomplished by the folloir ing sequence of operations: Overnight solution of a Iwighed sample in 10 ml. of IOA\hydrochloric acid follomed by a 2-hour heating period a t 35" to 40" C. Addition of 90 ml. of l 4 S sulfuric acid to provide a mixed acid hydrolyzate 9 to 1 in 14,V sulfuric acid:lOS hydrochloric acid. Reaction of a 10-ml aliquot of the above mixed acid hydrolyzate with 20 ml. of Schiff reagent and 20 ml. of nater. Determination of tran-mittance at 550 nip and calculation of results.
Limited n-ork performed subsequent to the development of the above procedures has indicated that the inclusion of acetic acid in the reaction medium enhances the sensitivity of the reagent, especially at low formaldehyde concentrations. Specifically, 10 ml. of viater in the reaction system were replaced with 10 ml. of glacial acetic acid.
Trrenty-five different samples, ranging from 0.01 to 0.8% formaldehyde, \yere analyzed in duplicate The data so obtained yield a standard deviation of 0 . 0 2 1 ~ ,formaldehyde This is considered good reproducibility, especiallv since duplicate determinations have been carried out on successive days rather than simultaneously. A further point of interest concerns the preparation of the standard curve for knon n amounts of formaldehyde. From an operational standpoint, it is desirable to determine this curve in the absence of hydrolyzed cellulose acetate. It has
. (1) Blaedel. W. .J., and Blacet, F. E.. ISD. ESG. CHmr., A & ~ . & ~ED., 13, 449 (1941). (2) Hoffpauir. C. L., Buckaloo, G. W., a n d Guthrie, J. D., Ibid., 15, 605 (1943). (3) F i t s c h m a n n , H., a n d H a d o r n , H., Hell.. C h i m Acta, 24, 237 (1941). (4) Segal. Leon. AS.AL.CHEM.. 23, 1499 (1951). (5) Tobie. W. C., ISD.ESG.C H E K ,; ~ N A L .ED.,14, 405 (1942). ( 6 ) Y o e , J. H.. a n d R e i d , L. C . . I b i d . , 13, 238 (1941). RECEIVED for review December 10, 1951. Accepted February 12. 1955.
None
i o no
14.00
60.00
50.00 50.00
LITERATURE CITED
