Anders Hofer

12 Questions 27 Answers 0 Followers

Questions related from Anders Hofer

Why does the pressure of my HPLC instrument increase when restarting it after being off over night?

I have a problem with my HPLC instrument that the pressure increases when it is turned off and restarted the next day and I wonder what I can do about it. I usually analyze nucleotides on a C18...

28 December 2024 2,521 4 View

How can Ki values be determined from Km,app and Vmax,app curves?

I am studying a deoxynucleoside kinase and was suggested by a reviewer to use Km,app and Vmax,app curves to determine the Ki value of dATP (with deoxyadenosine as substrate). dATP affects both the...

09 August 2024 4,613 14 View

What is the best way to express Goodness of fit in nonlinear regression (for Michelis-Menten)?

I have been asked by a reviewer to give Goodness of fits to some curves in a manuscript but I am uncertain what is the most correct way to do it. The data is from non-linear regression of...

13 April 2022 8,330 5 View

Where can I find a more pure source of trichloroacetic acid (TCA)?

I am analyzing nucleotides from TCA-precipitated cell extracts by HPLC coupled to UV detection (270 nm) and there is an interfering peak coming from the TCA itself. I have tried some sources of...

08 June 2020 592 4 View

How stable is Klenow exo- and can the stability be improved?

I wonder how stable Klenow Exo- is in -20 degrees and if the stability can be improved at -80 degrees. The source of the enzyme is from ThermoFischer Scientific and stored in 25 mMTris-HCl (pH...

08 June 2020 9,397 0 View

How can ion pairing agents cause peaks to split?

I have previously made a lot of nucleotide analyses with tetrabutylammonium as ion pairing agent but decided out of curiosity to try primary amines instead and then made a strange observation. One...

04 October 2019 7,089 13 View

How does the solubility of the buffer in the stationary phase affect resolution in ion-pair RP chromatography?

I analyze nucleotides with tetrabutylammonium ions as ion-pairing agent on a C18 column and I have made an observation that the resolution of the peaks often decreases when I use buffers that I...

28 August 2019 2,223 1 View

How do I know that the fittings in HPLC are optimal?

I usually do not get as high plate numbers as claimed by the manufacturers and been thinking about how I can know if the fittings (nuts + ferrules) are perfectly seated or not. I have used ACE and...

17 July 2019 6,056 15 View

How can a specific analyte cause fronting in HPLC?

I am running ion-pair reverse phase HPLC (C18 column, phosphate buffer, 7% acetonitrile or methanol, tetrabutylammonium bromide). All the nucleotides that I analyze look good but when I load cell...

27 July 2018 1,290 5 View

Is there anyway to extend the lifetime of C18 HPLC columns when used in the presence of tetrabutylammonium salts?

I am using C18 HPLC columns to analyze nucleotides but have the problem that their lifetime is so short. I have tried a lot of variatns of ACE columns (C18, C18aq, C18, hexyl-phenyl etc) from...

03 December 2017 9,388 15 View

Does the Stewart acid-base approach violate the law: pH+pOH=14?

I was asked to include Stewart acid-base chemistry into a lecture I have and then I became very confused when I tried to read about it. It is there stated that it is the ion gap between positive...

01 January 1970 9,825 3 View

Is the definition of H+ activity different from activities of other molecules and ions?

I am a bit confused by the definition of H+ activity. I have previously learned that activity and concentration follow each other in diluted solutions but when they get more and more concentrated...

01 January 1970 6,446 0 View