Aldehydes and ketones sampled as 2.4-dinitrophenylhydrazones
in impregnated tubes can be analysed in extracts with high performance liquid
chromatography (HPLC).
The following instruments and equipment may be used:
Acetonitrile, HPLC-quality, Rathburn Chemicals Ltd., No. RH 1016.
Methanol, Merc No. 6009.
Tetrahydrofuran, Merck No 8101.
Water, quartzdestilled and ion exchanged from a Millipore MilliQ water purification system.
Potassium iodide, p.a, Fluka No. 60400.
Sulfuric acid, Merc No 714.
Ethanol.
Carbonylcompounds needed.
2,4-Dinitrophenylhydrazine, Fluka No 42210.
Fill a 5 ml syringe with acetonitrile. (Collect the sample extract in a 3 ml narrow neck flask). Eluate the derivatives by slowly (approximate 1.5 ml/min) pushing acetonitrile through the cartridge. Stop the elution when the 3 ml mark is reached. Transfer approximately 0.5 ml of the sample solution to a 2 ml autosampler vial and seal the vial. The sample is now ready for HPLC analysis.
10 µl of a sample or standard solution is separated by using a quaternary mixture of methanol/water/acetonitrile/tetrahydrofuran. Table 4.16.1 shows the gradient profile which is used.
The detection and quantification is carried out at 369 nm (band width 22 nm) using 474 nm (band width 50 nm) as the reference wavelength. The detection and quantification of dicarbonyls is carried out at 440 nm (band width 22 nm) using 337 nm (band width 50 nm).
Following carbonylcompounds should
be measured: methanal, ethanal, propenal, propanal, propanone,
2-methyl-propenal, butanal, 2-butanone, 3-buten-2-one, pentanal, hexanal,
benzenecarbaldehyde, ethandial, oxopropanal.
Table 4.16.1: Quaternary gradient which separates the carbonylhydrazones of interest (EMEP) at a flowrate of 0.8 ml/min.
Time |
% Tetrahydrofuran |
% Acetonitrile |
% Water |
% Methanol |
0.0 |
18.0 |
22.0 |
60.0 |
0.0 |
0.5 |
18.0 |
22.0 |
60.0 |
0.0 |
20.0 |
8.4 |
37.4 |
54.2 |
0.0 |
24.0 |
0.0 |
0.0 |
34.0 |
66.0 |
40.0 |
0.0 |
0.0 |
15.0 |
85.0 |
41.0 |
0.0 |
0.0 |
15.0 |
85.0 |
45.0 |
0.0 |
100.0 |
0.0 |
0.0 |
48.0 |
18.0 |
22.0 |
60.0 |
0.0 |
Each day analyses of
carbonylcompounds are performed, a laboratory blank should be prepared. Periodically
field blanks should be obtained once every week. The blank levels of methanal,
ethanal, and propanone will probably change with cartridge batchnumber and the
batchnumber of acetonitrile. The blank level should not exceed
0.05 µg/m3 of
the carbonylcompound in a sample volume of 750 litres.
Prepare a stock solution from each
carbonylhydrazone by dissolving approximately 5 mg (+/- 1%) in 100 ml
acetonitrile. (These stock solutions will be ready for use.) Calibration
solutions are prepared by dilution of the stock solutions (1 µg/ml to
2 µg/ml is suitable for most analyses).
The concentration of carbonylcompounds in the air sample expressed as g/m3 , is given by:
C :
Concentration of the carbonylcompound in the
air sample [µg/m3]
c : Concentration of the
carbonylcompound in the standard [µg/ml]
H(s) : Peak height/area of the carbonylcompound in the
standard [counts]
H(p) : Peak height/area of the carbonylcompound in the sample
[counts]
k : Conversion factor (e.g. from
hydrazon to carbonyl) methanal:0.1429, ethanal:0.1964, propenal:0.2373 etc.
V : Sample volume [m3]
v : Volume of the prepared
sample [ml]
4.16.7 Interferences
Failure to remove ozone by the
ozone scrubber will result in serious underestimating of some carbonylhydrazones.
Vairavamurthy, A., Roberts, J.M. and Newman, L. (1992) Methods for determination of low molecular weight carbonyl compounds in the atmosphere: a review. Atmos. Environ., 26A, 1965-1993.
Slemr, J. (1991) Determination of volatile carbonyl compounds in clean air. Fresenius J. Anal. Chem., 340, 672-677.
Dye, C. and Oehme, M. (1992). Comments concerning the HPLC separation of acrolein from other C3 carbonyl compounds as 2,4-dinitrophenylhydrazones: a proposal for improvement. J. High Res. Chrom., 15, 5-8.