안녕하세요.
저는 현재 gc-ms 헤드스페이스를 사용하여 분석하고 있습니다.
저는 메탄올에 희석한 표준 용액의 고정된 양을 10mL 증류수 바이알에 첨가하고 있습니다.
여기에 몇 가지 질문이 있습니다.
1. 용매 지연은 메탄올이나 증류수를 말하는 것인가요?
2. SIM 방법에서 용매의 이온 값을 입력하지 않았는데도 용매 피크가 나타나는 이유는 무엇인가요?
3. 용매와 대상( 염화비닐) 물질의 머무름 시간이 겹칩니다. 용매를 더 빨리 용출(또는 분리)할 방법이 있나요? (RT 1.4분)
4. 겹치는 물질이 용매가 아니라면 무엇이 문제일까요? 공백에도 같은 피크 면적이 나타납니다.
귀하의 답변을 부탁드립니다.
감사합니다.
/ oven
| ℃/min | next ℃ | hold time |
| 35 | 4 | |
| 10 | 230 | 1.5 |
- 공백 스펙트럼
- std1 스펙트럼
- 빈칸 + 표준 오버레이 스펙트럼
Please forgive me, I used google translate and did not look closely that the language you posted in was Korean and not Chinese. Thank you for posting in English.
Good day.
I am currently analyzing using gc-ms headspace.
I am adding a fixed amount of the standard solution diluted in methanol to 10mL distilled water vials.
I have a few questions here.
1.Does the solvent delay refer to methanol or distilled water?
2. Why is the solvent peak appearing even though I did not input the ion value of the solvent in the SIM method?
3. The retention time of the solvent and the target(vinyl chloride) substance are overlapping.
Is there a way to elute the solvent faster (or separate them)?
4. If the overlapping substance is not the solvent, what could be the problem?
The same peak area appears in the blank as well.
column : 5ms 0.25mm 250um
oven
| ℃/min | next ℃ | hold time |
| 35 | 4 | |
| 10 | 230 | 1.5 |
I would appreciate your response. Thank you.
Solvent delay waits to turn on the filament until after the typically huge solvent peak has eluted with liquid injections. Headspace injects an air sample, so the solvent delay needs to be long enough at the very least to allow that air peak to go through. If there is appreciable water vapor it would be best to have the solvent delay wait until after the water has eluted as well.
There will typically be some baseline upset caused by inlet flow/pressure changes when the injection valve in the headspace switches or the CTC syringe plunger pushes in the sample. This can sometimes look very much like a small peak. The system response changes due to the flow change so this may even be seen in SIM. Anytime the system response changes, like when the solvent is eluting and the ion source is full of molecules that are not carrier gas, the baseline may be affected, even in SIM.
How much water is in the 10 ml vials? How much is the "fixed amount of the standard solution"?
In Windows Explorer underneath your run method's subdirectory -- like VinylChloride.M -- is a file called acqmeth.txt . Please share that file along with any other information you can provide about your system configuration and methodology including all of the headspace parameters.
INSTRUMENT CONTROL PARAMETERS: GCMSD
---------------------------------------
Mon Jul 08 13:06:39 2024
Control Information
------- -----------
Sample Inlet : GC
Injection Source : External Device
Mass Spectrometer : Enabled
No Sample Prep method has been assigned to this method.
=============================================================================
6890 GC METHOD
=============================================================================
OVEN
Initial temp: 35 'C (On) Maximum temp: 325 'C
Initial time: 4.00 min Equilibration time: 1.50 min
Ramps:
# Rate Final temp Final time
1 10.00 230 1.50
2 0.0(Off)
Post temp: 0 'C
Post time: 0.00 min
Run time: 25.00 min
FRONT INLET (SPLIT/SPLITLESS) BACK INLET (UNKNOWN)
Mode: Split
Initial temp: 250 'C (On)
Pressure: 6.77 psi (On)
Split ratio: 5:1
Split flow: 5.0 mL/min
Total flow: 8.6 mL/min
Gas saver: Off
Gas type: Helium
COLUMN 1 COLUMN 2
Capillary Column (not installed)
Model Number: Agilent 19091S-433
HP-5MS 5% Phenyl Methyl Siloxane
Max temperature: 325 'C
Nominal length: 30.0 m
Nominal diameter: 250.00 um
Nominal film thickness: 0.25 um
Mode: constant flow
Initial flow: 1.0 mL/min
Nominal init pressure: 6.78 psi
Average velocity: 36 cm/sec
Inlet: Front Inlet
Outlet: MSD
Outlet pressure: vacuum
FRONT DETECTOR (NO DET) BACK DETECTOR (NO DET)
SIGNAL 1 SIGNAL 2
Data rate: 20 Hz Data rate: 20 Hz
Type: test plot Type: test plot
Save Data: Off Save Data: Off
Zero: 0.0 (Off) Zero: 0.0 (Off)
Range: 0 Range: 0
Fast Peaks: Off Fast Peaks: Off
Attenuation: 0 Attenuation: 0
COLUMN COMP 1 COLUMN COMP 2
(No Detectors Installed) (No Detectors Installed)
THERMAL AUX 2
Use: MSD Transfer Line Heater
Description:
Initial temp: 280 'C (On)
Initial time: 0.00 min
