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Optimizing Chromatography by Using Higher Column Flows, Split Injections and Surge Pressure Splitless Injections in GC/MS

Jessie Crockett Butler, Eric Phillips

Abstract

Purpose: Describe GC parameters that may be adjusted in the analysis of semi-volatiles to improve column capacity, resolution and overall GCMS sensitivity. Methods: The DSQTM II, a quadrupole mass spectrometer with bent optics, was used with the TRACE GC UltraTM with a conventional split/splitless injector to study the effects of varying column flow rate, and injection parameters for the analysis of the target compounds in United States EPA Methods 525.2 and 8270D.1,2 Results: An improvement in peak shape, resolution, run time, and sensitivity were observed by optimization of the injection and separation phases of the analysis.

Thermo Fisher Scientific

Results: Higher Flow Rates for EPA Method 8270D

Several experiments were run to test the effect of higher carrier gas flows by GC/MS. An elevated flow rate of 3 mL/min and a scanning speed of 5 scans/sec or 1,618 amu/sec was selected for EPA Method 8270D. The actual capacity of the stationary phase was increased with this higher flow rate, allowing the use of thinner films. Run times were shortened, reducing the run time and column bleed rate. Another interesting advantage was observed in minimizing irreversible absorption of active compounds such as pentachlorophenol and pesticides by shortening the time spent in the stationary phase of the analytical column. FIGURE 2. The analysis time was reduced from 25 minutes to about 20 minutes by just increasing the column flow rate from 1 to 4 mL/min. 3 mL/min was chosen for the Productivity Solution based on other QC requirements.

RT: 0.00 - 34.04 5.23 6.86 6 17.84 4 2 Relative Abundance 0 6 4 2 0 6 4 2 0 6 4 2 0 0 5 10 15 Time (min) 20 25 30 5.05 6.16 20.96 3.68 4.32 5.89 7.51 5.47 9.72 11.54 13.49 15.64 15.87 19.15 21.83 18.44

NL: 8.39E7 TIC F: MS flow04

Austin, Texas, USA

Results: Surge Pressure Splitless Injections

Another parameter studied was the flow of the carrier gas thru the inlet during a splitless injection of drinking water samples. A surge pressure splitless injection increases the flow rate of the column only during the injection phase. Then the column flow reduces down to the optimum column flow for the separation. The advantage is an improvement of injection efficiency by shortening the residence time in the inlet, minimizing band broadening and thermal degradation of fragile pesticides in EPA Method 525. 3 Figure 6. Performance Mix showing no breakdown of endrin

RT: 6.73 - 12.51 100 RT: 10.57 BP: 234.9

Results: Split vs. Splitless Injections

A split injection is the preferred injection technique for dirty samples with high concentrations of matrix. The split vent remains open and only a portion of the sample is injected into the column. The flow rate thru the inlet during injection is very high (60 mL/min) and the column flow rate is 3 mL/min. This higher column flow rate minimizes irreversible adsorption of polar reactive compounds in the stationary phase and also increases the capacity of the phase, resulting in the selection of thinner films(0.5um), reducing column bleed rates associated with higher film thicknesses (1.0 µm). If a sensitive mass spectrometer is used with fast scanning rates, even the more difficult methods like EPA Method 8270D can be run with a split injection. A hot needle injection is used to provide a reduction of inlet temperature by 50°C without the loss of precision of the higher boiling polynuclear aromatic hydrocarbons. Operating at a lower injection temperature combined with shorter residence time in the inlet minimizes the thermal breakdown of fragile compounds. This in turn provides better precision than a conventional splitless injection, with less maintenance. Figure 4a. Comparison of a split and splitless Injection for EPA method 8270D(160ng) Figure 4b. Results of a robustness study of injecting sediment extracts spiked with diesel fuel with the precision of the check standard run at the beginning of each batch. The TIC of the sample is shown below.

Figure 4a

RT: 0.00 - 30.08 100 Relative Abundance 80 60 40 20 0 100 80 60 40 20 0 0 5 10 15 Time (min) 20 25 30 8.10 17.87 19.87 21.84 9.42 8.22 11.32

Relative Abundance 90

Figure 7. TIC of 20 µg/L standard for EPA method 525

RT: 0.00 - 31.35 NL: 1.44E8 TIC F: MS 080106_f00 8

DFTPP Endrin

NL: 6.85E7 TIC F: MS ICIS run02

8.13 min.

