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Fast, Accurate Semivolatiles Analysis!

Using Rxi-5Sil MS GC Columns


By Robert Freeman, Environmental Innovations Chemist
  • Ultra-low bleed columns save you time and money with faster baseline stabilization.
  • Highly inert for more accurate low-level analysis of active compounds.
  • Guaranteed column-to-column reproducibility.

Semivolatiles methods, such as EPA Method 8270, place stringent demands on gas chromatography (GC) systems—particularly on the analytical column. These test methods monitor for a broad range of environmental contaminants that are analyzed as a complex mixture of acidic and base/neutral analytes. The complexity of the samples, coupled with the increasing need for lower detection limits, has tightened analytical requirements for column bleed, efficiency, and inertness.

5% diphenyl/95% dimethyl polysiloxane (“5” phase) columns typically are used for this GC/MS analysis. Manufacturers have made significant advances to the standard “5” phase by incorporating phenyl rings into the backbone of the polymer (Figure 1). This stiffens the siloxane backbone, which then reduces thermal breakdown and column bleed. Conventional “5” phase selectivity is maintained by adjusting the content of this additional phenyl group. The silarylene polymer not only exhibits improved thermal stability and reduced bleed, but also shows increased peak efficiencies for polycyclic (polynuclear) aromatic hydrocarbons (PAHs), including benzofluoranthene isomers (Figure 2). Restek has applied its Rxi deactivation technology (1) to our existing silarylene phase resulting in the Rxi-5Sil MS column, a low bleed column with excellent inertness for active analytes. Here we evaluate the performance of two popular dimensions of Rxi-5Sil MS columns for semivolatiles analysis in terms of bleed, efficiency, and activity.

Figure 1  Silarylene stationary phase chemistry: aromatic rings lower bleed and increase efficiencies.

silarylene

Figure 2  Excellent resolution of benzo(b)fluoranthene and benzo(k)fluoranthene on the Rxi-5Sil MS column.

GC_EV00945BFor conditions see Figure 4.

Low column bleed reduces the amount of noise contributed by the column, and thereby increases the signal-to-noise ratio of the analytical system. Low bleed Rxi-5Sil MS columns are ideal for GC/MS applications requiring high sensitivity. For semivolatile analysis, bleed interferes with the ability to quantify low levels of late eluting compounds, most notably the PAHs. Here we evaluated bleed levels using 10ng on-column and found the Rxi-5Sil MS columns to be exceptionally low bleed (Figures 3 and 4). Increased sensitivity and subsequently lower detection limits are a direct result of improved signal-to-noise ratios. Decreased bleed also results in less bleed ion interference with the mass spectral data, making more accurate peak identifications possible.

The separation of several difficult PAHs is critical in semivolatiles analysis. The 30m x 0.25mm x 0.25df column (Figure 3) and the 20m x 0.18mm x 0.18df column (Figure 4) both show high efficiency for PAHs. The narrow bore 0.18mm ID column has slightly better resolution of the difficult to resolve isomeric pair, benzo(b)fluoranthene & benzo(k)fluoranthene. Two other polycyclic (polynuclear) aromatic hydrocarbons also are resolved better using the 0.18mm ID column, indeno(1,2,3-cd)pyrene and dibenzo(a,h)anthracene.

Figure 3  Separate difficult PAHs easily using a 30m x 0.25mm ID x 0.25µm Rxi-5Sil MS column.

