Figure 3, the following conclusions can be reached:
Table II.
A difference of 0.0018 absorbance unit between the upper and lower curves is equivalent to 1 mg. of niobium pentoxide per 100 ml. Under the conditions of the method, each 1 mg. of niobium pentoxide is equivalent to 0.001 absorbance unit (lower curve), Each 0.001 absorbance unit is equivalent to 0.0125 nig. of titanium dioxide per 100 mi.
Ti02
RESULTS
A n-eighed amount of titanium dioxide was carried through the procedure and the titanium was determined in four equal aliquots of the final solution. Various weights of titanium dioxide were also carried through the procedure. The results of these experiments, which illustrate the precision and accuracy of the method, are shown in Table I. Experiments were also performed with titanium dioxide to which iron or iron and niobium had been added. In the latter case the correction for niobium was applied. These results are shown in Table 11. Titanium dioxide was determined in a n ilmenite free of niobium (Table 111). The titanium dioxide content had previously been determined volumetrically and confirmed gravimetrically as 48.5%. With concentrated ilmenites-that is, those containing 40 to 60% titanium dioxide-the sample weight must be 0.2500 gram. I n such n case, if the
Present, Gram Fez03 Nb&
0.1250 0.1250 0.1250 0 1250 0 1250
0.1250 0.1250 0.1000 0 1000 0 1000 Table Ill.
This latter correction is applied to determine the contribution of niobium to the absorbance reading for titanium. Even though this method does not measure the amount of niobium accurately, it gives a sntisfactory correction.
Accuracy in Presence of Iron or Iron and Niobium
... 0.0050 0 0250 0 0500
Niobium TiOn Found, Correction, Gram Gram (Corr.)
Found, Gram TiOz Nb206 0.1248 0.1249 0.1250 0 1251 0.1257
... 0.0025 0 0240 0 0490
0.1250 0 1248 0 1251
0 0000 0 0003 0 0006
Determination of Titanium Dioxide in Ilmenite O r e
Ore Taken, Gram
Added, Gram
0.2500 0,2500 0 2500
0.01oo 0.0500
Nbn05
niobium pentoxide content of the ore is 5% (which is abnormally high), there is 0.0125 gram of niobium pentoside in the sample. This amount of niobium would increase the amount of titanium dioxide found by only 0.00015 gram, which is equivalent to about 0.06% of the amount actually present. Thus, with concentrated ilmenites there is no need to consider the interference of niobium because it is so small that the error it contributes is within the limits of accuracy of the method, If the niobium pentoxide content of the ore is greater than 5%, the correction must be applied. These cases are frequent in mixed ilmenites-columbites, impure columbotantalites, and the like. Some of the ores encountered in this laboratory have 30 to 50% niobium pentoxide and only 1 to 5y0 titanium dioxide. When the titanium dioxide content is betn-een 20 and 40%, 0.5 gram of the
+-
TiOJ Found, yo SnectroVolumetric p hdtometric 48.47 48.53 48.49
48.52 49.68 59.08
ore should be taken. For ores containing less than 20% the initial weight should be 0.75 gram. However, if the ore is a tantalite-columbite, it is not advisable to take more than 0.5 gram because of the voluminous precipitate obtained in the tannin precipitation. LITERATURE CITED
Hillebrand, K.F., Lundell, G. E. F., “Applied Inorganic Analysis,” 2nd ed., pp. 584-51 FT’iley, Kew York, 119531.
Me&er, R. A., \Tells, R. A., Analyst 79, 339 (1954).
Neal, W.T. L., Ibid., 7 9 , 4 0 3 (1954). Palilla, F. C., Adler, X., Ilislrey, C. F., ANAL.CHEM.25, 936 (1953). Reillev. C. N.. Crawford. C. hl.. Ibid.; 27, 716 ’(1955).
Schoeller, W. R., Powell, A. R., “Analysis of Minerals and Ores of the Rarer Elements,” 3rd ed., p. 126, Griffin, London, 1956. RECEIVEDfor
review December
1956. Accepted February 10, 1958.
11,
Fixation of Atmospheric Carbonyl Compounds by Sodium Bisulfite K. W. WILSON Department o f Engineering, University o f California, los Angeles ,The bisulfite method of Goldman and Yagoda for atmospheric formaldehyde has been evaluated for other aldehydes and ketones a t concentrations from 0.3 to 0.5 p.p.m. A modification is described which results in increased accuracy and precision.
