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Retention - Science topic

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Hello, I am doing lipidomics and use the LCMS/MS system. I am currently doing concentration analysis and ending up getting two almost identical peaks for the same analyte at different retention times. The fractions I am looking for are the same for each peak. Before I ran the reference samples separately at a specific concentration but the sample runs were done in a range of concentrations so I am not surprised the standard peaks do not match with the analyte peaks of interest. How could I make sure of which peak belongs to the analytes of interest? Thank you.
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W.J. Colonna, I am analyzing phospholipids and using a reverse phase column for it. As far as I know, the reverse phase column is not well suitable to separate isomers. I have not applied the spiking method before other than studying it theoretically in my classes. But it seems to be the safest way to identify which peak is for which analyte. Thank you for the suggestion.
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It is required to edit both pdf and word files of hplc and gc chromatograms.
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Are double op-in emails (for example: "press/click to confirm") more effective at retaining customer engagement and security than single op-in? Please share your thoughts as I would like to research this exciting topic.
If anyone is interested in collaborating I am in the AST timezone (Arab Standard Time). Kinld y feel free to reach out.
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A quick google search shows It is to make sure customers receiving them are real. Engagement was in fact brought up with other results.
I could not find any scholarly articles on the topic. Would be interesting to know if A) It is more more secure and B) are customers more engaged.
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So, after carrying out the analysis for a ternary system, i am supposed to get the mass fraction of each component in the organic and aqueous phases. All my analysis was able to provide were the %peak areas, comp. μg/g, Retention time.
Please can i get help with a formula or a procedure to get this? Attached is my anchor paper.
Thank you
Sonia Nkongho
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Thank you for your response Bruce Neagle . Actually, podophyllotoxin was used as the standard.
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Hi, I am working on an Agilent HPLC 1260 Infinity II with a RID detecter and a UV detector. I am trying to determine fructose and glucose with the RID on a Rezex RCU-USP Sugars Alcohols column. My mobile phase is ultrapure water. When I inject water after the reference cell has just been purged with this water the whole night, I get a negative peak on the same retention time as fructose is coming off ( when injecting a fructose standard). Because of this, I do a subtracting of the water so the calculations on my fructose are “ok”. But I want to be more accurate. When fructose is present in smaller amounts, this negative peak keeps appearing. I thought it was because of the column, so I bought the bio-rad aminex hpx-87c column. I purged the reference cell again, rinsed the whole system with water and injected again ( as the first injection on this completely new column) water. Again I am getting the negative peak in my RID signal on the retention time fructose is coming off ( here this retention time is around 15 min, on the rezex column it was around 8 min). I have no idea what I am doing wrong. Can somebody help me?
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Hi everyone,
I am looking for a qualitative survey tool on job retention, any advice would be much appreciated.
Kind Regards,
Laura Hynes
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Thank you very much for that advice that information is really helpful.
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How inadequate column conditioning with mobile Phase can affect Retention time (RT)?
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Variable RT can be observed if the column has been stored prior to use, if not properly conditioned. In reverse phase chromatography that usually involves fully hydrating the stationary phase. Once conditioned, RT should be consistent for each compound in the separation unless there is some other problem with the column.
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We have done GCMS of Plant sample and got a same compound with different retention index.
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it happened with me too, please let me know if you get an answer
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I am carrying out a Research on the effect of blended learning on senior secondary school students achievement and retention in Chemistry. Could someone
help me with materials?
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Dear Emmanuel, I suggest studying retention in the context of deep meaningful learning. In this way, retention leads to durable, lasting knowledge and skills tranfer to authentic settings, a staple of quality education. Another suggestion is applying a game-informed strategy such as playful design (playification), gameful design (gamification) or serious games (e.g. escape rooms). Here are some materials on relevant studies that should be useful.
DeLotell, P. J., Millam, L. A., & Reinhardt, M. M. (2010). The Use of Deep Learning Strategies in Online Business Courses to Impact Student Retention. In American Journal of Business Education (Vol. 3, Issue 12, pp. 49–56).
Fragkaki, M., Mystakidis, S., Hatzilygeroudis, I., Kovas, K., Palkova, Z., Salah, Z., Hamed, G., Khalilia, W. M., & Ewais, A. (2020). TPACK Instructional Design Model in Virtual Reality for Deeper Learning in Science and Higher Education: From “Apathy” to “Empathy.” 12th Annual International Conference on Education and New Learning Technologies (EDULEARN20), 3286–3292. https://doi.org/10.21125/edulearn.2020.0943
Herodotou, C., & Mystakidis, S. (2015). Addressing the Retention Gap in MOOCs: Towards a Motivational Framework for MOOCs Instructional Design. 16th Biennial EARLI Conference for Research on Learning and Instruction Proceedings.
Mystakidis, S. (2021). Deep Meaningful Learning. Encyclopedia, 1(3), 988–997. https://doi.org/10.3390/encyclopedia1030075
Mystakidis, S., Berki, E., & Valtanen, J.-P. (2019). The Patras Blended Strategy Model for Deep and Meaningful Learning in Quality Life‑Long Distance Education. Electronic Journal of E-Learning, 17(2), 66–78. https://doi.org/10.34190/JEL.17.2.01
Mystakidis, S., Cachafeiro, E., & Hatzilygeroudis, I. (2019). Enter the Serious E-scape Room: A Cost-Effective Serious Game Model for Deep and Meaningful E-learning. 2019 10th International Conference on Information, Intelligence, Systems and Applications (IISA), 1–6. https://doi.org/10.1109/IISA.2019.8900673
Yang, K.-H., & Chen, H.-H. (2021). What increases learning retention: employing the prediction-observation-explanation learning strategy in digital game-based learning. Interactive Learning Environments, 1–16. https://doi.org/10.1080/10494820.2021.1944219
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Calculation of retention index (RI) in CG-MS analysis.
