Fast GC Analyses of Volatiles

Transcription

1 6 Fast GC Analyses of Volatiles Michael D. Buchanan Introduction The primary aim of Fast GC is to maintain (compared to conventional GC) sufficient resolving power in a shorter time. Basically, Fast GC is accomplished by using a short column (reduces analysis time) with a narrow I.D. (offsets the loss of efficiency of the shorter column) while manipulating specific operating parameters, such as linear velocity and oven temperature ramp rates (). The use of Fast GC has previously been demonstrated for several applications (-7). In this space, Fast GC will be demonstrated for the analysis of volatiles using purge and trap (P&T). Options for Decreasing Analysis Time for P&T Methods The overwhelming number of samples that must be analyzed for the presence of volatiles is due to the ease with which many of these compounds are able to migrate through the environment, because of their water-soluble nature. Many regulatory agencies require constant monitoring for volatiles, resulting in heavy sample loads with short turnaround times. Therefore, laboratories are constantly looking for ways to reduce analysis times. Several options currently exist for decreasing analysis time.. Use two P&Ts for each GC. Synchronize so while the GC is analyzing the sample from one P&T, that P&T is in bake mode and the other P&T is purging the next sample. When the GC is ready, a sample is also ready for desorption so that the GC is never idle.. Use a P&T model that employs super high flow rates (i.e. 0 ml/min.) during the bake mode so that it is ready to purge the next sample sooner. 3. Convert the existing conventional GC method to a Fast GC method. Note that this option can be used with the current equipment found in most laboratories, or in combination with either (or both) option(s) listed above. Converting Conventional GC to Fast GC for Waste Water Volatiles Converting a conventional GC method to a Fast GC method is not as simple as just changing to a smaller I.D. column. Column dimensions, linear velocity, and oven temperature ramp rates must be optimized together. Changing only one parameter may decrease analysis time (desirable), but will likely cause a loss of resolution (undesirable). It is also critical to account for the reduced sample capacity of the smaller I.D. column. A method for the analysis of volatiles from waste water samples (US EPA Method 64, commonly performed in the United States) on the SPB -64 column was selected to illustrate the change from conventional GC to Fast GC. The optimized chromatogram obtained using conventional GC is shown in Figure. The analysis time is < minutes, peak shapes are good, and the mass spectrometer (MS) is able to mass resolve all analytes. The column dimensions were changed to Fast GC dimensions, and then linear velocity and oven temperature ramp rates were optimized to produce the chromatogram shown in Figure (parameters which were changed are highlighted). While analysis time is reduced to <0 minutes and the MS is still able to mass resolve all analytes, peak shape overall is not good. Why the poor chromatography? The reduced sample capacity of the smaller I.D. column was not accounted for. The primary aim of Fast GC is to maintain (compared to conventional GC) sufficient resolving power in a shorter time The capacity of the 0. mm I.D. column is significantly less than the 0.5 mm I.D. column, leading to sample overload. To alleviate this problem, the mass of sample reaching the column must be reduced. Diluting the sample, decreasing the injection volume, or increasing the split ratio are options to achieve this. The first two options are not as compatible with P&T methods as the third. Therefore, the split ratio was increased from : to 00:, and then the linear velocity was optimized to achieve the chromatogram shown in Figure 3 (parameters which were changed are highlighted). Now, the short analysis time (<0 minutes) and mass resolution of all analytes is accompanied with improved peak shape of all analytes. This represents a vast improvement in analysis time (from over 7 minutes to under 0 minutes) compared to the conventional GC chromatogram in Figure. Did you know...? (continued on page ) Supelco currently offers a total of nineteen columns in Fast GC dimensions, covering twelve popular phases (SPB- 64, VOCOL, SLB -5ms, Equity -, TCEP, SP -560, Omegawax 00, SUPELCOWAX 0, Equity-, SPB-, Equity-5, and SPB-5). If increasing sample throughput is your goal, consider a change to a Supelco Fast GC column. Volume.

