Science method

Gas Chromatography - Science method

Gas Chromatography is a type of chromatography used in analytical chemistry for separating and analyzing compounds that can be vaporized without decomposition.
Questions related to Gas Chromatography
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Dear Friends and Colleagues
I would like to do an extraction of D and L amino acids from sediment samples. However, I don't have any previous experience in extracting amino acids. Also, I don't have good experience in derivatization methods. I would like to run in GC with the chiral column. Does anyone have experience with this, and could you please advise me?
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We used to extract amino acids along with other peptides from bacteria using 67% methanol. We used Marfey’s derivatization and LC-MS/MS for their quantitation. You can find more details in the following manuscripts:
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Components are mono-, di- and tri- olein and oleic acid. Calibration curves are made for mono-, di- olein and oleic acid.
Method- GC-FID, Db-1HT column.
Problem: due to limitation in injection temperature, triolein is not detected.
A gas chromatography analyzed the glycerolysis products (GC) system equipped with a capillary column (DB-1HT, 15mx0.250mm i.d., 0.1 mm in film thickness, Agilent Technologies Inc.). The detector temperature was set to 290 °C. The oven temperature program was set as follows: 50 °C for 1min, then increased to 100 °C at a rate of 50° C/min, then to 220 °C at 50 °C/min, then to 290`C at 15` C=min, then increased by 40`C=min until the temperature reaches 330 °C for 2min, and then by 20°C/min until the temperature reaches 380`C for 3 min. The analysis solutions comprised 50mg of the obtained product dissolved in 5mL of acetone. Approximately 0.5 mL of the solutions were injected.
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You need an external standar calibration to each component to quantify, it is not corect to use the calibration of other component, because of the relative response factor, are different each other.
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In the lab, the temperature is often around 30 degrees Celsius and lately, the pre-vacuum pump has often stopped working. I wondered if this high temperature could cause the constant (daily) shutdown. The conditions are temporary, we will soon be back to 24 degrees, but until then I would like to know if we can use it or not.
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For a vacuum pump, 30°C is not a challenging environment. Internal operating temperatures of the pump are usually far higher, ~ +80°C.
Suggested things to check - in likely order:
1. Airflow round the pump. Lab may be +30°C but if the pump is under the bench, behind a box, under a package of lab supplies, and sucking dust into the motor ... the acutual pump operating temperature is MUCH higher.
2. If it is an oil pump - has the oil been changed and is there sufficient oil present? "normal" oil colour is a clear golden colour - a good lager. If darker, change the oil!
3. other things are far less likely, such as power dropping to minimum of the RMS supply to the pump.
Hope this helps.
Rob
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Can the change of oven temperature program and flow rate of the carrier gas lead to a change in the area of peaks and as a result the response factor values?
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Changing the temperature program and gas flow rate does not change the peak area.
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Hi everyone
How can I calibration for GC column?
Are there any references for these ?
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Hi
Thanks a lot for all of your useful comments.
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Hi all,
I am measuring acetate (C2), butyrate (C4) and caproate (C6) in my biological sample. Initial concentration of C2 was expected to be ~25,000ppm, and zero for C4 and C6. My standard range is from 10ppm to 200ppm. So, I prepared two samples, which one has been diluted 200 times to measure C2, and another has no dilution to measure C4 and C6.
However, the results I got were very confusing because the concentration of C2 from 200x dilution and 0x dilution did not match, and also C4 was detected in 200x dilution but not in 0x dilution.
Because C4 and C6 will be produced from C2, so isnt that C4 and C6 should be detected in 0x dilution instead of in the 200x dilution sample? Besides, my technician also mentioned that "Quantification for all analytes could only be done on the diluted samples". Does that mean, if the concentration difference between two analytes is too big, the measurement will be inaccurate?
Hope to hear from you all soon.
Cheers,
Kai
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Dear Kai
We are happy to help you and I agree with above mates, could you please elaborate your methodological approach? To me, it is suspicious from the sample preparation, here, I assume type II error from prepared instrumental sampling are well-prepared.
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Is it the chemical percentage graph?
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Without any context, I would likely say that it is the time for the run to complete and the oven to be cooled back down to do another run.
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I'm looking for a relative easy way to test the activity of CYP51. Are there any way that I can measure it without using LC-MS or gas chromatography. A simple absorbance or fluorescence test will be great.
Thank you.
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Maybe this article helps: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8996309/ It mentioned the method of using molecular docking and molecular dynamics simulations to model, targeting ligands specific proteins.
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Hello,
I intend on sampling a gas stream, with up to ~500 ppm H2S, with a flow rate varying from 0-10 litres per minute. I need to use FID to identify certain compounds in the stream, but I would like all the H2S to be removed before the GC to protect the column (Poraplot). Is there a method to remove H2S efficiently (99%+), and as a bonus, also measure the concentration of the H2S? The concentration measurement is less important than removal of the hydrogen sulfide, but would be an additional set of data.
Thank you,
Paul
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Do every castor oil has less FFA content? How can GC be used to find FFA content in oil
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FFA or 'free fatty acid' is mostly acetic acid, then propionic etc.... It comes from the degradation of the fatty acid molecules. Deorderization will reduce its severity. Normally, it is estimated by the phenolphthalein titration (see the AACC for the procedure). Usually, you can estimate the FFA on the GC by the proportion of the acetic acid ester peak by the FAME method (fatty acid methyl ester, again see the AACC for the procedure).