Peaks
1.1,4-Dioxane
2.N-Nitrosodimethylamine
3.Pyridine
4.2-Fluorophenol (SS)
5.Phenol-d6 (SS)
6.Phenol
7.Aniline
8.Bis(2-chloroethyl) ether
9.2-Chlorophenol
10.1,3-Dichlorobenzene
11.1,4-Dichlorobenzene-d4 (IS)
12.1,4-Dichlorobenzene
13.Benzyl alcohol
14.1,2-Dichlorobenzene
15.2-Methylphenol
16.Bis(2-chloroisopropyl) ether
17.4-Methylphenol/3-methylphenol
18.N-Nitrosodi-N-propylamine
19.Hexachloroethane
20.Nitrobenzene-d5 (SS)
21.Nitrobenzene
22.Isophorone
23.2-Nitrophenol
24.2,4-Dimethylphenol
25.Benzoic acid
26.Bis(2-chloroethoxy)methane
27.2,4-Dichlorophenol
28.1,2,4-Trichlorobenzene
29.Naphthalene-d8 (IS)
30.Naphthalene
31.4-Chloroaniline
32.Hexachlorobutadiene
33.4-Chloro-3-methylphenol
34.2-Methylnaphthalene
35.1-Methylnaphthalene
36.Hexachlorocyclopentadiene
37.2,4,6-Trichlorophenol
38.2,4,5-Trichlorophenol
39.2-Fluorobiphenyl (SS)
40.2-Chloronaphthalene
41.2-Nitroaniline
42.1,4-Dinitrobenzene
43.Dimethyl phthalate
44.1,3-Dinitrobenzene
45.2,6-Dinitrotoluene
46.1,2-Dinitrobenzene
Peaks
47.Acenaphthylene
48.3-Nitroaniline
49.Acenaphthene-d10 (IS)
50.Acenaphthene
51.2,4-Dinitrophenol
52.4-Nitrophenol
53.2,4-Dinitrotoluene
54.Dibenzofuran
55.2,3,5,6-Tetrachlorophenol
56.2,3,4,6-Tetrachlorophenol
57.Diethyl phthalate
58.4-Chlorophenyl phenyl ether
59.Fluorene
60.4-Nitroaniline
61.4,6-Dinitro-2-methylphenol
62.n-Nitroso-diphenylamine (diphenylamine)
63.1,2-Diphenylhydrazine (as azobenzene)
64.2,4,6-Tribromophenol (SS)
65.4-Bromophenyl phenyl ether
66.Hexachlorobenzene
67.Pentachlorophenol
68.Phenanthrene-d10 (IS)
69.Phenanthrene
70.Anthracene
71.Carbazole
72.di-n-Butyl phthalate
73.Fluoranthene
74.Benzidine
75.Pyrene-d10 (SS)
76.Pyrene
77.p-Terphenyl-d14 (SS)
78.3,3'-Dimethylbenzidine
79.Butyl benzyl phthalate
80.Bis(2-ethylhexyl) adipate
81.3,3'-Dichlorobenzidine
82.Benzo[a]anthracene
83.Bis(2-ethylhexyl)phthalate
84.Chrysene-d12 (IS)
85.Chrysene
86.Di-n-octyl phthalate
87.Benzo[b]fluoranthene
88.Benzo[k]fluoranthene
89.Benzo[a]pyrene
90.Perylene-d12 (IS)
91.Indeno[1,2,3-cd]pyrene
92.Dibenzo[a,h]anthracene
93.Benzo[ghi]perylene
c = contaminant (toluene)
Semivolatiles by EPA Method 8270 on Rxi-5Sil MS (30m, 0.25mm ID, 0.25 µm) w/Drilled Uniliner
GC_EV00943
ColumnRxi-5Sil MS, 30 m, 0.25 mm ID, 0.25 µm (cat.# 13623)
Sample8270 MegaMix (cat.# 31850)
Benzoic acid (cat.# 31879)
8270 Benzidines mix (cat.# 31852)
Acid surrogate mix (4/89 SOW) (cat.# 31025)
Revised B/N surrogate mix (cat.# 31887)
1,4-Dioxane (cat.# 31853)
SV internal standard mix (cat.# 31206)
Conc.:10 µg/mL (IS 40 μg/mL)
Injection
Inj. Vol.:1.0 µL pulsed splitless (hold 0.15 min)
Liner:4 mm drilled Uniliner (hole near bottom) (cat.# 20756)
Inj. Temp.:250 °C
Pulse Pressure:25 psi (172.4kPa)
Pulse Time:0.2 min
Purge Flow:60 mL/min
Oven
Oven Temp.:40 °C (hold 1.0 min) to 280 °C at 25 °C/min to 320 °C at 5 °C/min (hold 1 min)
Carrier GasHe, constant flow
Flow Rate:1.2 mL/min
DetectorMS
Mode:Scan
Transfer Line Temp.:280 °C
Ionization Mode:EI
Scan Range:35-550 amu

Figure 4  Semivolatile compounds resolved on a 20m x 0.18mm ID x 0.18µm Rxi-5Sil MS column.