2 7 Figure. Waste Water Volatiles on the SPB-64 purge trap: VOCARB 00 K (4-U) desorption flow: ml/min. column: SPB-64, m x 0.5 mm I.D.,.4 µm (5) oven: C ( min.), 7 C/min. to C, C/min. to C (3 min.) carrier gas: helium,. ml/min. injection: : split Figure. Waste Water Volatiles on the SPB-64 purge trap: VOCARB 00 K (4-U) desorption flow: ml/min. column: SPB-64, 0 m x 0. mm I.D.,.0 µm (66-U) oven: C ( min.), C/min. to 5 C, C/min. to C ( min.) carrier gas: helium,. ml/min. injection: : split Figure 3. Waste Water Volatiles on the SPB-64 desorption flow: ml/min. column: SPB-64, 0 m x 0. mm I.D.,.0 µm (66-U) oven: C ( min.), C/min. to 5 C, C/min. to C ( min.) carrier gas: helium,.5 ml/min. injection: 00: split Peak IDs for Figures -3. Chloromethane. Vinyl chloride 3. Bromomethane 4. Chloroethane 5. Trichlorofluoromethane 6.,-Dichloroethene 7. Methylene chloride. trans-,-dichloroethene.,-dichloroethane 0. Chloroform. Dibromofluoromethane (surr.).,,-trichloroethane 3. Carbon tetrachloride 4.,-Dichloroethane-d 4 (surr.) 5. Benzene.,-Dichloroethane 7. Fluorobenzene (I.S.). Trichloroethene.,-Dichloropropane 0. Bromodichloromethane CO 5 CO 5 CO Conventional GC Analysis, : Split 4,5 Fast GC Analysis, : Split Fast GC Analysis, 00: Split Chloroethyl vinyl ether. cis-,3-dichloropropene 3. Toluene-d (surr.) 4. Toluene 5. trans-,3-dichloropropene.,,-trichloroethane 7. Tetrachloroethene. Dibromochloromethane. Chlorobenzene-d 5 (I.S.). Chlorobenzene, 7 0 3, ,5 4,5 7 7, Ethylbenzene 3. Bromoform. 4-Bromofluorobenzene (surr.).,,,-tetrachloroethane.,3-dichlorobenzene.,4-dichlorobenzene-d 4 (I.S.) 37.,4-Dichlorobenzene 3.,-Dichlorobenzene G G G00 ordering: (US only) / 4--4 technical service: (US and Canada only) / 4--4 Volume.

3 Figure 4. Solid Waste Volatiles on the VOCOL desorption flow: ml/min. bake: 0 C for 0 min. Figure 5. Solid Waste Volatiles on the VOCOL CO column: VOCOL, m x 0.5 mm I.D.,.5 µm (5-U) oven: C ( min.), 7 C/min. to 5 C, C/min. to 0 C (5 min.) carrier gas: helium, 0.7 ml/min. injection: : split Conventional GC Analysis, : Split ,44 3, , ,3 4 4, , Fast GC Analysis, : Split ,44 57,5 67 dry purge: min desorption temp.: 0 C for min. 6 7 desorption flow: 46 ml/min. 7 3,4 3 37, , column: VOCOL, 0 m x 0. mm I.D.,.0 µm (463-U) 5 oven: C (0. min.), C/min. to 5 C, 3 C/min. to 0 C ( min.) 5 3,4, 4 0 CO MSD interface: 0 C, carrier gas: helium,.4 ml/min. injection: : split G G00 Figure 6. Solid Waste Volatiles on the VOCOL Fast GC Analysis, 00: Split , ,44 dry purge: min ,5 65 desorption temp.: 0 C for min. 7 3,4, desorption flow: ml/min , column: VOCOL, 0 m x 0. mm I.D.,.0 µm (463-U) oven: C (0. min.), C/min. to 5 C, 3 5 3, C/min. to 0 C ( min.) 7, CO MSD interface: 0 C carrier gas: helium,.5 ml/min. injection: 00: split G00 Peak IDs for Figures 4-6. Dichlorofluoromethane. Chloromethane 3. Vinyl chloride 4. Bromomethane 5. Chloroethane 6. Trichlorofluoromethane 7. Acetone.,-Dichloroethene. Iodomethane 0. Methylene chloride. trans-,-dichloroethene.,-dichloroethane 3. -Butanone 4.,-Dichloropropane 5. cis-,-dichloroethene. Chloroform 7. Bromochloromethane. Dibromofluoromethane (surr.).,,-trichloroethane 0.,-Dichloropropene. Carbon tetrachloride.,-dichloroethane-d 4 (surr.) 3.,-Dichloroethane 4. Benzene 5. Fluorobenzene (I.S.). Trichloroethene 7.,-Dichloropropane. Bromodichloromethane. Dibromomethane. 4-methyl--pentanone 3. cis-,3-dichloropropene 3. Toluene-d (surr.). Toluene. trans-,3-dichloropropene.,,-trichloroethane. -Hexanone 37.,3-Dichloropropane 3. Tetrachloroethene 3. Dibromochloromethane.,-Dibromomethane 4. Chlorobenzene-d 5 (I.S.) 4. Chlorobenzene 43. Ethylbenzene 44.,,,-Tetrachloroethane. m-xylene & p-xylene 46. o-xylene 47. Styrene 4. Isopropylbenzene 4. Bromoform. cis-,4-dichloro--butene 5.,,,-Tetrachloroethane 5. 4-Bromofluorobenzene (surr.).,,3-trichloropropane. n-propylbenzene 55. Bromobenzene 56. trans-,4-dichloro--butene 57.,3,5-Trimethylbenzene 5. o-chlorotoluene 5. p-chlorotoluene 60. tert-butylbenzene 6.,,4-Trimethylbenzene 6. Pentachloroethane 63. sec-butylbenzene 64. p-isopropyltoluene 65.,3-Dichlorobenzene 66.,4-Dichlorobenzene-d 4 (I.S.) 67.,4-Dichlorobenzene 6. Butylbenzene 6.,-Dichlorobenzene.,-Dibromo-3-chloropropane 7.,,4-Trichlorobenzene 7. Hexachlorobutadiene 73. Naphthalene 74.,,3-Trichlorobenzene Volume.

