The New U.S. EPA Method TO-15A blog series – Part 7: Known-Standard Challenge of Canisters
9 Mar 2022In our previous blogs on TO-15A (links below) we spent a lot of time focusing on cleanliness and meeting the new zero-air challenge requirements laid out in the method. However, to qualify the canisters there is also a known-standard challenge that tests them for inertness, outlined in TO-15A section 9.4.3. It states that canisters should be spiked with 100-500 pptv in 40-50% RH air, an initial analysis should be done more than 24 hours after standard preparation, and a final analysis done at a time equal to or exceeding the laboratory hold time (nominally given as 30 days). The results of the spike should be within the ±30% recovery limit given for continuing calibration verifications for both times, though I feel a change from the initial result would be a better measurement. For example, if a compound recovers low in the initial spike due to the calibration curve fit or other reasons, it could have significantly more room to grow than a compound that recovered high. For example, in the SilcoCans chloroform was spiked at 500 pptv, but the initial recovery was 590 pptv. This means that over the 30 days I could gain 60 pptv before reaching the maximum recovery of 540 pptv, but I could lose 240 pptv, or 4 times as much, before reaching the lower recovery limit of 350 pptv.
To try out this known-standard challenge, I spiked 3 TO-cans and 3 SilcoCans with 500 pptv of our TO-15 standard mix in 50% RH air. The canisters used are ones that have seen a fair amount of use in the laboratory over the years, and were cleaned with 12 cycles of evacuation and pressurization at 70°C using humid air. To see how the cans fared over time I tested them at weekly intervals instead of just at the start and end. Tables 1 and 2 below show the results for the TO-Cans and SilcoCans respectively. Compounds that changed more than 30% from the initial are highlighted in yellow.
| Name | TO-Cans | ||||
| Day 1 | Day 7 | Day 14 | Day 21 | Day 32 | |
|
Propylene |
100% |
98% |
95% |
97% |
106% |
|
Dichlorodifluoromethane |
100% |
94% |
94% |
96% |
97% |
|
1,2-Dichlorotetrafluoroethane |
100% |
86% |
92% |
90% |
99% |
|
Chloromethane |
100% |
93% |
90% |
89% |
97% |
|
Vinyl chloride |
100% |
89% |
85% |
91% |
98% |
|
1,3-Butadiene |
100% |
84% |
97% |
90% |
98% |
|
Bromomethane |
100% |
90% |
93% |
95% |
101% |
|
Chloroethane |
100% |
109% |
92% |
99% |
105% |
|
Trichlorofluoromethane |
100% |
89% |
94% |
92% |
99% |
|
1,1-Dichloroethene |
100% |
89% |
92% |
85% |
100% |
|
Carbon disulfide |
100% |
99% |
103% |
114% |
136% |
|
1,1,2-Trichlorotrifluoroethane |
100% |
86% |
93% |
92% |
99% |
|
Acrolein |
100% |
91% |
113% |
116% |
173% |
|
Isopropyl alcohol |
100% |
94% |
107% |
106% |
150% |
|
Methylene chloride |
100% |
86% |
106% |
103% |
123% |
|
Acetone |
100% |
109% |
136% |
138% |
182% |
|
trans-1,2-Dichloroethene |
100% |
85% |
95% |
85% |
101% |
|
Hexane |
100% |
87% |
96% |
84% |
101% |
|
Methyl tert-butyl ether (MTBE) |
100% |
89% |
94% |
86% |
104% |
|
1,1-Dichloroethane |
100% |
88% |
91% |
86% |
101% |
|
Vinyl acetate |
100% |
89% |
95% |
88% |
111% |
|
cis-1,2-Dichloroethene |
100% |
80% |
93% |
84% |
94% |
|
Cyclohexane |
100% |
88% |
89% |
84% |
105% |
|
Chloroform |
100% |
104% |
125% |
127% |
152% |
|
Carbon tetrachloride |
100% |
87% |
90% |
88% |
100% |
|
Ethyl acetate |
100% |
94% |
102% |
92% |
110% |
|
Tetrahydrofuran |
100% |
88% |
95% |
86% |
104% |
|
1,1,1-Trichloroethane |
100% |
86% |
90% |
89% |
96% |
|
2-Butanone (MEK) |
100% |
93% |
105% |
99% |
125% |
|
Heptane |
100% |
90% |
96% |
89% |
114% |
|
Benzene |
100% |
87% |
90% |
85% |
97% |
|
1,2-Dichloroethane |
100% |
87% |
94% |
88% |
102% |
|
Trichloroethylene |
100% |
84% |
87% |
86% |
