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Gas chromatography of polar compounds using a non-polar liquid phase
VOI;. 2 (q5cj)
GAS
JOURNAL
CHROMATOGRAPHY USING
65
OF CMROnIATOGRAPHY
A NON-POLAR
OF POLAR LIQUID
COMPOUNDS PHASE
IN'I-RODUCTION
The esamination of strongly polar solutes by gas-liquid chromatography (G.L.C.), using non-polar liquid phases, invariably results in poor separations, clue to the adsorption of the polar compounds on the surface of the support. This adsorption effect manifests itself by the production of asymmetric peaks with sharp “fronts” and very diffuse “tails”. Both Celite and ground insulating-brick, the supports commonly used in G.L.C., eshibit this effect, although the adsorption that occurs with Celite can be reduced slightly by treatment with acid and alkali. This adsorption effect has been overcome by S~~RENSEN AND %LTOI+ and by KWANTES AND RIJNDERS *, by using metal lielices as the support. Symmetrical peaks were obtainecl but the column resolution was poor due to the open nature of the support allowing considerable molecular diffusion?. .to take place in the column. The work of these authors indicated that a support with a metallic surface was preferable for use in G.L.C. and this paper describes a nlethod f&r coating brick dust with both gold and silver deposits. Preliminary work with Alings from a porous phosphor-bronze bearing as a support certainly produced symmetrical peaks with little or no tailing but the metal was insufficiently porous to hold a reasonable quantity of liquid phase ancl this support was discardecl.
ESI'ERIMENT;\L
Johns-Manville C.22 insulating-brick, ground to a particle size of 120-160 R.S. mesh, was used as the support. It was degreased with chloroform prior to the deposition of the metal. Silvering of the prepared brick dust was then carried out using the “l3ocllellc Salt” process 4, Ten grams of the brick clust were trcatecl with IOO ml of the silvering solution and clegassed under reduced pressure. This ensured that the solution penetrated into the pores of the brick. One hundrecl ml of the reducing solution was then added, and the solution was stirred for approsimately IO minutes. ;,lT,+1” ‘.’ Care was taken to avoid vigorous stirring, in order to eliminate possible reduction of the particle size of the support. The surplus liquid was decanted from the support and a further IOO ml of silvering s’olution added. This process was repeatecl for two I?ejsrWIcesII>*hS.
E. C. ORMEROD,
66
VOL.
R. P. W. SCOTT
2 (1959)
separate IO g portions of brick dust until they had been coated with 4 g and IO g of silver respectively. The gold plating of the degassed brick dust was cakried out using a solution of brow11 gold chloride in absolut, 0 alcohol. Sufficient solution, containing I g 0%gold chloride, was added to the brick dust to form a slurry and the misture degassed. The alcohol was then removed in a gentle stream of warm air and the brick dust heated to 250’ in a slow stream of hydrogen. The hydrogen was passed through the brick dust until no acid reaction was obtained from the exit gas. This procedure was repeated ten ..
:’ -A w
6
4
6
2
4
2
C
14
12
10
Tit-& 1n6min
4
2
(
I4
12
lo
6
.
6
-___A-_
4
2
0
Fig. I. Chromatogranx of nonanol. Column climcnsions 150 cm by 3.5 mm 1,D.; column tcmpergrease I,, aplxoxiniatel~ nturc I gs o ; flow of carrier gas _jZ 1111 per min; liquid phase: Apiczon I 50//oxv/\v of uncoated 130-1 Go mesh Silocel brick dust.
-_---
a. =joopg
l>. fjoopg c. 3oofvg cl. 30014.g
Uncoated brick dust Gold coated brick dust Sil\-or coatccl brick dust 3.9 : IO silver Silver coated brick dust 9.5 : 10 silver
to brick to brick
50 50 20 20
times, giving successive deposits of gold on the support, until a total of 6.5 g of gold had been deposited. Esamination of the coated brick dusts under the microscope showed a uniform covering of silver, but only a very patchy coating of gold. After degassing the coated support, the liquid pl!ase (Apiezon L grease) was placed on it in the usual manner. The ratio of liquid phase to support, based on the weight of the original uncoated support, was 15% w/w. To obtain comparative results a sample of uncoated support was also prepared. The supports carrying the liquid phase were packed in a ISO cm column 3.5 mm 1,D. and run at 195” in an apparatus utilizing the ,flame detector. A number of polar substances were examined and ttio sets of chromatograms obtained are shown in Figs. I and 2. I?cfereiices
p. GS.
VOL.
