- Email: [email protected]
The scope of pyrolysis methylation reactions
Journal of Analytical and Applied Pyrolysis, 20 (1991) 15-24
15
Elsevier Science Publishers B.V., Amsterdam
The scope of pyrolysis methylation
reactions
J.M. Challinor Forensic Science Laboratory, W.A. (Australia)
Chemistry Centre (W.A.), 125 Hay Street, East Perth 6004,
(Received June 15, 1990; accepted November 23, 1990)
ABSTRACT
Simultaneous pyrolysis-alkylation-gas chromatography procedures have recently been reported. The method is applicable to macromolecular material amenable to hydrolysis and subsequent alkylation, particularly esters and phenolic compounds. This paper outlines some further developments in the application of this procedure to the examination of saturated polyester resins, complex esters in drug formulations and UV light stabilisers, phenol-formaldehyde resins, fatty acid triglycerides, natural waxes, kerogen and proteins, indicating the wider potential for the method.
Derivatisation; drug analysis; fats; kerogen; oils; light stabilisers; phenol-formaldehyde resins; proteins; pyrolysis; saturated polyester resins; tetramethylammonium hydroxide; waxes.
INTRODUCTION
An overview of the application of simultaneous pyrolysis alkylation to the structure determination of polyesters, phenolic polymers and surface coating additives has been reported recently [l]. A detailed discussion of the analysis of alkyd resins by simultaneous pyrolysis methylation (SPM) has also been reported [2]. It was demonstrated that it was possible to identify the polybasic acid, polyhydric alcohol and drying oil type by the composition of the respective methyl esters and ethers. The estimation of degree of cure, an approximation of the oil length and confirmation of rosin or epoxy modification were facilitated by the procedure. The technique has advantages compared to chemical degradation and PyGC in that more structural information about the polar components of 016%2370/91/$03.50
0 1991 Elsevier Science Publishers B.V.
16
some polymers can be obtained, minimal sample manipulation is required and the method is therefore more cost effective. Further, the technique is more sensitive than existing methods and has the advantage that comparatively low cost instrumentation is utilised. The purpose of this report is to outline some of the developments in the application of the technique and describe the potential to other types of material such as saturated polyester resins, complex esters in drugs and UV adsorbers, vegetable oils, waxes, kerogen and proteins. A more detailed treatment of the individual material types will be addressed in future reports.
EXPERIMENTAL
Method The sample (about 5 pg) was placed in the hollow of a flattened, bent 770 o C Curie-point pyrolysis wire with approximately 0.5 ~1 tetramethylammonium hydroxide (TMAH) (25% w/w aqueous solution). The prepared wire was then immediately located in the pyrolyser without allowing the aqueous TMAH to evaporate and pyrolysis was carried out at 770 o C. Instrumentation A Pye Curie-point pyrolyser was fitted to a capillary column gas chromatograph via a stainless steel hypodermic needle as described in a previous paper [3]. Pyrograms were obtained by interfacing the pyrolyser to a Hewlett-Packard 5730 gas chromatograph equipped with a flame ionisation detector. The gas chromatograph was fitted with a fused-silica capillary column (J & W DB1701, bonded-phase 1 pm phase thickness, 30 m X 0.313 mm). Helium was used as carrier gas (linear velocity 30 cm s-l). The inlet mode was splitless with an injection interval of 25 seconds and inlet pressure 1.3 kg cm-*. Temperature programme settings were as follows: initial temperature 30 o C, hold 2 min, increase at 8 o C rnin-’ to 270 OC. All pyrolysis products referred to were identified by mass spectrometry. Mass spectral analysis was carried out with a Hewlett-Packard 5890 gas chromatograph interfaced to a VG TS250 mass spectrometer using electron impact ionisation (70 ev). The capillary column stationary phases were selected to obtain the most efficient separations of derivatives of the different materials analysed. For example, a more polar phase, e.g. DEGS or Carbowax, was selected for the separation of saturated and unsaturated fatty acid methyl esters. A methyl silicone phase, e.g. OVI, was chosen for the separation of fatty acid methyl esters from alkanes and alkenes in kerogens.
