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Environmental Article

Faster Organochlorine Pesticide Sample Throughput

On New Rtx®-CLPesticides & Rtx®-CLPesticides2 Columns

By Jason Thomas, Environmental Innovations Chemist
  • Dramatically improve sample throughput.
  • Results in <7min. by conventional analysis, or <5min. using the Gerstel MACH system.
  • Outstanding resolution on all columns.

As the environmental testing market continues to be very competitive, laboratory operating costs are of critical concern. Increasing sample throughput is one way to reduce costs, and shortening analytical run time is an effective way to do this. Here we offer methods for reducing run time for the organochlorine pesticides analyzed under US EPA Method 8081. This method requires dual column analysis for confirmation of 20 chlorinated pesticides using an ECD for detection. The significant reduction in both analysis time and more significantly, cycle time, offered here is a major benefit for environmental laboratories.

Restek developed the Rtx®-CLPesticides and Rtx®-CLPesticides2 column pair specifically for chlorinated pesticides. These phases were designed to separate the isomers and the structurally similar pairs on the list of target analytes. Here we introduce new film thicknesses with optimized phase ratios for some of the columns in this line. Using these new stationary phase film thicknesses and the optimized run conditions shown, the 20 compounds in US EPA Method 8081 can be analyzed in less than 8 minutes on 20m x 0.18mm ID columns with a 0.53mm ID guard column (Figure 1). If your lab prefers to use standard or mega-bore columns, Figure 2 and 3 show similar results for the 30m x 0.32mm ID and 0.53mm ID columns respectively. All compounds elute in less than 7 and 9 minutes respectively, and chromatography is similar to that obtained on the narrow bore Rtx®-CLPesticides counterparts. This allows rapid analysis without sacrificing column capacity, which translates, of course, into improved sample throughput for your laboratory.

An Even Faster Alternative

In the attempt to obtain faster analytical run times, several different concepts have been introduced to improve the stock performance of standard GCs. Some of the modifications available, such as EZ-Flash GC and GC Racer, rely on rapid column heating. One of the most recent and versatile concepts is the low thermal mass method by Gerstel using an apparatus called the MACH, (Modular Accelerated Column Heater) (Figure 4). This system operates by heating the capillary column outside of the GC oven in a small column module mounted on the oven door. The column is wound and encapsulated in foil along with a heating element and sensors. It is cooled with fans placed directly below the column module, and the entire unit is powered by an external control pad with the option of method control through ChemStation® software.

This apparatus provides several important advantages. First, due to the low thermal mass of the unit, very rapid heating times, up to 1800°C/min., can be realized. Second, because of the way the column is wrapped, very uniform heating occurs, eliminating the eddies and hot spots associated with the convective heating produced in a conventional GC oven. Third, because of the low thermal mass of the unit, very rapid cooling can take place allowing very short inter-run times, significantly shortening cycle times. For this application, considering the total run times and the subsequent cool-down times, the MACH unit has an analysis cycle that is approximately twice as fast as the GC alone. Finally, since the column modules are independently controlled, two different temperature programs can be run simultaneously, allowing each column to be optimized individually for a given method.

Restek applied this novel MACH technology to EPA Method 8081 using an Rtx®-CLPesticides and Rtx®-CLPesticides2 column pair. Almost 100% baseline resolution was obtained for all 22 pesticides and surrogates, on both columns, in under five minutes (Figure 5). This combination of ultra-fast analysis time and outstanding resolution is a result of the unique selectivity and high efficiency of the phases combined with the narrow peaks associated with fast temperature programming. The column dimensions used, 20m x 0.18mm x 0.18/0.14µm maintain the same phase ratios as the optimized 0.53mm and 0.32mm columns but with the smaller 0.18mm ID, attain a much greater level of efficiency which is needed for high-speed chromatography.

Regardless of whether you choose to embrace the new fast-GC technology, or continue to adhere to more conventional GC, Restek Rtx®-CLPesticides and Rtx®-CLPesticides2 columns can provide exceptional performance and very rapid run times when analyzing chlorinated pesticides.


