Application Note: Analysis of 117 VOCs Compounds by Using Nutech 8910 Preconcentrator System
By Using three stage cryogenic system + GC/MS technology (Full Scan and/or SIM) 117 VOC compounds (TO15 + PAMS + Aldehyde Compounds Mix by Linde) in air be analyzed to check the 8910 instrument performance. The results shows that in 0.1-10.0ppb range, the calibration, precision, accuracy, blank and MDL etc. all meet EPA TO-15 requirements. The Nutech instruments system is good for performing TO-15+PAMS+Aldehyde mixture VOCs in ambient air with a single run performance.
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 is listed . According to USA EPA experience China published HJ759-2015 in 2015 and the technology is similar with USEPA TO-15. In USA, TO-15 method is also used for Photochemical Air Monitoring System (PAMS) which includes 56 hydrocarbon compounds. In addition, USEPA also published EPA TO-11 and listed 13 aldehyde compounds by DNPH cartridge/HPLC method. The latest USEPA 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 application is trying to develop an lab analytical application with Nutech 8910 instruments and Nutech 3610 autosampler to cover TO-15+PAMS+Aldehyde target VOC compounds in 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 from their recent results. It shows that 117 target compounds can be analyzed in a single run without Dean Switch by those system and the calibration linear, the blank and the spike are all have the good results.
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 not used in this application)
As Shown as flowing：
1.2 Standard Gases
The standard gases are: EPA TO-15 mix 65 compounds, PAMS mix 56 compounds, and aldehyde mix 11 compounds which are all from Linde. Some compounds are in both TO-15 and PAMS mix and the total compounds in the whole mix standard is 117 compounds.
1.2.1 VOC Standards
65 Compounds TO-15 Standard，Concentration: 1.00ppm；
56 Compounds PAMS Standard, Concentration: 1.00ppm
11 Compounds Aldehyde Standard, Concentration: 1.00ppm
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 3 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 was humidified with 50% humidity.
1.4 Instruments Parameters
1.4.1 8910 Method Set
Trap 1 : -10℃，Trap 2: -50℃，Transfer from Trap 1 to Trap to : 10°C, 20ml/min with 4 minutes. Trap 2 desorption: 220℃. Focuser: -160°C，Focuser Injection impulse: Reach 80℃，Transfer line: 40℃
1.4.2 8890 GC Set
Buffer Column for Dean Switch：1.0m×0.18mm×0μm （May not use it if no Dean Switch not apply）
Temperature program：-40℃（ 5 min）- 15℃/min – 220℃（5min）
Carrier Gas：Constant flow at: 1.8 ml/m
1.4.3. 5977B MS
Ion Source：320 ℃
Connect temperature：250 ℃
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
2.1 117 Compounds by Nutech 8910/GCMS 8890/5977 Chromatography
It is clear that the chromatography of all 117 compounds are all show good peak shape with best separation.
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:
The results shows that the initial calibration of all 117 compounds are good and within <30% RSD and most compounds are <10% RSD.
Using 5ppb working standard，loading 120 ml，concentration is 2.0pp. The CCV results is shown in the flowing table and it shows the continue calibration verification is very good.
2.4 Recovery %（Accuracy %）
The Blank Spike (BS) sample for 117 compounds is performed for 0.5 ppb and 5ppb level separately with a different standard resource. The results are listed in the following table. The recovery for most compounds either at 0.5 ppb or 5.0ppb are between 90%-110% and only a few compounds are within 80%-120% or 70%-130%.
2.5 The MDL Study
According to TO-15 reference MDL study table for this experiment shows the results of our MDL both by full scan method. The results shows that our MDL can reach 0.1 ppb and most compounds are as low as 0.07ppb even some are 0.05 ppb. The selected lab results at full scan are listed as follows
2.6 The Blank
After analyzing 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 is shown as following. The small peaks are either silica compounds background or the small amount less than either full scan or SIM MDL.
3.1 Using Nutech 8910/3610 preconcentrator system with GC/MS full Scan the 117 target compounds (TO-15+PAMS+Aldehyde Mix) can be tested at one time performance by Nutech 8910/3610 with GC/MS full scan system. All QA/QC meets EPA TO-15, PAMS and Aldehyde Mix requirements.
3.2 The method and instrument configuration needs is just GC/MS and no Dean Switch with FID is necessary. That give the lab to using existing instruments a good example of application. The analysis cost can be saved by not using necessary gases supply for FID operation.
3.3 The results also shows 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 manufacture and our air VOC analysis products will continuously service the world with highest quality and better services.