B (.195c)j
GAS
GI-IRO~TATOGRAPI-IY
RESULTS
AND
OF POLAR
o7
COMPOUNDS
DISCUSSION
chromatograms shown in Fig. I for the gold-coated support show little improvement on the uncoated brick dust, whereas the silver coating almost eliminates the asymmetry of the nonanol peaks, The inability of the gold deposit to produce symmetrical peaks was thought to be due to its irregular deposition. The improved separations obtained by reduction of the asymmetry caused by adsorption is shown in Fig. 2. A 500 pg sample of impure metl~ylcyclol~esanol was injected to produce the
The
(d
I
(Cl
-II !J
4
2
--z---
06
c 2
Fig. 2. Chronlatograms of mcthylcyclohesanol. Column dimensions l_jO cm I>y 3.5 column tcmpcrature I gS” ; fio\v of carrier gas 52 in1 per min; liquid phase: Apiezon approsimatcly rgfl/” w/w of uncoated rzo-I60 mcsli Silocel brick clust.
mm I.D.; grcasc L,
SlIppOrt
EL0
jOOf.Cg
b. .=)oopg c, 3oopg cl. LCZO//,Q
Silver Silver
Uncoated brick dust Gold coated brick dust coated brick dust 3.9: I o silver coatccl brick dust 9.5 : I o silver
to brick to brick
50 50 20 170
first ,two chromatograms (a) and (b) and it will be seen that some impurities were present adjacent to the major peak. A 300 pg charge was sufficient to produce the chromatogram (c) and the reduction in asymmetry resulted in two of the three apparent impurities being. partially separated from the main peak. In the chromatogram (d) further decrease in adsorption resulting from increased silver coating has resulted in even better separation between the second and third peaks. The spread of the Y*e, original peak was in no way due to overloading of the column and the reduction in “
6s
E. C. ORMEROD,
li. P. TV. SCOTT
VOL.
2
(1959)
been esperienced when chromatographing amines such as diethylamine and diethylaminoethanol. Further improvements in the coating of the support to eliminate these effects might be obtained by coating gold on top 01 silver or possibly by using nickel coatings from the decomposition of nickel carbonyl”. ~~CI~NO~LEDG~MBNTS
The authors wish to thank Mr. G. S. I;. HAZELDEAN for his help with tile esperimental work and the directors of Benzole Froducers Limited for permission to publish these results. SUhlIkIARY
A reduction in the asymmetry of peaks produced by strongly polar compounds during gas chromatographic esamination on a non-polar liquid phase has been achievecl by using Johns-Manville C.zz’brick dust coated with silver.
GAS
JOURNAL
CHROMATOGRAPHY USING
65
OF CMROnIATOGRAPHY
A NON-POLAR
OF POLAR LIQUID
COMPOUNDS PHASE
IN'I-RODUCTION
The esamination of strongly polar solutes by gas-liquid chromatography (G.L.C.), using non-polar liquid phases, invariably results in poor separations, clue to the adsorption of the polar compounds on the surface of the support. This adsorption effect manifests itself by the production of asymmetric peaks with sharp “fronts” and very diffuse “tails”. Both Celite and ground insulating-brick, the supports commonly used in G.L.C., eshibit this effect, although the adsorption that occurs with Celite can be reduced slightly by treatment with acid and alkali. This adsorption effect has been overcome by S~~RENSEN AND %LTOI+ and by KWANTES AND RIJNDERS *, by using metal lielices as the support. Symmetrical peaks were obtainecl but the column resolution was poor due to the open nature of the support allowing considerable molecular diffusion?. .to take place in the column. The work of these authors indicated that a support with a metallic surface was preferable for use in G.L.C. and this paper describes a nlethod f&r coating brick dust with both gold and silver deposits. Preliminary work with Alings from a porous phosphor-bronze bearing as a support certainly produced symmetrical peaks with little or no tailing but the metal was insufficiently porous to hold a reasonable quantity of liquid phase ancl this support was discardecl.
ESI'ERIMENT;\L
Johns-Manville C.22 insulating-brick, ground to a particle size of 120-160 R.S. mesh, was used as the support. It was degreased with chloroform prior to the deposition of the metal. Silvering of the prepared brick dust was then carried out using the “l3ocllellc Salt” process 4, Ten grams of the brick clust were trcatecl with IOO ml of the silvering solution and clegassed under reduced pressure. This ensured that the solution penetrated into the pores of the brick. One hundrecl ml of the reducing solution was then added, and the solution was stirred for approsimately IO minutes. ;,lT,+1” ‘.’ Care was taken to avoid vigorous stirring, in order to eliminate possible reduction of the particle size of the support. The surplus liquid was decanted from the support and a further IOO ml of silvering s’olution added. This process was repeatecl for two I?ejsrWIcesII>*hS.
E. C. ORMEROD,
66
VOL.