I mention that the name of the plant from which I have isolated the essential oil is Neem (Azadirachta indica). it is a new essential oil not investigated by researcher previously at my country level, but surely this oil is investigated by researchers in other contries. I hope this detail can be useful for your answers dear researchers.
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I can remember that RI (retention index) or KI (Kovats index) values are not absolute but comparative to reference/standard compounds.
They are also dependent on the type of column used. certainly, I therefore need standards. GC-MS has suggested my hits from the internal libraries (not exhaustive) which I need to be confirmed by comparison with authentic samples, RI or KI.
Please help.
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Hello everyone :)
I am trying to research the impact on corporate merchandise given to the employees (like t-shirts, hoodies, coffee cups, notebooks, etc. with the company logo) has any effect on the employees experience and cannot find any papers that have approached the subject.
Which honestly surprised me since it seems to be such a common practice that both big Companies (like Google) to small start ups engage in. So I am interested to see if it improves any key factor like motivation, satisfaction, retention, or performance, or if it is just a waste of resources that fills employees homes with objects they do not need.
Do you know of any research papers/studies or surveys that looks at this? Or do you otherwise know, if this topic has been studied at all? Or do you otherwise have any idea, where I might look to find some info on this?
Thanks a lot in advance!!!
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Hi Daria, doing a quick literature search will help you to get a basic answer to your question. As with any search, the keywords used are important. In your case, you might first use "Total Rewards." I attached an article that I hope will help to get you started. You can also take a look at the sources used in the article.
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I am in the process of doing my dissertation and I am interested in the best way of finding a correlation between the three topics. Any ideas how best to tackle it or where would be good places to do my literature review?
All ideas welcome and thank you,
Ben
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It is so difficult to live with stress, how can we work with It? We should manage our stress ,then life will looks better and people too! ,then you can work better.Regards
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After 200 cycles of vanadium flow battery, the capacity retention rate is less than 10%, and the electrolyte will not be able to charge and discharge. What is the method to reuse the electrolyte?
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Vanadium Redox Flow Batteries are one of the most sustainable battery storage system. This is, mainly, due to the recyclability[1,2] of the vanadium electrolyte. VRFBs will see increased demand in the coming years[2,3,4].
1. a)Method of restoring electrolyte of vanadium redox flow battery through electrolysis https://patentimages.storage.googleapis.com/af/b8/25/9ed813de284474/US11251452.pdf https://patents.google.com/patent/US11251452B2/en b)Method for producing vanadium electrolytic solution https://patents.google.com/patent/US5368762
2. How VRFBs and Vanadium Electrolyte Support a Circular Economy https://www.ctechinnovation.com/how-vrfbs-and-vanadium-electrolyte-support-a-circular-economy/
4. Argonne National Lab achieves battery patents for redox flow, solid-state, multivalent-ion and more https://pv-magazine-usa.com/2022/05/16/argonne-national-lab-achieves-battery-patents-for-redox-flow-solid-state-multivalent-ion-and-more/
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I'm trying to seprate xylooligosacch rides (x1-x5) but getting the same peak and retention time. I have also tried different mobile solvents and column but the issue remain same. Kindly suggest possible outcomes to resolve this.
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Maybe you can try using a size exclusion method, searching a porous column that suits you depending of the mobile phase you are using
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Customet service strategies and customer retention journals 2017-2022
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I don't have a citation for you, but customer retention is the result of the feeling of a relationship between the consumer and the business (or the product). Good customer service increases the positive feeling of the relationship. Bad customer service reduces positive feelings.
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I performed a H/D exchange by adding D2O to my sample, then analyzed it with RP-HPLC/MS (targeted SIM) using ACN/D2O as mobile phase, and discovered that the retention time of the isomers of my molecules had changed.
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Thank you for your answer Tabrez Shaikh
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Although much is made of Carbon Retention causing Global Warming, I feel that it would be helpful to know how fast heat moves in air, and water, when there is an exceptional heat-event.
I would be grateful for any ideas and information.
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Dear Sebastian,
interesting question! But I think it's not a question that can be answered in any straightforward way. Heat moves through the Earth's atmosphere in very diverse ways and on an array of different spatio-temporal scales. Please note that a certain amount of the energy released in what you referr to as an "exceptional heat event" would be absorbed by water bodies such as the ocean, the soil and other Earth system components. Please also consider for your calculations the fact that extensive wild fires may sometimes result - with some time-lag - in (regional-scale) scale cooling through ash particles being released into the atmosphere ("nuclear winter effect"). So this is all very complex. Heat transport through the atmosphere is governered by highly complex thermodynamic equations.
Where are you aiming to get at with such a calculation? Just interested :-)
Best,
Julius
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To dear community
One of the important marketing tasks is to increase the CLTV by increasing retention. I agree with this practice. However, it isn't easy to retain the customers, especially in the B to C business. So do the organization's marketing still need to focus more on retaining the customers, or should they spend more time and cost on acquiring new customers?
Looking forward to having an energetic discussion.
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It is significant for companies to employ customer retention strategies in order to retain talented manpower
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The working volume of the reactor is 80 liters, retention time is 40 days, and feed supplied to the reactor was at 5 days interval. The total solids of the feed are fixed at 10%. let's say the feed given on the first day is 3kg and the reactor was operated for 100 days at this organic loading rate. Now, in order to double the organic loading rate without changing the total solids, what should be the procedure.
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Dear Harsha,
this is certainly a very interesting technical question, but unfortunately I'm not an expert in this field of research as we work in synthetic inorganic chemistry. However, you can easily find some helpful information right here on RG. For example, please have a look at the answers given to the following closely related question which has been posted earlier on RG:
How can one increase the organic loading rate of a newly started 20 L biogas digester targeted to be fully functional in a month time gradually?
(5 answers)
There are also some relevant literature references available, which have been posted by the authors as public full exts on RG:
Pushing organic loading rate in a full scale anaerobic digester with thermal hydrolysis pre-treatment
and
Modeling of the Anaerobic Digestion of Organic Wastes: Integration of Heat Transfer and Biochemical Aspects
I hope this helps. Good luck with your work!
