Restek
Resource Hub / Technical Literature Library / Reduce Helium Consumption by 68 Using Nitrogen Purge Gas for VOCs in Water

Reduce Helium Consumption by 68% Using Nitrogen Purge Gas for VOCs in Water

articleBanner
  • Save 490 mL of helium per sample by switching to nitrogen purge gas.
  • Spend less money on lab gases and reduce your dependence on helium.
  • Easily resolve critical Method 524.4 compounds using an Rtx-VMS column.

By now, everyone has felt the impact of the helium supply problem—even regulatory agencies. In order to help laboratories reduce helium use, EPA has revised Method 524.3 to allow for the use of nitrogen as a purge gas. Although labs have been doing this for years with other methods, substantial reductions in helium consumption can now be obtained when analyzing purgeable organic compounds in water by GC-MS using the revised method. By switching to nitrogen purge gas using Method 524.4, you can save an impressive 490 mL of helium per sample, which translates into a 68% reduction in helium consumption (Table I). Saving nearly 0.5 L of helium per sample quickly adds up to considerable cost savings and also insulates labs from the impact of fluctuating helium availability.

In addition to reducing helium consumption by using nitrogen purge gas, employing an Rtx-VMS column for this analysis allows all Method 524.4 criteria to be easily met. The Rtx-VMS column is recommended for purge-and-trap GC-MS analysis of VOCs by Method 524.4 because the selectivity of this column provides ample separation between all critical compounds. As shown in Figure 1, good resolution is obtained for target analytes, including o-xylene and styrene, as well as 1,1,1-trichloroethane and carbon tetrachloride. The Rtx-VMS column is listed in Method 524.4 and was used by the EPA to establish method performance [1]. No interference from overlapping peaks was observed, and the small bore 0.25 mm column results in higher column efficiency and improved separations.

Labs analyzing purgeable organic compounds in water can save money and reduce helium dependence by using Method 524.4 with nitrogen purge gas and an Rtx-VMS column.

Table I: Using nitrogen purge gas allows labs to reduce helium use by 68%.

Instrument Analysis Step He Volume N2 Volume
P&T Purge 440
Dry Purge 50
Desorb 30.9
GC-MS Split Vent* 140
Carrier 13.5
Septum Purge 45
  Total Gas Volume 719.4
  Volume of Helium Saved 490
    Percent of Helium Saved

68%

*Gas saver is turned to 10 mL/min @ 1 min.
 

Figure 1: The Rtx-VMS column is specifically designed for separating purgeable organic compounds, which means it provides excellent resolution of the Method 524.4 VOCs analyzed here using nitrogen purge gas.

cgarm-img
GC_EV1351
Peaks
1.Dichlorodifluoromethane
2.Chlorodifluoromethane
3.Chloromethane
4.Vinyl chloride
5.1,3-Butadiene
6.Bromomethane
7.Trichlorofluoromethane
8.Diethyl ether
9.1,1-Dichloroethene
10.Carbon disulfide
11.Methyl iodide
12.Allyl chloride
13.Methylene chloride
14.trans-1,2-Dichloroethene
15.Methyl acetate
16.MTBE-d3 (SS)
17.MTBE
18.tert-Butyl alcohol (TBA)
19.Diisopropyl ether (DIPE)
20.1,1-Dichloroethane
21.tert-Butyl ethyl ether (ETBE)
22.cis-1,2-Dichloroethene
23.Bromochloromethane
24.Chloroform
25.Carbon tetrachloride
26.Tetrahydrofuran
27.1,1,1-Trichloroethane
Peaks
28.1,1-Dichloropropene
29.1-Chlorobutane
30.Benzene
31.tert-Amyl methyl ether (TAME)
32.1,2-Dichloroethane
33.Trichloroethene
34.1,4-Difluorobenzene
35.tert-Amyl ethyl ether (TAEE)
36.Dibromomethane
37.1,2-Dichloropropane
38.Bromodichloromethane
39.cis-1,3-Dichloropropene
40.Toluene
41.Tetrachloroethene
42.trans-1,3-Dichloropropene
43.1,1,2-Trichloroethane
44.Ethyl methacrylate
45.Dibromochloromethane
46.1,3-Dichloropropane
47.1,2-Dibromoethane
48.Chlorobenzene-d5
49.Chlorobenzene
50.Ethylbenzene
51.1,1,1,2-Tetrachloroethane
52.m-Xylene
53.p-Xylene
54.o-Xylene
Peaks
55.Styrene
56.Bromoform
57.Isopropylbenzene
58.4-Bromofluorobenzene (SS)
59.Bromobenzene
60.n-Propylbenzene
61.1,1,2,2-Tetrachloroethane
62.2-Chlorotoluene
63.1,3,5-Trimethylbenzene
64.1,2,3-Trichloropropane
65.4-Chlorotoluene
66.tert-Butylbenzene
67.Pentachloroethane
68.1,2,4-Trimethylbenzene
69.sec-Butylbenzene
70.4-Isopropyltoluene
71.1,3-Dichlorobenzene
72.1,4-Dichlorobenzene-d4
73.1,4-Dichlorobenzene
74.n-Butylbenzene
75.Hexachloroethane
76.1,2-Dichlorobenzene-d4 (SS)
77.1,2-Dichlorobenzene
78.1,2-Dibromo-3-chloropropane
79.Hexachlorobutadiene
80.1,2,4-Trichlorobenzene
81.Naphthalene
82.1,2,3-Trichlorobenzene
C. Contamination from nitrogen gas line; * Toluene-d8
ColumnRtx-VMS, 30 m, 0.25 mm ID, 1.40 µm (cat.# 19915)
Standard/Sample524.3 Internal standard/surrogate mix (cat.# 30017)
524.3 Gas calibration mix (cat.# 30014)
524.3 VOA MegaMix standard (cat.# 30013)
Diluent:RO water
Conc.:40 ng/mL (5 mL sample)
Injectionpurge and trap split (split ratio 30:1)
Liner:Premium 1.0 mm ID straight inlet liner (cat.# 23333)
Inj. Temp.:200 °C
Purge and Trap
Instrument:EST Encon Evolution
Trap Type:Vocarb 3000
Purge: 11 min, flow 40 mL/min
Dry Purge: 1 min, flow 50 mL/min
Desorb: 1 min @ 260 °C, flow 30.9 mL/min
Bake: 8 min @ 265 °C
Interface Connection:injection port
Transfer Line Temp.:150 °C
Oven
Oven Temp.:45 °C (hold 4.5 min) to 100 °C at 12 °C/min to 240 °C at 25 °C/min (hold 1.32 min)
Carrier GasHe, constant flow
Flow Rate:0.9 mL/min
DetectorMS
Mode:Scan
Scan Program:
GroupStart Time
(min)
Scan Range
(amu)
Scan Rate
(scans/sec)
11.547–3005.4
22.935–3005.19
Transfer Line Temp.:240 °C
Analyzer Type:Quadrupole
Source Temp.:230 °C
Quad Temp.:150 °C
Electron Energy:70 eV
Solvent Delay Time:1.5 min
Tune Type:BFB
Ionization Mode:EI
InstrumentAgilent 7890A GC & 5975C MSD
NotesNitrogen was used as the purge gas for the EST Encon Evolution.

 

References

  1. U.S. Environmental Protection Agency, Method 524.4, Measurement of Purgeable Organic Compounds in Water by Gas Chromatography/Mass Spectrometry Using Nitrogen Purge Gas, May 2013.  http://water.epa.gov/scitech/drinkingwater/labcert/upload/815R13002.pdf (accessed December 19,  2013).
EVSS1938A-UNV