1-Methyl-1-(2,4-dinitrophenyl)hydrazine as a New Reagent for the HPLC Determination of Aldehydes

Article abstract of DOI:10.1021/ac970146p

The synthesis and first application of an N-alkylated hydrazine reagent for the HPLC determination of aldehydes and ketones is described. 1-Methyl-1-(2,4-dinitrophenyl)hydrazine (MDNPH) reacts with aldehydes to give the corresponding hydrazones in the presence of an acid as catalyst. In contrast to other hydrazine reagents, MDNPH is oxidized by both ozone and nitrogen dioxide quantitatively to N-methyl-2,4-dinitroaniline (MDNA), which can be separated from the hydrazones of the lower aldehydes by means of HPLC. Unexpected elution orders are observed for the 1-methyl-1-(2,4-dinitrophenyl)hydrazones compared to those of 2,4-dinitrophenylhydrazones. Dual-wavelength detection is employed as a means for identification of different groups of the hydrazones and MDNA.

Full text of DOI:10.1021/ac970146p

Anal. Chem. 1997, 69, 3617-3622
1-Methyl-1-(2,4-dinitrophenyl)hydrazine as a New
Reagent for the HPLC Determination of Aldehydes
Andrea Bu1 ldt and Uwe Karst*
Abteilung Analytische Chemie, Anorganisch-Chemisches Institut, Westfa¨lische Wilhelms-Universita¨t Mu¨nster,
Wilhelm-Klemm-Strasse 8, 48149 Mu¨nster, Germany
The reaction products of both ozone and nitrogen dioxide may
interfere with the aldehyde determination by coelution with the
hydrazones in chromatography, which requires measures to
unambiguously identify the hydrazones and indicate the absence
of coeluting interferents in complex samples. Dual-wavelength
detection has been described as a rapid and convenient tool for
this purpose.11 Further problems may arise from the consump-
tion of the reagent, thus reducing the capacity of the sampling
device. Additionally, it should be considered that the oxidizing
agents may react not only with the reagent but also with the
hydrazones and therefore reduce the recovery rate for the
carbonyl compounds. Similar problems have been described for
the use of 5-(dimethylamino)-1-sulfonylhydrazide (dansylhydra-
zine) in ozone-contaminated gaseous samples.12
The synthesis and first application of an N-alkylated
hydrazine reagent for the HP LC determination of alde-
hydes and ketones is described. 1 -Methyl-1 -(2 ,4 -dinitro-
phenyl)hydrazine (MDNP H) reacts with aldehydes to give
the corresponding hydrazones in the presence of an acid
as catalyst. In contrast to other hydrazine reagents,
MDNP H is oxidized by both ozone and nitrogen dioxide
quantitatively to N-methyl-2 ,4 -dinitroaniline (MDNA),
which can be separated from the hydrazones of the lower
aldehydes by means of HP LC. Unexpected elution orders
are observed for the 1 -methyl-1 -(2 ,4 -dinitrophenyl)hy-
drazones compared to those of 2 ,4 -dinitrophenylhydra-
zones. Dual-wavelength detection is employed as a means
for identification of different groups of the hydrazones and
MDNA.
An approach to overcome these problems is the development
and use of new hydrazine reagents with reduced or more defined
reactivity toward ozone and nitrogen dioxide.
Hydrazine reagents have been used for the determination of
aldehydes and ketones in liquid and air samples for decades.
Hydrazines react with these carbonyl compounds, forming the
corresponding hydrazones. Among a large series of other
hydrazines, 2,4-dinitrophenylhydrazine (DNPH) has become the
most popular, and several standardization bodies have published
standard procedures based on the derivatization of aldehydes and
ketones with DNPH and subsequent HPLC separation. The
DNPH method is employed with a large variety of sampling
procedures for liquid1,2 and gas samples,3-7 including impingers,3,4
test tubes,5 and passive sampling devices.6,7 In recent years,
problems have become apparent with the DNPH method due to
reaction of the reagent with ozone8,9 and nitrogen dioxide10 in air
samples. In the case of ozone, several products are formed and
have not been identified yet. Nitrogen dioxide yields one product
with DNPH. This product has been identified as 2,4-dinitrophenyl
azide, which may eliminate nitrogen and react further to 5-ni-
trobenzofurazan 3-oxide under cyclization.10
EXPERIMENTAL SECTION
Chemicals. All chemicals were purchased from Aldrich
Chemie (Steinheim, Germany) in the highest quality available.