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While working on method development and simultaneous determination of two drugs, we have experienced that peaks of the plasma appear in between the peaks of two drugs. The retention time of the first drug was 2.69, while plasma peaks appeared between 3.3 to 3.7 min however, the retention time of the second drug was about 6.692 min. one drug was eluted earlier than the plasma and the second drug was eluted after the plasma. Is there any issue in acceptance of such method?
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As per my experimental experience, it is surely possible. The main concern is the effect of the matrix. Another point to be noted is that the first peak is coming out very early and it will be highly affected by the matrix in your case plasma, hence unsuitable for developing the bioanalytical protocol. As such a normal RHPLC protocol will not work, u also need to add an internal standard to maintain the integrity of the data. Furthermore, plasma peaks will not be stable so I don't think they will remain in the same place throughout the analysis.
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Evaporation is the process linked with the temperature, RH, and water supply below soil through capillary. In zero tillage and in conventional tillage system they are different so the evaporation dynamics also being different.
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Evaporation happens when a liquid turns into a gas. It can be easily visualized when rain puddles “disappear” on a hot day or when wet clothes dry in the sun. In these examples, the liquid water is not actually vanishing—it is evaporating into a gas, called water vapour. Evaporation happens on a global scale
There is lot of evidence that in conventional tillage system more water evaporated then zero tillage system because in conventional tillage systems soil organic carbon is less than zero tillage system. And soil organic carbon content increase total porosity in soil hence increase in soil porosity total water holding capacity of soil also increases. And in zero tillage system more organic carbon content increases soil water holding capacity.
Kindly check the following very good link:
Conservation tillage impacts on soil, crop and the environment
https://www.sciencedirect.com › science › article ›
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I have 6 plant extracts prepared in ethanol. HPLC analysis of all is showing the retention time between 2.2 to 2.5 min but their mAU is different. GC-MS analysis showed different compounds in these 6 ethanol extracts. Is this okay or there is anything wrong
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Mrs/Miss Saxena,
By means of chromatography, there is unable to be determined tautomers and different protonated forms; if any. This can be done only by means of mass spectrometry; furthermore, exactly in terms of both quantitative and 3D molecular structural analyses.
Please, consider the following work. It deals, namely, with this issue:
The shown method is applicable to a set of different MS ionization and fragmentation MS methods. Please, consider the reference section, therein.
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For example, I ran a handful of standards today, each standard three times.
For one standard I got the following height and area:
First time - Area = 1360.5; Height = 400.3
Second time - Area = 1747.6; Height = 629.1
Third time - Area = 2216.7; Height = 801.7
Retention times are staying the same.
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This is a mass spectrum of a compound: retention time on the horizontal axis, intensity on the vertical axis, different lines representing different samples.
My question is: How to juxtapose many curves spatially?
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As per my opinion you have to go for GraphPad.
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Know about retention time during HPLC.
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Thanks to all.
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I am working on the adsorption of MPs and heavy metals under hydrothermal processing. Most of the adsorption kinetics I know (Pseudo-first-order, Pseudo-second-order, Langmuir, ...) use the variables of retention time and solution concentrations. I wonder if there is other kinetics using temperatures instead?
Your help is much appreciated!
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Hi @Phat Tan Vo@, even of so, and depending on the complexity of the processes and experimental way you do that, I would be very cautious with non-isothermal kinetics. The use of formal equations will need plenty of the data across of the temperature rise. When using thermal or calorimetric methods, there are continuous scanning curves of a heat flow or mass changes vs. temperature. If adsorption is studied when continuously scanning temperature, it could be similar. However, if the effect of temperature on adsorption is determined at selecting only several (e.g., 2-5) temperatures, it will hardly be enough to go this way when the empirical kinetics is unknown. A common way to recover rate constants from adsorption kinetics measured at each temperature and applying the Arrhenius analysis would be more confident, to predict the effect of temperature
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Is MS or NMR recommended for further elucidation? Or, is there any standard library available and accessible?
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If you are looking for a specific metabolite, you can use the various papers that they have been published on HPLC (which that depend on the peak absorption range of the desired compound in different concentrations of the standard sample and using the calibration curve produced). However, if you are looking for a different range of various metabolites, it is necessary to prepare/purchase the standard of each samples, separately and it is prepare the calibration curve for each compound in different concentrations. Finally, it must be compared the unidentified peak made of output of (HPLC) and analyzed with standard of each of them, accurately. Then, it could be expected that the identity of the unknown/unidentified absorption peak is identified.
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Are there any recommendations for publications on freemium and customers retention/termination?
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You might have a look at the below articles for your research:
Ross, N. (2018). Customer retention in freemium applications. Journal of marketing analytics, 6(4), 127-137.
Ascarza, E., Netzer, O., & Runge, J. (2020). The Twofold Effect of Customer Retention in Freemium Settings. Available at SSRN 3725224. https://papers.ssrn.com/sol3/papers.cfm?abstract_id=3725224
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Hello,
I am using macro modelling to model using a solid element masonry triplet. When using the CDP model in ABAQUS the model runs completely and gives me satisfying results compared to the experimental data. However, I am trying to compare the CDP with the Concrete Smeared Cracking model, but the analyses terminate quite early (Probably before cracking).
The material model is defined using density, Elastic and Concrete Smeared Cracking model including Failure Ratios (as default) and Tension Stiffening, did not add Shear retention.
Has anyone from the community came across such situations? and how did you make your model work?
I was thinking that maybe besides the aforementioned parameters other damage criteria has been introduced when using the Concrete Smeared Cracking model.
Many thanks in advance and I would be please if anyone could share their similar experience with me.
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Dear Ali Gamra, I tested some series of triplets within this masonry project (the simulation had been done by a colleague):
In my project "CC" I did the experiments and the simulation (smeared cracking based on experimental data).