4 (continued from page 6) Fast GC methods can be used with complex samples, Converting Conventional GC to Fast GC for and with any column, regardless of its selectivity. Further- Solid Waste Volatiles more, Fast GC is compatible with the current equipment Fast GC is also compatible with more complex samples. A method for the analysis of volatiles from solid waste found in most laboratories, and also with newer equipment that is designed for speed. samples (US EPA Method 0, also commonly performed in the United States) was selected as an example, this time using the VOCOL column. The optimized chromatogram obtained using conventional GC is shown in Figure 4. The analysis time is <3 minutes. The column dimensions were changed to Fast GC dimensions, and then conditions were optimized to produce the chromatogram shown in Figure 5 (parameters which were changed are highlighted). While analysis time is reduced to < minutes, the shapes of the first several peaks are not good due to the lower capacity of the 0. mm I.D. column. Therefore, the split ratio was increased from : to 00:, and then the linear velocity was optimized to achieve the chromatogram shown in Figure 6 (parameters which were changed are highlighted). Again, the short analysis time (< minutes) is accompanied with improved peak shapes. This represents a vast improvement in analysis time (from over minutes to under minutes) compared to the conventional GC chromatogram in Figure 4. Fast GC of Hazardous Waste Site Volatiles A method for the analysis of volatiles from hazardous waste site samples (US EPA Method OLM04. VOA) was selected to show the selectivity differences between the SPB-64 column and the VOCOL column. Optimized Fast GC chromatograms are shown in Figure 7 (SPB-64) and Figure (VOCOL). Both show quick analysis times and good shapes of all peaks. Note the change in elution order for several peaks (0/, /, 3/3, 37/3, 47/4, and 4/) due to the selectivity difference between the two columns. Conclusion Converting methods from conventional GC to Fast GC can result in decreased costs (less people and/or instruments are needed) and increased revenue (more samples can be processed). However, care must be taken to ensure that all Fast GC method parameters are optimized together. Changing only one may decrease analysis time (desirable), but will likely cause a loss of resolution (undesirable). With any Fast GC method, the reduced sample capacity of the smaller I.D. column must be accounted for so that unacceptable chromatography is not created. + +! References. Fast GC: A Practical Guide for Increasing Sample Throughput without Sacrificing Quality, Supelco Brochure; T6 JTW: K. Stenerson, Fast GC Analysis of Bacterial Acid Methyl Esters (BAMEs) on Equity- Columns, Supelco The Reporter, Apr 004; Vol..: K. Stenerson, Fast Analysis of Fish Oils and Animal Lipids on the SUPELCOWAX 0 Column, Supelco The Reporter, Aug 004; Vol..4: M.D. Buchanan, SLB-5ms Fast GC Columns for Semivolatile Analysis, Supelco The Reporter, Aug 006; Vol. 4.4: L. Mondello and M.D. Buchanan, Analysis of Adulterated Lemon Essential Oil on the SLB-5ms, Supelco The Reporter, Oct 006; Vol. 4.5: M.D. Buchanan, Fast GC Analysis of Detailed cis/trans Fatty Acid Methyl Esters (FAMEs) on the 75 m SP-560 Capillary Column, Supelco The Reporter, Aug 007; Vol. 5.4: L.M. Sidisky, K.K. Stenerson, G.A. Baney, and M.D. Buchanan, NEW! Capillary Column for Fast Omega-3 and Omega-6 FAME Analyses, Supelco Reporter, Oct. 007; Vol. 5.5: -0. Featured Products Description SPB-64 Fused Silica Columns (continued on page 0) Cat. No. 0 m x 0. mm I.D.,.0 µm 66-U m x 0.5 mm I.D.,.4 µm 5 VOCOL Fused Silica Columns 0 m x 0. mm I.D.,.0 µm 463-U m x 0.5 mm I.D.,.5 µm 5-U VOCARB 00 K Purge Traps Fits OI Analytical Eclipse 4660 / 60 4-U Related Products Description SPB-64 Fused Silica Columns Cat. No. 60 m x 0.5 mm I.D.,.4 µm 6 m x 0.3 mm I.D.,. µm 3-U 60 m x 0.3 mm I.D.,. µm m x 0. mm I.D., 3.0 µm 60 m x 0. mm I.D., 3.0 µm 663-U 75 m x 0. mm I.D., 3.0 µm 3 05 m x 0. mm I.D., 3.0 µm 664-U VOCOL Fused Silica Columns 0 m x 0.0 mm I.D.,. µm 4-U 60 m x 0.5 mm I.D.,.5 µm 4 m x 0.3 mm I.D.,. µm 464-U 60 m x 0.3 mm I.D.,. µm 47-U 60 m x 0.3 mm I.D., 3.0 µm 7 m x 0. mm I.D., 3.0 µm 0-U 60 m x 0. mm I.D., 3.0 µm 05 m x 0. mm I.D., 3.0 µm 5 60 m x 0.75 mm I.D.,.5 µm 3-U VOCARB 00 K Purge Traps Fits Tekmar Velocity XPT / 000 / U Fits Tekmar 00 / 300 -U Fits OI Analytical U Fits Dynatech Dyna Models 05-U Fits CDS Peak Master 5 Related Information The complete list of our analytical standards can be viewed at sigma-aldrich.com/standards ordering: (US only) / 4--4 technical service: (US and Canada only) / 4--4 Volume.

