| 1 |
A case to eliminate retention time drift in ANP using the Cogent Diamond Hydride in LCMS.
We had a significant run to run RT drift ( up to 1 min for 10 repeated runs) using the new Diamond Hydride HPLC column we ordered two weeks ago. After conditioning the column with 90% IPA and 10X 1% phosphoric… |
| 2 |
A Tip to improve or obtain flat baselines in HPLC-UV gradient applications.
Due to differences in UV absorbance between two solvents at a particular monitored wavelength, you will generally observe a sloped baseline when performing gradient methods with HPLC-UV. As the solvent… |
| 3 |
Acetone as the Organic Mobile Phase Component
“Green” substitute for separation of amino acids Discussion Acetone has a high UV cutoff and therefore is generally unsuitable for UV detection. However, this is not a problem when using LCMS or ELS… |
| 4 |
Activity
It is the relative strength of the surface of the stationary phase in adsorption chromatography. In the case of silica gel, the more silanol groups are available on the surface, the more active it is.… |
| 5 |
Adjusted retention time
Adjusted retention time (tR') is the retention time adjusted for the hold-up time: tR' = tR - tM where tR is the retention time and tM is the hold-up time. The hold-up time is the time of an analyte (small… |
| 6 |
Analysis of Cysteine by LC-MS
Cysteine is difficult to analyze by LC-MS because it is hard to ionize and also very sensitive to any metals in the instrument such as tubing, injectors, seals, joints etc. We do not currently have an… |
| 7 |
Asymmetry factor
Measure the left half of the peak width at 10% peak height (A) and then measure the right half of the peak width at 10% peak height (B) (see figure below). The ratio of B over A is the asymmetry factor.… |
| 8 |
Autoclaving inserts with plastic feet is not recommended.
Autoclaving glass or plastic inserts with attached plastic springs is not recommended. While the glass can withstand temperatures up to 1,000°F, the polyetheylene spring will become deformed, may crack… |
| 9 |
Buffer concentration can affect ANP retention of acids.
If you are using ammonium acetate or formate in an ANP method, the concentration used may play a significant role in the retention of organic acid analytes. Although buffer concentration may affect a… |
| 10 |
Calculating Theoretical Plates N half height
The theoretical plate number N0.5 can be calculated from a chromatogram using the equation below: N 0.5 = 5.54 (t R /w 0.5 )2 Where tR is retention time and w0.5 is the peak width at half its height.… |
| 11 |
Can concentration changes effect retention time in HPLC? Is this a difference between HILIC and ANP?
No, it can happen at any mode, so it is not a contrast between HILIC and ANP. Of course retention can change with concentration from two sources. All separation processes follow a "Langmuir model"; when… |
| 12 |
Can I make the PTFE syringe filter more hydrophilic?
Yes, if you are wiling to introduce Methanol into your method. For a 25mm device, if you use 15-20mls of methanol as a blank filtrate, the membrane will give you less back pressure after that for aqueous… |
| 13 |
Can I use acetone as a mobile phase solvent in ANP?
If you are using LCMS, the simple answer is yes but pH is also something to consider. Acetone has a high UV cutoff and therefore can be a problem for UV detection. However, this is not a problem when… |
| 14 |
Can I use primary amines with acetone as the mobile phase component in LCMS?
Yes, you can. However, some labs react acetone with primary amines (+heat) to form acetone adducts (imines) in GC and GCMS. This reaction while using acetone as a mobile phase component in LCMS along… |
| 15 |
Can I use the knitted reactor coils (KRC) of the post column photochemical reactor with my HPLC fluorescence detector?
The only restriction on whether or not you can use the knitted reactor coils of the post column photochemical reactor is the inlet tubing of your detector. The absolute minimum ID can be 0.008". It is… |