In my opinion, this should also work on your mentioned masonry project.
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I am transferring methods to a colleague's GCFID and trying to align our database, so we can use our retention times to identify analyte peaks on his instrument. Our two instruments have a ~0.3min difference in retention time for all of our analytes and the newer instrument has ~1/4 the area count for each peak compared to my instrument. These area counts are used to calculate PPM for our research and need to be closer.
I have already checked the following:
Septum replaced
Method identical (pressure, temp, ramp time, run time, etc.)
Identical column (My column is a few hundred samples older)
Same gases
Same solvent, injection volume
My hunch is the column should be replaced but it is only about 13 months old so I want to avoid that if there are other possibilities for the differences in area.
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This is perfectly normal in GCMS, do not worry about that. When you transfer a method to a new instrument, even if you have the same column, you MUST do a new calibration curve on the new instrument, and you have to assess again the retention times.
As for the old column... 13 months seems quite a lot, maybe you'd better change it regardless the difference with the other instrument. By the way, instead of months, you should better talk about number of injections (most instruments have a count, take a look), and how was the column conditioned and stored.
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Can anyone tell me what is the data retention policy for research in India? My team will be using electronic data capture and not paper CRFs.
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yes
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I came across the research done by Taiwo O. Soetan, Impact of support areas on the perceived academic success of international students in community colleges in Canada, and I want to find out if I can get a copy of the questionnaire he used.
I am currently developing my dissertation proposal on measuring success among international students in a northern rural community college in Canada.
Also, I wonder if there were research done on the same area but focusing on different variables such as GPA, retention and graduation rates, and student satisfaction in academic and non-academic experiences.
Thank you.
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Gülrenk Hayırcıl We actually do a research on online students' success during Covid. Our paper is under review. We can share it with you after reviewing process.
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~85% pure one of unknown impurity by HPLC shows multiple mass by LC-MS.
I run the samples in scan mode as well SIM mode in (+)ve ionization mode to confirm the correct mass but always getting multiple mass.
Retention time of impurity is 16.8 min (HPLC run time 50 min) and during LC-MS in (+)ve ionization mode mass shows at 16.8 min as 615.3 , 276.05.158.05, 146.0 with almost same intensity.
Note:
1. HPLC method is well capable to separate.
2. There is a no mass observed while run the diluent (MeOH:water 50:50) couple of times in LC-MS.
please advise.
Best Regards,
Gaurav.
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Hi Gaurav,
Which ionization source do you use in LCMS?
In LCMS sytems, extra peaks are common and this doesnt always mean that you have a big impurity.
As the ionization efficieny of analytes greatly depends on their structureand the matrix, Seni quantitative approach generally doesnt work well.
There may be several possibilities:
-The impurity may ionize more efficiently than your analyte.
-Dimer, trimer formation may be occured.
To clarify, you can change the gradient and check if retention time of unexpected ion changea or not. Secondly, you can use isotope labelled standard to observe the possible adducts of your analyte.
Regards,
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Is it possible to get a theoretical biogas yield if you change the retention time in an anaerobic process? This is assuming that I have actual data from using say, 40 days retention time and I want to find the effect of changing HRT into 20 or 60 days theoretically.
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I am a pharmaceutical chemist and we are receiving Febuxostat (API) from a Company from several years. Recently we have received a lot which IR Spectra is not matching with its reference standard. (Instrument Alpha Bruker ATR). I have also compared it with Primary Reference Standard but the results are same. On the other hand the sample is identified by HPLC Relative retention time. I have checked all instrument parameters and found ok. I have tested the retained samples these are comparable with reference standard But only for Current Lot IR spectra is not matching with reference standard which is already saved in Library.
If anyone respond I can share Interferogram and more information also.
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The FT-IR spectra may be very sensitive to the liquid(s) the sample and reference are dissolved in. Have you confirmed they are all dissolved in exactly the same liquid, at similar concentrations and temperature?
You say you ran "HPLC" and saw similar retention times. "Retention Times" are only one dimension of analysis and not enough to make any qualitative ID on. The full method would need to be evaluated to determine if it was selective for the same, used multiple dimensions of analysis and followed good chromatography practices. An additional dimension of detection such as MS may be helpful too.
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How can i reduce the retention time to around 18 mins for the second major peak just by adjusting pH and mobile phase composition ratio only. With a C18 column and buffer, acetonitrile and methanol as mobile phase (225.5mL : 17mL : 7.5mL).I was able to have a seperation, with the adjustment of buffer using 10M NaOH to pH 3.5. Both peaks came out late but my challenge is how can i reduce the eluting time without changing the flow rate, column temperature or column. I need advice and suggestion.
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1) Mobile phase
Try increasing the organic content of your mobile phase. You can also try using a different organic solvent. There are some cases when methanol will provide better selectivity, such as with biphenyl phases. Otherwise, acetonitrile may provide shorter retention times because it is more nonpolar. The solvent choice should be made on a case by case basis, though, as sometimes it may surprise you what works better.
2) Gradient mode
Try starting with higher organic and/or ramping up to more organic faster and see if that helps.
3) pH adjustments
Try to make the two components completely ionized to make them more polar to elute faster. use pH suitable for components according to their pKa.
you can know more from recently published papers about optimizing conditions for separation for example :
( K.M. Kelani, E.S. Elzanfaly, A.S. Saad, M.K. Halim, M.B. El-Zeiny, Different greenness assessment perspectives for stability-indicating RP-HPLC method used for the assay of isoxsuprine hydrochloride and four nephrotoxic and hepatotoxic photothermal degradation products, Microchem. J. 171 (2021) 106826. doi: 10.1016/j.microc.2021.106826.) .
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Dear Colleagues,
Kindly guide
Suppose we want to calculate the monetary costs of the sediment retention services provided by natural vegetation for providing the clean drinking water supply to people, how to do that?
