SLS Content in Empty Capsule Shells

[vikmurush]

We do not know how much it has and believe to be low levels.

[XL]

If the "low levels" means above 10 ppm, an ELS-like detector may detect SLS standard satisfactorily. However, since ELSD is an "universal" detection method, interferences from other components and matrix can be significant. Therefore, a more selective and more sensitive method for SLS is justified if you are looking at lower detection limit of 0.1 ppm or lower.

We developed a RP-HPLC with suppressed conductivity detection method for anionic suffactants analysis. I am attaching a poster on this subject for your information. Feel free to contact me if you have any questions.

"Analysis of Anionic Surfactants Using RPLC and Suppressed Conductivity Detection" : http://www.dionex.com/en-us/webdocs/614 ... 951-02.pdf

[vikmurush]

Thank you XL for the information. May i know if i could use ELSD or UV to detect sodium dodecyl sulfate? I have seen on this poster it was used acclaim PA2 column with acetonitrile and borate buffer. Do you think i get some detection by using these conditions and use ELSD or UV as a detections technique.

by the way what is suppressed conductivity detection? are there any special kind of detections for this?

Thanks again for your information and input.

[XL]

SLS doesn't have chromophore, thus UV detection is out of the question. For samples containing higher concentration of SLS (>20 ppm), I would recommend using of MeCN/ammonium acetate buffer mobile phase system and ELSD method.

In general, a RP column (e.g. C18) should retain SLS. However, for more complicated samples, a column specially designed for analyzing surfactants is justified because you will have the flexibility to adjust column selectivity to avoid interference. The following links bring you to the information on the Acclaim Surfactant column in which you will find that this column is suitable for analyzing all types of surfactants (anionics, cationics, nonionics and amphoterics) including SLS (Peak 9 in Figure 2 of the poster).
Poster: http://www.dionex.com/en-us/webdocs/388 ... actant.pdf
Product information: http://www.dionex.com/en-us/columns-acc ... 25924.html

If you need to detect lower than 10 ppm SLS in the sample, and stay with MeCN/ammonium acetate buffer, you may have to use MS. The detector limit can be easily down to 10 ppb without extra cares. The downside is the cost (capital and operational cost). For your application, it might be an over-kill.

Suppressed conductivity detection is a selective and sensitive method for detecting ionic analytes. To put it in a simple way, all ionic analytes are conductive thus can be detected by a conductivity detector. To achieve high sensitivity, the conductivity contributed by the mobile phase background must be minimized. A device called "suppressor" is used for this purpose. Dionex is the world leader in the field and provides turn-key solutions. More information can be found in the following link: http://www.dionex.com/en-us/columns-acc ... 60689.html

When using PA2 column and suppressed conductivity detection, I recommend that you do need an IC system described in the poster I mentioned in the previous poster. Please note that MeCN/borate buffer mobile phase system is not volatile, thus not compatible with ELSD. What it provides is good sensitivity (LOD~10 ppb) and excellent selectivity (all cationic and neutral species in the sample are "transparent").

Thanks for reading.

[vikmurush]

Thank you verymuch XL for your information. I will definetely try your suggestion. I will try this and correct me if there is anything i could do

C18 column if it dont work acclaim

detection by ELSD

mobilephase: Acetonitrile with 20mM ammonium acetate
Sample diluent: water

Please add your suggestions

Thanks again

[XL]

Here is my recommendation:

If the sample contains higher concentration SLS (>20 ppm), you have two options:

The first option is to use a reversed-phase column (if you already have one) with MeCN/NH4OAc mobile phase with ELSD. The buffer concentration can be 20 to 50-mM since you need certain ionic strength to make SLS behave itself (better peak shape). You need to experiment the MeCN content. I would start from 40% MeCN and go from there. However, you might run into problem like other components interfere with SLS and you don't have much control over the selectivity of a RP column.

Therefore, I prefer to use Acclaim Surfactant column with MeCN/NH4OAc mobile phase with ELSD. With this column, you can easily adjust the mobile phase to avoid the potwential interferences because of the uniqueness of the column chemistry. The mobile phase is MeCN/100 mM NH4OAc v/v 75/25. You can tune the retention of SLS in the range of 2 to 6 by adjust NH4OAc concentration and/or MeCN content. In addition, if you need to work with other surfactants such as cationic ones, this column is your best choice.

If you are sure you will deal with sample that contains less than 10 ppm, or even 1 ppm, SLS and this application is an important part of your work, I would strongly recommend the RP-LC/suppressed conductivity detection method. The first poster I gave you contains the instrumentation information as well as other details. If you want to go with this route, please contact me so that I will direct you to appropriate party that will help you further.

[vikmurush]

Thank you XL. I will first try with ELSD using acclaim column and if i dont get what i want i will definetely contact you about further details.

Thanks again