# Rate Final temp Final time
1 0.0(Off)
POST RUN
Post Time: 0.00 min
TIME TABLE
Time Specifier Parameter & Setpoint
GC Injector
Front Injector:
Injector not configured, use these parameters if it becomes configured
Sample Washes 0
Sample Pumps 6
Injection Volume 1.00 microliters
Syringe Size 10.0 microliters
PostInj Solvent A Washes 0
PostInj Solvent B Washes 0
Viscosity Delay 0 seconds
Plunger Speed Fast
Back Injector:
No parameters specified
Column 1 Inventory Number : 19091S-433
Column 2 Inventory Number :
MS ACQUISITION PARAMETERS
General Information
------- -----------
Tune File : atune.u
Acquistion Mode : SIM
MS Information
-- -----------
Solvent Delay : 1.20 min
EMV Mode : Gain Factor
Gain Factor : 1.00
Resulting EM Voltage : 1424
[Sim Parameters]
GROUP 1
Group ID : 1
Resolution : Low
Plot 1 Ion : 62.00
Ions/Dwell In Group ( Mass, Dwell) ( Mass, Dwell)
( 62.00, 100) ( 64.00, 100)
GROUP 2
Group ID : 2
Resolution : Low
Group Start Time : 1.56
Plot 1 Ion : 53.00
Ions/Dwell In Group ( Mass, Dwell) ( Mass, Dwell) ( Mass, Dwell)
( 51.00, 100) ( 52.00, 100) ( 53.00, 100)
GROUP 3
Group ID : 3
Resolution : Low
Group Start Time : 2.50
Plot 1 Ion : 70.00
Ions/Dwell In Group ( Mass, Dwell) ( Mass, Dwell)
( 70.00, 100) ( 96.00, 100)
GROUP 4
Group ID : 4
Resolution : Low
Group Start Time : 5.00
Plot 1 Ion : 117.00
Ions/Dwell In Group ( Mass, Dwell) ( Mass, Dwell)
( 82.00, 100) (117.00, 100)
GROUP 5
Group ID : 5
Resolution : Low
Group Start Time : 7.00
Plot 1 Ion : 173.00
Ions/Dwell In Group ( Mass, Dwell) ( Mass, Dwell) ( Mass, Dwell)
(171.00, 100) (173.00, 100) (175.00, 100)
(254.00, 100)
GROUP 6
Group ID : 7
Resolution : Low
Group Start Time : 9.00
Plot 1 Ion : 152.00
Ions/Dwell In Group ( Mass, Dwell) ( Mass, Dwell) ( Mass, Dwell)
(115.00, 100) (150.00, 100) (152.00, 100)
[MSZones]
MS Source : 230 C maximum 250 C
MS Quad : 150 C maximum 200 C
Timed Events
----- ------
[Timed MS Detector Table Entries]
Time (min) State (MS On/Off)
15.00 Off
END OF MS ACQUISITION PARAMETERS
TUNE PARAMETERS for SN: US60522243
-----------------------------
Trace Ion Detection is OFF.
EMISSION : 34.610
ENERGY : 69.922
REPELLER : 26.940
IONFOCUS : 90.157
ENTRANCE_LE : 32.000
EMVOLTS : 1270.588
Actual EMV : 1423.53
GAIN FACTOR : 1.02
AMUGAIN : 1619.000
AMUOFFSET : 123.375
FILAMENT : 1.000
DCPOLARITY : 0.000
ENTLENSOFFS : 17.569
MASSGAIN : -680.000
MASSOFFSET : -33.000
END OF TUNE PARAMETERS
------------------------------------
END OF INSTRUMENT CONTROL PARAMETERS
------------------------------------
The reason I set the split ratio to 5:1 is that the vinyl chloride peak was too small,
so I had no choice but to reduce the split.
Please take this into consideration and provide your advice.
Thank you.
+) 20ml vial / 10ml DW
The GC inlet must have 20 ml/min or more total flow for good inlet pressure/flow control. If the total flow is too low, air can actually diffuse into the system and the oxygen will damage the column.
Using an Agilent Headspace Sampler the samples are swept out of the sample loop into the GC inlet by the total flow. If that flow is too low the sample transfer to the injection port takes a longer time. The splitting is not efficient at very low flows in the liner. The early eluting peaks will be very wide. The typical sample loop volume is 1 ml. If the total flow is only 8.6 ml/min, the sample transfer onto the column takes 7 seconds. At 20 ml/min the transfer takes only 3 seconds, so the peaks will be much narrower from that setpoint alone.
An easy setpoint to help would be to increase the column flow to 1.2 or 1.4 ml/min, so even at low split ratios, the total flow volume is higher. Always tune at the run column flow setpoint. This may require a longer oven temperature initial time, a slightly slower ramp rate, or a different column or column configuration.
It's important to transfer the sample into the inlet quickly and to have high enough flow in the liner for decent splitting and inlet pressure/flow control. Newer systems are designed to do this better.
Try running with GAIN 2 or 3 or even a bit higher. This increases the run electron multiplier voltage and so will increase the signal. It also increases the apparent noise, but in SIM that is typically negligible.
Please share the headspace method parameters and an autotune report.
It would also be good to run a blank using SCAN mode 15-350 to see what else is coming out.