Acids were Merck (Darmstadt, Germany) analytical grade. Aceto-
nitrile for HPLC and TLC was Merck gradient grade. Stationary
phases for thin-layer chromatography were also from Merck.
Instrumentation for P roduct Identification. 1H NMR
measurements were performed with the AC 200 spectrometer
(200.13 MHz) from Bruker (Bremen, Germany), and 13C NMR
measurements were done with the unity plus (600 MHz) from
Varian (Darmstadt, Germany). Solvent for all NMR measure-
ments was CDCl3. All peaks are given with δ in ppm. COSY
spectra of MDNPH, MDNA, and the MDNP hydrazones of
acetaldehyde, propanal, 2-butanone, and acrolein were recorded
to confirm C-H correlation on the unity plus instrument from
Varian. FT-IR spectral information was obtained for the products
in KBr pellets by using the IFS48 from Bruker. Mass spectra
were recorded on the MAT 212 from Varian. All spectroscopic
data are included as Supporting Information.
(1) Takami, K.; Kuwata, K.; Sugimae, A.; Nakamoto, M. Anal. Chem. 1 9 8 5 ,
57, 243-245.
Synthesis. 1-Methyl-1-(2,4-dinitrophenyl)hydrazine (MDNPH).
According to a procedure suggested by Allen,13 6 mL of methyl-
hydrazine (0.11 mol) in ethanol (30 mL) was added to a solution
of potassium acetate (10.8 g, 0.11 mol) in deionized water (50 mL).
After the mixture was heated to reflux, a solution of 2,4-
dinitrochlorobenzene (20.2 g, 0.1 mol) in ethanol (100 mL) was
(2) Ogawa, I.; Fritz, J. S. J. Chromatogr. 1 9 8 5 , 329, 81-89.
(3) Grosjean, D.; Fung, K. Anal. Chem. 1 9 8 2 , 54, 1221-1224.
(4) Lipari, F.; Swarin, S. J. J. Chromatogr. 1 9 8 2 , 247 (2), 297-306.
(5) Beasley, R. H.; Hoffmann, C. E.; Rueppel, M. L.; Worley, J. W. Anal. Chem.
1 9 8 0 , 52, 1110-1114.
(6) Levin, J. O.; Andersson, K.; Lindahl, R.; Nilson, C.-A. Anal. Chem. 1 9 8 5 ,
57, 1032-1035.
(7) Levin, J. O.; Lindahl, R. Analyst 1 9 9 4 , 119, 79-83.
(8) Arnts, R. R.; Tejada, S. B. Environ. Sci. Technol. 1 9 8 9 , 23, 1428-1430.
(9) Smith, D. F.; Kleindienst, T. E.; Hudgens, E. E. J. Chromatogr. 1 9 8 9 , 483,
431-436.
(11) Po¨ tter, W.; Karst, U. Anal. Chem. 1 9 9 6 , 68, 3354-3358.
(12) Rodier, D. R.; Nondek, L.; Birks, J. W. Environ. Sci. Technol. 1 9 9 3 , 27,
2814-2820.
(10) Karst, U.; Binding, N.; Cammann, K.; Witting, U. Fresenius J. Anal. Chem.
1 9 9 3 , 345, 48-52.
(13) Allen, C. F. H. Org. Synth. 1 9 3 3 , 13, 36-37.
S0003-2700(97)00146-7 CCC: $14.00 © 1997 American Chemical Society
Analytical Chemistry, Vol. 69, No. 17, September 1, 1997 3617

added dropwise under stirring. The solution was cooled to 0 °C
after a reaction time of 8 h. The precipitate was filtered off,
washed with warm ethanol (60 °C) to remove unreacted 2,4-
dinitrochlorobenzene and finally washed with hot water. The
product was obtained as a yellow-orange solid. The yield was 84%.