Figure 1  Baseline resolution of organochlorine pesticides on the 0.18mm ID Rtx®-CLPesticides column pair in less than 8 minutes.

  1. 2,4,5,6-tetrachloro-
    m-xylene (surr.)
  2. α-BHC
  3. γ-BHC
  4. β-BHC
  5. δ-BHC
  6. heptachlor
  7. aldrin
  1. heptachlor epoxide
  2. γ-chlordane
  3. α-chlordane
  4. endosulfan I
  5. 4,4′ DDE
  6. dieldrin
  7. endrin
  8. 4,4′ DDD
  1. endosulfan II
  2. 4,4′ DDT
  3. endrin aldehyde
  4. endosulfan sulfate
  5. methoxychlor
  6. endrin ketone
  7. decachlorobiphenyl (surr.)

Column:
Rtx®-CLPesticides, 20m, 0.18mm ID, 0.18µm (cat.# 42102) (top) and Rtx®-CLPesticides2, 20m, 0.18mm ID, 0.14µm (cat.# 42302) with 5m x 0.53mm ID intermediate-polarity deactivated guard tubing (cat.# 10045), connected using SeCure™ "Y" Connector Kit (cat.# 20276) with Universal "Y" Press-Tight® Connector
Sample:
Organochlorine Pesticide Mix AB #2 (cat.# 32292), 8-80µg/mL each component in hexane/toluene, Pesticide Surrogate Mix (cat.# 32000), 200µg/mL each component in acetone
Inj.:
0.5µL splitless (hold 0.75 min.), 2mm single gooseneck inlet liner (cat.# 20795)
Inj. temp.:
250°C
Carrier gas:
helium, constant flow
Linear velocity:
20cm/sec. @ 140°C
Oven temp.:
140°C (hold 1 min.) to 250°C @ 35°C/min. (hold 1 min.) to 330°C @ 35°C/min. (hold 3 min.)
Det.:
ECD @ 350°C

GC_EV00892 and GC_EV00893

Figure 2   Baseline resolution of organochlorine pesticides on the 0.32mm ID Rtx®-CLPesticides column pair in less than 7 minutes.

  1. 2,4,5,6-tetrachloro-m-xylene (SS)
  2. α-BHC
  3. γ-BHC
  4. β-BHC
  5. δ-BHC
  6. heptachlor
  7. aldrin
  8. heptachlor epoxide (isomer B)
  9. γ-chlordane
  10. α-chlordane
  11. endosulfan I
  1. 4,4′-DDE
  2. dieldrin
  3. endrin
  4. 4,4′-DDD
  5. endosulfan II
  6. 4,4′-DDT
  7. endrin aldehyde
  8. endosulfan sulfate
  9. methoxychlor
  10. endrin ketone
  11. decachlorobiphenyl (SS)

Column:
Rtx®-CLPesticides 30m, 0.32mm ID, 0.32µm (cat.# 11141) and Rtx®-CLPesticides2 30m, 0.32mm ID, 0.25µm (cat.# 11324) with 5m x 0.32mm ID Rxi™ deactivated guard tubing (cat.# 10039), connected using Universal "Y" Press-Tight® connector (cat.# 20405-261)
Sample:
Organochlorine Pesticide Mix AB #2, 8-80µg/mL each component in hexane/toluene (cat.# 32292), Pesticide Surrogate Mix, 200µg/mL each component in acetone (cat.# 32000)
Inj.:
1.0µL splitless (hold 0.3 min.), 4mm single gooseneck inlet liner (cat.# 20799)
Inj. temp.:
250°C
Carrier gas:
helium, constant flow
Linear velocity:
60cm/sec. @ 120°C
Oven temp.:
120°C to 200°C @45°C/min. to 230°C @15°C/min to 330°C (hold 2 min.) @ 30°C/min.; Det.: ECD @330°C

GC_EV00933

Figure 3   Comparable resolution of organochlorine pesticides on the 0.53mm ID Rtx®-CLPesticides column pair.

