1708
Anal. Chem. 1981, 53, 1708-1709
and make it suitable for screening purposes. Moreover the possibility of obtaining information at temperatures not attainable by GLC should not be disregarded. Possible improvements that can render the present technique more specific are (a) the utilization of “tailored” devices for the sample heating, (b) the use of different spectrometric detections (UV fluorescence, FTIR spectrometry), and (c) the application of computerized data processing systems.
(3) Thompson, K. C.; Wagstaff, K. Anaksf (London) 1979, 704, 666-679. (4) Brown, Chris W.; Lynch, Patricia F. Anal. Chem. 1978, 48, 191-195.
Paolo Tittarelli* Luigi Turrio Baldassarri Tiziana Zerlia Stazione Sperimentale per i Combustibili Viale A. De Gasperi 3 20097 San Donato Milanese, Italy
LITERATURE CITED (1) Bentz, Alan P. Anal. Chem. 1978, 48, 454A-472A. (2) Bentz, Alan P. Adv. Chem. Ser. 1980, No. 785, Chapter 3.
RECEIVED for review March 2,1981. Accepted May 11,1981.
Determination of Total Aliphatic Aldehydes in Auto Exhaust by a Modified 3-Methyl-2-benzothiazolinone Hydrazone Method Sir: The 3-methyl-2-benzothiaolinone hydrazone (MBTH) test for total aliphatic aldehydes developed by Sawicki et al. ( I ) has been widely used for auto exhaust analysis. Although not documented in the literature, most analysts now agree that the MBTH method is subject to a significant negative interference from the SO2 present in auto exhaust. Because other methods for aldehyde analysis are complex, we have attempted to salvage this simple yet useful colorimetric technique. We have found that the addition of 1% sulfamic acid (amidosulfuric acid) to the MBTH absorbing solution will reduce the SO2 interference to 1-2%, which is believed to be acceptable. EXPERIMENTAL SECTION Reagents. All reagents were AR grade and were prepared in distilled water. The MBTH reagent was prepared daily by dissolving 0.20 g of 3-methyl-2-benzothiazolinone hydrazone hydrochloride monohydrate (Aldrich Chemical Co.) in 200 mL of a stock solution of 1% sulfamic acid. The 1% FeC13-6H20solution was prepared as needed; it is stable for several days. The use of reagent grade acetone is important to avoid turbidity in the samples. Procedure. For both auto exhaust analyses and interference tests, 20 mL of the 0.1% MBTH-1% sulfamic acid reagent was added to a midget impinger (Ace Glass 7531C), and a measured volume of the test gas was drawn through the impinger. The impinger solution or an aliquot was transferred to a 100-mL volumetric flask with about 25 mL of distilled water and, after the mixture was allowed to stand at least 1 h, 3 mL of 1% FeC13 was added. After 60 & 5 min, acetone was added to the mark; within minutes, the absorbance at 635 nm against distilled water was measured with a Beckman Model 26 spectrophotometer using 1-cm cuvettes. A blank was prepared from the same amounts of reagents and distilled water. The method was calibrated with a standard solution of formaldehyde prepared from assayed Formalin. The molar absorbance ( E ) was about 50000 L g-mol-l cm-’. The total aldehyde concentration in the (CVS-diluted)auto exhaust was calculated as the equivalent formaldehyde from the absorbance reading, the calibration factor, and the gas sample volume. RESULTS SECTION The effect of the sulfamic acid modification on the MBTH test is shown in Figure 1. Nitrogen with and without SO2 (5 ppm) was passed through impinger solutions containing 0.1% MBTH and up to 1.5% sulfamic acid. Twenty micrograms of formaldehyde was added to each sample immediately before treatment, and the color was developed in the usual manner. The difference between the two curves, which is due to SO2interference, practically disappeared when the sulfamic 0003-2700/81/0353-1708$01.25/0
Table I. Spiked-Sample Formaldehyde Recovery by Modified and Briginal MBTH Methods formaldehyde recovered ____modifieda original av std dev no. of testsC a 1%sulfamic acid. diesel vehicles.
0.986 0.066 11
Reference 1.
0.71 7 0.136 33 Gasoline and
Table 11. Auto Exhaust Aldehyde Determinations by Modified and Original MBTH Methods total aldehyde, PPm modified/ modified‘“ original original cold start hot start composite FTPC
Gasoline 1.33 0.99 0.036 Diesel
cold start hot start composite FTPC
1.26
0.76 0.059
0.91 0.71 0.025
1.46 1.39 1.44
0.67 0.47 0.033
1.88 1.62 1.79
a 1%sulfamic acid. Reference 1. procedure in grams per mile.
.
Federal test
acid concentration exceeded 1% Sulfamic acid also decreased the sensitivity of the MBTH test, but the modified method still has adequate sensitivity for auto exhaust analysis. The 1% sulfamic acid modification was further evaluated in bench tests over a range of SO2 concentrations, aldehyde levels, and gas-sample volumes expected to be encountered in auto exhaust analysis. The results showed a small but statistically real negative interference from SO2 equivalent to 1-2% of the formaldehyde present. This is considered acceptable. The modified method was next evaluated with auto exhaust in several ways. The results of spiked-sample recovery tests, a classical method of checking for interferences, are summarized in Table I. One of two paired samples was spiked with formaldehyde, and the excess of aldehyde found in that sample after exposure to auto exhaust was compared to the original amount added to determine the recovery. The average recovery for the modified MBTH method was 98%, compared to only 71% for the original, unmodified method ( I ) . There 0 1981 Amerlcan Chemical Society
Anal. Chem. 1981, 53, 1709-'1710
0.45 c
"
t'"O
0.40
-
0.35
- i
Q rn
rn
g
high-premre liquid chromatography (2) are shown in Table 111. The agreement is considered satisfactory for both gasoline and diesel vehicles. It should be pointed out that formaldehyde was the dominant aldehyde in all three samples. Less satii3factory agreement would be expected if other aldehydes predominate, since the molar absorbance of other aldehydehi is less than that of formaldehyde in the MBTH test.
