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16 Can concentration changes effect retention time in HPLC? Is this a difference if I use HILIC or 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…

17 Can I make the PTFE Syringe Filter 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…

18 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…

19 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…

20 Can I use trimethylamine with Cogent™ HPLC Columns such as the Diamond Hydride™?

Most of the Cogent HPLC columns have an upper pH use limit of 8. However short exposure and possible use depends on how concentrated the solution is, what the pH of the solution is, and how long the column…

21 Caution when using the term of robustness for HILIC columns.

It is reported that HILIC columns can be less robust than traditional reversed-phase (RP) columns. Partly this is due to the fact that the surface can be easily contaminated and is hard to clean. In other…

22 Changing analyte recovery when using syringe filters

Question: I am doing a sunscreen analysis which requires that the sample solution is filtered. My diluent is 95/5 methanol/DI water and I am using MTC 0.45um nylon syringe filters. One day I observe consistent…

23 Cogent TYPE-C HPLC Columns offer faster results compared to Ordinary Silica Based Columns.

It has been well documented in the literature over the years that using Cogent TYPE-C™ HPLC columns offers chromatographers faster results during method development and even with routine use. How? 1.…

24 Column cleaning and care in the reduced particle sized UHPLC Columns

Despite meticulous care, sometimes non-dissolved chemicals and sample particulates may adsorb onto your UHPLC column, causing high pressure issues. Before cleaning your column, it is suggested to remove…

25 Compatibility of Cogent TYPE-C Silica HPLC Columns with UHPLC instruments.

Cogent™ HPLC columns are compatible with ultra high performance liquid chromatography (UHPLC) instrumentation. However, it is important to note the low pressure produced in ANP and the pressure limits…

26 Contaminants leaching into an HPLC analysis, suggestions for troubleshooting.

Have you ever run across a situation where Teflon-like compounds where contaminating an analysis? PFA (PerFlourAlkoxy film, a type of Teflon) is leaching out of something from pipette to HPLC and I have…

27 Cysteine Analysis 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 have a method for cystine,…

28 Determining Efficiency of HPLC Methods, comparing 4um v. 2.o HPLC Columns.

Question: In Application Note A307, it may appear that the 4um column produces a narrower peak width than the 2.o column. Does this mean it is more efficient than the 2.2um column? Answer: Efficiency…

29 Determining HPLC Method Accuracy. A Primer.

The accuracy of an HPLC method is the closeness of the measured value to the true value for the sample. To determine the accuracy of a proposed method, different levels of the analyte concentrations:…

30 Determining the Asymmetry Factor in HPLC. Primer.

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.…

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