Peaks
1.1,4-Dioxane
2.N-Nitrosodimethylamine
3.Pyridine
4.2-Fluorophenol (SS)
5.Phenol-d6- (SS)
6.Phenol
7.Aniline
8.Bis(2-chloroethyl) ether
9.2-Chlorophenol
10.1,3-Dichlorobenzene
11.1,4-dichlorobenzene-d4 (IS)
12.1,4-Dichlorobenzene
13.Benzyl alcohol
14.1,2-Dichlorobenzene
15.2-Methylphenol
16.Bis(2-chloroisopropyl) ether
17.4-methylphenol/3-methylphenol
18.N-Nitrosodi-N-propylamine
19.Hexachloroethylene
20.nitrobenzene-d5 (SS)
21.Nitrobenzene
22.Isophorone
23.2-Nitrophenol
24.2,4-Dimethylphenol
25.Bis(2-chloroethoxy)methane
26.Benzoic acid
27.2,4-Dichlorophenol
28.1,2,4-Trichlorobenzene
29.Naphthalene-d8 (IS)
30.Naphthalene
31.4-Chloroaniline
32.Hexachlorobutadiene
33.4-Chloro-3-methylphenol
34.2-Methylnaphthalene
35.1-Methylnaphthalene
36.Hexachlorocyclopentadiene
37.2,4,6-Trichlorophenol
38.2,4,5-Trichlorophenol
39.2-Fluorobiphenyl (SS)
40.2-Chloronaphthalene
41.2-Nitroaniline
42.1,4-Dinitrobenzene
43.Dimethyl phthalate
44.1,3-Dinitrobenzene
45.2,6-Dinitrotoluene
46.1,2-Dinitrobenzene
Peaks
47.Acenaphthylene
48.3-Nitroaniline
49.acenaphthene-d10 (IS)
50.Acenaphthene
51.2,4-Dinitrophenol
52.4-Nitrophenol
53.Dibenzofuran
54.2,4-Dinitrotoluene
55.2,3,5,6-Tetrachloro phenol
56.2,3,4,6-Tetrachlorophenol
57.Diethyl phthalate
58.Fluorene
59.4-Chlorophenyl phenyl ether
60.4-Nitroanaline
61.4,6-Dinitro-2-methylphenol
62.n-Nitroso-diphenylamine (diphenylamine
63.1,2-Diphenylhydrazine (as azobenzene)
64.2,4,6-Tribromophenol (SS)
65.4-Bromophenyl phenyl ether
66.Hexachlorobenzene
67.Pentachlorophenol
68.Phenanthrene-d10 (IS)
69.Phenanthrene
70.Anthracene
71.Carbazole
72.di-n-Butyl phthalate
73.Fluoranthene
74.Benzidine
75.Pyrene-d10 (SS)
76.Pyrene
77.p-terphenyl-d14 (SS)
78.3,3'-Dimethylbenzidine
79.Butyl benzyl phthalate
80.Bis(2-ethylhexyl) adipate
81.Benzo[a]anthracene
82.3,3'-Dichlorobenzidine
83.Chrysene-d12 (IS)
84.Chrysene
85.Bis(2-ethylhexyl)phthalate
86.Di-n-octyl phthalate
87.Benzo[b]fluoranthene
88.Benzo[k]fluoranthene
89.Benz[a]pyrene
90.Perylene-d12 (IS)
91.Indeno[1,2,3-cd]pyrene
92.Dibenzo[a,h]anthracene
93.Benzo[ghi]perylene
Semivolatiles by EPA Method 8270 on Rxi-5Sil MS (20m, 0.18mm ID, 0.18µm)
GC_EV00945
ColumnRxi-5Sil MS, 20 m, 0.18 mm ID, 0.18 µm (cat.# 43602)
Sample8270 MegaMix (cat.# 31850)
benzoic acid (cat.# 31879)
8270 Benzidines Mix (cat.# 31852)
Acid Surrogate Mix (4/89 SOW) (cat.# 31025)
Revised B/N Surrogate Mix (cat.# 31887)
1,4-dioxane (cat.# 31853)
SV Internal Standard Mix (cat.# 31206)
Conc.:10 ng/mL on-column concentration
Injection
Inj. Vol.:1.0 µL pulsed splitless (hold 0.15 min)
Liner:Drilled Uniliner (hole near bottom) (cat.# 20756)
Inj. Temp.:250 °C
Pulse Pressure:30 psi (206.8kPa)
Pulse Time:0.2 min
Purge Flow:60 mL/min
Oven
Oven Temp.:50 °C (hold 0.5 min) to 260 °C at 20 °C/min to 280 °C at 5 °C/min to 330 °C at 20 °C/min (hold 1.0 min)
Carrier GasHe, constant flow
Flow Rate:1.0 mL/min
DetectorMS
Mode:Scan
Transfer Line Temp.:280 °C
Ionization Mode:EI
Scan Range:35-550 amu

