Making Solutions

It often seems to me that the art (or science) of making solutions is becoming a lost one. In this current day and age when most of our solutions come in a pre-made form and only require mixing, or at most, thawing and mixing, I believe we’re losing the ability to make solutions ourselves.

This thought came to me when I overheard a comment in a hallway about a shortage of physiological saline. It was back-ordered and we’d be in dire straits soon if we didn’t get any in. And I wondered: if we have solid sodium chloride in the laboratory and we have water, how can we have a shortage of physiological saline? And physiological saline is incredibly easy because you don’t even need to know the molecular weight of sodium chloride. If you want 0.9% physiological saline, that 0.9 grams of NaCl in 100 ml of water.

The same is true for any other easily made-up solution. We’re so used to having them pre-made for us, that we’re forgetting everything we learned in school about how to make solutions. Of course, being able to make solutions from scratch does presuppose that the lab still has chemicals, a balance and a pure water source. My lab does, but that’s because we run a lot of laboratory developed tests (LDT). Most laboratories may no longer keep chemicals, and even if they do, using a home-made reagent turns your assay into a LDT. Plus so many pre-made reagents have proprietary formulas that making them up from scratch is not possible. But for simple reagents like physiological saline, that perhaps is being used to perform dilutions or wash cells, I find it kind of sad that we rely on “store bought” reagents so much that we never consider making them ourselves. In that respect, I guess I’m something of a lab dinosaur.

Don’t get me wrong. I’m totally in favor of making our lab lives as easy as possible and pre-made solutions are one of the wonderful things that do that for us. In addition, if you buy pre-made reagents, you remove one variable that can affect results – was the reagent made up correctly, using the correct chemicals. On the other hand, I believe it’s also a good idea to know how to make up a solution if you should need to do so.

It’s a little comforting to know that this loss of ability may not be confined to the lab. I heard a pharmacist talk about a shortage of total parenteral nutrition (TPN) solution, which I suspect at one time every pharmacist knew how to make up from scratch.



-Patti Jones PhD, DABCC, FACB, is the Clinical Director of the Chemistry and Metabolic Disease Laboratories at Children’s Medical Center in Dallas, TX and a Professor of Pathology at University of Texas Southwestern Medical Center in Dallas.

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