Picogram levels of detection by EPA 8270E using GC-MS/MS

EPA 8270E allows for the use of tandem mass spectrometry allowing for low pg levels of detection (Figure 1).

Column	Rxi-SVOCms, 30 m, 0.25 mm ID, 0.25 µm (cat.# 16623)
Standard/Sample
	SVOC MegaMix 150 kit (cat.# 31907)
	SV internal standard mix (cat.# 31206)
	Acid surrogate mix (4/89 SOW) (cat.# 31063)
	Revised B/N surrogate mix (cat.# 31888)
Diluent:	Dichloromethane
Conc.:	1 µg/mL (0.1 ng on-column)
Injection
Inj. Vol.:	1 µL split (split ratio 10:1)
Liner:	Topaz 4.0 mm ID single taper inlet liner w/ wool (cat.# 23303)
Inj. Temp.:	250 °C
Oven
Oven Temp.:	40 °C (hold 1 min) to 280 °C at 12.4 °C/min to 330 °C at 3.3 °C/min (hold 3.65 min)
Carrier Gas	He, constant flow
Flow Rate:	1.2 mL/min

Detector	TSQ8000
Transfer Line Temp.:	280 °C
Analyzer Type:	Quadrupole
Source Temp.:	330 °C
Quad Temp.:	180 °C
Electron Energy:	70 eV
Solvent Delay Time:	2 min
Tune Type:	PFTBA
Ionization Mode:	EI
Instrument	Thermo Trace GC
Sample Preparation	Solutions were mixed and diluted to 1 ppm or lower with dichloromethane in amber 2 mL, 9 mm short-cap, screw-thread vials (cat.# 21143) and sealed with 2.0 mL, 9 mm short-cap, screw-vial closures (cat.# 23842).
Notes	The compounds in the inserts are at lower concentrations than the full chromatogram and are showing specific transitions as noted in the inserts. The SVOC MegaMix 150 kit (cat.# 31907) contains one ampul each of the following standards: • 8270 MegaMix (cat.# 31850) • SVOC additions standard (cat.# 31909) • Appendix IX mix #1, revised (cat.# 32459) • Methapyrilene (cat.# 32460) • Appendix IX mix #2 (cat.# 31806) • Benzoic acid (cat.# 31879)

Figure 1: SVOC 150 Mega mix on Rxi-SVOCms. The list of SRMs is in Table 1.

Much of the method has remained the same although the lower levels of detection provide new challenges to include dynamic calibration range, and retention time shifts of reactive compounds. The calibration range is limited by lower levels of detection at the lower end and overloading & MS saturation at the higher end of the calibration range. Using our conditions the upper limit was found to be 0.5ng on-column. This shifts the typical range of calibration (0.1-100 µg/mL) to concentrations 100 to 1000 lower. A wider range could be used by adjusting the split ratio.

The second challenge is the analysis of reactive compounds, such as pyridine, benzoic acid and acrylamide. These compounds exhibit a shift in retention for different concentrations, which can make the detection challenging when using SRM windows. As the concentration of active analytes decreases, the retention time increases. The best concentration range for these compounds is 1-10 ng on column.

Figure 2: Pyridine retention time shift with decreased concentration.

GC-MSMS is a great detection technique for ppb concentration range, albeit with some caveats.

Finally, Table 1 contains the SRMs used for Figure 1.

Table 1: SRMs for the SVOC 150 Mega mix