Finally, since the analysis of semivolatiles covers such a diverse range of compounds it is critical that the column perform well for both basic and acid compounds at low levels. Surface activity in a column is revealed by peak shape and response for active analytes such as 2,4-dinitrophenol (acidic) and pyridine (basic). Most manufacturers struggle with adequate response and good peak shapes for both types of analytes. By using the unique Rxi deactivation process Restek has developed a silarylene phase that shows unsurpassed inertness and excellent response for both of these active analytes. Figures 5 and 6 illustrate the response of 2,4-dinitrophenol and pyridine at 10ng on-column, respectively. Analytically, 2,4-dinitrophenol is considered the most problematic compound in the Method 8270D target list. The Rxi-5Sil MS column passed method requirements even in the single ng on-column range (Figure 7).

Figure 5  Excellent peak shape for 2,4-dinitrophenol at 10ng on-column.

GC_EV00943DFor conditions see Figure 3.

Figure 6  Excellent response for pyridine at 10ng on-column.

GC_EV00943AFor conditions see Figure 3.

Figure 7  Low-level response for 2,4-dinitrophenol exceeds method requirements (1ng on-column, 20m x 0.18mm ID x 0.18df Rxi-5Sil MS column).

2,4-Dinitrophenol on Rxi-5Sil MS
GC_EV00950
ColumnRxi-5Sil MS, 20 m, 0.18 mm ID, 0.18 µm (cat.# 43602)
Sample8270 MegaMix (cat.# 31850)
Benzoic Acid (cat.# 31879)
8270 Benzidines Mix (cat.# 31852)
Acid Surrogate Mix (4/89 SOW) (cat.# 31025)
Revised B/N Surrogate Mix (cat.# 31887)
1,4-Dioxane (cat.# 31853)
SV Internal Standard Mix (cat.# 31206)
Conc.:1 µg/mL (IS 40μg/mL)
Injection
Inj. Vol.:1.0 µL pulsed splitless (hold 0.15 min)
Liner:Drilled Uniliner (hole near bottom) (cat.# 20756)
Inj. Temp.:250 °C
Pulse Pressure:20 psi (137.9kPa)
Pulse Time:0.2 min
Purge Flow:60 mL/min
Oven
Oven Temp.:50 °C (hold 0.5 min) to 260 °C at 20 °C/min to 280 °C at 5 °C/min to 330 °C at 20 °C/min (hold 1.0 min)
Carrier GasHe, constant flow
Flow Rate:1.0 mL/min
DetectorMS
Mode:Scan
Transfer Line Temp.:280 °C
Ionization Mode:EI
Scan Range:35-550 amu
NotesInjection: (1ng on-column concentration)

The Rxi-5Sil MS columns most commonly used for semivolatiles analysis are the 30m x 0.25mm ID columns with either 0.25µm or 0.5µm film thicknesses. These dimensions generally offer the best balance of sample capacity, analysis time, and column lifetime. However, if sample throughput is paramount, shorter narrow bore columns such as the 20m x 0.18mm ID with either 0.18µm or 0.36µm film thicknesses are preferred. Due to increased peak efficiencies, temperature programs can be accelerated without compromising key separations. Regardless of which dimension you choose, the Rxi-5Sil MS columns are ideal for analyzing semivolatile compounds.

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