The progress of the reaction was monitored using thin-layer
chromatography (stationary phase, silica gel; mobile phase,
toluene/ acetonitrile 7:3 (v/ v)). The purity of the product was
examined by means of HPLC (conditions see below, λ ) 360 and
finally dried in vacuo. TLC control of the reaction was performed
as described above. The yield was 76% in both cases. The
identities of the products of both approaches were confirmed by
complete spectroscopic and HPLC analysis. The reaction product
was fully characterized in the same way as MDNPH and its
hydrazones. These data are available as Supporting Information.
P reparation of the MDNP H Solution for Real Sample
Analysis. A 5 × 10-3 mol/ L MDNPH solution was prepared by
adding 105 mg of MDNPH to 0.5 mL of concentrated sulfuric acid
in 99.5 mL of acetonitrile. Of this solution, 80 mL was transferred
into an impinger. After sampling, acetonitrile was added to a total
volume of 100 mL.
1
300 nm). The product was fully characterized by means of H
NMR, 13C NMR, IR, MS, elementary analysis, and its melting point.
These data are available as Supporting Information.
Air Sampling P rocedure and Analysis. Air sampling was
performed using a personal air sampler pump (A. P. Buck, Inc.,
Orlando, FL) with the impinger located directly at the end of the
exhaust pipe of the car. The sampling rate was 0.25 L/ min, and
the sampling time was 2 min.
P hotometer. The HP 8453 diode array spectrophotometer
(Hewlett-Packard, Waldbronn, Germany) with HP Chem Station
845x biochemical UV/ VIS system software was used.
UV Absorption Measurements. All UV/ visible measure-
ments were performed within a concentration range from 2.3 ×
10-5 to 1.3 × 10-4 mol/ L of the reagent and the hydrazones in
acetonitrile. The spectra were recorded in the range from 250 to
470 nm.
HP LC Instrumentation and Analysis. A high-performance
liquid chromatograph consisting of the following components was
used: two LC-10AS pumps (Shimadzu, Duisburg, Germany), SPD-
10AV detector (Shimadzu), SIL-10A autosampler (Shimadzu),
Class LC-10 Version 1.4 software (Shimadzu), and CBM-10A
controller unit (Shimadzu). The injection volume was 10 µL. The
column consisted of Deltabond AK reversed-phase C18 material
(Keystone, Bellefonte, PA): column dimensions, 150 mm × 4.6
mm; particle size, 5 µm; pore size, 300 Å.
1-Methyl-1-(2,4-dinitrophenyl)hydrazones. None of these deriva-
tives has been subject to a full spectroscopic characterization yet.
Only some of the derivatives have been described in literature.14,15
The derivatives were prepared according to a procedure published
by Behforouz et al.16 for the synthesis of DNPH derivatives:
1-methyl-1-(2,4-dinitrophenyl)hydrazine (100 mg, 4.7 × 10-4 mol)
was dissolved in 0.5 mL of concentrated sulfuric acid and then
added to a solution of 0.7 mL of water in 2.5 mL of 95% ethanol.
A 50% molar excess of the aldehyde or ketone (7.1 × 10-4 mol)
was added as solution in ethanol (10-20 mass %). The hydrazones
precipitated as yellow or orange crystalline material. The pre-
cipitate was filtered off and washed first with a 5 mass % aqueous
solution of sodium bicarbonate, until no further development of
carbon dioxide was observed, and then with distilled water. The
progress of the reaction was monitored using thin-layer chroma-
tography (conditions as with MDNPH, see above). Yields ranged
from 72% to >95%, depending on the degree of purification
required for the individual hydrazones.
Notes for the preparation of particular hydrazones:
(i) Acetone MDNP hydrazone is formed after heating of the
solution to 80 °C for 3 h.
(ii) The hydrazones of the aldehydes and ketones with chain
lengths of more than four carbon atoms precipitated only after
the addition of ice to the reaction mixture.
For separation, a binary gradient consisting of acetonitrile and
water was selected with the following profile:
(iii) Pentanal MDNP hydrazone was isolated as an oil, as the
crystallization of the substance could not be achieved.
(iv) For the preparation of glutaraldehyde hydrazone, the
stoichiometric amount of only 3.5 × 10-4 mol of the dicarbonyl
compound was used.
time (min)
0
1
6.5
9.5
100
10 12 13 (stop)
100 30
c(CH3CN) (%)
flow (mL/ min)
30
1.5
30 42
The reaction products were fully characterized by means of
1H NMR, 13C NMR, IR, MS, elementary analysis, and their melting
points. These data are available as Supporting Information.
