Friday, 8 March 2013

06:47 – While I was concentrating on other things, the finished-goods inventory of biology kits got away from me. We sold two of those yesterday, which took us down to only three biology kits in stock. We have all the subassemblies to build two more, but that’s still only five total. Fortunately, with minor exceptions, we have all the components we need to build another 60 biology kits, but it will take some time to get those assembled.

One of those exceptions is the 100 mL polypropylene beakers, of which we have only 34 in stock. I have 600 more on order, but they won’t arrive until the end of this month. Biology kits include one of those beakers and chemistry kits two. So I think I’ll build a dozen biology kits, which leaves me enough for 11 more chemistry kits to go with the dozen that are already in finished inventory. We’ll keep our fingers crossed that 17 biology kits and 23 chemistry kits will hold us through the end of the month. Meanwhile, I’ll be getting everything assembled for 60 more biology kits and 48 more chemistry kits, less those beakers.

11:29 – So, I’m down in the lab making up a liter of phosphate-buffered saline 10X concentrate. I opened a new gallon of distilled water, poured some into the container I was using to make up the PBS, and noticed a puddle on the counter top. I’m not usually that sloppy, so I soaked it up with a towel and replaced the gallon jug of DI water on the counter. A moment later, I looked down. There was another puddle. Apparently, just removing the cap from the jug was enough to start it leaking. I’ve never had that happen before.

One can buy PBS tablets that simply need to be dissolved in the specified amount of DI water to make up PBS, but I didn’t have any. So I made up the PBS from reagent-grade sodium chloride, sodium hydroxide, potassium hydroxide, and phosphoric acid. I was using a clean 1-liter softdrink bottle as a disposable mixing container, planning to transfer the solution later to a 1-liter polypropylene bottle and autoclave it to sterilize it. Then I realized that autoclaving was gratuitous. Of course, I’ll autoclave the working dilution before using it, but I wanted the 10X concentrate sterile as well just to make sure nothing grew in it. But of course I didn’t need to autoclave to sterilize the 10X batch. I’d already dissolved the sodium hydroxide and potassium hydroxide in 250 mL of so of DI water, making a solution that was extremely alkaline, probably 0.5 molar with respect to hydroxide. More than enough to kill microorganisms and spores on contact. So I transferred that solution to the 1-liter bottle, swished it around to contact all parts of the bottle and cap, and declared the storage bottle sterile. I then added the phosphoric acid, creating the buffer, and topped up with DI water. That should be sufficient. It’s a water-clear solution in clear plastic bottle. If the next time I pull it out it looks at all cloudy, I’ll just autoclave the hell out of it. But I don’t think that’ll be necessary.