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how do we calibrate the gas chromatography for CO2 CH4 and N2O. and how do we get to know our unknown sample concentration in ppm. please explain step by step. how do we perform all these steps in GC software.
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I can only provide a general answer to you as there are a lot of missing information (GCMS manufacturer and etc.). I assume that your GC is set up for gas analysis.
Based on my experience, this is how I would go about it. May not be the best way to do it though.
You will need the following supplies/items for calibration:
1. Obtain a Standard gas from a supplier (ie: Linde or Air Products) with known concentration.
2. GCMS Syringe - Leur Lock Gas-Tight syringes (comes with push button valve to lock, prevent gas from leaking after sampling). Size wise, depends on your target Limit of detection and GCMS system. I suggest 1000uL and 100uL but please adjust accordingly based on your calibration curve. The air tight syringe is to ensure noting is leak to the atmosphere after sample is drawn and prior to injection.
3. Get sealed (crimped) headspace vials (comes in 10 ml or 20ml volume) filled with Nitrogen gas or other inert gases that does not interfere with the target gases. Inject a certain concentration of the standard gas bought from the supplier into the vials for dilution. You will need and do serial dilution from there. So your volume is always 10x or 20x dilution when you inject 1 ml of gas into the vial. These will be your gas with standard concentration/calibration points (with known concentration - usually in ppm).
4. Inject all the gas standard with known concentration into GCMS and obtain the chromatogram. In the software, key in the concentration value for peak (it is calculated based on area under the peak). Sorry not able to provide a more specific answer here. GCMS software wise, it defers based on the manufacturer of the GCMS you are using. Please find out from your supplier/manufacturer or the software manual. To setup the calibration curve, usually 3 points calibration is used (3 concentrations). You probably need to use SIM mode as this is a Quantitative analysis.
6. After calibration, run your unknown sample. You may need to dilute your sample depending on the concentration of your calibration curve.
Hope this will help you in design the analysis or as a starting point.
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From few days I have problem with my GC-FID Chromatogram in which there is huge tailing in my solvent peak which adversely affecting baseline and analyte peaks that elute near to solvent peak. In the attached picture A = Solvent peak in normal condition, and B = Solvent peak in tailing condition.
I changed liner, septa, even cut columns both ends, and i am also using same method that i used before, each thing is same but still it persist. Is anyone has idea what should I do to solve this issue?
The instrument I am using Scion GC 456 equipped with FID.
Thanks
Muhammad Ayub
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Hi Edmar Martendal , I tried split injection although it reduce tailing but also affect our detection limits. The main issue is that, in chromatogram A the solvent peak is elute with pulse (a good peak) and in Chromatogram B it is eluting from column slowly (having bad elution).
I think problem is not the method conditions because for both chromatograms method conditions are same, its looks hardware issue where i am unable to trace root cause.
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Currently, im doing my project for GC Method Development.
I have calibrated the method with my 10% standard.
The method is capable to check standard which content 70% of the component.
But when i run analysis for my sample, GC give me result of 130%. The result is expected to be 90%. The result remains the same after i dilute the sample 10 times with a solvent.
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Rod's Law - the more you don't tell me the more I can't help you.
State your detector, compound, solvent, injection volume, injector temperature, column, oven temperature(s), other pertinent conditions.
You have told us next to nothing about your problem and are expecting a solution? We are scientists, not clairvoyants.
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Hello everyone,
My lab plans to use Phospholipid Fatty Acid Stable Isotope Probing (PLFA-SIP) to see if a specific microbe utilises a certain substrate as a carbon source. Luckily our microbe has a unique lipid molecule only found within its group.
However, we are trying to figure out what analytical machine will be best for our purposes. I have found in some literature using gas chromatography/isotope ratio mass spectrometry (GC-c-IRMS). Therefore, would this be suitable for detecting potential isotope uptake in our microbe?
Thank you very much
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Hello Dr. Noel Davies,
Fantastic! Thank you very much for telling me this and for your help it is much appreciated!
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Hello all,
I would like to ask about the gas chromatography GC ms, which minimum area variation is measurable (maximum and minimum area accuracy) and analyzer sensitivity (minimum and maximum range).
For example, I would like to see if the difference in concentration for a gas between the initial state and the final state is 40 mole/m3, is this measurable or not.
Thanks in advance
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Depending on compound (and instrument) currently I would expect the systems are able to detect about 1 pg of compound. - now the rest is dependent on You injection technique. I have been running injection volumes from 0.1-50 µL solvents in routine.
A bit above the absolute limit of determination I would expect 10% relative standard deviation (lower RSD can be achieved if using internal standards).
I hope this helps
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My project is methanol conversion to jet fuel but I have problem with GC method to analyze liquid product which is hydrocarbon mixture.
for GC - simulated distillation cost for analysis is too expensive for me
I hope someone can help me
thank you.
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I think you can refer to ASTM D3710 "Standard Test Method for Boiling Range Distribution of Gasoline and Gasoline Fractions by Gas Chromatography" https://civilengineersstandard.com/wp-content/uploads/2019/02/D-3710.pdf
This document should give you hints to replicate the method in your lab.
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There are plenty of choices when it comes to finding a ferrule for a GC column, including pure graphite and vespel-graphite.
What is the difference between these two materials, and when to use each of them for column installation?
Please share your experience with us.