17 RESULTS
AND DISCUSSION
Saturated polyester resins
A brief description of the use ‘of SPM for identification of unsaturated polyester resins in contrast to Py-GC showed that it was possible to identify the polybasic acid and polyhydric alcohol components of the resin [l]. The same procedure can be used to identify saturated polyester coatings. An example of the determination of a neopentyl glycol, trimethylol propane, isophthalic acid polyester modified with adipic acid is shown in Fig. 1. Complex esters Proprietary
drugs
The application of SPM-GC to the structural identification of complex esters used in some proprietary products has proved useful in this laboratory. The drug, haloperidol, is formulated as the decanoate ester, I, dissolved in sesame seed oil and contains approximately one percent benzyl alcohol as preservative. 0 : - (CH,),
- CH3
NPGIME
TMy?ME ‘.
DMA
TMT3ME“ : \
i : :
M?
*I
A-l
AJ 4
6
12
16
.I
20
2’4
I!4
1.
26 ’
Fig. 1. SPM-GC of a saturated polyester identified as a neopentyl glycol, trimethylol propane, isophthalic acid type. NPGZME, neopentyl glycol dimethyl ether; NPGlME, neopentyl glycol monomethyl ether; TMP3ME, trimethylol propane trimethyl ether; MB, methyl benzoate; TMPZME, trimethylol propane dimethyl ether; DMA, dimethyl adipate; DMIP, dimethyl isophthalate.
18
Cl?1 ..
‘..,
H20Me
3 6 ::
.1,, :: :
: lj3.2
ClyJ
Cl8
‘,
,/
‘:: :
-
‘i”
G3,ME
i
ti
I
12
i’s
2b
j 2i
n'e
3;
Fig. 2. SPM-GC of a proprietary drug (haloperidol) formulation chromatographed on a DEGS type column. BME, benzyl methyl ether; G3ME, glycerol trimethyl ether; ClO, C16, C18.0, C18.1, C18.2, respective fatty acid methyl esters.
SPM results in the formation of benzyl methyl ether from the preservative, methyl decanoate from the active ingredient and fatty acid methyl esters of sesame seed oil (Fig. 2). Fragments of the haloperidol molecule resulting from the hydrolysis reaction have not at this stage been detected. UV Absorbers
Some of the hindered amine type UV absorbers used in surface coatings and plastics are complex esters. One such product (Tinuvin 292) has the structural formula II.
cH;$_;_[c”,j8_;_-5;n3 3
3
II
When subjected to SPM, octanedioic acid dimethyl ester (dimethyl sebacate), pentamethyl piperidol and its methyl ether are detected (Fig. 3). Phenolic resins
Pyrolysis methylation of phenolic polymers results in the formation of the respective phenol methyl ethers in contrast to phenolic compounds on conventional pyrolysis. For example, epoxy resins, which give phenol, isopropenyl phenol and bisphenol-A by Py-GC, result in phenol methyl ether, isopropenyl phenol methyl ether and bisphenol-A dimethyl ether on pyroly-
19 0
0 CH,-O+H&$-0-CH3
PMP :
PMPME
Q
4
:
:
:
:
/ 8’
DMS
I 12
20
16
24
28
3’2
1
Fig. 3. SPM-GC of a hindered amine light stabiliser. DMS, dimethyl sebacate; PMP, pentamethyl piperidol; PMPME, pentamethyl piperidol methyl ether.
sis methylation [l]. Phenol formaldehyde methyl ethers (Fig. 4).
resins give corresponding
phenol
Fatty acid triglycerides
Animal fats and vegetable oil triglycerides are converted to their respective fatty acid methyl esters when subjected to SPM. Only nanogram EPOXY
: :--,* L
PHENOL-FORMALDEHYDE
OMe
OMe
0
Me
OMe
:
’
:
4
8
12
Me
CK Me
16
20
24
2’.6
Fig. 4. SPM-GC of epoxy and phenol-formaldehyde
3;
resins.