Regards
Gowhar Meraj
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Thank you very much for this sharing this essential piece of information.'
Sincerely yours
Gowhar Meraj
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Should the material with better coulombic efficiency show better capacity retention?
  • I have optimized high voltage spinel with Al2O3 coating on the particle surface.
  • However, the bare LNMO show better capacity retention.
  • On the other hand, at the same time, it shows lower coulombic efficiency when compared to Al2O3 coated LNMO materials.
Any comments on this behaviour?
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For half-cells, coulombic efficiency (CE) is just a rough indicator how the cells are working. Once you get into high CEs( above 99.8%) always assemble full cells to get the accurate coulombic efficiency. As mentioned above half-cell CE values are masked by the excess supply of lithium. Ioannis Samaras thinner lithium electrodes or Cu foil half cells are ONLY useful if you are assessing for lithium metal battery application, not for lithium-ion batteries application. This is due to traditional organic electrolytes which are compatible with graphite doesn't work well with lithium metal.
For LIBs (full cells) assuming the cells are working well, there is a relationship between capacity retention, cycle number and coulombic efficiency. As an example if the capacity retention is 80% after 1000 cycles using the following equation you can calculate the average coulombic efficiency.
(capacity retention)^(1/cycle number) = coulombic efficiency
(0.8)^(1/1000) = 0.9997 = 99.97%
Therefore, for full cells if your cells are not following the above relationship, that means there are parasitic reactions which might be affecting in the process of coulomb counting. Either the parasitic reactions can consume electrons or produced extra electrons. There are some instances, where extra electrons are produced by a parasitic reaction and these electrons are consumed by a different parasitic reaction.
Hope this helps!
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I ran a GC-MS assay for three different samples and there are little variations in retention times on the chromatogram and the library search report ( a maximum difference of 0.003). For instance, the first retention time on the chromatogram is 2.458 and the corresponding retention time in the library search report is 2.456. Is this a problem?
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Thank you Dr. Jaderson for your invaluable answer.
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We have performed GC-MS analysis of 2 different samples (essential oil and the fraction). Both revealed the presence of some similar compounds in different compositions. However, some compounds showed slightly different RT in their chromatograms, but have been confirmed as the same based on their MS spectra. How is it possible? Why does a compound show slightly different retention times in different chromatograms of GC-MS?
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If your RT change is within a window of 1 second, that's normal. If you are working in a testing laboratory like myself and you are running hundreds of injections weekly, you'll get used to this slight shift.
You don't need to investigate the cause if the change is so little that your software can still pick up the peak of interest without manually integrating it. Just get used to it. But if you are in a research institution, your supervisor or reviewer may not accept this change even if it is small, in this case you'll need more elaboration in your report or manuscript on the technical inconsistencies in analytical instruments.
Bottom line, ignore that RT shift if it is so small.
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Hello,
does anybody know how to convert NIST library into *.MSP format? I have used lib2nist for this purpose; however, there is no retention information in the *.MSP file.
any answer will be appreciated.
Thank you in advance.
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Dear all, I have developed an R package (mspcompiler) to compile either EI or tandem mass libraries from various sources into a single msp file that can be used in MS-DIAL. If you are interested in it, please feel free to try. Any questions and suggestions will be appreciated. For EI libraries, the NIST library (if you have it installed) can be exported by Lib2NIST,  but the obtained msp file does not have retention index (RI) and SMILES which is now can be used to see the chemical structures in MS-DIAL. The mspcompiler package offers ways to add the SMILES and experimental RI (from your NIST installation). And you can also compile the RIKEN, MoNA, and SWGDRUG GC-MS libraries as well. For tandem mass libraries, the NIST msms library (if you have NIST GC-MS library installed, you may probably have the NIST msms library as well, which might not be well recognized) can be organized with SMILES as well. In addition, you are able to add and re-organize the RIKEN, MoNA, and GNPS libraries as well. Please read https://github.com/QizhiSu/mspcompiler for more detail.
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We know the beneficial effects of residue retention in soil. But both the system ( residue in surface and residue incorporated) have some pros and cons, in the point of GHG emission which one is sustainable.
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Yes! returning the residues to the soils is very vital to improve the levels of soil organic matter since inherent OM is influenced by C addition and decomposition rate. When I came to your question incorporating plant residues into the soils can aggravate the decomposition process and thus, C in the form of carbon dioxide will escape to the surrounding environment therefore surface retention is more suitable to minimize GHG emission.
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For undergraduate lab class
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Metformin Hydrochloride is freely soluble. Not suddenly it will soluble requires some time.
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The research question is "What is the impact of deliberate practice on the psychomotor skill retention of first year nursing students"
The outcome to be measured is skill retention.
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what is appropriate and approved in one environment might not be useful in another part of the world. Nothing is approriate and approved until and unless a
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Hello;
In an analytical Method validation whose intermediate precision was carried out by following the same analytical procedure (Assay of an API by HPLC) and by changing the day, the equipment, the analyst ...;
In our laboratory we carried out this criterion with the previous changes in addition we changed the column to another brand (we kept the same dimensions); the retention time changed more than 7 minutes (compared to the retention time obtained in repeatability) can I say that the  intermediate precision is compliant (RSD of the 12 tests is less than 2%) and I accept this validation despite the fact that there is a variation over time in the retention of the main peak? After investigation the column is the cause of this variation.
Thank you in Advance
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There is no specific answer to your question. It is up to you decide and evaluates the result. According to me the difference of 7 min is very much and it suggests that columns are not equivalent.
For intermediate precision, two changes are sufficient, a different day and different analysts.
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I have performed an EFA on my data set using psych package in R studio, if I run a 5 factor solution on my data set if provides perfect SS loadindings > 1 and according to kaisor criterion eigenvalue > 1 can be considered as a component. I am aware that Kaiser, 1960, 1970 criterion is a bit less reliable when it is compared to parallel analysis but the problem is parallel analysis (PA) provides me only 3 components while I am sure it should be 5 components. A reviewer asked me to use PA for factor retention criteria. If anybody knows the solution to this situation?