'
E ~
5 ppm
0.30
\*
so2
(n
-
4 a
0.25
z
0.5
0
1.0
1.5
5 S u i i a m l c A c i d i n MBTH SOlutlDn
Flgure 1. Effect of sulfamio acid on MBTH test with and without SO2 in test gas. Each sample contained 20 pg of CH,O and was treated with 14.2 L of test gas at 750 mL/min.
Table 111. Auto Exhaust Aldehyde Determinations by Modified MBTH and DNPH Methods total aldehydes, ppm vehicle MBTH" DNPHb gasoline (catalyst)
a
1709
0.53
0.61
gasoline (no catalyst) 4.65 4.82 1.31 1.10 diesel Reference 2. 1%sulfamic acid modification.
DISCUSSION We are not the first to use sulfamic acid in the MBTH test. Hauser and Cummins (3) added sulfamic acid to the FeCIS solution in their modification for atmospheric analysis. However, their purpose was to increase sensitivity by eliminating the need for acetone to keep the samples free of turbidity. They did not mention SO2interference. Sulfamic acid has also been used to eliminate the interference from NO2 in the pararosaniline test for SO2 ( 4 , 5 ) . This is attributed to the ability of sulfamic acid to decompose nitrite in aqueous solutions. We believe that the tests described in this report demonstrate the superiority of the sulfamic acid modification over the original MBTH test for auto exhaust analysis. The mechanisim of sulfamic acid in reducing SO2interference in the MBTH test is not known. LITERATURE CITED
was no significant differience between the tests with gasoline and diesel vehicles. Some typical comparisons between the original and modified MBTH methods art? shown in Table 11. On the average, the aldehyde emissions measured by the modified method were about 40% greater than those measured by the original method for gasoline cars, and about 80% greater for diesel cars. Presumably, the greater discrepancy for the diesel cars is due to the higher SO;! content of diesel exhaust. Some comparisons between the modified MBTH method and a 2,4-dinitrophenylhjrdrazine(DNF") method employing
(1) Sawicki, E.; Hauser, T. R.; Stanley, T. W.; Elbert, W. Anal. Chem. 1961, 33, 93-96. (2) Kwata, K.; Uebori, M.; Yamasaki, Y. J. Chromatogr. Scl. 1979, 77, 264-269. (3) Hauser, T. R.; Cummins, R. L. A n d . Chem. 1964, 36, 679-881. (4) West, P. W.; Ordoveza, F. Anal. Chem. 1962, 34, 1324-1325. (5) Scaririgelli, F. P.; Saltzman, B. E.; Frey, S.A. Anal. Chem. 1967, 39, 1709- 17 19.
George J. Nebel Environmental Science Department General Motors Research Laboratories Warren, Michigan 48090
RECEIVED for review April 1,1981. Accepted June 17,1981.
Ion Chromatographic Separation of Cations on an Anion Separator Column Sir: In their classic publication on ion chromatography, Small, Stevens, and Bauman describe their technique for preparing anion exchangers of very low capacity ( I ) . In a later publication, Stevens and Small describe their work for optimization of cross-linking and degree of sulfonation (2). Simply stated, the proceclure involves mixing macroparticles of surface sulfonated styrene/divinylbenzene cationic resin with microparticles of strong base type anion exchange resin. The strong electrostatic interaction between the polycationic and polyanionic materials causes them to agglomerate. One can visualize the agglomeration process by means of the following equation: OH-Ph-CH,N'(CH,),
anion exchanger
+ -Ph-SO;H'
cation exchanger
+ -Ph--CH,N+(CH,),
- Ph-S
+
H,O 0
agglomerated resin
As is well-known to the practitioners of ion chromatography, 0003-2700/81/0353-1709$01.25/0
these agglomerated resins make excellent anion separators. Apparently, there are sufficient exchange sites (quarternary amine functional groups) available for anions to be separated. If this assumption is correct then one might expect that the agglomerated resin would contain exchange sites (sulfonic acid functional groups) which would allow for cation separations. Our work has proven this prediction.
EXPERIMENTAL SECTION The instrument used for this work was a Dionex Autoion 12 ion chromatograph. Columns employed were Dionex 3 X 150 mm anion and &ion precolumns, 6 X 250 mm cation separator, 3 X 500 mm anion separator, 3 X 250 mm anion suppressor, and 6 X 250 mm cation suppressor. The eluent used for anion analysis was 0.003 M:NaHC03-0.0024 M Na2C03and 0.005 M HN03 or 0.0025 M ~ N 0 3 - 0 . 0 0 2 5M n-phenylenediamine hydrochloride for cation analysis. All chemicals used were prepared from reagent grade materials. RESULTS AND DISCUSSION In our initial work we used an old anion separator column which had lost most of its ability to separate phosphate, 0 1981 American Chemical Society