R. P. W. SCOTT
2 (1959)
separate IO g portions of brick dust until they had been coated with 4 g and IO g of silver respectively. The gold plating of the degassed brick dust was cakried out using a solution of brow11 gold chloride in absolut, 0 alcohol. Sufficient solution, containing I g 0%gold chloride, was added to the brick dust to form a slurry and the misture degassed. The alcohol was then removed in a gentle stream of warm air and the brick dust heated to 250’ in a slow stream of hydrogen. The hydrogen was passed through the brick dust until no acid reaction was obtained from the exit gas. This procedure was repeated ten ..
:’ -A w
6
4
6
2
4
2
C
14
12
10
Tit-& 1n6min
4
2
(
I4
12
lo
6
.
6
-___A-_
4
2
0
Fig. I. Chromatogranx of nonanol. Column climcnsions 150 cm by 3.5 mm 1,D.; column tcmpergrease I,, aplxoxiniatel~ nturc I gs o ; flow of carrier gas _jZ 1111 per min; liquid phase: Apiczon I 50//oxv/\v of uncoated 130-1 Go mesh Silocel brick dust.
-_---
a. =joopg
l>. fjoopg c. 3oofvg cl. 30014.g
Uncoated brick dust Gold coated brick dust Sil\-or coatccl brick dust 3.9 : IO silver Silver coated brick dust 9.5 : 10 silver
to brick to brick
50 50 20 20
times, giving successive deposits of gold on the support, until a total of 6.5 g of gold had been deposited. Esamination of the coated brick dusts under the microscope showed a uniform covering of silver, but only a very patchy coating of gold. After degassing the coated support, the liquid pl!ase (Apiezon L grease) was placed on it in the usual manner. The ratio of liquid phase to support, based on the weight of the original uncoated support, was 15% w/w. To obtain comparative results a sample of uncoated support was also prepared. The supports carrying the liquid phase were packed in a ISO cm column 3.5 mm 1,D. and run at 195” in an apparatus utilizing the ,flame detector. A number of polar substances were examined and ttio sets of chromatograms obtained are shown in Figs. I and 2. I?cfereiices
p. GS.
VOL.
B (.195c)j
GAS
GI-IRO~TATOGRAPI-IY
RESULTS
AND
OF POLAR
o7
COMPOUNDS
DISCUSSION
chromatograms shown in Fig. I for the gold-coated support show little improvement on the uncoated brick dust, whereas the silver coating almost eliminates the asymmetry of the nonanol peaks, The inability of the gold deposit to produce symmetrical peaks was thought to be due to its irregular deposition. The improved separations obtained by reduction of the asymmetry caused by adsorption is shown in Fig. 2. A 500 pg sample of impure metl~ylcyclol~esanol was injected to produce the
The
(d
I
(Cl
-II !J
4
2
--z---
06
c 2
Fig. 2. Chronlatograms of mcthylcyclohesanol. Column dimensions l_jO cm I>y 3.5 column tcmpcrature I gS” ; fio\v of carrier gas 52 in1 per min; liquid phase: Apiezon approsimatcly rgfl/” w/w of uncoated rzo-I60 mcsli Silocel brick clust.
mm I.D.; grcasc L,
SlIppOrt
EL0
jOOf.Cg
b. .=)oopg c, 3oopg cl. LCZO//,Q
Silver Silver
Uncoated brick dust Gold coated brick dust coated brick dust 3.9: I o silver coatccl brick dust 9.5 : I o silver
to brick to brick
50 50 20 170
first ,two chromatograms (a) and (b) and it will be seen that some impurities were present adjacent to the major peak. A 300 pg charge was sufficient to produce the chromatogram (c) and the reduction in asymmetry resulted in two of the three apparent impurities being. partially separated from the main peak. In the chromatogram (d) further decrease in adsorption resulting from increased silver coating has resulted in even better separation between the second and third peaks. The spread of the Y*e, original peak was in no way due to overloading of the column and the reduction in “
6s
E. C. ORMEROD,
li. P. TV. SCOTT
VOL.
2
(1959)
been esperienced when chromatographing amines such as diethylamine and diethylaminoethanol. Further improvements in the coating of the support to eliminate these effects might be obtained by coating gold on top 01 silver or possibly by using nickel coatings from the decomposition of nickel carbonyl”. ~~CI~NO~LEDG~MBNTS
The authors wish to thank Mr. G. S. I;. HAZELDEAN for his help with tile esperimental work and the directors of Benzole Froducers Limited for permission to publish these results. SUhlIkIARY
A reduction in the asymmetry of peaks produced by strongly polar compounds during gas chromatographic esamination on a non-polar liquid phase has been achievecl by using Johns-Manville C.zz’brick dust coated with silver.