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graphite ferrules:
easy to use
general used in FID & ND
High temperature analysis rated to 450 oC
Vespel/Graphite ferrules 80/15%: good for MS and other oxygen sensitive detector but not reusable
Vespel/Graphite ferrules 60/40%: Easier to use than 85/15% but Easier to deform than 85/15%. recommended for MS or other oxygen sensitive detectors
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The glass wool in packed liners from the manufacturer is moving after a couple weeks of injections on the GC-FID. It is only happening on one out of the 6 GC systems. One cause for this that I was told is that the glass wool packing may be inconsistent, but this doesn't seem likely since the other instruments are ok. The other thing I have been told is that the split vent trap may be plugged and therefore causing back pressure and the wool to move. Does any of these sound plausible or do you have any other solutions? I prefer not to pack them in house. Thanks.
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- Check your septum. Leakage in the septum may cause glass wool to move during needle exit.
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I am synthesizing coumarin-3-carboxylic acid but products are not pure. I have done crystallization to purify them , they are still impure .Besides GC and HPLC , what other techniques should I use for purification.
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Hello All,
Can CO2 purging during Electrochemical reduction of CO2 removes produced alcohol from electrolyte, if so what are the proposed solution to solve this issue, knowing that this reaction can not be done without continously purging due to CO2 depletion.
Many thanks in advace
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What alcohol? Temperature? Design of the reactor? You need to plot the dependence of partial pressures of alcohol and water at a required temperature on the alcohol:water ratio. This is a time consuming job. Do your part of the job and then I would be willing to discuss your question
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I am working with a 7820A GC and 5977B MS. Recently, we changed the helium tank and since then we have been seeing baseline noise in the chromatogram which is high enough to interfere with my peaks. We also found that the N2 and O2 counts have been higher than we used to see; 5-8% and 1-1.8% respectively. Previously, the counts used to be 1-2% and <1%
We replaced the helium regulator, purged the inlet, changed the septum, baked out the MS and the baseline noise still exists. Any ideas why this might be happening?
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Perhaps you have found the answer, but apparently the Helium cylinder can be contaminated with N2 which explains the high N2 ratio.
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Length, inner diameter and film thickness : of the column ;
The temperature program for GC analysis ;
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I suppose that this adduct or salt is not volatile enough for GC analysis.
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Using a shimadzu GCMS I want to integrate my MICs. It is insisted to me by my more experienced colleagues, that this is impossible. Under the quantitative menu dropdown that is correct, it only integrates the TIC. But if I use the qualitative dropdown I can integrate quite happily. I am far from a GC expert so before I bring it up with those people telling me its impossible, I wanted to check that I'm not missing something. Is there a difference between qualitative and quantitative integration? Surely and area is an area is an area, no? If anyone can offer any explanation why its possible in qualitative but not in quantitative, I would be very grateful.
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First, I suggest you contact Shimadzu about this. They have experts who can answer all your software questions. I'm not sure I understand what you need, but if you are using LabSolutions software you can select the m/z in the fragment table you want to display and integrate. This can be part of your quantitative method also, in the peak table you specify the m/z or TIC for integration.
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We have a separate lab scale pyrolysis apparatus. Can we heat the sample here, extract the gas, and then inject it into the GCMS?
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A detailed spectrum of analytical techniques of microplastics can be found in (open accessible):
Kyriakopoulos GL, Zamparas MG, Kapsalis VC. Investigating the Human Impacts and the Environmental Consequences of Microplastics Disposal into Water Resources. Sustainability. 2022; 14(2):828. https://doi.org/10.3390/su14020828
This review paper also contains the paired information of (microplastic size, analytical technique), which can offer a more precise guidance of your method proposed.
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Is there a special design for an electrochemical cell used for CO2 reduction reaction that is commercially available? the cell is supposed to be a gas tight cell so can be connected to a GC to allow the online analysis of various possible reduction product.
Thanks Heaps!
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it is CO2 reduction reaction, so after purging the electrochemical cell with argon and and adding your catalyst you use a CO2 flow, saturate the cell by CO2 and then record the electrochemical data.
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Dear everyone,
I am cloning a plasmid containing CAG promoter, which has high and repeatable %GC.
I have currently tried to do sequencing it, but it has no responses.
Has anyone experienced on determining the sequence of CAG promoter or any replaced methods used for?
Thank you so much for your help.
Best regards,
Lam Hong
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Hi,
I will share the notional sequence information of the vector containing the CAG promoter that I have on hand. As I am sure you know, you can find them as CAGGS vectors by searching Google.
I have also tried PCR amplification for the CAG promoter, but it was difficult.
However, when I used a PCR enzyme called KOD one and added 4.5% DMSO as a PCR enhancer, sometimes I could amplify it about one out of every three times. It would not be a very good method.
Also, I never performed Sanger sequencing analysis.
I am not sure if this is an answer because I don't know why you want to sequence analyze the CAG promoter sequence.
I hope this is of some help to you.
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Dear all who may have experience on GC-MS,
Recently I am working on developing an Gas Chromatography (GC) method profile on an organic compound, which is thermal liable with melting about 60-70degC and decomposited around 115degC. I have tried an existed method profile and even lowered the starting temperature of column, which showed some sort of seperation in retention time of solvent (ethylene acetate) and target, still is close to each other.
The current results is kind of suggesting me i) some other organic solvents with lower BP around 30-55 degC, ii) lower the column temperature range of 80-100 degC with a rate of 5 or 10.
To what other aspects I should pay attention ? Your suggestions and experience tips would be of great help to me. Thank you all in advance for your time and help.
