Re: [Histonet] Off topic_recycling xylene

From:Bryan Llewellyn

I think you are forgetting the context in which the comments are made. The 
impetus for recycling of histological grade xylene as done by histotechs is 
to avoid disposal costs usually, and as a bonus it reduces the amount spent 
on new supply. Due to those two factors it becomes cost effective. Again to 
a histotech, that means the costs are lowered and some money is left over. 
>From the histotech's viewpoint xylene is good when it is pure enough to 
remove ethanol or some other dehydrant and make the tissue 
transparent/translucent and easily infiltrated with paraffin wax.

When it is said that recycled xylene is "better", "purer" or some other 
superlative, they are really saying that it accomplishes that function well, 
perhaps even slightly better than fresh xylene. My own experience from many 
years of recycling, is that the recycled stuff was as good as the fresh 
stuff, but not particularly better. We did use fresh xylene prior to 
coverslipping, but that was just to be sure and had no factual basis.

Bryan Llewellyn

----- Original Message ----- 
Sent: Saturday, March 17, 2007 10:07 PM
Subject: [Histonet] Off topic_recycling xylene

>     This post is an inquiry regarding recycling of xylene in histology 
> labs but is kind of off topic so please simply delete at will.  I like to 
> use the HistoNet for scientific inquiry and not debate.
>     I fully support the concept of recycling of xylene in histology labs. 
> But for several years, I've read on the HistoNet many statements from 
> users of various recycling instruments and am curious about their 
> declarative statements.  I've read that with (name the brand) recycler, 
> the xylene becomes "purer".  The xylene is "better".  All the impurities 
> are completely removed.  You get purer xylene than you started with.  The 
> xylene is absolutely pure.  All contaminants, even those that came in the 
> bottle, are removed in recycling.  A whole set of declarations that I'm 
> finding hard to accept at face value.
>     When we went through a large study,  trying to figure out in a former 
> lab if recycled xylene was good for us, we collected and had analyzed 
> sample after sample from bottles, before recycling after recycling and 
> after multiple recyclings.  Had them analyzed by gas chromatography at a 
> good reference lab.  Although the recycling worked, we saw little in the 
> change of the readout from pure to recycled.  A bit of a change but not 
> much to affect anything.  So we recycled and were happy.
>     It is my understanding that tens of millions of pounds of xylenes are 
> produced every year.  Histologic grade mixed xylenes (o-, m- and p-) come 
> with a good percentage of ethyl benzene and a minor percentage of various 
> other hydrocarbon contaminants.  To remove ethylbenzene and these other 
> contaminants to obtain pure xylenes (needed for upstream processes) 
> requires 100 million dollar chemical plants, hydrogen atmospheres, 
> catalysts and 200 foot high fractionation columns.
>     Do the people who are saying that their lab recyclers are removing 
> these contaminants, follow this xylene stream with critical GC testing? 
> If the xylenes are "better" or "purer" why are there all the warnings to 
> not use recycled xylene for certain procedures?  It is "too" pure?  Is 
> there such a thing?   If this is so easy to accomplish it seems that one 
> could buy a (your brand) recycler, find the cheapest mixed histologic 
> grade xylene you can find, don't use it for histology but simply recycle 
> it, bottle it in 25 or 100 ml bottles as ultrapure for HPLC or gold 
> standard mass spec analysis for 100 times the cost of the original impure 
> xylene and retire rich.
>     I agree xylene recyling is cost-efficient, morally acceptable, 
> environmentally friendly, useful, efficient and everything else.  I'm 
> having a hard time accepting that these common lab recyclers do so easily 
> what it takes massive chemical plants and incredible organic chemistry 
> know how to do.
>     If anyone has read this far, and you do recycling of xylene, I'd like 
> to hear about your thoughts on the subject.
> Raymond Koelling
> Phenopath Laboratories
> Seattle, WA
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