  1. 2,4,5,6-tetrachloro-m-xylene (SS)
  2. α-BHC
  3. γ-BHC
  4. β-BHC
  5. δ-BHC
  6. heptachlor
  7. aldrin
  8. heptachlor epoxide (isomer B)
  9. γ-chlordane
  10. α-chlordane
  11. endosulfan I
  1. 4,4′-DDE
  2. dieldrin
  3. endrin
  4. 4,4′-DDD
  5. endosulfan II
  6. 4,4′-DDT
  7. endrin aldehyde
  8. endosulfan sulfate
  9. methoxychlor
  10. endrin ketone
  11. decachlorobiphenyl (SS)

Two column heading
Column:
Rtx®-CLPesticides 30m, 0.53mm ID, 0.50µm (cat.# 11140) and Rtx®-CLPesticides2 30m, 0.53mm ID, 0.42µm (cat.# 11340) with 5m x 0.53mm ID Rxi™ deactivated guard tubing (cat.# 10054), connected using Universal Siltek® "Y" Press-Tight® connector (cat.# 20486)
Sample:
Organochlorine Pesticide Mix AB #2, 8-80µg/mL each component in hexane/toluene (cat.# 32292), Pesticide Surrogate Mix, 200µg/mL each component in acetone (cat.# 32000)
Inj.:
1.0µL splitless (hold 0.3 min.), 4mm single gooseneck inlet liner (cat.# 20799)
Inj. temp.:
250°C
Carrier gas:
helium, constant flow
Linear velocity:
45cm/sec. @ 120°C
Oven temp.:
120°C to 200°C @ 45°C/min. to 230°C @12.5°C/min. to 325°C (hold 2 min.) @ 30°C/min
Det.:
ECD @ 330°C

GC_EV00936 (bottom), GC_EV00937 (top)

Figure 4  Two column modules in a Gerstel MACH column heating system.


The MACH system allows independent temperature programming of up to four columns, simultaneously.

Thank you
Instrument provided courtesy of Gerstel USA.

Figure 5   Resolve organochlorine pesticides in less than 5 minutes using the Rtx®-CLPesticides columns and the MACH system.

  1. 2,4,5,6-tetrachloro-m-xylene (SS)
  2. α-BHC
  3. γ-BHC
  4. β-BHC
  5. δ-BHC
  6. heptachlor
  7. aldrin
  8. heptachlor epoxide
  9. γ-chlordane
  10. α-chlordane
  11. endosulfan I
  1. 4,4′-DDE
  2. dieldrin
  3. endrin
  4. 4,4′-DDD
  5. endosulfan II
  6. 4,4′-DDT
  7. endrin aldehyde
  8. endosulfan sulfate
  9. methoxychlor
  10. endrin ketone
  11. decachlorobiphenyl (SS)
Sample: Organochlorine Pesticide Mix AB #2 (8-80µg/mL each component in hexane/toluene 1:1, (cat.# 32292), Pesticide Surrogate Mix (200µg/mL each component in acetone, cat.# 32000)

Column:
Rtx®-CLPesticides, 20m, 0.18mm ID, 0.18µm (cat.# 42102)
Inj.:
0.5µL split (split ratio 20:1)
Column temp.:
Gerstel Modular Accelerated Column Heater: 150°C (10 sec.) to 190°C @ 300°C/min. (hold 0.5 min.), to 320°C @ 40°C/min (hold 2 min.)
Det.:
ECD
GC_EV00904


Column:
Rtx®-CLPesticides2, 20m, 0.18mm ID, 0.14µm (cat.# 42302)
Inj.:
1.0µL split (split ratio 20:1)
Column temp.:
Gerstel Modular Accelerated Column Heater; Gerstel module temp.: 140°C to 220°C (hold 1 min.) @ 120°C/min., to 305°C @ 50°C/min., to 330°C @ 300°C/min. (hold 2 min.)
Det.:
ECD
GC_EV00895