94% |
|
1,2-Dichloropropane |
100% |
91% |
96% |
96% |
95% |
|
Bromodichloromethane |
100% |
93% |
100% |
97% |
100% |
|
Methyl methacrylate |
100% |
87% |
95% |
90% |
97% |
|
1,4-Dioxane |
100% |
93% |
99% |
100% |
114% |
|
cis-1,3-Dichloropropene |
100% |
92% |
97% |
90% |
95% |
|
Toluene |
100% |
94% |
93% |
93% |
97% |
|
4-Methyl-2-2pentanone (MIBK) |
100% |
99% |
97% |
96% |
103% |
|
Tetrachloroethene |
100% |
96% |
91% |
94% |
94% |
|
trans-1,3-Dichloropropene |
100% |
93% |
91% |
93% |
99% |
|
1,1,2-Trichloroethane |
100% |
94% |
102% |
96% |
99% |
|
Dibromochloromethane |
100% |
94% |
95% |
93% |
96% |
|
1,2-Dibromoethane |
100% |
95% |
93% |
94% |
96% |
|
2-Hexanone (MBK) |
100% |
93% |
96% |
92% |
101% |
|
Chlorobenzene |
100% |
99% |
95% |
97% |
95% |
|
Ethylbenzene |
100% |
97% |
96% |
98% |
108% |
|
m- & p-Xylene |
100% |
97% |
98% |
99% |
107% |
|
o-Xylene |
100% |
99% |
99% |
102% |
112% |
|
Styrene |
100% |
97% |
93% |
98% |
106% |
|
Bromoform |
100% |
95% |
98% |
101% |
107% |
|
1,1,2,2-Tetrachloroethane |
100% |
95% |
99% |
107% |
111% |
|
4-Ethyltoluene |
100% |
103% |
106% |
108% |
109% |
|
1,3,5-Trimethylbenzene |
100% |
106% |
97% |
101% |
110% |
|
1,2,4-Trimethylbenzene |
100% |
97% |
98% |
102% |
112% |
|
1,3-Dichlorobenzene |
100% |
96% |
93% |
96% |
100% |
|
1,4-Dichlorobenzene |
100% |
91% |
93% |
94% |
96% |
|
Benzyl chloride |
100% |
92% |
93% |
97% |
103% |
|
1,2-Dichlorobenzene |
100% |
96% |
92% |
100% |
100% |
|
Hexachlorobutadiene |
100% |
99% |
96% |
101% |
102% |
|
1,2,4-Trichlorobenzene |
100% |
89% |
83% |
91% |
92% |
|
Naphthalene |
100% |
85% |
82% |
87% |
91% |
Table 1: Stability results for 500 pptv spike in TO-Cans filled with 50% RH air. Average of 3 canisters.
| Name | SilcoCans | ||||
| Day 1 | Day 7 | Day 14 | Day 21 | Day 32 | |
|
Propylene |
100% |
101% |
108% |
103% |
126% |
|
Dichlorodifluoromethane (CFC-12) |
100% |
89% |
97% |
98% |
103% |
|
1,2-Dichlorotetrafluoroethane (CFC-114) |
100% |
92% |
95% |
96% |
100% |
|
Chloromethane |
100% |
100% |
112% |
109% |
126% |
|
Vinyl chloride |
100% |
106% |
110% |
116% |
118% |
|
1,3-Butadiene |
100% |
88% |
107% |
99% |
111% |
|
Bromomethane |
100% |
93% |
96% |
92% |
98% |
|
Chloroethane |
100% |
105% |
98% |
106% |
130% |
|
Trichlorofluoromethane (CFC-11) |
100% |
93% |
99% |
97% |
104% |
|
1,1-Dichloroethene |
100% |
91% |
99% |
99% |
104% |
|
Carbon disulfide |
100% |
114% |
119% |
130% |
150% |
|
1,1,2-Trichlorotrifluoroethane (CFC-113) |
100% |
93% |
98% |
95% |
102% |
|
Acrolein |
100% |
107% |
155% |
180% |
223% |
|
Isopropyl alcohol |
100% |
137% |
155% |
160% |
192% |
|
Methylene chloride |
100% |
87% |
97% |
96% |
113% |
|
Acetone |
100% |
119% |
135% |
146% |
182% |
|
trans-1,2-Dichloroethene |
100% |
92% |
101% |
98% |
100% |
|
Hexane |
100% |
89% |
99% |
88% |
101% |
|
Methyl tert-butyl ether (MTBE) |
100% |
90% |
98% |
96% |
103% |
|
1,1-Dichloroethane |
100% |
90% |
100% |
94% |
101% |
|
Vinyl acetate |
100% |
89% |
100% |
93% |
107% |
|
cis-1,2-Dichloroethene |
100% |
92% |
101% |
98% |
101% |
|
Cyclohexane |
100% |
91% |
97% |
90% |
105% |
|
Chloroform |
100% |
96% |
105% |
101% |
113% |
|
Carbon tetrachloride |
100% |
90% |
95% |
94% |
100% |
|
Ethyl acetate |
100% |
89% |
104% |
101% |
112% |
|
Tetrahydrofuran |
100% |
90% |
102% |
95% |
110% |
|
1,1,1-Trichloroethane |
100% |
90% |
98% |
96% |
102% |
|
2-Butanone (MEK) |
100% |
110% |
132% |
138% |
172% |
|
Heptane |
100% |
98% |
107% |
109% |
124% |
|
Benzene |
100% |
86% |
95% |
90% |
98% |
|
1,2-Dichloroethane |
100% |
88% |
95% |
93% |
100% |
|
Trichloroethylene |
100% |
87% |
94% |
95% |
98% |
|
1,2-Dichloropropane |
100% |
91% |
97% |
93% |
97% |
|
Bromodichloromethane |
100% |
93% |
100% |
99% |
100% |
|
Methyl methacrylate |
100% |
90% |
98% |
99% |
100% |
|
