Abstract
By Using three stage cryogenic preconcentration system + GC/MS technology (Full Scan and/or SIM) 85 TX (TCEQ) target VOC compounds (PAMS+TO-15 Mix by Linde and diluted by our lab) in air will be analyzed in a single run. The results show that in 0.5-10.0ppb range the calibration, precision, accuracy, blank etc. all meet EPA TO-15 requirements. The MDL may reach 0.02ppb or lower. It is good for the TX (TCEQ) 85 targeted VOCs in ambient air.
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. The US EPA published EPA TO-15 method which includes 65 target compounds in 1999 and has been continuously used in USA labs from then. In USA, TO-15 method is also used for Photochemical Air Monitoring System (PAMS) which includes 56 hydrocarbon compounds. The Texas (TECQ) requires 85 target compounds to be analyzed and reported to the State of Texas. Scientific research and new instrument development is focusing on combining all the targeted compounds together and analyzed them by using the same method and/or technology. This application note is trying to develop a method to cover 85 VOC compounds listed by TX (TCEQ) in a single sample run. Nutech team in both the USA and China’s applications air Lab and instrument R&D department in USA tried by using Nutech preconcentration system with GC/MS to achieve this goal. This application note is their recent results.
1 Experiment
1-1 Configuration of Used Instruments
Preconcentration System Nutech 8910/3610 Preconcentrator with autosampler, Nutech 2203 Static Dilutor, Nutech 2104 Canister Clean System and 6 L Summa or Silica coated Canisters.
GC/FID/MS：Agilent 8890/5977B（Optional Deans Switch with FID but 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
57 Compounds PAMS Standard (Linde) ，Concentration: 1.00ppm；
65 Compounds TO-15 Standard Linde) ，Concentration: 1.00ppm；
8 Compounds TCEQ Special (By Liquid), Concentration: 1.00ppm,
1.2.2 Internal Standard/Surrogate Standard
Bromochloromethane, 1,4-Difluorobenzene, Deuterichlorobenzene, 4- Bromofluorobenzene，IS/SS Standard (Linde) Concentration: 1.00ppm
1.3 Making Working Standard
Connect 3 high concentration standard and certified clean 6-liter Summa canister to Nutech 2203 and set up 5 ppb as working standard to make working standard. Do same as internal/Surrogate standard but concentration as 10.0 ppb. The canisters were humidified with 50% humidity.
1.4 Instruments Parameters
1.4.1 8910 Method Set:
Trap 1: -170℃，Trap 2: -40℃，Transfer from Trap 1 to Trap to: 20°C, Trap 2 Desorption: 230℃. Focuser: -170°C，Focuser Injection impulse: 80℃，Transfer line: 40℃。
1.4.2 8890GC Set
Injection：250℃
Split Split/Splitless
Column Restek Rtx-1，60m×0.32mm×3.0μm
Buffer Column for Deans Switch：2.5m×0.18mm×0μm （Not use as no Deans Switch was needed）
Temperature program：-50℃（ 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: 26, 27,41,42,43, 95,128,130,114,117 amu
1.5 Initial Calibration
“8910/3610 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 1.00 ppb.
2 The Results
2.1 85 Compounds Chromatography (with mixed 65 TO-15 compound and 13 aldehydes)
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 BD/BSD %（Accuracy %）
Spike 5.0 ppb into a canister as a blank spike evaluation standard to performed by the instrument the recovery as shown as follows: (10ppb is due to some compounds are replicate in standard. ):
2.5 Replicates
The replicates are selected 0.5ppb and 2.0ppb with 7 points The data shows that the RSD% of most compounds are less than 10%.
2.5.1 Replicate Data, 0.5 ppb Level
2.6 The MDL Study
The data shows that the MDL of all 117compounds are ＜0.1 ppb, and some compounds may go as low as ＜0.01 ppb,
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 blank chromatography shows as following.
3 Conclution
3.1 Using Nutech 8910 preconcentrator system with GC/MS full Scan and/or SIM the 85 TX (TCEQ) target compounds can be tested at one run performance. All QA/QC meets EPA TO-15 and TECQ requirements. ，
3.2 The method and instrument configuration needs are just GC/MS and no Deans Switch with FID is necessary. That give the lab to using existing instruments a good example of this application. The analysis cost can be saved by not using necessary gases 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.