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at this point, you are way ahead of me. I am not familiar with the intricacies of parallel analysis in different R packages. Perhaps another researcher will be able to assist you. From the looks of it, you are on the right path - bothering to do PA at all and different types of PA at that.
Best of luck!
Marcel
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I followed up a protocol from some good papers about the quantification of anthocyanins and it's use in chemo-taxonmy, by the HPLC separation we should only get two molecules with a specific retention time for each molecule, can I conclude which molecules they are by using retention time and comparing it to the previous study which I followed the same procedures?
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Hello Dr. Elmir
I think it would be possible. However, I believe that using retention time only as a parameter to identify your molecules might be difficult because there are compounds that may be present in your sample that would have a similar retention time which would affect your study moving forward. I think it would be best to have a standard to verify your compound of interest, or utilize other detection instruments such as mass spectrometry or colorimetric assays to further identify your compound.
If you will try to replicate the protocol and conditions of your reference paper, you can check if your sample has similar or same retention time, with the reference compound in the paper. However, there is a possibility that the RT of your experimental results might deviate (slightly or largely) from the RT of your reference paper.
Hope this helps.
Best,
Simon
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Hi,
What is the reason for decreasing the capacitance retention with respect to the number of cycles increased in the electrochemical super-capacitor studies?
I have performed the cycling stability performance of the metal oxide based electrode (3000 cycles) and I got around 85 % of capacitance retention. Some cases the capacitance retention is decreasing or increasing but here my doubt is when the cycle number is increasing (after 3000 cycles) the capacitance retention or stability was decreasing..... Why..?
Thank you in advance...!
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electrolyte problems
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Blending two theoretical foundations of Planned Behavior Theory and Relationship Marketing Theory, exploring four main marketing constructs of Customer Retention, Satisfaction, digital service quality (e-service Quality, e.g., (Parasuraman, 2005)) in a multivariate model using Structural Equation Analysis (PLS-SEM, SmartPLS, Ringle 2015) targeting Customer Retention as dependent variable, if anyone has something in mind, I would love to hear. Thanks in advance!
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Thank you for your insightfull answer. I will try to do first step of your recommended options.
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Hi, I am a chemistry undergraduate doing my dissertation project on HPLC. In my project, I need to predict the HPLC retention time of 20 aromatic molecules, the calibration set. To do this I will require a large database of the retention time and other chemical properties such as logP, polarizability, dipole moment or intrinsic solubility in water of between 100 and 1000 molecules. these molecules will constitute the training set. I was therefore wondering whether you know of any databases which contain data on retention time and various other chemical properties.
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Pietro: I am sorry to say that I do not think you will be satisfied with this choice. It does not take into account the basic fundamentals of liquid chromatography. * "Retention time" (rT) data are only valid for specific methods. Retention times are not fixed values under all conditions. Peak order can change as conditions change. rT's change when the methods used to obtain them change. So any database used would have to contain sample data from just one HPLC method on the exact same HPLC system, acquired on the same day.
The proposed demonstrations have been done many times by others. Google search for many examples. Some employed neural network analysis! Commercial software products can be purchased for chromatographic retention time (rT) prediction (though they do not work very well, unless many of the parameters and mode of chromatography are locked-down in advance. Good for training though). The quality of the data obtained is always limited by the training data set used and the similarity it has to the final samples used as 'test candidates'. Someone with proper HPLC method development knowledge is not likely to use them as we can generally develop better methods in less time using our experience to guide us (great job security as no software based systems can come close).
Background: The predictive software and methods start by first collecting lots of data points (samples) from ONE HPLC Method (same HPLC system, column and dimensions, flow rate, delay volume, detector, same parameters, same integration settings and so on). As noted, this has been reported before for generalized samples and depending on the mode of chromatography used, simple patterns emerge for some samples, based on simple properties. However, in the real word of HPLC analysis, many samples show multiple interactions with the chromatography support (NOT just one, which would make it easy). This is why predictions based on just a single property alone may be unreliable.
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What is the hydraulic retention time HRT and Sludge retention time?
can you give example in nitrification process
thank u
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Thanks in Advance.
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As Noel has stated, your question is irrational and the data provided are not relevant. Is this part of a homework question? If so, please ask your instructor for guidance.
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Can anyone help in the calculation of relative retention indices (RRI), kovat's indices in GCMS data?
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Is it possible for the same compound but origins from two different pathways (one synthetic and the other is biological) behave slightly different on LC in terms of retention time?
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Hi Emad
On the level of GC analysis I have the experience to say that:
The retention times of both synthetic and natural compounds are the same
I think that in case of LC it should be also the same, but i hope that a colleague who have some expertise in LC can answer that question too
Good luck
Amr
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I have get three peaks, 4.5, 6.4 and 9.0 on the basis of retention time. How can I interpret these types of peaks?
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Yes C-18 RP column
Gradient elution
Yes acetonitrile is also best and reported
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I'm preparing a table of composition of my essential oil. And I see in so much papers that we have to put retention indice (Kovats indice) than the retention time.
Are we allowed to put Retention time in the table?
Because the results that I recovered from the GC-MS device are in retention time!
Secondly, can we compare retention time with the data library?
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This is a very critical and useful question for the analyst. I do agree with Md. Atikul Islam. I want to add something:
Retention indices are retention times normalized to adjacently eluting n-alkanes. Usually, for multi residue analysis, it is used. You may also visit the following link:
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We want to characterize a memory resistive device. In this regard, we have to measure endurance up to 1000 cycles, retention up to 10,000 seconds, and I-V for a certain pulse train to illustrate the artificial synaptic behavior.