36
20
PALYITATE C!,6
II_.._.._.__
6UTYliAIk
6.
7”
?: /
:
CAPRATE
i
,‘I3
1’2
Ii
%,
MYRISTATI Cl4 LAW”’‘AIC ’ c: 12
G3ME CAPROATE
. ..*
STCE%iTE ; ’
I
2’0
..
E
: Og;yE : : : I .
: : :
I
2’4
Fig. 5. SPM-GC of butter fat chromatographed on a DEGS type column. C4, C6, C8, ClO, C12, C14, C16, C18.0 and C18.1, respective fatty acid methyl esters; G3ME, glycerol trimethyl ether.
quantities are required for the determination. The results of SPM-GC of butter fat are shown in Fig. 5. When triglycerides containing significant polyunsaturated fatty acids were analysed it was observed that additional peaks were detected in the chromatograms. For linoleic and linolenic acid-containing triglycerides these compounds were identified by mass spectrometry as isomers of these fatty acids. These isomers were not detected in conventional analysis by transesterification. Fig. 6 illustrates SPM-GC of linseed oil indicating the isomers of the two unsaturated fatty acids. This isomerisation is known to occur in pyrolytic methylation of free fatty acids [4]. The problem was overcome by neutralising excess TMAH with dilute hydrochloric acid. In later work, methyl acetate was used to remove excess TMAH [5]. Attempts to adopt a similar procedure using methyl
II
C18.1
C18.2
C
Fig. 6. SPM-GC of linseed oil chromatographed on a DEGS type column. C16.0, C18.0, C18.1, C18.2, and C18.3, respective fatty acid methyl esters.
21
acetate to remove excess TMAH fell short of a complete solution to the problem. In spite of this partial isomerization it is possible to infer the presence of the particular polyunsaturated fatty acid based on the pattern of these artefacts produced. In the absence of a specific detector, e.g. mass spectrometer, these isomers provide corroboration of the identity of the compounds. Waxes
Natural waxes have a wide variety of uses in polishes, candles and finishes for paper, leather, textiles and wood. Cosmetics and medicinals incorporate waxes in lipsticks, creams and ointments.
C 1.6.0
WHITE
,_-*
BEESWAX
JOJOBA
OIL
C2O;pL *.
C16-OH
a
i
SPERMACETI
lh
l’s
2’0
2;
2’8
i2
&
Fig. 7. SPM-GC of white beeswax, jojoba oil and spermaceti. (X4.0, C16.0, C18.0, C18.1, C20, C22 and C24, respective fatty acid methyl esters; C16-OL, C20-OL, C22-OL and C24-OL, respective fatty alcohols.
22
Beeswax is largely composed of myricyl palmitate Ci5H3iC02C3iH6s, and contains cerotic and homologous acids, C,,H,,CO,H, smaller amounts of hydrocarbons, cholesterol esters and ceryl alcohols. Approximately 60% of beeswax comprises equal proportions of monohydric alcohols and acids. Hydroxy-acids are present to the extent of approximately 15% [6]. Jojoba oil and spermaceti are also used in commercial preparations including cosmetics and pharmaceuticals and similarly contain higher molecular weight esters. A comparison of the results of SPM-GC is shown in Fig. 7. The different waxes may be readily distinguished by the distribution of fatty acid methyl esters and fatty alcohols. It is also interesting to note the series of groups of compounds (boxed) in the chromatogram of beeswax which have not yet been identified. The compounds corresponding to the annotated peaks were identified by mass spectrometry.
70 80
PY-GC
Fig. 8. SPM-GC/MS and Py-GC of Rundle shale. C6.0 to C25.0, respective saturated fatty acid methyl esters; C6, ClO, C14, respective n-alkenes.