N-Methyl-2,4-dinitroaniline. First, 100 mg of 1-methyl-1-(2,4-
dinitrophenyl)hydrazine (4.7 × 10-4 mol) was dissolved in 0.5 mL
of concentrated sulfuric acid. Next, 3 mL of distilled water was
added to obtain a reagent solution. Nitrogen dioxide gas was
produced by adding 10 mL of concentrated nitric acid to 2 g of
copper wire and transported into the reagent solution by nitrogen
carrier gas. Alternatively, ozone from an ozone generator was
transported into the reagent solution by oxygen carrier gas. In
both cases, a yellow-orange precipitate was formed, and nitrogen
was blown into the solutions after the reaction to remove
unreacted oxidant. The precipitate was filtered off, washed with
sodium bicarbonate solution (5 mass %) and then with water, and
RESULTS
MDNPH was synthesized by a nucleophilic substitution reac-
tion of N-methylhydrazine with 2,4-dinitrochlorobenzene:
The reagent has been described before in the literature for the
preparation of pharmaceutical products,17 but has not been applied
for any analytical purposes yet. The corresponding hydrazone
standards of a series of aldehydes and ketones were prepared by
(14) Bohlmann, F. Chem. Ber. 1 9 5 1 , 84, 490-504
(15) Rappoport, Z.; Sheradsky, T. J. Chem. Soc. B 1 9 6 8 , 277-291.
(16) Behforouz, M.; Bolan, J. L.; Flynt, M. S. J. Org. Chem. 1 9 8 5 , 50, 1186-
1189.
(17) Popp, F. D. J. Heterocycl. Chem. 1 9 8 4 , 21, 617-619.
3618 Analytical Chemistry, Vol. 69, No. 17, September 1, 1997

Table 1. UV/Visible Spectroscopic and Chromatographic Data for a Series of
1-Methyl-1-(2,4-dinitrophenyl)hydrazones, MDNPH, and MDNA
ꢀ (L mol-1 cm-1) × 103
ꢀ(368 nm)/
ꢀ(290 nm)
A(368 nm)/
A(290 nm)
ꢀ(λmax)
compound
368 nm
290 nm
λmax
(L mol-1 cm-1) × 103
N-methyl-2,4-dinitrophenylhydrazone of
formaldehyde
acetaldehyde
propanal
acetone
acrolein
butanal
2-butanone
octanal
decanal
14.7
15.7
15.1
14.9
16.7
15.1
14.5
14.4
15.3
33.1
14.4
13.8
15.9
12.1
1.7
1.4
1.2
1.6
6.0
1.5
1.2
1.3
1.3
3.2
9.2
11.1
1.5
1.6
8.6
11.2
12.6
9.3
9.7
10.1
10.8
9.1
2.2
10.9
9.2
10.7
12.1
8.8
1.7
1.2
368
380
384
384
393
384
386
385
385
385
401
405
373
351
14.7
16.6
16.4
16.4
19.9
16.5
17.2
15.0
16.1
36.3
19.6
20.6
16.1
15.8
2.8
10.1
12.1
11.1
11.8
10.3
1.6
1.2
10.6
7.6
glutaraldehyde
benzaldehyde
p-tolualdehyde
MDNPH
9.7
6.5
MDNA
visible absorption maxima and minima and their molar absorp-
tivities. The spectroscopic data of related hydrazones are listed
in Table 1. Compared to the spectra of the nonalkylated DNPH
derivatives,15 a general shift of the maxima to longer wavelengths
is observed. Bohlmann14 has interpreted this shift as the result
of the missing interaction between the R-N-based hydrogen atom
of the hydrazine group with the nitro group in the 2-position of
the aromatic ring. This shift, however, is advantageous for HPLC
detection, as selectivity toward other aromatic compounds is
enhanced. In analogy with the DNPH derivatives, the absorption
maxima and minima of the saturated aldehyde hydrazones are
located at lower wavelengths compared to unsaturated hydra-
zones, as can be seen in Figure 1. The aromatic hydrazones
exhibit their absorption maxima at the longest wavelengths.