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I guess that no one has enough time to tell you what you have to do exactly in LabView programming. In general you have to get the LabView drivers or library from Keithley first to get connected to your device. When you are able to control the device by LabView and do the right setup for your experiment then you can program the automatic steps for doing the measurements, storing data, creating result sheets and so on. Of course this can be done with LabView but you have to be experienced in LabView programming. I keep the fingers crossed for you.
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The boiling point of α-Pinene surrounding 155 °C and that of β-Pinene surrounding 166 °C.
And we find always the α-Pinene before the β-Pinene.
Does the boiling point go necessarily with the retention time?
Because I have linalool and Nonanal in my essential oil but the retention time of linalool is superior to that of Nonanal ! Rt ( Nonanal) > Rt ( Linalool)
  • Rt ( Linalool) = 24,116 min ( boiling point = 198 °C)
  • Rt ( Nonanal) = 24,283 min ( boiling point = 195 °C)
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Dear Alexander Sinko,
from my experience I can say that in gas chromatography a separation is not performed by boiling points but by polarity.
The boiling point certainly follows the polarity of a substance , but the polarity is also structure-dependent. Therefore, branching of the C-sting or changing the position of the functional group can influence the separation in such a way that it no longer corresponds to the boiling points.
According to my observations, the correspondence between retention time and boiling point is greatest for very apolar separation phases. If the phase polarity becomes higher, this agreement increasingly fades.
Since you are probably running GC-MS with a universal moderately polar column, typical would be an HP5-MS, Factor Four 5 MS, RTX5-MS or comparable, this column polarity will limit the separation by boiling point.
With much more polar separation columns like DB1701, FFAP, Carbowax, this effect will be intensified.
I hope to have helped with this explanation.
Many greetings and stay healthy
Joachim Horst
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Hi all,
What this sentence mean , α-NiS showed the highest capacitance of 1,287 F/g, with 100% of Coulombic efficiency and 79% of capacitance retention?
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thanks for this advice I actually did it and waiting for the answer
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The Performance consists of Attitude, Achievement and Retention
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I need to give more information about the design of your study and the scale of measurement of your variables before a statistical tool can be recommended.
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Hello,
I am in search of a valid and reliable tool for measuring nurse educator retention or job satisfaction for my DNP project.
Thank you,
Amanda
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I would recommend reading the following article:
-BROWN P., FRASER K., WONG C.A., MUISE M. & CUMMINGS G. (2013) Factors influencing intentions to stay and retention of nurse managers: a systematic review, Journal of Nursing Management 21, pp. 459–472.
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Recently I was searching for degradation intermediate of aniline degradation using the Xcalibur software. Due to the behavior of the aniline concentration in the system I assumed that an -SO2 group might be added to the benzene ring and I then proceeded to search for the corresponding M/Z ratio. I got a clear peak appearing indicating the presence of the compound. out of curiosity I added an extra O atom making an -SO3 group, to my surprise the same peak appeared at about the same retention time. I am not sure how to interpret this result. Any guidance will be most appreciated. Thanks alot
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I think the compound is the one with an -SO3 group, it fragments with loss of oxygen in MS.
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I design the MBBR plant for wastewater treatment. I calculated the volume of Tank and Media. Suppose 60 percent media volume is equal to 3 m3 of a typical MBBR tank with a 4-5 hours retention period. In the market, FAB media trades as kilograms.
How many kilograms of 3 m3 (k3 model suppose) FAb media?
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We actually normally sell the media in Price / m3. If you go to Alibaba to search for Chinese copies of our K3 and take the risk with the quality of the product you will find a price in kg of Plastic since this is what they are selling and not also the knowhow necessary to follow the process. The density of our media - as you will be able to read in the original patent is 0.93 -0.97 kg/dm3 so 1 m3 has a weight of 95 kg. Any media been out of that range will either swim or sink when Biofilm starts to grow.
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Hello everyone
How can I choose the appropriate theory to my MA thesis entitled " the effect of using humorous video on the Saudi EFL Learners’ Idiom Retention?
All my regards,
Manal
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Mohammed:
Here is a PowerPoint about "Humor Theories" that will help you in designing your humor thesis:
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I am preparing to conduct a systematic review and one of the aims will be to do quantitative analysis on the relationship between predictor variables (covariates) and retention/adherence (if data is available). I am trying to find out:
(1) What data do I need in the papers I include, in order to be able to conduct a feasible meta-regression?
(2) If a regression on the relationship is provided in the paper, what do I extract? What if there is no regression done in the paper and only aggregate data of the variables are provided?
Any help is highly appreciated. Thank you for your time.
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You may combine aggregate data using mixed-models effect and sensitivity analysis.
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Satisfying employees could not be enough to ensure improving their loyalty and retention rate. The influence of job delight on loyalty and retention can be larger than that of job satisfaction.
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Mahfuz Judeh Employee satisfaction is key , as an alternative, the concept of job delight, is having expectations surpassed; a delight brought about by augmentation.
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Grateful if anyone could point me to clear studies that show actual percentages or measurable results on how much reinforcement increases retention. Thanks in advance!
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Read multiple papers by Nancy Petry on contingency management using positive reinforcement; the classic paper out of Anna State Hospital in Illinois on the effects of contingent rewards for disulfiram treatment; and the chapter on Community Outcome on Narcotic Antagonists in the book (The Heroin Stimulus, Eds: Meyer and Mirin) where $1.00/ day improved patient adherence with this medication.
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According to metcalf and eddy, SRT= working volume * MLSS in reactor/(volumetric flowrate* MLSS of sludge return+ volumetric flow rate *MLSS of clarifier effluent).
But for SBR sludge return is zero. It will contain only the MLSS and volume of decant (50% of working volume). But if the growth is less and settling process brings the sludge level below the 50% of working volume, would the SRT be very large?
How does sludge wastage can control the SRT?. Would decanting itself maintains the SRT? How does letting SRT to vary affects SBR?