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Hello, the main requirements for analysis sample in GC under your mentioned temperature range you need to be sure that your have valuate substances in your temperature range or you need to perform derivatization esterification methylation etc. to make them volatile to be able to analyse by GC.
Based on your column specification you can use the solvent with lover BP than ethylene acetate.
For example:
Chloroform which has boiling point point 61.2
Acetone 56.3
Pentane 36.1
Low fraction Petroleum Ether 35.0
Diethyl Ether 34.6
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We have a GC Shimadzu with a BID detector without a headspace autosampler in our laboratory.
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As I worked during many years at the Food Research Institute - SIK in Gothenburg, got familiar with several headspace methods. Attached file should help you on your way to prepare a suitable method of yours. The column proposed and the GC parameters are as following:
Capillary column (DB-WAX, 58 m × 0.32 mm I.D., film thickness 0.50 μm). Temperature program: 30°C hold for 8 min, 14°C/min up to 200°C, hold for 10 min.
You are always welcome with more questions!
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Hello all,
I am working on a project of quantifying viral titer. I read some paper, and there are different units for viral titer. Among of them are TCID50 value, GC/ml and VP/ml. I do not understand much about the differences between them. Can anyone please give some explanation about this?
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Dear Marziyeh,
I suppose my reply is much to late to be helpful.
Nevertheless I would like to mention that a more specific articleregarding SARS-CoV-2 has been published in May 2021 by Brandolini et al ( ).
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Hi, i would like analize phosphoethanolamine content on a sample. What is the best technique to this analysis? I have been trying by HPLC-Fluorescence methods, however the fluorogenic product dont have shown stability above 1 hour. Are there some suggestion about other techniques or specification about HPLC-fluorescence methods?
Thanks for all
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Phosphoethanolamine is aalysed by method described by Atkinson et al., 1980; Harzer et al., 1984.
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which is best method for 5 hmf analysis, gas chromatography or HPLC?
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Dear Ganesh Parsai,
HPLC is used for detecting and measuring 5-Hydroxymethylfurfural/5-HMF. I have attached one article. I hope it would be useful.
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After GC analysis how to calculate total FAME based on internal standard and FAME standard.
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Hi
The calculation and processing protocols are well explained in the following paper:
I hope this helps!
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Hello,
I carried out a GCMS analysis for two samples of methanolic plant extract (stems and leaves), I obtained the chromatograms in attachments.
Can someone help me calculate the peaks area please, the GC software is missing an update and I can no longer retrieve these results.
How can I calculate it? thank you in advance
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Dear Khawla Bouaouda . You can use classical integrator. Just connect it to GC and you will see the peaks printed out on the paper with the area under the peak for each peak.
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There are many articles published showing the use of GC-MS to quantify PHA. I am struggling and ended up damaging GC column. I have been advised by a reliable and experienced GC supplier that NONE of the GC column would elute PHA, in fact, it will be hard to remove PHA from the injector once injected. But there are many report demonstrating the use of GC for PHA quantification, I am bit confused, WHO is right?. HELP
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A component analyzed in the GC, it must be gaseous! I am not an expert on GC, but I think that normally components with a boiling temperature <250°C (at normal pressure) are analyzable here - or at least have sigificant partial pressure at this temperature. I guess the monomers of PHAs can be analyzed by GC, but no polymer.
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There are many articles published showing the use of GC-MS to quantify PHA. I am struggling, it showed butyric acid and valeric acid peaks but then disappeared after few samples, perhaps GC column got damaged.
I have been advised by a reliable and experienced GC supplier that NONE of the GC column would elute PHA, in fact, it will be hard to remove PHA from the injector once injected. But there are many report demonstrating the use of GC for PHA quantification, I am bit confused, WHO is right?. HEL
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Make sure that you sample is salt-free. For PHA to be remotely volatile you will need to be certain that it is fully protonated, which means 1% formic or acetic acid added to the sample before injection and zero cation salts.
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A question about gas chromatography
I'm using gas chromatography for my research.
I am using gas chromatography in my research, and the peaks in the measurement results are rising in two steps.
I would appreciate it if you could tell me the cause and how to improve it.
Solvent is ethanol
Column is non-polar
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Thank you , Dr Davies for your reply.
Sorry for the late reply.
I'm method splitless.
The peaks had normal shapes.
The poor chromatography , I used ethanol as the solvent.
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Hello all,
In GC method the RSD limit is set at "less than 15%" compared to LC method where RSD limit is around 5%..Is there any theoretical/technical basis to set RSD "less than 15%" for GC methods?
Please explain
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I am able to attend two conferences/events with a focus on gas chromatography in 2022. Do you have a recommendation? Preferably in the US, and in the field of chemistry, safety, environment, fire or forensics.
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Hello!
For our current research project, we want to analyse (as simple as possible) the dendritic spine density of our mouse brains.
Apart from the Golgi staining, which methodology could be usefull?
Thank you very much,
GC
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Thank you for this information!
I'm gonna see that!
Best
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how can I separate oxygen and nitrogen using Carboxen columns in GC with PDD (Pulsed discharge detector)as He is carrier gas ? the two peaks are always overlapping that it is impossible to quantify oxygen amount.