Reactivity of MDNPH with aldehydes and ketones was inves-
tigated by means of UV/ visible spectroscopy. Special experimen-
tal conditions have to be chosen for this purpose, because
MDNPH exhibits its UV/ visible absorption maximum in the same
region as most aliphatic hydrazones. Even if the reagent is
protonated by strong acids, a significant absorption of MDNPH
remains at the location of the absorption maxima of the hydra-
zones. UV/ visible spectroscopic observation of the reaction is,
therefore, only useful when MDNPH reacts quantitatively. For
this reason, an excess of the carbonyl compounds was added to
an acidified reagent solution. The hydrazones are, in contrast to
MDNPH, only weak bases and are, therefore, not protonated, even
in strongly acidic solution. In Figure 2, the reaction of MDNPH
with acetaldehyde in sulfuric acid is presented. The band of the
protonated MDNPH disappears, and the product band is formed
at a longer wavelength. Note the isosbestic point, indicating a
direct reaction of protonated MDNPH with the aldehyde to the
hydrazone. In Figure 3, the time dependence of this reaction is
displayed. Quantitative reaction is observed after slightly more
than 20 min. Compared to DNPH, reactivity was reduced for all
carbonyl compounds investigated but could be enhanced signifi-
cantly by using the strong Lewis acid boron trifluoride hydrate
instead of sulfuric acid as catalyst in the same concentration. For
both catalysts, aliphatic aldehydes with chain lengths from C2 to
Figure 1. UV/visible spectra of the 1-methyl-1-(2,4-dinitrophenyl)-
hydrazones of acetaldehyde (s), acrolein (- - -), and p-tolualdehyde
(‚‚‚).
reacting MDNPH with the carbonyl compounds in the presence
of sulfuric acid as catalyst:
UV/ visible spectra of the reagent and of the hydrazones were
recorded to determine the optimum wavelengths for HPLC
detection. It is known from the literature that different groups of
aldehydes (aliphatic, olefinic, and aromatic) yield products with
significantly different UV/ visible spectra when reacting with
DNPH. To demonstrate that these differences, which can be used
to identify groups of aldehydes by means of dual-wavelength
detection,11 occur in a similar way for the MDNPH derivatives,
the UV/ visible spectra of the MDNP hydrazones of acetaldehyde,
acrolein, and p-tolualdehyde are presented in Figure 1. Each of
these hydrazones is representative for its group of aldehydes
(aliphatic, olefinic, and aromatic, respectively) in terms of UV/
C
10 reacted faster than formaldehyde. p-Tolualdehyde reacted as
fast as acetaldehyde, while acetone and 2-butanone exhibited very
slow reactions with MDNPH, even under catalysis of a Lewis acid.
Analytical Chemistry, Vol. 69, No. 17, September 1, 1997 3619

Figure 3. Absorbance/time curves for the formation of acetaldehyde
1-methyl-1-(2,4-dinitrophenyl)hydrazone at the wavelength of 380 nm
(×) and the consumption of MDNPH at 290 nm (O). Concentrations
are given in see Figure 2.
Figure 2. UV/visible spectroscopic investigation of the formation
of acetaldehyde 1-methyl-1-(2,4-dinitrophenyl)hydrazone in acidic
solution (6.5 × 10-7 mol of MDNPH in a mixture of 1.4 mL of H2SO4,
1.9 mL of H2O, and 6.7 mL of ethanol) (v) and of the consumption of
1-methyl-1-(2,4-dinitrophenyl)hydrazine (V). The time interval between
the measurements was 1 min.
Therefore, MDNPH sampling tubes for gas analysis were pre-
pared, applied, and analyzed by HPLC according to DNPH tubes
as described in refs 11 and 18, and the recovery rate for different
aldehydes was investigated depending on the flow rate of the
gaseous sample. p-Tolualdehyde and acetaldehyde were recov-
ered quantitatively at flow rates of up to 1 L/ min, while formal-
dehyde was recovered only at flow rates up to 0.25 L/ min. The
order of reactivity was identical to the order obtained using the
UV/ visible spectrophotometric measurements.