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Thank you very much for your clarification, I do a landfill leachate treatment with RBS, with a total volume of mixed liquor of 1.6 l, is it important in my case to control the TRS? Sameer Kumar
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Hi!
Does anyone know any libraries where we can access retention index data (gas chromatography) of aroma compounds for free?
Thanks!
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The handbook of chemistry and physics may contain information relevant to your question. You can access it in PDF at the following internet address:
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In high pressure liquid chromatography (HPLC), the compound is injected through a column of different sized beads.The amount of time it takes for the compound to pass through the column is the retention time (RT).
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RRT Relative Retention Time and RRF Relative Response Factor
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Dear to whom it may concern,
May I ask you about the difference between porous graphitic carbon (PGC) and graphitized carbon black (GCB) in terms of surface properties, retention mechanisms, and redox potentials?
Thank you so much,
Quynh Khoa Pham.
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I think the following link will be very much useful to know about porous graphitic carbon and GCB as well:
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Lipidomics analysis is quite complex and presents a significant challenge to accurately identify the lipids (fatty acids, phospholipids, or sterols...) using desorption electrospray ionization mass spectrometry (DESI-MS). Liquid chromatography coupled to mass spectrometry provides the user with ion retention time, otherwise not measurable with strictly MS. Unknown metabolites and lipids may be identified using the retention time.
However, how can one simply identify lipids in mass spectrometry without having access to LC-MS and hence retention time?
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Liquid chromatography is used as an orthogonal method to mass spectrometry in order to provide a second dimension of separation. Thus, LC is tackling phenomena like ion suppression, ambiguous identification of isobaric/isomeric lipid species etc.
However, LC is not strictly necessary to identify lipids, and there are ongoing efforts to balance out the negative effects of shotgun lipidomics [1].
For tools regarding data analysis you could take a look at ALEX [2], LipidXplorer [3] or the more recent LipidXte [4].
[1] Hu C, Duan Q, Han X. Strategies to Improve/Eliminate the Limitations in Shotgun Lipidomics. Proteomics. 2020;20(11):e1900070.
[2] Husen P, Tarasov K, Katafiasz M, Sokol E, Vogt J, Baumgart J, Nitsch R, Ekroos K, Ejsing CS. Analysis of lipid experiments (ALEX): a software framework for analysis of high-resolution shotgun lipidomics data. PLoS One. 2013;8(11):e79736
[3] Herzog R, Schwudke D, Shevchenko A. LipidXplorer: Software for Quantitative Shotgun Lipidomics Compatible with Multiple Mass Spectrometry Platforms. Curr Protoc Bioinformatics. 2013 15;43:14.12.1-14.12.30
[4] Schuhmann K, Moon H, Thomas H, Ackerman JM, Groessl M, Wagner N, Kellmann M, Henry I, Nadler A, Shevchenko A. Quantitative Fragmentation Model for Bottom-Up Shotgun Lipidomics. Anal Chem. 2019 17;91(18):12085-12093
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Hello all,
I am specifically seeking scholarship on the history of students with disabilities, as it pertains to challenges of the past and current obstacles, to higher education inclusion, programming, and retention. Creating a timeline for challenges for this student group.
My thanks!
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Hello Francesca,
Thank you so much!
Grazie!
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Due to temperature occurred Maillard reaction in parboiled rice and change the rice color. In dairy industry the test of furosine is very common but in cereals its not common. what is the minimum and maximum amount could be detect in parboiled rice by HPLC. I have run standard 2 micro gram to 200 microgram, peak was very good and retention time was 11.05 min but case of my sample don't show any peak in this retention time. Here given my method....suggest me, what should I Do?
Sample preparation:
Hydrolysis of rice flour (500.0 mg) with HCl solution (10.6 M, 6.0 ml), suspensions were
saturated with nitrogen gas (2 min) and heated (25 h, 110 C). The filtrates (0.50 ml) were applied to a Maxi-Clean cartridge (C18, 500 mg, Alltech, Laarne, Belgium) prewetted with water
(5.0 ml), and eluted with HCl (3.0 M, 2.0 ml). Furosine was quantified by RP-HPLC (Shimadzu, Kyoto, Japan)
Lamberts et al 2008.
RP-HPLC condition:
Column type: C18; Length: 250 mm; I.D. 4.6 mm (Alltech Furosine-dedicated); Column temperature: 30°C; U.V. detection: 280 nm; Flow rate: 0.6 mL/min; Injection volume:
10μL; Runtime: 30min; Solvent A: 0.1% Trifl uoroacetic acid solution; Solvent B: Methanol; HPLC apparatus: Waters Model 2996. (DOI: 10.17352/2455-815X.000044)
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@ Md Arif Hossain, please see the attachment of Chinaza Godswill Awuchi.
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I am developing a method for FAMEs using normal phase chromatography and ELSD as detector. I observe shift in Retention times (more retention) for subsequent injections. also there is a minor fluctuation in the nebulizer gas pressure. Can the retention affects due to the fluctuation of nebulizer gas pressure?
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Do they shifting back and forth or drifting to just one direction, are you observing increased retention times or loss of retention at every subsequent injection? Depending on your answers we may say that it is a column equilibration problem or defective pump or oven indicator as Markus Christ indicated. I also think that is not the result of the nebulizing gas fluctuation, since you say approx. 1min retention shifts are being occurred during analysis. It seems to be more chromatographic rather than the molecule detection configuration.
Thanks
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Hey everyone! I’m doing a research about Customer Success Management in SaaS industríes! Does anyone has information of the main challenges that this newly concept of customer relationship to increase customer retention is facing?
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Hi Colleague
The following URL may help you:
Regards..
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I run full scan for Dimethomorph (a fungicide) in GC-MS/MS, and it gives two peaks with different retention times 11.1 and 11.3. I increased temperature from 280 to 320°C and peaks little bit come closer but this is final temperature limit of column and i can't go beyond. Can anybody explain what is possible reason and how i can overcome it. For assistance spectrum is attached below. Thanks