preservatives in laundry detergents

Discussions about sample preparation: extraction, cleanup, derivatization, etc.

8 posts Page 1 of 1
Hi everybody! and thxs in advance for your valuable time and help :-)
Could any of you give me some initial hints to develop a method for the determination of preservatives (classic ones, BIT, MIT pyrithione ...) in liquid soaps, and laundry detergents with the mínimum sample cleanup ?
I tried with a sort of SPE in C18 phases but recoveries were low and chroms stills pretty dirty...
many thanks!!

Tiron
Tiron wrote:
Hi everybody! and thxs in advance for your valuable time and help :-)
Could any of you give me some initial hints to develop a method for the determination of preservatives (classic ones, BIT, MIT pyrithione ...) in liquid soaps, and laundry detergents with the mínimum sample cleanup ?
I tried with a sort of SPE in C18 phases but recoveries were low and chroms stills pretty dirty...
many thanks!! Tiron



I make my living doing stuff like this!

We assay for MIT, CMIT, BIT preservatives by diluting the sample with water or methanol, then filtering; that's it, no SPE or clean up, over 30 years now.

We haven't modified our test methodology much over that time except to move to some more-modern (read: available/able to be purchased) C18 columns, nothing special needed. We do use gradient, starting at quite low organic, and with a 100% organic clean up step built in to the gradient (very important), before the requisite post-run equilibration. We've used both methanol and ACN as the organic, primary difference is lower pressure (duh !) using ACN. The aqueous phase has a little acid in it, but we've never had the need to study this. We use UV detection for these, with a higher wavelength used for BIT as it's more sensitive there than the wavelength used for MIT and CMIT (chlorinated MIT/Kathon). No, we don't use a nonspecific wavelength like 220nm either, and we typically inject 3µl.

As to pyrithione, we've only assayed for that in hair products at down to 0.1% level, or as sodium omadine in a different product (where it was fully degraded within 2 days). That's a tougher assay, but the higher detection wavelength helps with specificity there too.

We've done other preservatives too in consumer products, like parabens, phenoyxethanol, antioxidants.....puts food on the table....
Consumer Products Guy wrote:
Tiron wrote:
Hi everybody! and thxs in advance for your valuable time and help :-)
Could any of you give me some initial hints to develop a method for the determination of preservatives (classic ones, BIT, MIT pyrithione ...) in liquid soaps, and laundry detergents with the mínimum sample cleanup ?
I tried with a sort of SPE in C18 phases but recoveries were low and chroms stills pretty dirty...
many thanks!! Tiron



I make my living doing stuff like this!

We assay for MIT, CMIT, BIT preservatives by diluting the sample with water or methanol, then filtering; that's it, no SPE or clean up, over 30 years now.

We haven't modified our test methodology much over that time except to move to some more-modern (read: available/able to be purchased) C18 columns, nothing special needed. We do use gradient, starting at quite low organic, and with a 100% organic clean up step built in to the gradient (very important), before the requisite post-run equilibration. We've used both methanol and ACN as the organic, primary difference is lower pressure (duh !) using ACN. The aqueous phase has a little acid in it, but we've never had the need to study this. We use UV detection for these, with a higher wavelength used for BIT as it's more sensitive there than the wavelength used for MIT and CMIT (chlorinated MIT/Kathon). No, we don't use a nonspecific wavelength like 220nm either, and we typically inject 3µl.

As to pyrithione, we've only assayed for that in hair products at down to 0.1% level, or as sodium omadine in a different product (where it was fully degraded within 2 days). That's a tougher assay, but the higher detection wavelength helps with specificity there too.

We've done other preservatives too in consumer products, like parabens, phenoyxethanol, antioxidants.....puts food on the table....



You've heard it from "the guy', so there's no beating that! If you do want to clean-up first (my bias), you can transfer the assay to preparative HPLC to collect just the fractions that contain your analytes.

Don
Don Shelly
LGC Standards
Many thanks !!! I appreciate very much your answers !!

@"the guy" - Thank you for this detailed description. There is plenty of useful details in your answer!!... I learnt I should explore a bit further the HPLC method, as initially I got some overlapping and I thought I'd need some clean up to proceed. But I'll insist in getting a nice separation before anything else... and I'll work as you recomended.

@Don - Thank you also for the PrepHPLC hint. Much more elaborated approach, but I note that as an alternative.

Tiron.
Hi everybody!
Since the days I posted my first comment about determination of preservatives I left apart the determination of sodium omadine... but now I have to face it !
After some intial tests I noticed it won't be an easy one. The high complexing capacity of pyrithione and the reactivity of the thiol group are causing some troubles in my initial strategies for the method development (HPLC)
I know some of you have great skills dealing with this kinds of products ... so any initial hint to find a working HPLC method would be of unvaluable help.
I am thiking on derivatization as an alternative to the bad compound behavior but aqueous matrix a well as the high number of samples to process are clear drawbacks, and I want to get rid of any intermediate steps if possible.

many thanks for your advice!

Tiron.
What level of Na omadine are you looking for? Anyway, in the past a product had used Na omadine as preservative (it didn't stay around too long) and we were asked to assay for it.

We developed two ways.

Underivatized: C18 column, 290 nm UV, Mobile phase was 8% H3PO4 as the aqueous phase, and ACN as the organic. We held at 20% ACN for a few minutes, then programmed in the ACN and then kept ACN steady at like 80-90% to clean off the column, then requilibrated at starting conditions.

Derivatized: we used NBD-Cl derivatizing chemical: NBD reagent: weigh 0.14 – 0.16 g NBD-Cl into a vial; add 15.0 ml ACN and mix well. Protect from light. We used C18 column, 400 nm detection (visible), and H2O-ACN gradient.

Have fun.
Many thanks CPG !!!
I already owe you a beer for the info ! :D
I'll test the H3PO4 method and I'll definitelly give a try to the derivatization.
Levels of Na Omadine are in the range of 50 to 500 ppm

I'll keep you updated!!

Tiron.
Tiron wrote:
Many thanks CPG !!!
I already owe you a beer for the info ! :D


I'm ready !
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