Surprisingly, both ozone and nitrogen dioxide react with
MDNPH under formation of N-methyl-2,4-dinitroaniline (MDNA)
as the single product in high yields:
Figure 4. Chromatogram of a solution of an MDNPH excess (6 ×
10-3 mol/L), formaldehyde 1-methyl-1-(2,4-dinitrophenyl)hydrazone
(3.3 × 10-4 mol/L), and acetaldehyde 1-methyl-1-(2,4-dinitrophenyl)-
hydrazone (2.6 × 10-4 mol/L) before (s) and after (- - -) addition of
nitrogen dioxide.
Figure 4 shows the chromatogram of an acidified solution of an
excess of MDNPH with formaldehyde and acetaldehyde MDNP
hydrazone before and after oxidation by nitrogen dioxide. The
peak of MDNPH decreases and the one of MDNA increases
appropriately, while the amounts of formaldehyde and acetalde-
hyde MDNP hydrazones remain constant. Therefore, no hydra-
zones are decomposed by nitrogen dioxide to MDNA as long as
a MDNPH excess is present. However, the pure hydrazones are
decomposed to MDNA after consumption of MDNPH. Only one
significant product is formed during these reactions.
by UV/ visible properties similar to those of the aliphatic aldehyde
MDNP hydrazones. Formaldehyde MDNP hydrazone and MD-
NPH are very similar in terms of their UV/ visible maxima and
minima and even their molar absorptivities. MDNA shows its
absorption maximum at shorter wavelengths than the MDNPH
derivatives.
MDNA exhibits chromatographic properties similar to those
of formaldehyde MDNP hydrazone and acetone MDNP hydrazone
(see below). The UV/ visible spectra of MDNA, MDNPH, acetone
MDNP hydrazone, and formaldehyde MDNP hydrazone are
presented in Figure 5, and additional data are provided in Table
1. It is obvious that acetone MDNP hydrazone is characterized
Therefore, dual-wavelength detection is a useful tool to identify
the different groups of aldehyde or ketone hydrazones. The ratio
of the absorptions at two selected wavelengths is chosen for this
purpose. As formaldehyde is the most important analyte among
the aldehydes, its hydrazone absorption maximum and minimum
at λ ) 368 and 290 nm, respectively, are selected. The molar
absorptivities of all synthesized hydrazones, MDNPH, and MDNA
at these wavelengths determined on a spectrophotometer are
(18) Binding, N.; Thiewens, S.; Witting, U. Staub-Reinhalt. Luft 1 9 8 6 , 46, 444-
446.
3620 Analytical Chemistry, Vol. 69, No. 17, September 1, 1997

Figure 7. Chromatogram of a series of aldehyde and ketone 2,4-
dinitrophenylhydrazones and DNPH at the detection wavelengths λ
) 368 (s) and 290 nm (‚‚‚). The concentration range of the
compounds dissolved in acetonitrile was 9.2 × 10-5-1.7 × 10-4 mol/
L.
Figure 5. UV/visible spectra of MDNPH (s), MDNA (‚‚‚), and the
1-methyl-1-(2,4-dinitrophenyl)hydrazones of formaldehyde (- - -), and
acetone (-‚-).
Figure 6. Chromatogram of a series of aldehyde and ketone
1-methyl-1-(2,4-dinitrophenyl)hydrazones, MDNPH, and MDNA at the
detection wavelengths λ ) 368 (s) and 290 nm (‚‚‚). The concentra-
tion range of the compounds dissolved in acetonitrile was 1.1 × 10-4
-
2.1 × 10-4 mol/L.
listed in Table 1. For comparison, the quotient of the peak areas
at these two wavelengths obtained in HPLC with dual-wavelength
detection is listed as well. Characteristic absorption ratio ranges
for different groups of hydrazones and MDNA can be obtained
from Table 1. It is obvious that the wavelength ratios (λ(368 nm)/
λ(290 nm)) are larger for the hydrazones of aliphatic aldehydes
than for those of unsaturated aldehydes or even aromatic alde-
hydes. MDNPH exhibits wavelength ratios similar to those of
aliphatic aldehyde hydrazones, and MDNA is characterized by a
slightly smaller ratio compared to those of aliphatic aldehyde
hydrazones. The ratios determined using the two methods
coincide well when considering the typical sources of variations
as listed in ref 11.