THE
wlfite method of Goldman and bib Yagoda (S), in which excess bisulfite is removed with iodine and the
24, Calif.
aldehyde bisulfite compound is titrated with standard iodine after decomposition with a n acetate-carbonate buffer, has been widely used to estimate atmospheric aldehydes (2, 5, 7‘). Goldman and Yagoda demonstrated t h a t formaldehyde a t concentrations of 7 p.p.m. (by volume) and higher could be trapped from air in 1% sodium bisulfite with 957, or higher efficiency when air flows as high as 28 liters per minute were
used. Other investigators used the method to determine mixtures of various aldehydes in the atmosphere at concentrations as low as 0.1 p.p.m. Occasional comments about the probable trapping efficiency of bisulfite under these conditions (1, 6) indicate that higher aldehydes are not trapped quantitatively; however, formaldehyde is the only carbonyl compound which has been studied in controlled experiments. VOL. 30, NO. 6, JUNE 1958
1127
Table 1.
Analyses of Air-Aldehyde Mixtures
Bisulfite Temp. of Concn., Trapping Soln. 70 1 Ambient
Carbonyl Compound Formaldehyde
Sampling Rate, L./Min.
Propionaldehyde
1
Ambient
%-Butyraldehyde
1
Ambient
Isobutyraldehyde
5 1 1
Ambient Ice bath Ambient
Acetone
5 I 1
Ambient Ice bath Ambient
1
Ice bath Ambient
5 1
Ambient Ice bath
1 2 1 2 1 2 1 1 2 2 2 1 2 2 2 1 2 2 1 2 2 2
1
ilmbient Ice bath Ambient Ice bath
1 2 1 2
Ice bath
Methyl ethyl ketone
7cin 2nd Impinger 0 0 0 0 0 0 0 0 10 10 0
5 20 25 0 25 25 15 50 50 35
Found,a P.P 31
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
45 43 50 18 35 36 27 26 27 25 34 29 28 31 30 22 19 42 12 00 02 0 23
Theory,
P,P.?*I. 0.48 0.48 0.48 0.48 0 36 0.36 0.35 0.33 0.35 0.35 0.33 0.33 0.33 0.33 0.30 0.42 0.42 0.42 0.34 0.34 0.34 0.34
Atmosoheric aldehydes, 7/9/57 10 :30-11 :30
1
0 0 0 0
0 . 1 6 0.05 0.12 1 0 . 0 2 0.06 =k0.05 0.08 f 0 . 0 3
Values are averages of two to four determinations.
The work reported determines the trapping efficiency of the conventional bisulfite method for a series of carbonyl compounds, and presents an improvement which increases precision and trapping efficiency. ACCURACY
OF BISULFITE TITRATION
An average atmospheric sample of 100 liters of air contains less than 10-6 mole of aldehyde and requires less than 0.3 ml. of 0.006N iodine for titration. Although the bisulfite titration is accurate and dependable for a wide variety of aldehydes with relatively concentrated iodine (0.1N) (4, 6), the precision was tested with very dilute aldehyde solutions titrated with 0.006.V iodine. The method of Goldman and Yagoda was modified slightly by using only 10 ml. of buffer instead of 25 ml. Keeping the volume of solution to be titrated to a minimum results in a sharper end point. Titrations of solutions prepared b y pipetting small volumes of 0.02% solutions of formaldehyde, propionaldehyde, n-butyraldehyde, and isobutyraldehyde into 1% bisulfite were reproducible t o within 0.03 to 0.04 ml. of O.OO6N iodine. Titrations of freshly prepared aldehyde solutions gave results which were within 10% of theoretical values. This accuracy is adequate for most air pollution work and is probably all that can be expected in view of the instability 1128
ANALYTICAL CHEMISTRY
of the aldehydes and the small volumes of solutions which must be measured. Two ketones, acetone and methyl ethyl ketones, were investigated in a similar manner. The initial end point obtained upon titration of the excess bisulfite fades slowly with acetone and somewhat more rapidly with methyl ethyl ketone. Less than the theoretical amount of iodine was required to titrate the ketone bisulfite compounds. If the titration was made on ice cold solutions, nearly the theoretical amount of iodine was required for acetone, and the amount for methyl ethyl ketone R-as greater than a t room temperature but still less than the theoretical. Acidifying the bisulfite solution to pH 1 as recommended by Joslyn and Comar (4) and titrating in the cold gave still higher results which were quantitative for acetone and about 90% of the theoretical for methyl ethyl ketone. I n all other experiments, the bisulfite solutions were not acidified before titrating the excess. A slight increase in accuracy would not warrant an acidification step, particularly as titration of acidified formaldehyde bisulfite solutions requires prior neutralization with sodium hydroxide or addition of 25 ml. of buffer rather than 10 ml. PREPARATION OF STANDARD ALDEHYDE-AIR MIXTURES
The successful investigation of alde-