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Maybe you should start the analysis at a low temperature or even use crio? Good method described for this column on other forums, eg (https://www.chromforum.org/viewtopic.php?t=12059)
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While trying to test out a new method (taken from the literature, nothing crazy for GCMS) The GC starts preping for the run and goes through the usual equilibration stage for pre-set amount of time. Everything is in green, counter runs down and GC enters Pre-run stage where the split is being ramped up and down, the used ratio is 10:1, so during the pre-run its continuosly changed from 0-10/12. After going from 0-10:1 the split tanks to 0 which casues the carrier gas pressure to drop significantly and GC becomes 'not ready' and the whole process starts again. Anyone has any idea why this is the case? Method equilibrates fine and GC is fine while idle. The issue starts when I try to inject. Thank you for any suggestions or comments. I am attaching video of the issue.
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Have you worked before with such low carrier gas pressure (1.3 psi)? I have an older PerkinElmer GCMS device (Autosysem XL/TurboMass Gold) and its pneumatic system becomes unstable at pressure values significantly below 20 kPa (~3 psi). Try to increase the carrier gas pressure.
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I have tested GAPDH and two different primers (1 and 2) in qPCR (SYBR). The Ct of Primer 1 is 30 and 2 is 36 (Fig.). The cDNA and reaction conditions tested were the same for all primers (TM 60°), according to the SYBR protocol.
The two primers (1 and 2) have the same amplicon size (bp), GC% and t. annealing.
GAPDH and Primer 2 have a normal exponential curve, but the curve of Primer 1 is not exponential and starts with a lower ct value than Primer 2.
How can I interpret these differences?
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What are the measured efficiencies of each pair of primers?
If your efficiency is 95-105%, then it's worth discussing your data. If you don't know the efficiencies, you 1) can't make any valid conclusions and 2) can't publish these data.
But, since you've asked, I'll give you what I think is most likely happening:
  • GAPDH has a higher transcript abundance that the gene-of-interest for Primer pair 1 or Primer pair 2.
  • Primer pair 1 is not efficient enough to make any reliable conclusions.
  • The variation in your Ct values for your 2 (technical I assume?) replicates is too high. You need at least 3 replicates, and less variation. Even very small differences in volume show up in qPCR.
Good luck!
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dear all, i need pdf of this bookidentification of essential oil components by gas chromatography/mass spectrometry.robert p. adams?
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Dear Amin Lotfi,
Did you finally found the ADAM´s book in pdf ?? I would also be interested in having it if you could share it ?
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I'm looking for the elution order of the following fatty acids in C18:1n9t, C18:1n9c, C18:1n7, C24:1, C22:4n6, C22:5n3, C22:5n6, and C22:6n3.
I use Supelco SP 2560 Capillary GC Column.
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This will help. It’s a handout for a workshop I did.
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I would like to do product analysis of phenol hydrogenation products: cyclohexanone and cyclohexanol using GC-MS. I tried creating a calibration for a mixture of cyclohexanone and cyclohexanol (concentrations ranging between 0.325mM to 5mM) and find that since their respective peaks evolve at very similar times, I cannot get proper peak separation when they are in a mixture to do any quantification. I have tried using dichloromethane and ethyl acetate as solvents. A co-worker has seen some peak separation using acetonitrile, however, I will be extracting my products from the aqueous phase and acetonitrile is miscible with water. I am using an Agilent 8890 GC system and Agilent 5977B GC/MSD with a HP-5MS UI column. My method is start at 33C, hold 2 mins, and ramp at 26C/min to 150C. I have tried decreasing ramp rate as well. If anyone has any advice how I can get this peak separation it would be greatly appreciated.
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Dear Brianna Markunas
I have 3 possible solutions that could be successful.
1. use the possibilities of the MS to generate extracted ion chromatograms (EIC).
The mass spectra of both substances show differences like masse 55 (ketone) - 57 (alcohol), mass 98 (ketone)- mass 82 (alcohol), you will find some more. By extracting significant masses you produce a mass-dependent separation, even if your separation column does not physically separate the analytes cleanly. However, the calibration must then also be performed with the extracted masses.
2. adding salt to the aqueous phase. This method is used in various Quetchers methods to be able to shake out with ACN. The salt concentration in the water is then correspondingly high.
3. extraction with ethyl acetate or dichloromethane followed by derivatization of the OH group of the alcohol with a silylating agent, e.g. 1,1,1,3,3-hexamethyldisilazane. Silylation takes about 20 minutes at 70°C and has the advantage of changing the retention time of the alcohol so that separation occurs. The ketone is not derivatized in the process.
I would try method 1 first, since the effort is minimal.
If this is not successful, try the alternatives.
Best regards and stay healthy
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I am looking for the surface energy of 2D hBN
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Hi Navid Namdari , thanks!
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Hoping that a Model 5977B GC-MS can be used for quantitative. Are there details to follow to insure accuracy? I assume the standard issues of column capacity and resolution would apply as in an FID detection and quantitation. I have never used a GC-MS for quantitation but hope to be able to eliminate the GC in our lab and simply us GC-MS for both qantitative and qualitative analysis. I would appreciate any comments. Thanks
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Use the correct separation and preparation methods, and suitable standard curve cover the point you need to measure from CRM materials
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In most of the literatures Gas Chromatography has been used to calculate the yield % of aldehydes, is there any other ways?
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I have just acquired a GC Thermo 1310 and the technician is having a hard time to set up a method to determine O2, CO2, and C2H4 using respiration samples of fruit and vegetables.
The GC came with TDC, FID and methanizer.
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I have recently synthesized Linagliptin (DPP-4 inhibitor). All the parameters have been matched with the specification except LOD (loss on drying). According to specification LOD should be less than 0.5%. I have also checked residual solvents by GC and found it's not interfering in higher LOD. Finally, I discovered that higher water content is the reason of higher LOD.