1,4-Dioxane |
100% |
97% |
100% |
91% |
109% |
|
cis-1,3-Dichloropropene |
100% |
96% |
96% |
99% |
102% |
|
Toluene |
100% |
92% |
98% |
97% |
103% |
|
4-Methyl-2-2pentanone (MIBK) |
100% |
95% |
99% |
98% |
105% |
|
Tetrachloroethene |
100% |
93% |
94% |
96% |
95% |
|
trans-1,3-Dichloropropene |
100% |
91% |
96% |
96% |
98% |
|
1,1,2-Trichloroethane |
100% |
94% |
101% |
101% |
101% |
|
Dibromochloromethane |
100% |
93% |
95% |
98% |
99% |
|
1,2-Dibromoethane |
100% |
95% |
99% |
103% |
98% |
|
2-Hexanone (MBK) |
100% |
97% |
104% |
102% |
109% |
|
Chlorobenzene |
100% |
96% |
97% |
97% |
98% |
|
Ethylbenzene |
100% |
94% |
100% |
102% |
108% |
|
m- & p-Xylene |
100% |
96% |
101% |
103% |
110% |
|
o-Xylene |
100% |
95% |
102% |
106% |
109% |
|
Styrene |
100% |
94% |
101% |
103% |
107% |
|
Bromoform |
100% |
94% |
100% |
105% |
109% |
|
1,1,2,2-Tetrachloroethane |
100% |
95% |
103% |
110% |
115% |
|
4-Ethyltoluene |
100% |
83% |
91% |
92% |
101% |
|
1,3,5-Trimethylbenzene |
100% |
111% |
102% |
109% |
115% |
|
1,2,4-Trimethylbenzene |
100% |
95% |
104% |
105% |
114% |
|
1,3-Dichlorobenzene |
100% |
95% |
98% |
104% |
108% |
|
1,4-Dichlorobenzene |
100% |
93% |
101% |
103% |
104% |
|
Benzyl chloride |
100% |
96% |
95% |
97% |
104% |
|
1,2-Dichlorobenzene |
100% |
98% |
102% |
106% |
106% |
|
Hexachlorobutadiene |
100% |
95% |
100% |
103% |
105% |
|
1,2,4-Trichlorobenzene |
100% |
93% |
93% |
95% |
100% |
|
Naphthalene |
100% |
95% |
98% |
99% |
107% |
Table 2: Stability results for 500 pptv spike in SilcoCans filled with 50% RH air. Average of 3 canisters.
As can be seen from the tables, both SilcoCans and TO-cans fared well for most compounds. The compounds that showed a large amount of growth tended to be solvents that are in use within the lab here, which is shared with LC and semivolatile GC instruments, along with acrolein, a known bad actor. The differences between the canister types were due to outliers in each set. One TO-Can had a much higher level of chloroform growth, while one of the SilcoCans had a higher amount of MEK and a larger growth for carbon disulfide, acrolein, and isopropyl alcohol. This shows that, despite the perception of SilcoCans or equivalent being all around superior, for many compounds such as the suite of TO-15A components tested here a TO-Can can provide the same level of stability as a SilcoCan. Some compounds, such as reactive sulfurs will certainly benefit from the use of SilcoCans, but many labs will do quite well using only TO-Cans.
This data also seems to indicate that the main issue for stability, at least for relatively clean canisters, is laboratory contamination rather than any reactivity of the canisters themselves. This stresses the need for clean fill gas and water for humidification, as seen in the previous TO-15A blogs. However, as canisters see more heavy field use and potentially build up hard to remove semivolatile contaminants, adsorption and active sites are more likely to play a role in canister stability.
Having done this, I can see several ways to improve my process. I left the canisters attached to the autosampler the entire time with the valves open. This, coupled with the weekly analysis of the cans, gives more chances for background contamination to influence the canisters or analytical system. A better process would have been to store the canisters outside the lab and only perform the initial and final runs. Also, while I did run blanks before each set of samples, I did not blank check each autosampler port. Running a blank on each autosampler port would let me know if the high results were due to the canisters or if the autosampler lines had become contaminated due to our lab background. Stay tuned for future work, where I’ll see if these steps help improve my stability results.