I am in the process of setting up a method for determination nitroso diethanolamine in shampoo. This method is performed using derivatization and post-column with HPLC device and UV detector. I use a 15 cm - C18 column. The mobile phase of the method is ammonium acetate buffer with pH 6.7. My method is according to ISO 10130 . Nitrosamines: Detection and determination of N-nitrosodiethanolamine (NDELA) in cosmetics by HPLC, post-column photolysis and derivatization) The permissible limit of nitrosoethanolamine in shampoo is 5 ppb, but the LOQ my method is currently 20 ppb. The shape of the peaks becomes very wide, so at low levels the peak looks like the baseline. How can I reduce the width of the peaks so that I can have sharper peaks? Thankful
Mahsa Ostadgholami I was working with nitrosamines in rubber products. Not with HPLC but GC-based analysis. I faced a similar issue due to the requirement of tracer level analysis. My approach was to focus on preconcentrating the nitrosamines before analysis. Since nitrosamines are also semi-volatile, careful design of this step is necessary. In my experience, the K-D flask method is ideal, but you can also consider other pre-concentration options.
You can try using a 5 cm C18 column with a smaller particle size (3 um?). Otherwise you may have to use UPLC. Inject the maximum volume (>100 uL)
Inject each standard in triplicate and use the average (
Dear Egodage
Thanks for your answer and attention.
Because nitrosamines are very dangerous and, as you said before, they are semi-volatile, I do not use the vaporization method for preconcentration. Are there any selective sorbents for nitrosamines that can give better pre-concentration results?
The post-column reaction system causes a lot of peak broadening, thus a shorter column with smaller particles does not solve this problem: a narrow peak elutes form the column, but becomes subsequently considerably broader in the post-column reactor. In principle a column having a larger internal diameter could be a solution, because you can then inject e.g. 400 µL (depending on the ID of the column).
Depending of the type of UV/VIS detector you are using you might also consider to use a flow cell having a longer light path (the theoretical increase in peak broading is negligible compared to that of post-column reaction). In case you are using a diode-array detector: increase the band with (5 nm > 20 nm) around the the wavelength used.
The method you cites is very old (2009) and uses old column with poor efficiency ( too long with wide diameter and large particle size). You can squeeze the peak height using a shorter column, small diameter and small particle size such as Agilent Zorbax Eclipse plus C18 3x100 mm 1.8 um and use a gradient elution. You should use a newer reaction knitting to minimize band broadening. Your mobile phase on page 5 does not have organic solvent so I am wondering how would you elute the compound from the C18 column? Please Google available method from the internet and compare. Most of the methods use a gradient elution. I have the method from Agilent but the Reserchergate would not allow me to download here.
https://www.agilent.com/Library/applications/5991-1291EN.pdf
use this as a guide for HPLC conditions
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