Now, could you please tell me that how I can get minimum water content in my samples?
Thank you everyone in advance.
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In recent years different methods of ML were considered to detect abnormal TL glow curves for TL dosimeter. Abnormal GC can lead to wrong dose estimation if not properly detected. ML methods could make identification of abnormal GC more robust and at lower cost than using trained technician.
Among the forest of ML methods what would be the most performant methods that could be used for that purpose, knowing that quite large of database of classified GC can be used (about severals thousands of GC). Random forest (RF), artificial neural network (ANN) or support vector machine (SVM) methods?
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Do you know where I can find a good STM and a gas chromatography system for hydrogen detection?
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Agilent is your answer to both queries.
Reliable company with technicians working all over the world to provide solutions
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The GC columns I have come across have a high affinity for either polar or non-polar compounds. Moreover, the websites of the sellers do not have a detailed description of the GC columns (pertaining to use for a specific class of compounds).
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The most suitable stationary phase for the polar and non-polar molecules is the USP G43 (6% cyanopropyl-phenyl 94% dimethyl polysiloxane) and the column equivalent to this is DB-624 of Agilent make.
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Hi all,
I am setting up a new lab with G/MS capabilities and I want to start ordering chemicals for it. Can you guys share with me what are the most basic solvents needed for a GC lab? We will be analyzing all sorts of samples but especially polymers, air samples, and volatiles. So far, we have methanol, ethyl alcohol, acetonitrile, and 2-propanol.
Thank you!
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Why not wait and see what you need? Buying the correct grade is just as important as the type. The most appropriate solvents to have on-hand for GC-MS will depend on the exact types of samples and matrix present. Most chemicals used for GC-MS analysis need to be GC-MS grade ($$$), but many other types of chemicals used may not need to be. This is not a task for an inexperienced user. Please ask the person with several years of formal training in developing GC-MS methods for advice at your place of work. Guessing at what you might need is wasteful.
  • Optionally, to save money, ask your employer to hire someone with the needed experience (10+ years of demonstrated industrial analytical GC-MS experience) to set-up your GC laboratory and provide training. Professional set-up will be far more cost-effective and you will be ready to run actual methods for new samples much sooner.
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I have a 1 mg/mL stock of C24 in hexane. I added 50 uL of this to Organic Acids extract before drying down and derivatizing. I then add 100 uL BSTFA and 1 uL is injected (total 0.5 ug).
Relevant GC conditions are:
20:1 split ratio
Run time 45 minutes
Front inlet: 250C
Split flow: 20mL/min
Total flow: 24 mL/min
Column: Rtx-1 (non polar) 30m x 0.25 mm x 0.25 um
Initial temp 90C for 4 min - various ramps and temps up to 275C.
I have seen a tiny peak doing it this way.
When I do straight injection in hexane (0.5 and 1 ug injected), there is nothing even after ion extraction.
Thanks!
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Florian Morsbach Thanks for your thoughtful reply! We figured it out - turns out the run wasn't long enough to detect it! C22 eluted at the end of our run, so mystery solved. Thanks again.
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I would like to analyse monocarboxylic acids higher than C20 (at least up to C30), but I cannot find a company for buying them. I prefer a mixture of more acids in an organic solvent but it can be solid standards. Thank you.
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Hi Kamil,
You may make an inquiry at Alfa Chemistry, they offer kinds of good-quality chemicals.
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I need to run glycerol on my sample. I only have N, O-Bis (trimethylsilyl) acetamide, degree of synthesis, ≥95% as derivatization agent. However, do I need BSA for GC derivatization degree> 98%?
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95% purity can be ok or even better than the 98% purity, usually it's a very hard task to really tell the difference. What you should definitively check is the possible presence of your (derivatized) analyte in the reagent itself. This is very common for small and ubiquitary compounds such as simple alcohols (and glycerol too!!) or fatty acids (C16 and C18 in particular)
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Irrespective of other noble gas elements such as Ne , Argon or the easily available gas in atmosphere i.e. N2 , why Helium is used largely ?
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Van Deemter plot and corresponding equation in the calculation of HETP as Prof.Noel W Davies indicated is the answer. It is the observation for an ideal gas flow where the sweet spot is needed in terms of optimum linear velocity serving reasonable run time with the lowest HETP possible.
Emir
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I am analyzing VOCs in the air and have a question about choosing a column for good separation of VOCs. I use GC-FID and inject 1 uL (split ratio: 1:10).
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It depends of injection and concentration technics, detector is also important: if you have MS then cappilary column is better because of lower gas flow to vacuum.
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I am using a fermentation media of composition mentioned below and yeast (S. cerevisiae) culture
•3g/L yeast extract
•43g/L reducing sugars(glucose),
•3g/L peptone,
•1g/L KH2PO4
•0.5g/L (NH4)2SO4
•And 0.5g/L MgSO4·7H2O
•10%v/v inoculum
Can anyone suggest me the best way to recover and quantify ethanol (without HPLC/ GC)
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You can use an ethanol meter to measure the ethanol percentage, but the accuracy is a little bit doubtable. However, it is possible to make an alternative method to detect ethanol production, such as the Durham tube test while fermentation. The inverted Durham tubes trap carbon dioxide gas that indicates sugar fermentation. But it cannot use to quantify the ethanol content.