Relative Abundance

100 90 80

14.14 11.69 12.68

90 RT: 8.13 BP: 197.8 80 70 Relative Abundance 60 50 40 30 20 10 0 7.0 7.5 8.0 8.5 9.0 9.5 10.0 Time (min) 10.5 11.0 11.5 12.0 12.5 RT: 10.09 BP: 262.8

Introduction

Conventional chromatography follows the theory of the Van Deemter curve where the best separation is achieved for helium at a linear velocity of 20 to 50 cm/sec at low column flow rates of 1 mL/min.3 Most analyses are performed with a 1 µL splitless injection with an injection time of 0.75 minutes. While the conventional splitless injection is quite easy to set up and quite robust, it may be run at very different settings with a more sensitive fast scanning mass spectrometer. Some of the advantages of optimizing the injection and column parameters will be shown with examples of performance for the analytes in EPA Method 8270D and EPA Method 525.2.

10.09 min. 10.57 min.

70 60 50 40 30 20 10 0 0 5 10 15 Time (min) 20 25 30 9.81 7.45 8.22 19.38 20.23 20.38 23.58 24.58 10.19 10.90 16.05

9.06 10.86

14.63

17.26 19.24

3.69 3.24

4 mL/min

NL: 7.96E7 TIC F: MS flow02

4,4'-DDT

16.61

5.13

5.50 7.12

9.33 11.13 12.99 15.03

17.73 18.33 19.93

3 mL/min

NL: 8.72E7 TIC F: MS flow03

2.5000 2.0000 1.5000

5.85 9.50 13.53 12.89 14.74 15.18 17.10

NL: 5.80E8 TIC F: MS C07

3.32 3.95

Materials & Methods

In order to achieve the best precision and linear range, the injection and separation must be reproducible. The mass spectrometer and gas chromatograph studied demonstrated a wide linear range and excellent precision in the statistical evaluation of the EPA Methods studied in the development of two Productivity Solutions for EPA Method 525.2 and EPA method 8260D. These Productivity Solutions contain all of the consumables required to operate the instrument for two weeks and show complete validation of the method in only a few days with snap and shoot ampoules of prepared calibration curves and performance solutions specified in the methods. The column, liner, and septa have all been tested to ensure that the performance of the instrument would be consistent from system to system. A environmental reporting software, EnviroLabTM Forms 2.0, is included with master processing methods with all quantitation and qualifier ions and reference spectra for the complete list entered. Batch sequence templates are also provided for running the first calibration curve, Method Detection Limit study, Method Validation study, and a Daily batch sequence for the analysis of a check standard and spiked unknowns. A CD of typical validation data results are also provided for comparison in the laboratory. These two Productivity Solutions were tested over 6 months to carefully study each parameter in the injection, separation and detection phase of the analysis. The results shown here are typical for the DSQ II and TRACE GC Ultra when the appropriate Productivity Solution is installed. One of the more dramatic improvements was found in the incorporation of a hot needle injection for EPA Method 8270D. This method covers a wide range of boiling points and polarities. It is very difficult to select the best parameters for each type of compound without compromising the results of others. The hot needle injection is the closest technique in injection efficiency to the cold on-column injection and was the preferred technique for the Productivity Solution for EPA Method 8270D.

1.0000 0.5000 0.0000 1 3

RT: 0.00 - 17.11 100 8.33 7.77 7.18 6.53 5.01 5.82 4.04 11.51 40 30 2.34 3.97 11.90 12.26 8.87 9.36 9.83 10.28 10.71 11.12

8.92 8.72 5.05 5.40

2 mL/min

5 7 9 11 13 15 17 19 21 23 25

Phenol(CCC) 2% 1,4-Dichlorobenzene(CCC) 1% 2-Nitrophenol(CCC) 2% 2,4-Dichlorophenol(CCC) 1% Hexachlorobutadiene(CCC) 2% 4-Chloro-3-methylphenol(CCC) 2% 2,4,6-Trichlorophenol(CCC) 1 % Acenaphthene(CCC) 1% Pentachlorobenzene(CCC) 2% Diphenylamine(CCC) 2% Pentachlorophenol(CCC) 2% Fluoranthene(CCC) 2% Di-n-octylphthalate(CCC) 3% Benzo(a)pyrene(CCC) 1%