23
Kerogen
It is well known that kerogen, the solvent insoluble fraction of oil shales, contains a proportion of oxygenated compounds and some of these are fatty acids. How those compounds are bound to the substrate is not generally known. Pyrolysis methylation gas chromatography/mass spectrometry, reconstructing the total ion chromatogram to show those compounds whose mass spectra include ions, m/z 74 and 87, characteristic of saturated fatty acid methyl esters, was used to study the composition of these compounds in Rundle shale (Fig. 8). For contrast, the pyrogram of the same shale using flame ionisation detection is shown. It is observed that the fatty acid methyl esters detected ranged from C4 to C25. Compounds C8, C12, and Cl6 were dominant in contrast to C6, Cl0 and Cl4 n-alkenes in the Py-GC determination. Doublets and/or triplets are detected in the series. Proteins
Pyrolysis methylation of proteinaceous fibres has been attempted. results of SPM-GC of wool and silk are shown in Fig. 9.
WOOL
SILK
4
Fig. 9. SPM-GC
8
12
16
of wool and silk.
The
24
The differences in chromatographic profiles reflect the differences in amino acid composition. Phenol methyl ether and o-cresol methyl ether have been identified in the products from silk. It might be expected that these fragments result from hydrolysis and methylation of tyrosine, present in fibroin (silk) to the extent of approximately 13%. Other products have not yet been identified.
CONCLUSIONS
In this paper it has been shown how SPM can be applied to a wide range of oxygen-containing materials susceptible to hydrolytic reaction and which are capable of alkylation. Many of these materials may only be identified by more lengthy and complex chemical degradation and derivatisation reactions.
ACKNOWLEDGEMENTS
The author wishes to thank Professor R. Alexander and Dr. A. Jefferson of Curtin University for their helpful advice. This paper is published with the approval of the Director, Chemistry Centre (WA), Department of Mines, Perth, Western Australia.
REFERENCES 1 2 3 4 5 6
J.M. Challinor, J. Anal. Appl. Pyrolysis, 16 (1989) 323. J.M. Challinor, J. Anal. Appl. Pyrolysis, accepted for publication. J.M. Challinor, Forensic Sci. Int., 21 (1983) 269. D.T. Downing and R.S. Greene, Anal. Chem., 40 (1968) 827. M.G. Williams and J. MacGee, J. Chromatogr., 234 (1982) 468. H. Bennett, Industrial Waxes, Chemical Publishing Company, Inc., New York, Vol. 1, 1975.
15
Elsevier Science Publishers B.V., Amsterdam
The scope of pyrolysis methylation
reactions
J.M. Challinor Forensic Science Laboratory, W.A. (Australia)
Chemistry Centre (W.A.), 125 Hay Street, East Perth 6004,
(Received June 15, 1990; accepted November 23, 1990)
ABSTRACT
Simultaneous pyrolysis-alkylation-gas chromatography procedures have recently been reported. The method is applicable to macromolecular material amenable to hydrolysis and subsequent alkylation, particularly esters and phenolic compounds. This paper outlines some further developments in the application of this procedure to the examination of saturated polyester resins, complex esters in drug formulations and UV light stabilisers, phenol-formaldehyde resins, fatty acid triglycerides, natural waxes, kerogen and proteins, indicating the wider potential for the method.
Derivatisation; drug analysis; fats; kerogen; oils; light stabilisers; phenol-formaldehyde resins; proteins; pyrolysis; saturated polyester resins; tetramethylammonium hydroxide; waxes.
INTRODUCTION
An overview of the application of simultaneous pyrolysis alkylation to the structure determination of polyesters, phenolic polymers and surface coating additives has been reported recently [l]. A detailed discussion of the analysis of alkyd resins by simultaneous pyrolysis methylation (SPM) has also been reported [2]. It was demonstrated that it was possible to identify the polybasic acid, polyhydric alcohol and drying oil type by the composition of the respective methyl esters and ethers. The estimation of degree of cure, an approximation of the oil length and confirmation of rosin or epoxy modification were facilitated by the procedure. The technique has advantages compared to chemical degradation and PyGC in that more structural information about the polar components of 016%2370/91/$03.50
0 1991 Elsevier Science Publishers B.V.