5 0 Figure 7. Hazardous Waste Site Volatiles on the SPB-64 desorption flow: 4 ml/min. Fast GC Analysis, 00: Split 0 3,4 0,,7 column: SPB-64, 0 m x 0. mm I.D.,.0 µm (66-U) oven: C ( min.), C/min. to 5 C, 5 37 CO C/min. to C ( min.) carrier gas: helium,. ml/min. injection: 00: split Figure. Hazardous Waste Site Volatiles on the VOCOL desorption flow: ml/min. column: VOCOL, 0 m x 0. mm I.D.,.0 µm (463-U) oven: C (0. min.), C/min. to 5 C, 3 C/min. to 0 C ( min.) carrier gas: helium,.4 ml/min. injection: 00: split 7,, 3,4 Fast GC Analysis, 00: Split 3 7, 4,5 0, 0, 3 CO 5 4 7, , G G00475 Peak IDs for Figures 7-. Dichlorofluoromethane. Chloromethane 3. Vinyl chloride 4. Bromomethane 5. Chloroethane 6. Trichlorofluoromethane 7.,,-Trichloro-,,-trifluoroethane.,-Dichloroethene. Acetone 0. Carbon disulfide. Methyl acetate. Methylene chloride 3. Methyl-tert-butyl ether 4. trans-,-dichloroethene 5.,-Dichloroethane. -Butanone 7. cis-,-dichloroethene. Bromochloromethane (I.S.). Chloroform 0.,,-Trichloroethane. Cyclohexane. Carbon tetrachloride 3.,-Dichloroethane-d 4 (surr.) 4. Benzene 5.,-Dichloroethane.,4-Difluorobenzene (I.S.) 7. Trichloroethene. Methylcyclohexane.,-Dichloropropane. Bromodichloromethane 3. cis-,3-dichloropropene 3. 4-Methyl--pentanone. Toluene-d (surr.). Toluene. trans-,3-dichloropropene.,,-trichloroethane 37. Tetrachloroethene 3. -Hexanone 3. Dibromochloromethane.,-Dibromomethane 4. Chlorobenzene-d 5 (I.S.) 4. Chlorobenzene 43. Ethylbenzene 44. m-xylene & p-xylene. o-xylene 46. Styrene 47. Bromoform 4. Isopropylbenzene 4. 4-Bromofluorobenzene (surr.).,,,-tetrachloroethane 5.,3-Dichlorobenzene 5.,4-Dichlorobenzene.,-Dichlorobenzene.,-Dibromo-3-chloropropane 55.,,4-Trichlorobenzene Did you know...? The 007 brochure Fast GC: A Practical Guide for Increasing Sample Throughput without Sacrificing Quality (T6 JTW) contains valuable information concerning Fast GC principles that is not covered in this article. Included are practical considerations, theoretical discussions, a listing of columns in Fast GC dimensions, twenty-six chromatograms, a listing of related products designed to maximize performance, plus a list of literature for additional reading. Request a copy of this brochure on the attached postcard or contact Supelco Technical Service at (US and Canada only), 4--4, or at techservice@sial.com! Related Information The Supelco Purge-and-Trap System Guide (T7 BIN) contains both theory as well as troubleshooting information. Request a copy of this bulletin on the attached postcard or contact Supelco Technical Service at (US and Canada only), 4--4, or at techservice@sial.com (Available in electronic form only. Please provide address.) Volume.