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Hi,
Has anyone seen the tune mass spectrum changing after new installation of the GC column into the MS? Intensitties change for the single masses in the spectrum.
Can anyone help?
Best,
Julia
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One of the reason of this problem may be the new installed column - bleed or leaks. Repeat the MS tuning after installing the other column.
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I have purchased a lot of commercial MoS2 catalysts. After the experiment, I found that the activity was so low that the gas chromatography did not detect the product. Therefore, I want to modify these MoS2 and load them with alkali metals such as K and Cs, hoping to increase the activity. Is there any way to achieve this?
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Dear Jundao Wu many thanks for asking this very interesting technical question on RG. Molybdenum disulfide is a layered material such as graphite. Thus it is not surprising that intercalation of alkali metals into MoS2 is also possible. In the case of graphite this is normally done by heating graphite powder with metallic potassium to give golden-brown "potassium graphite", C8K. In the case of molybdenum disulfde this has been successfully done for example electrochemically. In this context please have a look at the following useful reference:
MoS2 as a long-life host material for potassium ion intercalation
(see attached pdf file)
For more general information about the intercalation of alkali metals into molybdenum disulfide please also see the following potentially useful article:
Alkali metals inside bi-layer graphene and MoS2: Insights from first-principles calculations
This paper has been posted by the authors as public full text on RG, so you can freely download it as pdf file.
I hope this helps answering your question. Good luck with your research and best wishes, Frank Edelmann
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We are using a GC with ISQ 7000 Mass Spectrometer. Today we did an air and water check and it was higher than usual, so we just tightened the ferrules. In the last two days, however, the N2 and O2 have increased and went up to 100% and 70% respectively. We checked for leaks, and there was no sign of any leakage. Any solutions?
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It's not just about tightening the ferrules. If they are too tight and misplaced, it could also be a problem. In addition, there is also the quality of the septum.
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I am analyzing natural gas by gas chromatography technique. The main molecules to identify basically are light hydrocarbons such as methane, ethane, propane, butane (i- and n-), pentane (neo, i- and n-), however, natural gas also contains negligible amounts of hexane, heptane, and higher hydrocarbons, besides content of hydrogen sulfide and carbon dioxide are very important; density and liquefaction process are affected by such molecules and higher hydrocarbons.
For instance, during separation of methane using a PDMS column, it is possible that carbon dioxide can be adsorbed quickly to stationary phase affecting its chromatographic properties and producing a displacement of retention time. How can I correct this and improve separation?
Equipment and conditions: Agilent 7890A GC, injector (temp. 110ºC), column of PDMS phase (30m), chromatograph oven (temp. 150ºC), TCD detector (temp. 200ºC), and Argon gas as carrier. I will appreciate your comments and information.
Additionally, I would like to read your comments about advantages and disadvantages when a TCD or mass spectrometry detectors are used?
Thank you very much
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Dear Alejandro J. Cortés-López as a synthetic inorganic chemist I'm unfortunately not an expert enough to provide a qualified answer to your interesting question. All I can do is suggest to you some useful literature references which might help in your analysis. For example, the following relevant article is freely available as public full text on the internet:
Separation of light hydrocarbons by gas chromatography using serpentine as stationary phase
(see attached pdf file)
Yet another potentially useful article is the following:
Separation of Light Hydrocarbons on Micropacked Bidentate Alkylsilane Silica Columns by Gas Chromatography
(also attached)
Good luck with your research and best wishes!
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Based on the chromatogram of the blank hexane, it shows that there are ghost or unknown peaks in that chromatogram even though most of the parts of the GC have been changed to new prior analyzing the blank hexane.
Plus, the running of another blank hexane showed only one peak which can be confirmed as the hexane peak.
Is it possible the first blank hexane is contaminated?
Another question is:
Is it possible if the retention time of different concentrations FAME standard are different in big margins as compared with the retention time in the Certificate of Analysis ( COA- less than 20 minutes, all peaks were observed, prepared FAME Standard- more than 70 minutes).
If it is possible, how can we identify which compound is which because of the FAME standard retention time is very different compared with the COA?
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If your blank was the first injection of the day then you are probably seeing septum bleed that has accumulated on the head of the column or in the injection liner. Very common - one of the reasons you always run a blank injection before you inject actual samples.
If you are trying to match a COA then you have to use EXACTLY the same conditions and column as are shown on the COA. Even then you may not be successful - I had a standard from a major reference standards manufacturer that showed pentane eluting after octane on the COA. Uhhhhh.......
Given the fact that your FAME analysis took 70 minutes and the COA shows 20 tells me you need to match conditions first. Try that and see if your retention issues don't go away.
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I have a method for analysis of a herbicide in GC-ECD. can I use the same method of analysis in GC-FID or GC-FID TCD?
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If the method you found is for herbicide with halogens (Cl probably) and you want to measure low concentrations and you have a dirty matrix, it will not work. The FID is most probable not sensitive and specific enough. And forget about the TCD.
"but many studies have been carried out with the help of FID detector."
10, 20 or 30 years back maybe, and what sort of studies? Current studies of halogenated herbicides, I doubt they use a FID or even an ECD, or the concentrations must be high. Current studies will be with GCMS or GCMSMS.
I suggest to upgrade your equipment.
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Hello everyon! I am using an Agilent 7890 based refinery gas analyzer, and I found a strange phenomeno. If I analyse sample with lo concentration of oxygen (our CRM gas is 0,5 V/V%) the oxygen peak elutes in a double peak. I calculated the response factors, and the oxygen‘s response factor is two or three times higher than the nitrogen’s ( I assume that it should be nearly the same). I think that a part of the oxygen is trapped or lost during the analysis. Do you have any ideas what can be the problem?
