Using a three-stage cryogenic system + GC/MS technology (Full Scan and/or SIM) 57 PAMS target VOC compounds (PAMS Mix by Linde) in air will be analyzed in a single run performance test. The results show that in 0.5-10.0ppb range the calibration, precision, accuracy, blank etc. all meet EPA TO-15 and PAMS requirements. The MDL may reach 0.02ppb or lower. It is within specifications for PAMS target VOCs in ambient air.
“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 reliable technology. US EPA published EPA TO-15 method on 1999 and has been continuously used in USA labs from then on. The major target compounds are the listed 65 VOCs. According to USA EPA experience China published HJ759-2015 in 2015 and the technology is similar with US EPA. In USA TO-15 method is also used for Photochemical Air Monitoring System (PAMS) which includes 57 hydrocarbon compounds. This application is focused on the PAMS 57 compounds analyzed in the labs. The application presents the method and conditions for using Nutech preconcentrator with a GC/MS system to achieve the above purpose.
Usually using the preconcentrator with a GC/FID can achieve this PAMS analysis. This is also used the Nutech preconcentrator system. Here we give the lab another approach by using the preconcentrator system with GC/MS. By doing this the lab may combined TO-15 and PAMS together and save their resources and cost for the analysis. Our results show that in a relative wide concentration range (0.5-10.0ppb), the analysis precision, accuracy, blank, initial calibration, continue calibration verification etc. all meet the QA/QC control requirements in EPA TO-15 and PAMS targets.
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/FID/MS：Agilent 8890/5977B（Optional Deans Switch with FID, but not used in this application) As shown in the following flow path.：
1.2 Standard Gases
The standard gases are all from Linde. ：
1.2.1 VOC Standards
57 Compounds PAMS Standard Concentration: 1.00ppm；
65 Compounds TO-15 Standard Concentration: 1.00ppm (as additional)
13 Compounds TO-11A Aldehyde Standard Concentration: 1.00 ppm (as additional)
1.2.2 Internal Standard/Surrogate Standard
Bromochloromethane, 1,4-Difluorobenzene, Deuterichlorobenzene, 4- Bromofluorobenzene
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 the working standard. Do same as internal/Surrogate standard but concentration as 30ppb. The canisters were humidified with 50% humidity.
1.4 Instruments Parameters
1.4.1 8910 Method Set:
Trap 1: -160℃，Trap 2: -40℃，Transfer from Trap 1 to Trap to 20°C, Trap 2 desorption: 230℃. Focuser: -160°C，Focuser Injection impulse: 80℃，Transfer line: 40℃。
1.4.2 8890GC Set
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: 26,27,29,30,31,39,40,41,42,43,95,128,130,114,117 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 20ml and the concentration is 6.67 ppb.
2 The Results
2.1 57 Compounds (with mixed 65 TO-15 compound and 13 aldehydes)
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:
Using 5ppb working standard loading 120 ml concentration is 2.0pp. The CCV results are shown in the flowing table:
2.4 Blank Spike Recovery %（Accuracy %）
Spike 5.0 ppb into a canister as 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. ）
The duplicated samples 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 117 compounds are ＜0.1 ppb, and some compounds may go as low as ＜0.05 ppb,
|MDL is based on 600mL Loading Volume with 7 replicate Run|
|Number||Compound||Spike Conc. (ppbv)||Avg. Conc. (ppbv)||% RSD||MDL|
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 the following.
3.1 Using Nutech 8910 preconcentrator system with GC/MS full Scan and/or SIM the 57 PAMS target compounds can be tested at one time performance. All QA/QC meets EPA PAMS requirements. ，
3.2 The method and instrument configuration needs is just GC/MS and no Deans Switch with FID is necessary. That give the lab to using existing instruments a good example of a successful application. The analysis cost can be saved by combined PAMS and TO-15 target compounds together.
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.