16
some polymers can be obtained, minimal sample manipulation is required and the method is therefore more cost effective. Further, the technique is more sensitive than existing methods and has the advantage that comparatively low cost instrumentation is utilised. The purpose of this report is to outline some of the developments in the application of the technique and describe the potential to other types of material such as saturated polyester resins, complex esters in drugs and UV adsorbers, vegetable oils, waxes, kerogen and proteins. A more detailed treatment of the individual material types will be addressed in future reports.
EXPERIMENTAL
Method The sample (about 5 pg) was placed in the hollow of a flattened, bent 770 o C Curie-point pyrolysis wire with approximately 0.5 ~1 tetramethylammonium hydroxide (TMAH) (25% w/w aqueous solution). The prepared wire was then immediately located in the pyrolyser without allowing the aqueous TMAH to evaporate and pyrolysis was carried out at 770 o C. Instrumentation A Pye Curie-point pyrolyser was fitted to a capillary column gas chromatograph via a stainless steel hypodermic needle as described in a previous paper [3]. Pyrograms were obtained by interfacing the pyrolyser to a Hewlett-Packard 5730 gas chromatograph equipped with a flame ionisation detector. The gas chromatograph was fitted with a fused-silica capillary column (J & W DB1701, bonded-phase 1 pm phase thickness, 30 m X 0.313 mm). Helium was used as carrier gas (linear velocity 30 cm s-l). The inlet mode was splitless with an injection interval of 25 seconds and inlet pressure 1.3 kg cm-*. Temperature programme settings were as follows: initial temperature 30 o C, hold 2 min, increase at 8 o C rnin-’ to 270 OC. All pyrolysis products referred to were identified by mass spectrometry. Mass spectral analysis was carried out with a Hewlett-Packard 5890 gas chromatograph interfaced to a VG TS250 mass spectrometer using electron impact ionisation (70 ev). The capillary column stationary phases were selected to obtain the most efficient separations of derivatives of the different materials analysed. For example, a more polar phase, e.g. DEGS or Carbowax, was selected for the separation of saturated and unsaturated fatty acid methyl esters. A methyl silicone phase, e.g. OVI, was chosen for the separation of fatty acid methyl esters from alkanes and alkenes in kerogens.
17 RESULTS
AND DISCUSSION
Saturated polyester resins
A brief description of the use ‘of SPM for identification of unsaturated polyester resins in contrast to Py-GC showed that it was possible to identify the polybasic acid and polyhydric alcohol components of the resin [l]. The same procedure can be used to identify saturated polyester coatings. An example of the determination of a neopentyl glycol, trimethylol propane, isophthalic acid polyester modified with adipic acid is shown in Fig. 1. Complex esters Proprietary
drugs
The application of SPM-GC to the structural identification of complex esters used in some proprietary products has proved useful in this laboratory. The drug, haloperidol, is formulated as the decanoate ester, I, dissolved in sesame seed oil and contains approximately one percent benzyl alcohol as preservative. 0 : - (CH,),
- CH3
NPGIME
TMy?ME ‘.
DMA
TMT3ME“ : \
i : :
M?
*I
A-l
AJ 4
6
12
16
.I
20
2’4
I!4
1.
26 ’
Fig. 1. SPM-GC of a saturated polyester identified as a neopentyl glycol, trimethylol propane, isophthalic acid type. NPGZME, neopentyl glycol dimethyl ether; NPGlME, neopentyl glycol monomethyl ether; TMP3ME, trimethylol propane trimethyl ether; MB, methyl benzoate; TMPZME, trimethylol propane dimethyl ether; DMA, dimethyl adipate; DMIP, dimethyl isophthalate.
18
Cl?1 ..
‘..,
H20Me
3 6 ::
.1,, :: :
: lj3.2
ClyJ
Cl8
‘,
,/
‘:: :
-
‘i”
G3,ME
i
ti
I
12
i’s
2b
j 2i
n'e
3;
Fig. 2. SPM-GC of a proprietary drug (haloperidol) formulation chromatographed on a DEGS type column. BME, benzyl methyl ether; G3ME, glycerol trimethyl ether; ClO, C16, C18.0, C18.1, C18.2, respective fatty acid methyl esters.
