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Low-Level GC/MS for Semivolatiles in Drinking Water

Excellent Responses at 10ng On Column, Using an Rxi-5ms Column


By Robert Freeman, Environmental Innovations Chemist
  • Inert, ultra-low bleed column improves low level analyses.
  • Excellent peak shapes and responses for active analytes.
  • Drilled Uniliner inlet liner minimizes sample breakdown in the injector.

Semivolatile organic chemical contaminants in drinking water are target compounds in many analytical methods, worldwide. US EPA Method 525.2, for example, is a general purpose solid-phase extraction/GC/MS procedure for identifying and quantifying a wide range of semivolatile compounds. Analytes, and introduced internal standards and surrogates, are extracted from a 1-liter water sample by passing the sample through a solid phase extraction disk containing a bonded C18 phase (e.g., Resprep-C18, cat. #24004). Target compounds are trapped on the disk, then eluted in a small amount of solvent. The extract is concentrated by evaporating the solvent, and the sample components are separated, identified, and quantified by GC/MS.

As is true for many other semivolatiles methods, the extensive target compound list for Method 525.2 encompasses numerous classes of analytes. These diverse compounds present varying difficulties in the analysis, including differing modes of degradation. Coupled with the continual need for lower levels of detection, these challenges make extreme demands on the chromatography column, and the analysis requires an inert, thermally stable, low-bleed stationary phase. To meet these needs, we recommend a 30 meter, 0.25mm ID, 0.25µm Rxi-5ms column. Enhanced surface deactivation provides Rxi-5ms columns with exceptional inertness and ultra-low bleed, ensuring resolution and symmetric peaks for these difficult analytes.

Figure 1 shows the total ion chromatogram for semivolatiles commonly analyzed in drinking water, and listed in US EPA Method 525.2, at 10ng each on an Rxi-5ms column. Resolution and peak shapes are exceptionally good.

To minimize analyte degradation in the injection port, and discrimination among analytes by molecular weight, we recommend installing a Drilled Uniliner inlet liner in the injection port. This liner forms a Press-Tight seal with the inlet end of the column, eliminating contact between the sample and the hot metal surfaces in the injection port and assuring near-complete sample transfer. The small hole in the wall of the liner allows the liner to be used with split/splitless injections. As an additional precaution to minimize analyte breakdown, we use a pulsed splitless injection (50psi / 0.3 min.; 1µL sample) to reduce the time the analytes spend in the injection port.

Exceptional inertness and ultra-low bleed enable an Rxi-5ms column to perform exceptionally well in analyses of complex mixtures of semivolatile compounds. We recommend pairing an Rxi-5ms column with our recently revised reference mixes for semivolatile pollutants in water. Restek can provide all the materials needed for a semivolatiles analysis: extraction disks, reference materials, and a column capable of excellent responses for all target analytes at low on-column concentrations.


Figure 1  Excellent resolution and symmetric peaks for commonly analyzed drinking water semivolatiles, at 10ng each on an Rxi-5ms column.

Peaks
1.Isophorone
2.2-Nitro-m-xylene (SS)
3.Naphthalene
4.Dichlorvos (DDVP)
5.Hexachlorocyclopentadiene
6.EPTC
7.Mevinphos
8.Butylate
9.Vernolate
10.Dimethyl phthalate
11.Pebulate
12.Etridiazole
13.2,6-Dinitrotoluene
14.Acenaphthylene
15.Acenaphthene-d10 (IS)
16.Chloroneb
17.Tebuthiuron
18.2,4-Dinitrotoluene
19.Molinate
20.Diethyl phthalate
21.Fluorene
22.Propachlor
23.Ethoprop (ethoprophos)
24.Cycloate
25.Chlorpropham
26.Trifluralin
27.Atraton
28.Hexachlorobenzene
29.Prometon
30.Simazine
31.Atrazine
32.Propazine
33.Pentachlorophenol
34.Terbufos
35.Propyzamide
36.Diazinon
37.Phenanthrene-d10 (IS)
38.Phenanthrene
39.Disulfoton
40.Methylparaoxon
41.Anthracene
42.Terbacil
43.Chlorothalonil
44.Metribuzin
45.Simetryn
46.Ametryn
47.Alachlor
Peaks
48.Prometryn
49.Terbutryn
50.di-n-Butyl phthalate
51.Bromacil
52.Cyanazine (Bladex)
53.Metolachlor
54.Chlorpyrifos
55.Triadimefon
56.DCPA methyl ester (Chlorthal-dimethyl)
57.MGK-264 (isomer A)
58.Diphenamid
59.MGK-264 (isomer B)
60.Merphos
61.Heptachlor epoxide
62.Fluoranthene
63.Stirofos
64.Disulfoton sulfone
65.Butachlor
66.Pyrene-d10 (SS)
67.Fenamiphos
68.Pyrene
69.Napropamide (Devrinol)
70.trans-Nonachlor
71.Merphos oxide
72.Tricyclazole (Beam)
73.Carboxin
74.Chlorobenzilate
75.Benzyl butyl phthalate
76.Norflurazon
77.Bis(2-ethylhexyl) adipate
78.Hexazinon (Velpar)
79.Triphenylphosphate (SS)
80.Benz[a]anthracene
81.Chrysene-d12 (IS)
82.Chrysene
83.Bis(2-ethylhexyl) phthalate
84.Fenarimol
85.cis-Permethrin
86.trans-Permethrin
87.Di-n-octyl phthalate
88.Benzo[b]fluoranthene
89.Benzo[k]fluoranthene
90.Benzo[a]pyrene
91.Fluridone (Sonar)
92.Perylene-d12 (SS)
93.Indeno[1,2,3-cd]pyrene
94.Dibenzo[a,h]anthracene
95.Benzo[ghi]perylene
Semivolatiles on Rxi-5ms by EPA Method 525.2
GC_EV00859
ColumnRxi-5ms, 30 m, 0.25 mm ID, 0.25 µm (cat.# 13423)
SampleMethod 525.2 semivolatile mix (revised) (cat.# 31899)
Organonitrogen pesticide mix #1 (rev), Method 525.2 (cat.# 33012)
Organochlorine pesticide mix #2 (rev), Method 525.2 (cat.# 33011)
Organophosphorus pesticide mix #1 (rev), Method 525.2 (cat.# 33013)
Method 525.2 nitrogen/phosphorus pesticide mix #2 (cat.# 32423)
Method 525.2 internal standard mix (cat.# 31825)
Method 525.2 surrogate standard mix (cat.# 31826)
Conc.:25 µg/mL for each IS and SS, 10 μg/mL each analyte
Injection
Inj. Vol.:1.0 µL pulsed splitless (hold 0.15 min)
Liner:Drilled Uniliner (hole near bottom) (cat.# 20771)
Inj. Temp.:250 °C
Pulse Pressure:50 psi (344.7kPa)
Pulse Time:0.3 min
Purge Flow:80 mL/min
Oven
Oven Temp.:90 °C (hold 1 min) to 270 °C at 20 °C/min to 315 °C at 6 °C/min
Carrier GasHe, constant flow
Flow Rate:1.2 mL/min
DetectorMS
Mode:Scan
Transfer Line Temp.:280 °C
Analyzer Type:Quadrupole
Solvent Delay Time:3.00 min
Tune Type:DFTPP
Ionization Mode:EI
Scan Range:35-550 amu
InstrumentHP6890 GC & 5973 MSD
NotesGas saver is on at 15 mL/min. (1 minute).

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