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An Agilent 7890 is the make and model of a Gas Chromatography (GC) system. By itself, it is not a specific "gas analyzer". A GC is used with a column, detector and a proper method of analysis to provide data. Collectively, that makes up the GC Method. You did not provide any GC method information and the possible reasons, esp training, to see a peak doublet (if that is in fact what it is) number in the hundreds. If you could provide a chromatogram, with clear scales and the detailed analysis method, then it may be possible to provide some constructive suggestions.
  • Note: REAL peak 'doublets' are often caused by things like: overloading the column, wrong temperature profile, damage to the column inlet and/or incorrect connection to the column, contamination, co-elution, injector conditions which are inappropriate for the sample etc. Try to create a multi-level calibration table with stds to measure the retention, response and linearity of your method. Confirm the GC and method used are appropriate for the application. If possible, please contact the professionally trained GC chromatographer at your facility to assist you with the method and interpret the observation.
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many researchers have analyzed pesticide residue in soil by using GC/MS or GC-ECD. But my lab has GC-FID. can I get the result by using GC-FID?
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No. You will need an MS detector to gain an additional dimension of analysis. Retention time alone is not enough for pesticide ID. Either GC-MS and/or LC-MS (or better yet, LC-MS/MS) are needed for basic quant and ID. Using just GC-FID alone may provide only a limited amount of information (qualitative) so even when used with proper standards may or may not be enough for your application.
Please define your exact goals and objectives, then research your question online using a keyword search for examples.
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I conducted potential nitrous oxide emission assessment from soil samples following the method previously used by Zhong et al 2018. The samples were incubated for 48 hours, taking gas samples at 0, 24 and 48 hours respectively.
I have read the N2O concentrations from the gas samples collected using GC, and this data is available. Also, available is the soil-dry weight of the soil samples used in the assessment.
I feel somehow stuck at the procedure for final calculation of the potential N2O production using the available concentration readings from the GC.
Has anyone previously undertaken such, or a similar study, and can quickly unstuck me?
How do i proceed to determine the final N2O emitted from the soil samples ?
Thanks in advance
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Best wishes and interested
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I'm working on photocatalytic water splitting and I'm trying to measure the H2 by GC. I know the best carrier gas is Ar and TCD is most common for this purpose. Could anyone tell me about the best choice of column to separate the H2 and O2? What is the best temperature to do that?
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The problem is not to separate H2 and O2, but to separate O2 and N2. The latter is always present as a contaminant from air. The best would be a molecular sieves capillary column with Ar and TCD. The T< 100C is advised. Just try. Don't forget to bake your column from time to time at ~ 180C overnight to remove adsorbed water.
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If it can...Then please provide me the suitable parameters to be set on GC for the determination of methanol dissolved in water.
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you can analyze methanol in water using gc-fid. You need to dilute the sample in organic solvent to lower the water concentration. It is likely that you have poor retention due to the low polarity of the column, you must work at a temperature close to room temperature. I recommend you change the column to a more polar
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My material is purely carbonaceous. For ORR experiment, I have to make ink with high dispersibility. I am dispersing it in water. I can make a fine layer of catalyst on GC, but this catalyst layer just gets detached in form of a disc in the electrolyte. it means the catalyst cannot make a proper attachment with GC. what changes can I make so that material remains intact to GC.
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Dear Sakshi, I suggest that you directly search the "Publications" section of RG for relevant references which might help you in your analysis. Please also have a look at the following closely related question which has been asked earlier on RG:
Why observing a ORR peak at -0.4 V vs Ag/AgCl even in blank GC electrode?
(10 answers)
Perhaps the following research article is also of interest in this context:
Hydrothermal Carbon/Carbon Nanotube Composites as Electrocatalysts for the Oxygen Reduction Reaction
(see attached pdf file)
Good luck with your research and best wishes!
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Determination of different analytes through electro-analytical techniques is easy but can we rely on the obtained results without validating them by standard analytical tools as HPLC, GC, ICP-OES etc.
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Electrochemistry has very poor molecular discrimination for most organic compounds. A high resolution physical separation method (GC or LC) combined with a tunable spectroscopy or mass spectrometry is well accepted because impurities can be seen in small amounts and automation is readily available for multiple samples. Flow methods are more efficient and are more easily calibrated.
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We just noticed that our GC column is contaminated due to overloading with sample. We tried a method for cleaning it which consisted of a T of 240°C for the injector, a ramp of 200 to 220 °C, and 5uL of solvent injection, to no avail. Do you have any method or technique to clean a GC column that you could share with us?
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This is a very important issue to clean the GC column. After few injections, it is wise to clean the GC column. In order to clean the Gccolumn, the best way is to increase the column oven temperature in a isothermal method for long time, this way the column will be cleaned.
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So recently weve been using a GC but we have a problem: we always get contamination from previous samples, although we rinse the syringe several times (between 15 and 20 times) with the solvent, some sample leftover is carried on for the next measure. We can only do manual injection since the automated sampler got screwed. Any of you who have used a GC manually has had this issue?, how do you clean your syringe between samples?
Thank you
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For manual Gas Chromatography injection, it is very much essential to clean the GC syringe. After several injections, you have to take off the syringe and ringe with methanol. I think, ringe is the best way.