Benzyloxime Derivatization

Derivatization of simple aldehydes and ketones to benzyloximes was developed by Magin. The reaction proceeds as follows:

aPerkin-Elmer F-11 gas Chromatograph equipped with a coiled glass column, 6 ft long and 1/8 in i.d. bRelative retention times of secondary peaks. Reproduced with permission from Kallio H etal. (1972) Gas-liquid chromatographic analysis of 2,4-dinitrophenylhydrazones of carbonyl compounds. Journalof Chromatography 65: 355.

and a typical chromatogram of DNPHs of carbonyl compounds is shown in Figure 1. The peaks of the DNPHs of propanal, propenal and acetone are not separated under these conditions. The sensitivity was of the order of nanograms of carbonyl compounds when FID was used and five-hundred times greater with an ECD.

Saito et al. reported an improved GC method with DNPH for the determination of trace low molecular weight aliphatic carbonyl compounds in auto exhaust. They used a glass capillary column, 30 mx 0.27 mm i.d., coated with OV-17 and operated iso-thermally at 210°C. Aldehydes and ketones in the exhaust were selectively collected by passing 600 ml min"1 of exhaust gas through two impingers which were connected in series and which contained hydrochloric acid saturated with DNPH. The derivatives were extracted twice with chloroform in a separating funnel. After concentration by evaporation under a stream of nitrogen, anthracene was added as internal standard, and 1 |L of the solution was injected into a GC equipped with an FID. Six aliphatic aldehydes and three aliphatic ketones were analysed (Figure 2). The derivatives of C3 carbonyl compounds, propionaldehyde, acetone and acrolein, were completely separated, and simultaneously determined with formaldehyde and acetaldehyde. The minimum

The GC used for the analysis of these derivatives was equipped with a nitrogen-selective detector and

Figure 1 Chromatogram of a mixture of 2,4-dinitrophenyl-hydrazones of carbonyl compounds on a 2% SE-30 column. 1, Formaldehyde; 2, acetaldehyde; 3, acetone; 4, 2-butanone; 5, 2-butenal; 6, hexanal; 7, heptanal; 8, octanal; 9, nonanal. Programmed temperature analysis from 200 to 270°C (4°C min~1) on a Perkin-Elmer F-11 chromatograph equipped with a hydrogen flame ionization detector. Injected sample: 1.0 |L of ethyl acetate containing about 1000 ng of each of the derivatives. Attenuation 128, range 1. (Reproduced with permission from Kallio H et al. (1972). Gas-liquid chromatographic analysis of 2,4-dinitrophenyl-hydrazones of carbonyl compounds. JournalofChromatography 65: 355.)

Figure 1 Chromatogram of a mixture of 2,4-dinitrophenyl-hydrazones of carbonyl compounds on a 2% SE-30 column. 1, Formaldehyde; 2, acetaldehyde; 3, acetone; 4, 2-butanone; 5, 2-butenal; 6, hexanal; 7, heptanal; 8, octanal; 9, nonanal. Programmed temperature analysis from 200 to 270°C (4°C min~1) on a Perkin-Elmer F-11 chromatograph equipped with a hydrogen flame ionization detector. Injected sample: 1.0 |L of ethyl acetate containing about 1000 ng of each of the derivatives. Attenuation 128, range 1. (Reproduced with permission from Kallio H et al. (1972). Gas-liquid chromatographic analysis of 2,4-dinitrophenyl-hydrazones of carbonyl compounds. JournalofChromatography 65: 355.)

Time (min)

Figure 2 Chromatogram of the 2,4-dinitrophenylhydrazonesof carbonyl compounds. 1, Formaldehyde; 2, acetaldehyde; 3, acetone; 4, propionaldehyde; 5, isobutyraldehyde; 6, acrolein; 7, methyl ethyl ketone; 8, butryraldehyde; 9, methyl isopropyl ketone; 10, diethyl ketone; 11, methyl t-butyl ketone; 12, isovaleraldehyde; 13, methyl propyl ketone; 14, methyl s-butyl ketone; 15, methyl isobutyl ketone; 16, valeraldehyde; 17, crotonaldehyde, 18, methyl butyl ketone; 19, capronaldehyde. (Reproduced with permission from Saito T etal. (1983) Determination of trace low molecular weight aliphatic carbonyl compounds in auto exhaust by gas chromatography with a glass capillary column. Bunseki Kagaku32: 33.)

a glass capillary column (12 m x 0.4 mm i.d.) coated with a 0.4 |im film of free fatty acid phase (FFAP); helium was used as the carrier gas. The column temperature programme was 100-180°C at 2°Cmin~1; the temperature was kept at 180°C to the end of the analysis. The retention times of the ben-zyloximes of a number of aldehydes and ketones (1-7 carbon atoms) are shown in Table 2. The results show almost complete separation under these conditions.

