Pro-Par Clearant

Flash point and fire rating are important for storage and disposal. Unlike flammable materials, combustible liquids usually do not require specialized storage containers and cabinets. They also do not incur freight surcharges when shipped via ground transport. Products with flash points below 100° F should be avoided, particularly since they offer no counterbalancing advantages.

Molecular size (chain length) determines evaporation rate, feel, coverslip drying time and boiling point (important in recycling). Short-chain aliphatics outperform their longer chain relatives on all counts. You do not need a clearant that is little more than light mineral oil.

Drain disposal is touted as an advantage by suppliers of some long-chain aliphatics, but the simple fact of the matter is that all clearants are insoluble in water and hence not suitable for wastewater treatment plants. No aliphatic is biodegradable in any reasonable time period (1-3 days) appropriate for wastewater treatment.

Aliphatics are notoriously intolerant of water, and only one, PRO-PAR, has any ability at all to deal with it. This has made PRO-PAR a leader in its field because it poses fewer problems for users. That, plus the extraordinary level of technical support behind the product, means that it should be your clearant of choice.

There are just five things to keep in mind when using PRO-PAR. Follow these recommendations and you should make the transition smoothly. Note that none of the items is burdensome.

First, use three stations of clearant on the processor, usually for 45-60 minutes each (unless the run is short anyway for biopsies). Rotate after every 3-5 runs if the processor is filled to capacity, throwing one away each rotation. Stretch your rotation if the load is lighter. In addition to allowing longer rotation periods, having three stations lets you do a better job of removing the fat from troublesome bowel, breast and brain specimens. Unlike xylene, PRO-PAR will not harden or dry the delicate specimens. By the way, you may purge the processor with PRO-PAR. If you use a high-polymer wax, we suggest a double purge each time, just to be certain all wax residue is removed.

Second, , use three stations, 3 minutes each, to deparaffinize slides. The textbooks recommend this for xylene, but most labs have shortened the time considerably. You cannot take that shortcut here, but then, you probably should not do it with xylene either, especially for immunohistochemistry. For automatic stainers, note that two stations, 5 minutes each is not the same. You want that third station to economize on reagent usage (your rotation schedule will be better with three stations).

Third, rotate the last anhydrous alcohol after eosin the instant it turns the slightest bit pink. If there is eosin in it, there is water. Too much water will create hazy optical images and may cause bleeding of the eosin from the section after coverslipping. Because of PRO-PAR's limited tolerance for water, this is far less of a problem than you would have with other aliphatics. However, in extremely humid weather, when the alcohol picks moisture out of the atmosphere, it may be impractical to rotate the alcohols frequently enough. For this special case, we have another way to avoid the problem. Call us for details if it might pertain to you.

Fourth, choose your mounting medium with care. Many of the modern products are not compatible with any aliphatic clearant, and the older, yellow media are becoming difficult to get. We, like some other manufacturers of aliphatic clearants, have a suitable product. Ours is called REFRAX. Is it better than the others? It is fast drying and non-oxidizing (stains won't fade). In other words, it works like some of the competition. It is unique in having a reduced toluene content. Mounting media that purportedly contain no xylene or toluene either are very slow to dry or contain other, equally harmful aromatic solvents.

Finally, be aware that aliphatic clearants do not behave like xylene when it comes to coverslipping, even with proper mounting media. Drop a bit of mounting medium onto a slide wet with xylene and the resin immediately flows across the glass. We say that the resin is soluble in xylene. Try the same test with an aliphatic and the resin just sits there in a blob until the weight of the coverslip forces it across the glass. The resin prefers to stay associated with its solvent and thus does not spread out into the clearant. You can coverslip any way you want with our products, but many of our customers have found that coverslipping upside down seems to works better. (To do this, drop the mounting medium onto the coverslip and lower the drained slide over it, pressing the edge against the countertop. It may simply be a matter of what you don't see won't concern you. PRO-PAR may not behave like xylene, but in the end it works just as well.

So that's it: just five little modifications that, once done, should have no impact upon your busy day other than to make it safer.

What about automatic coverslippers? We recommend that xylene be used inside these machines, whether they apply actual coverslips or plastic tape to the slides. Both types of machine depend upon slides being wet with xylene. This is not a serious problem. PRO-PAR is perfectly miscible with xylene. Simply transfer slides out of the last PRO-PAR bath in staining to the chamber filled with xylene within the coverslipper. Your exposure to xylene will be insignificant.

Speaking of coverslipping, you will want a small quantity of xylene or toluene handy in case you must remove a coverslip. PRO-PAR will do the job, but it will take longer than most of you will want to wait. Again, your exposure risk is minimal. By switching to PRO-PAR, you can eliminate exposure to gallons of xylene each day. That is significant.