In Figure 6, a chromatogram of a mixture of hydrazone
standards, MDNPH, and MDNA at both selected detection
wavelengths is presented. It should be noted that the aliphatic
aldehyde MDNP hydrazones elute in the order of increasing alkyl
chain length, as could be expected by comparison with the data
of the corresponding DNPH derivatives when using the same
chromatographic conditions (compare to Figure 7). Surprisingly,
and in contrast to the DNPH derivatives, the MDNP hydrazones
of acetone and 2-butanone elute significantly in advance of the
aliphatic aldehyde MDNP hydrazones with shorter alkyl chain
lengths. It should be noted in Figure 6 that the separation of
Figure 8. Chromatogram of a car exhaust sample at the detection
wavelength λ ) 368 nm.
MDNA and the acetone MDNP hydrazone succeeds without
problems when the selected chromatographic conditions are used.
To examine if the new reagent is suitable to analyze real
samples, an exhaust sample was taken from a cold-started car by
pumping the exhaust through an impinger filled with MDNPH
solution (for sampling conditions, see Experimental Section). The
corresponding chromatogram is shown in Figure 8. The product
of MDNPH with nitrogen dioxide, MDNA, is formed as well as
formaldehyde MDNP hydrazone and acetaldehyde MDNP hy-
drazone. Since the total exhaust volumes per time scale may vary
with different cars, the total amount of each analyte cannot be
directly calculated from this information. Nevertheless, the
chromatogram proves the suitability of the new reagent for the
determination of aldehydes and nitrogen dioxide in real air
samples.
Analytical Chemistry, Vol. 69, No. 17, September 1, 1997 3621

CONCLUSIONS
aldehyde 1-methyl-1-(2,4-dinitrophenyl)hydrazone, propanal 1-methyl-
1-(2,4-dinitrophenyl)hydrazone, butanal 1-methyl-1-(2,4-dinitro-
phenyl)hydrazone, pentanal 1-methyl-1-(2,4-dinitrophenyl)hydra-
zone, octanal 1-methyl-1-(2,4-dinitrophenyl)hydrazone, decanal
1-methyl-1-(2,4-dinitrophenyl)hydrazone, acetone 1-methyl-1-(2,4-
dinitrophenyl)hydrazone, 2-butanone 1-methyl-1-(2,4-dinitro-
phenyl)hydrazone, acrolein 1-methyl-1-(2,4-dinitrophenyl)hy-
drazone, glutaraldehyde bis[1-methyl-1-(2,4-dinitrophenyl)hydra-
zone], benzaldehyde 1-methyl-1-(2,4-dinitrophenyl)hydrazone, p-
tolualdehyde 1-methyl-1-(2,4-dinitrophenyl)hydrazone, and N-methyl-
2,4-dinitroaniline, including 1H NMR, 13C NMR, IR, MS, elementary
analysis, and melting points (5 pages). Ordering information is
given on any current masthead page.
MDNPH has been synthesized as a new reagent for the
determination of aldehydes and ketones with interesting properties
concerning its reactions with nitrogen dioxide and ozone, both
of which form MDNA. MDNPH is suitable to determine alde-
hydes and nitrogen dioxide in real air samples by means of
impingers. The MDNP hydrazones can be detected by UV/ visible
spectroscopy at longer wavelengths compared to the respective
DNPH derivatives. MDNA, the hydrazones, and the reagent can
be separated easily using reversed-phase HPLC. The elution
orders of the corresponding ketone hydrazones in reversed-phase
HPLC differ significantly from those of the DNP hydrazones.
ACKNOWLEDGMENT
Financial support by the DFG (Deutsche Forschungsgemein-
schaft, Bonn, Germany) and the Fonds der Chemischen Industrie
(Frankfurt, Germany) is gratefully acknowledged. A.B. thanks the
Richard-Winter-Stiftung (Stuttgart, Germany) for a scholarship.
Received for review February 5, 1997. Accepted June 6,
1997.X
AC970146P
SUPPORTING INFORMATION AVAILABLE
Characterization data of 1-methyl-1-(2,4-dinitrophenyl)hydra-
zine, formaldehyde 1-methyl-1-(2,4-dinitrophenyl)hydrazone, acet-
X Abstract published in Advance ACS Abstracts, July 15, 1997.
3622 Analytical Chemistry, Vol. 69, No. 17, September 1, 1997