Magin also reported the application of the ben-zyloxime-GC analysis of aldehydes and ketones to the semi-quantitative analysis of simple monocarbonyls in cigarette smoke. The smoke was passed through a silica gel column to trap the carbonyls, followed by elution with water. About 15 mL of eluted solution was collected in a screw-capped bottle, and the ben-zyloximes of the carbonyls were prepared. Separation was accomplished by a temperature-programmed 12 m glass capillary FFAP column. An internal standard (hexanal) was added both as a reference for retention time determination, and as an aid in estimating the amounts of the individual carbonyls in the smoke samples. Levels of some carbonyls in the cigarette whole smoke samples are shown in Table 3. One problem with this method was that acetal-dehyde, one of the major carbonyl compounds in cigarette smoke, could not be determined since peaks corresponding to the benzyloxime derivative of acet-

aldehyde appeared in the reagent blanks. Mass spectra of these peaks were identical to the spectra of the genuine acetaldehyde derivatives, but the source

Table 2 Adjusted retention times of O-benzyloxime derivatives

Aldehydes

Retention

Ketones

Retention

time (min)

time (min)

Formaldehyde

6.5

Acetone

12.6

Acetaldehyde

9.9

2-Butanone

14.2

Propanal

11.7

2-Pentanone

16.1

Butanal

17.6

Pentanal

22.5

3-Pentanone

16.8

Hexanal

30.0

4-Heptanone

22.1

Heptanal

36.5

Octanal

43.5

Cyclopentanone

34.5

Cyclohexanone

38.4

Isobutanal

13.9

Cycloheptanone

45.0

Isopentanal

20.0

3-Methyl-2-butanone

14.4

Propenal

15.9

3-Methyl-2-pentanone

15.4

2-Butenal

27.9

2-Hexenal

44.0

4-Methyl-2-pentanone

15.2

Methacrolein

17.9

5-Hexen-2-one

25.9

Benzaldehyde

67.7

Perkin-Elmer Model 3920 gas chromatograph equipped with glass capillary column, 12 m long and 0.4 mm i.d. Reproduced with permission from Magin DF (1979) Preparation and gas chromatographic characterization of benzyloximes and p-nitrobenzyloximes of short-chain (C1-C7) carbonyls. Journal of Chromatrography 178: 219.

Table 3 Levels of selected carbonyls in the whole smoke of some cigarettes

Carbonyl

Cigarette A

Cigarette B

Cigarette C

(fitter)

(filter, low delivery)

(non-filter)

Formaldehyde

31 (10-50)

10 (9-10)

21 (12-30)

Acetone

400 (325-475)

137 (130-144)

330 (310-350)

Propanal

61 (37-100)

37 (30-40)

50 (50-53)

Acrolein

23 (13-37)

3 (3-4)

22 (20-25)

Methacrolein

17 (14-38)

18 (18-19)

27 (20-32)

Butanal

20 (9-29)

13 (12-13)

18 (17-20)

Levels are tabulated as average; values in parentheses indicate the range. The values are given in |ig per cigarette.

Reproduced with permission from Magin DF (1980) Gas chromatography of simple monocarbonyls in cigarette whole smoke as the benzyloxime derivatives. Journal of Chromatography 202: 255.

Levels are tabulated as average; values in parentheses indicate the range. The values are given in |ig per cigarette.

Reproduced with permission from Magin DF (1980) Gas chromatography of simple monocarbonyls in cigarette whole smoke as the benzyloxime derivatives. Journal of Chromatography 202: 255.

in the blanks was unknown. Another problem was the lack of reproducibility from run to run. For this reason, the method was described as semi-quantitative.

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