NL: 1.08E9 TIC F: MS rep96

Figure 8. Linearity (0.1 to 20 µg/L) of vernolate, endrin, diazinon, and diphenamid

6.61 8.23

10.46 12.31 14.10

16.78

20.03

1 mL/min

23.58 24.65

NL: 5.99E7 TIC F: MS flow01

NL: 1.37E8 TIC F: MS A07

80 70 60 50

Figure 4b

7.49 7.34 6.37 6.90 4.87

12.12 13.34 14.74 15.10 15.82 17.41 18.73 22.26

25.26

20

26.19

10 0 0

1.40 1.70

12.61 12.96 4 6 8 Time (min) 10 12

14.00 14.87 14 16

2

FIGURE 3. 5 ng and 160 ng of pyridine and NDMA (Figure 3a) and indeno(1,2,3-c,d)pyrene and benzo(g,h,i)perylene (Figure 3b) show excellent peak symmetry, indicating no overloading of the stationary phase at the higher concentration. Linearity curves for Figure 3b are shown in EnviroLab Forms 2.0 software

RT: 1.85 - 3.23

FIGURE 5. Linearity of pyridine, N-nitrosodimethylamine, pentachlorophenol, and pronamide

RT: 16.21 - 19.39

RT: 2.58 AA: 28341552 BP: 78.98

NL: 2.56E7 m/z= 73.50-74.50+ 78.50-79.50 F: MS ICIS 031706_b_008

Figure 3a

100 80 60 40 20 0

Figure 3b

Relative Abundance 100 80 60 40 20 0

RT: 17.47 AA: 38042327 BP: 276.07

RT: 18.07 AA: 32375912 BP: 276.08

Relative Abundance

RT: 2.53 AA: 8476751 BP: 73.97

NL: 1.14E7 m/z= 275.50276.50 F: MS ICIS 031706_b_0 08

Relative Abundance

80 60 40 20 0 2.0 2.2

RT: 2.52 AA: 260570 BP: 73.98

Relative Abundance

100

RT: 2.60 AA: 820867 BP: 78.98

NL: 5.01E5 m/z= 73.50-74.50+ 78.50-79.50 F: MS ICIS 031706_b_003

100 80 60 40 20 0 16.5 17.0

RT: 17.45 AA: 1357507 BP: 276.08

RT: 18.05 AA: 1192699 BP: 276.08

NL: 4.27E5 m/z= 275.50276.50 F: MS ICIS 031706_b_0 03

FIGURE 1. The hot needle injection technique was selected for the EPA Method 8270D Productivity Solution

2.4

2.6 Time (min)

2.8

3.0

3.2

17.5

18.0 Time (min)

18.5

19.0

Conclusions

No adverse effects were noted in precision, sensitivity, or separation by using the optimized parameters illustrated in the Productivity Solutions for EPA Method 8270D and EPA Method 525.2. The elevated column flow rate of 3 mL/min for the target compounds in EPA method 8270D resulted in shorter run times and the maintenance requirement was reduced by incorporation of the split injection. The split injection actually enhanced the separation of more volatile compounds like N-nitrosodimethylamine (NDMA) and pyridine. A surged pressure splitless injection gave excellent linearity for the target compounds in the drinking water method, EPA Method 525.2.

References

(1) (2) Note the precision of the linearity (5ng to 160 ng) for benzo(g,h,i)perylene (2.9%RSD) and dibenzo(a,h)anthracene (4.6%RSD) (3) EPA Method 525.2 Determination of Organic Compounds in Drinking Water by Liquid/Solid Extraction and Capillary Column Gas Chromatography/Mass Spectrometry Rev. 2 1995. EPA Method 8270D Semi-volatile Organic Compounds by Gas Chromatography/Mass Spectrometry Rev. 4 1998 Capillary Gas Chromatography in Food Control and Research, Dr. Karl-Heinz Engel, 1993, pg 33.

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