Application Note by Using Nutech Preconcentrator System for EPA TO-15A Lab Analysis
【Abstract】
By Using three stage cryogenic system + GC/MS technology (Full Scan and/or SIM) 82 VOC compounds (TO15A Mix by Linde) in air was analyzed in a single run. The results show that in 0.5-10.0ppb range the calibration, precision, accuracy, blank and MDL etc. are all meet EPA TO-15A requirements. The MDL may reach 1-2ppt level in SIM mode for those EPA selected compounds. The Nutech instruments system is good tool for performing TO-15A target VOCs in ambient air analysis.
Introduction
“Using Summa or silica coated canister to take ambient air samples to the lab and using three stage cryogenic preconcentration system + GC/MS to analyze air VOCs is an approved good technology. US EPA published EPA TO-15 method on 1999 and is continuously used in USA labs from then. The major 65 VOCs target compounds are listed. According to USA EPA experience China published HJ759-2015 in 2015 and the technology is similar with US EPA TO-15. In USA, TO-15 method is also used for Photochemical Air Monitoring System (PAMS) which includes 56 hydrocarbon compounds. In addition, US EPA also published EPA TO-11 and listed 13 aldehyde compounds by DNPH cartridge/HPLC method. The latest US EPA published TO-15A still using the preconcentration method to handle more VOCs in ambient air. The new TO-15A increased 17 target compounds and make it to totally 82 target compounds. This note is trying to develop a lab analytical application to cover TO-15A all 82 VOC compounds is a single run. Nutech team in both USA and China tried in their labs by using Nutech preconcentrator system with GC/MS. This application note is their recent results.
1 Experiment
1-1 Configuration of Used Instruments
Preconcentration System: Nutech 8910/3610 Preconcentrator/Autosampler, Nutech 2203 Static Dilutor, Nutech 2104 Canister Clean System and 6 L Summa or Silica coated Canisters.
GC/MS: Agilent 8890/5977B（Optional Deans Switch with FID，but it was not used in this application)
As Shown as flowing：
1.2 Standard Gases
The standard gases are all from Linde. ：
1.2.1 VOC Standards
81 Compounds TO-15A Standard，Concentration: 1.00ppm；
1 Compound (Ethylene oxide) Concentration: 1.00 ppm。
Due to stability for ethylene oxide, Linde has to make two different bottles of standard separately.
1.2.2 Internal Standard/Surrogate Standard
Bromochloromethane, 1,4-Difluorobenzene, Deuterichlorobenzene, 4- Bromofluorobenzene, concentration are all 1.0ppm.
1.3 Making Working Standard
Connect 2 high concentration standard and a certified clean 6-liter Summa/Silica coated canister to Nutech 2203 and set up 5 ppb as working standard final concentration. Making the working standard by following the dilutor operation manual. Do same as internal/Surrogate standard but concentration as 50ppb. The canisters were humidified with 50% humidity. Another APP for how to humidify the canister and how to make the working standard professionally will be published separately.
1.4 Instruments Parameters
1.4.1 8910 Method Set:
Trap 1: -150℃，Trap 2: -20℃，Transfer from Trap 1 to Trap to : 10°C, 20ml/min with 5 minutes. Trap 2 desorption: 220℃. Focuser: -150°C，Focuser Injection impulse: Reach 80℃，Transfer line: 40℃。
1.4.2 8890 GC Set
Injection：250℃
Split：Split/Splitless
Column：Restek Rtx-1，60m×0.32mm×3.0μm
Buffer Column for Dean Switch：2.5m×0.18mm×0μm （May not use it if no Dean Switch not apply）
Temperature program：40℃（ 5 min）- 10℃/min – 220℃（18min）
Carrier Gas：Constant flow at: 1.8 ml/m
1.4.3. 5977B MS
Ion Source：320 ℃
Connect temperature：250 ℃
Scan：Full Scan/SIM
Scan range：Full Scan: 25-300 amu
SIM: (All the target compounds quantity ion and 95,128,130,114,117 amu
1.5 Initial Calibration
loading 30ml, 60 ml, 120 ml, 240 ml, 300 ml, 600 ml，Basic volume is 300 ml.
Using 5 ppb working standard gas，the related concentration will be: 0.5 ppb, 1.0 ppb, 2.0 ppb, 4.0 ppb, 5.0 ppb, 10.0ppb，The curve will be concentration ppb vs. Responses (Peak area). The internal/surrogate standard is loaded 30ml and the concentration is 5.0 ppb.
2 The Results
2.1 82 Compounds TO-15A Chromatography
2.2 Ical
Using 0.5 ppb, 1.0 ppb, 2.0 ppb, 4.0 ppb, 5.0 ppb, 10.0ppbto set up an initial calibration the linear range is 1:20. By using Bromochloromethane and Duterochlorobenzene as internal standard (IS), Difluorobenzene and bromofluorobenzene as surrogate standard (SS), The calibration data shown as follows:
2.3 CCV
Using 5ppb working standard，loading 120 ml，concentration is 2.0pp. The CCV results is shown in the flowing table:
2.4 Recovery %（Accuracy %）
TO-15A listed about 20 labs recovery report with the selected target compounds.
The concentration level is from 0.2 to 0.9 ppb. Here we spike 0.5 ppb a an average and report the recovery for those same selected compounds.
2.5 Replicates
The replicates testing was selected 2.0ppb with 7 points. Using response factors to show the average and standard deviation as well as RSD% to present the replicate results. The data shows that the RSD% of most compounds are less than 10%.
2.6 The MDL Study
According to TO-15A reference MDL study table this experiment shows the results of our MDL by SIM method. The blank MDL is also done according to TO-15A reference MDL on TO-15A table. The results are also listed in the following table. The results shows that our MDL is as good as the TO-15A selected lab results. Most MDL for listed compounds as low as 1 to 2 ppt level.
2.7 The Blank
After analyzed 600ml 10 ppb standard gas immediately load 300ml nitrogen blank and there is no compound tested above MDL. The Both blank chromatography for full scan and SIM are shown as following. The small peaks are either silica compounds or the small amount less than either full scan or SIM MDL.
3 Conclusion
3.1 Using Nutech 8910/3610 preconcentrator system with GC/MS full Scan and/or SIM the 82 target compounds (TO-15A) can be tested at one time performance. All QA/QC meets EPA TO-15A requirements. The MDL for EPA TO-15A selected compounds can be as low as 1 ppt by SIM with preconcentrator, which is as same as reference labs which listed in TO-15A
3.2 The method and instrument configuration needs are just GC/MS and no Dean Switch with FID is necessary. That gives the lab to using existing instruments a good example of application. The analysis cost can be saved by not using necessary gas supply for FID operation.
3.3 The results also show that the linear range can be from 0.5ppb to 10ppb and is better than similar application (1.25-10ppb). The performance is stable and no carry over is another advantage.
Nutech Instruments Inc. is one of the EPA TO-15A listed preconcentrator manufacturer and our air VOC analysis products will continuously service the world with highest quality and better service.