SPM results in the formation of benzyl methyl ether from the preservative, methyl decanoate from the active ingredient and fatty acid methyl esters of sesame seed oil (Fig. 2). Fragments of the haloperidol molecule resulting from the hydrolysis reaction have not at this stage been detected. UV Absorbers
Some of the hindered amine type UV absorbers used in surface coatings and plastics are complex esters. One such product (Tinuvin 292) has the structural formula II.
cH;$_;_[c”,j8_;_-5;n3 3
3
II
When subjected to SPM, octanedioic acid dimethyl ester (dimethyl sebacate), pentamethyl piperidol and its methyl ether are detected (Fig. 3). Phenolic resins
Pyrolysis methylation of phenolic polymers results in the formation of the respective phenol methyl ethers in contrast to phenolic compounds on conventional pyrolysis. For example, epoxy resins, which give phenol, isopropenyl phenol and bisphenol-A by Py-GC, result in phenol methyl ether, isopropenyl phenol methyl ether and bisphenol-A dimethyl ether on pyroly-
19 0
0 CH,-O+H&$-0-CH3
PMP :
PMPME
Q
4
:
:
:
:
/ 8’
DMS
I 12
20
16
24
28
3’2
1
Fig. 3. SPM-GC of a hindered amine light stabiliser. DMS, dimethyl sebacate; PMP, pentamethyl piperidol; PMPME, pentamethyl piperidol methyl ether.
sis methylation [l]. Phenol formaldehyde methyl ethers (Fig. 4).
resins give corresponding
phenol
Fatty acid triglycerides
Animal fats and vegetable oil triglycerides are converted to their respective fatty acid methyl esters when subjected to SPM. Only nanogram EPOXY
: :--,* L
PHENOL-FORMALDEHYDE
OMe
OMe
0
Me
OMe
:
’
:
4
8
12
Me
CK Me
16
20
24
2’.6
Fig. 4. SPM-GC of epoxy and phenol-formaldehyde
3;
resins.
36
20
PALYITATE C!,6
II_.._.._.__
6UTYliAIk
6.
7”
?: /
:
CAPRATE
i
,‘I3
1’2
Ii
%,
MYRISTATI Cl4 LAW”’‘AIC ’ c: 12
G3ME CAPROATE
. ..*
STCE%iTE ; ’
I
2’0
..
E
: Og;yE : : : I .
: : :
I
2’4
Fig. 5. SPM-GC of butter fat chromatographed on a DEGS type column. C4, C6, C8, ClO, C12, C14, C16, C18.0 and C18.1, respective fatty acid methyl esters; G3ME, glycerol trimethyl ether.
quantities are required for the determination. The results of SPM-GC of butter fat are shown in Fig. 5. When triglycerides containing significant polyunsaturated fatty acids were analysed it was observed that additional peaks were detected in the chromatograms. For linoleic and linolenic acid-containing triglycerides these compounds were identified by mass spectrometry as isomers of these fatty acids. These isomers were not detected in conventional analysis by transesterification. Fig. 6 illustrates SPM-GC of linseed oil indicating the isomers of the two unsaturated fatty acids. This isomerisation is known to occur in pyrolytic methylation of free fatty acids [4]. The problem was overcome by neutralising excess TMAH with dilute hydrochloric acid. In later work, methyl acetate was used to remove excess TMAH [5]. Attempts to adopt a similar procedure using methyl
II
C18.1
C18.2
C
Fig. 6. SPM-GC of linseed oil chromatographed on a DEGS type column. C16.0, C18.0, C18.1, C18.2, and C18.3, respective fatty acid methyl esters.
21
acetate to remove excess TMAH fell short of a complete solution to the problem. In spite of this partial isomerization it is possible to infer the presence of the particular polyunsaturated fatty acid based on the pattern of these artefacts produced. In the absence of a specific detector, e.g. mass spectrometer, these isomers provide corroboration of the identity of the compounds. Waxes
Natural waxes have a wide variety of uses in polishes, candles and finishes for paper, leather, textiles and wood. Cosmetics and medicinals incorporate waxes in lipsticks, creams and ointments.