hyde fixation by sodium bisulfite requires a method for preparing mixtures of air and constant amounts of aldehydes of the order of 0.3 to 0.5 p.p.m. b y volume. Aldehydes other than formaldehyde are oxidized in air so rapidly that it is impossible to prepare a stock mixture for a series of experiments lasting several hours. Mixtures prepared from aldehydes and ordinary tank nitrogen were also unstable. Dilute aqueous solutions of aldehydes are much more stable; they were kept for 25 days n i t h only a 10% decrease in concentration as measured by bisulfite titration. The method adopted for preparing t h e mixtures was t o add to a 10 liter per minute stream of carbon filtered air an approximately 0.2% aqueous solutioq of aldehyde a t a rate of 0.38 ml. per hour. This was accomplished with a motor-driven syringe which delivered the solution to a glass tube, nhich was heated to 60" to 70" C. over a 1-inch length to ensure complete vaporization, The remaining 7 inches of the tube con, stituted a sampling manifold which al, lon-ed two samples to be withdrawn simultaneously. The concentration of aldehyde in the air stream was determined in three ways: A, by calculation from the measured amount of aldehyda used to prepare the aqueous solution (assuming that the aldehyde was 100% pure) and the knon-n air and solution flow rates; B, by calculation from tha concentration of the aqueous solution as determined b y bisulfite titration and the knob-n air and solution flow rates; and C, by adding the aldehyde solution directly to bisulfite for a measured length of time using the motor-driven syringe and determining the amount added b y bisulfite titration. The concentration of aldehyde in the air stream was calculated from the known air flow rate. Although results by all three methods agreed within 10 to l5%, method C was less precise than method B. This indicated that the rate of delivery from the syringe was not absolutely constant. As sampling times of the order of 1 hour were usually used, it was hoped that the variation in delivery rate would not cause serious errors. The concentrations of ketones in the air stream could be determined only by method A, because the bisulfite titration is not very reliable for estimating ketones. EXPERIMENTAL PROCEDURE
Before any samples were taken, the air stream, syringe drive, and heater were turned on and the dilution system was allowed to run for 30 minutes. During this warm-up period, samples. of the aldehyde solution used to fill the syringe were diluted tenfold, pipetted into 1% bisulfite, and titrated. When the blending system reached equi-.
librium, samples of the resulting gas stream were passed through two fritted midget impingers connected in series. Usually two samples were taken simultaneously for approximately 1 hour. Air flow rates were measured with rotameters. The contents of each inipinger were titrated separately. Blank runs vere niade on the carbon filtered air, and these values (0 03 to 0 05 ml. of 0.006.Y iodine for 60 liters of air) were subtracted from the sample values. The concentration of aldehyde in the gas stream was calculated from the following equation: (Sof iodine) (ml. of iodine) (12,000) (liters of air sampled) p.p.m. at 20” C. (1) INFLUENCE OF TEMPERATURE
A large fraction of the 1% bisulfite was oxidized when 60 or more liters of air were passed through the bubbler. The amount of bisulfite remaining varied with the time of day, the flow rate, and the porosity of the fritted disk in the impinger. The amounts of bisulfite remaining in the first and second inipingers were approximately the same. Occasionally all of the bisulfite was oxidized, and very low aldehyde values were obtained. Increasing the bisulfite concentration did not increase the amount remaining at the end of the sampling period. K h e n the impingers were cooled in a n ice bath, more than 50% of the bisulfite remained after sampling 120 liters of air as compared with 2 or 37, which usually remained in an impinger d i i c h mas not cooled. RESULTS AND DISCUSSION
The experimental results are presented in Table I. Some excess bisulfite remained a t the end of each sampling period. Titrations ivere done a t room temperature hen trapping was at room temperature and in cooled aolutions n-hen the impingers were cooled. Ketones were always titrated cold. Formaldehyde and propionaldehyde TI ere trapped quantitatively and retained entirely in the first impinger regardless of cooling when sampling rates up to 2 liters per minute were used. This wac: the highest rate at which air could be passed through the impingers without excessive frothing. Although acetaldehyde v a s not tested in this series, it should also be quantitatively trapped. T h e C4 aldehydes were trapped less efficiently a t room temperature and were partly retained in the Tecond impinger. Cooling the impingws in a n ice bath quantitatively trapped all of the aldehyde in the first impinger. Acetone was trapped only 50% effi-
ciently a t room temperature; however, substantially all of i t was trapped if the impinger was cooled in a n ice bath. Part of the acetone was trapped in the second impinger even m hen a n ice bath was used. The values for methyl ethyl ketone will be only about 85% of the theoretical even if trapping is 100% efficient, because the bisulfite titration gives low results for this ketone. The values found varied from 0% a t ambient temperature to 70% when a cooled impinger was used. thus indicating only partial trapping. A large fraction of the ketone is retained in the second impinger. These data indicate that the original Goldnian and Tagoda method, \Then used for analysis of aldehyde and ketone mixtures, is dependent on the design of the impinger and the flow rates used. K i t h a midget impinger containing a medium porosity fritted disk and using a sampling rate of 2 liters per minute, the CI, CZ, and C3 aldehydes are determined quantitatively; low results are obtained for C4 aldehydes and acetone. There is little basis for predicting results for aldehydes of higher molecular weight, as the factors which determine the efficiency of bisulfite as a trapping medium have not been clearly determined. It may depend on the reaction rate of aldehyde with bisulfite or on a combination of reaction and diffusion rates. The C6 and higher aldehydes should be trapped no more efficiently than C4 aldehydes, and possibly less efficiently. Ketones should be trapped only to a very slight extent. When 1% bisulfite is used in the field without cooling for trapping atmospheric aldehydes a t low concentrations, erratic results may be expected because a large fraction of the bisulfite may be destroyed by oxidation in m r n i weather. RECOMMENDED MODIFIED METHOD
The follon-ing procedure ensures quantitative trapping of acetone and aldehydes up through C4 and partial trapping of methyl ethyl ketone. Xothing is known about the trapping efficiency for higher aldehydes. Place 10 nil. of lyG aqueous sodium bisulfite in each of two midget impingers mith fritted disks. Chill thoroughly in a n ice bath. Connect the impingers in series, and draw air through a t 2 liters per minute until a t least 12 pl, of aldehyde have been trapped. Keep the impingers cooled in ice during the sampling period. Remove the bisulfite from the impingers without using wash water, and titrate each separately. While the solution is cold, titrate with 0 . 5 N iodine to a yellow color. Remove the yellom- color with 0 0 5 S thiosulfate,
add 1 nil. of starch solution, and titrate with 0.005N iodine to a faint blue color. Read the buret. Add 10 ml. of buffer (80 grams of sodium carbonate and 20 ml. of glacial acetic acid per liter), titrate with 0.005N iodine until the faint blue color returns, and read the buret again. The end point should be stable for about 30 seconds but will gradually fade. R u n a blank determination on a 10-ml. sample of bisulfite. From the difference between the two buret readings for the sample subtract the value of the blank. Calculate the parts per million of aldehyde from the sum of the titration values for the first and second impingers, using Equation 1. COMPARISON
OF METHODS
An attempt was made t o compare the original Goldman and Yagoda method with the proposed modification in the analysis of atmospheric aldehydes. Representative results obtained on a smoggy day are listed a t the bottom of Table I. The large uncertainties are calculated b y assuming a n uncertainty of 0.04 ml. of iodine. The small concentrations of aldehydes present required such small volumes of iodine for titration that very poor accuracy was obtained. From these data i t is not possible to conclude whether higher results are obtained when the impingers containing the bisulfite are aooled. l l u c h more meaningful results would be obtained if numerous analyses could be made during intense smog where aldehyde concentrations are 0.5 p.p.m. and higher. The comparatively lo^ sensitivity of this aldehyde method coupled d h the long sampling time does not make it attractive as a routine method for air monitoring. LITERATURE CITED
,P. L., “Air Pollution Handbook, Chap. 3, P. L. Magill, others, eds., McGrawHill, S e w York, 1956. (2) Cholak, J., Proc. Natl. Air Pollution Symposium, Second Symposium, pp. 6-15, Stanford Research Institute, Los Angeles, Calif., 1952. (3) Goldman, F. H., Yagoda, H., IND. EYG.CHERI.,ANAL.ED. 15, 377-8 (1) Cadle, R. D., Magill,
(1943). (4) Joslyn, M. A., Comar, C. L., Ibid., 10,
364-6 (1938).
( 5 ) Larson, G. P., Second Technical and Administrative Report, Los Angeles
Countr Air Pollution Control District, Los Angeles, Calif., 1950-51. (6) Parkinson, A. E., Wagner, E. C., IND. ENG. CHEJI., ANAL.ED. 6, 433-6 (1934). ( 7 ) Stanford Research Institute, Second Interim Report, “Smog Problem in Los Angeles County,” Western Oil and Gas Association, Los hngeles, Calif., 1949. RECEIVEDfor review July 24, 1957. Accepted December 23, 1957. Work supported by the State of California.
VOL. 30,
NO. 6, JUNE 1958
1129
‘