C 1.6.0
WHITE
,_-*
BEESWAX
JOJOBA
OIL
C2O;pL *.
C16-OH
a
i
SPERMACETI
lh
l’s
2’0
2;
2’8
i2
&
Fig. 7. SPM-GC of white beeswax, jojoba oil and spermaceti. (X4.0, C16.0, C18.0, C18.1, C20, C22 and C24, respective fatty acid methyl esters; C16-OL, C20-OL, C22-OL and C24-OL, respective fatty alcohols.
22
Beeswax is largely composed of myricyl palmitate Ci5H3iC02C3iH6s, and contains cerotic and homologous acids, C,,H,,CO,H, smaller amounts of hydrocarbons, cholesterol esters and ceryl alcohols. Approximately 60% of beeswax comprises equal proportions of monohydric alcohols and acids. Hydroxy-acids are present to the extent of approximately 15% [6]. Jojoba oil and spermaceti are also used in commercial preparations including cosmetics and pharmaceuticals and similarly contain higher molecular weight esters. A comparison of the results of SPM-GC is shown in Fig. 7. The different waxes may be readily distinguished by the distribution of fatty acid methyl esters and fatty alcohols. It is also interesting to note the series of groups of compounds (boxed) in the chromatogram of beeswax which have not yet been identified. The compounds corresponding to the annotated peaks were identified by mass spectrometry.
70 80
PY-GC
Fig. 8. SPM-GC/MS and Py-GC of Rundle shale. C6.0 to C25.0, respective saturated fatty acid methyl esters; C6, ClO, C14, respective n-alkenes.
23
Kerogen
It is well known that kerogen, the solvent insoluble fraction of oil shales, contains a proportion of oxygenated compounds and some of these are fatty acids. How those compounds are bound to the substrate is not generally known. Pyrolysis methylation gas chromatography/mass spectrometry, reconstructing the total ion chromatogram to show those compounds whose mass spectra include ions, m/z 74 and 87, characteristic of saturated fatty acid methyl esters, was used to study the composition of these compounds in Rundle shale (Fig. 8). For contrast, the pyrogram of the same shale using flame ionisation detection is shown. It is observed that the fatty acid methyl esters detected ranged from C4 to C25. Compounds C8, C12, and Cl6 were dominant in contrast to C6, Cl0 and Cl4 n-alkenes in the Py-GC determination. Doublets and/or triplets are detected in the series. Proteins
Pyrolysis methylation of proteinaceous fibres has been attempted. results of SPM-GC of wool and silk are shown in Fig. 9.
WOOL
SILK
4
Fig. 9. SPM-GC
8
12
16
of wool and silk.
The
24
The differences in chromatographic profiles reflect the differences in amino acid composition. Phenol methyl ether and o-cresol methyl ether have been identified in the products from silk. It might be expected that these fragments result from hydrolysis and methylation of tyrosine, present in fibroin (silk) to the extent of approximately 13%. Other products have not yet been identified.
CONCLUSIONS
In this paper it has been shown how SPM can be applied to a wide range of oxygen-containing materials susceptible to hydrolytic reaction and which are capable of alkylation. Many of these materials may only be identified by more lengthy and complex chemical degradation and derivatisation reactions.
ACKNOWLEDGEMENTS
The author wishes to thank Professor R. Alexander and Dr. A. Jefferson of Curtin University for their helpful advice. This paper is published with the approval of the Director, Chemistry Centre (WA), Department of Mines, Perth, Western Australia.
REFERENCES 1 2 3 4 5 6
J.M. Challinor, J. Anal. Appl. Pyrolysis, 16 (1989) 323. J.M. Challinor, J. Anal. Appl. Pyrolysis, accepted for publication. J.M. Challinor, Forensic Sci. Int., 21 (1983) 269. D.T. Downing and R.S. Greene, Anal. Chem., 40 (1968) 827. M.G. Williams and J. MacGee, J. Chromatogr., 234 (1982) 468. H. Bennett, Industrial Waxes, Chemical Publishing Company, Inc., New York, Vol. 1, 1975.