redfox

I’ve been presented with a one man study that has very little information. The one presenting it is trying to prove that silver is easily excreted from the body. This is the entire materials and methods portion. I know nothing about testing for the presence of silver but this doesn’t seem complete to me. can someone please tell me what’s missing and what they could have done instead? thanks ’ The present study is based on using a 180-volt DC current between a stainless steel container (cathode) and a silver strip (anode) suspended in about a half gallon of distilled water (less than 2 ppm total dissolved solids). The water distiller, as well as the electrolytic set-up and power supply, were commercial units purchased through the Internet. A milliammeter was added to the circuit to measure current to both monitor and help achieve process reproducibility.’

Ah ok, I know very (very) little about plants and hadn't really thought about the contents of the membranes being released. Something to consider in future! Thanks:)

I've recently frozen some guacamole with listeria in it. The original pH was about 6.5 then we added some citric and ascorbic acid, bringing the pH down to about 4.9 - tested several times. When removed and thawed out the listeria died off more than expected so we tested the pH again to find that it had gone below the critical level of 4.1. What might make it drop by this much? I know pH is affected by temperature, but could it have a lasting effect even once thawed and back at room temperature? Obviously everything was not back in its pre-frozen state so I'm thinking it was permanently damaged and that's perhaps why the pH was different. But do -10 and -20 degrees take the pH down or is that more likely to raise it and something else was a factor in lowering it? Or perhaps the acid had more of an effect once the product was frozen? Could the pH actually go up by a lower temperature? Really don't know how to even test which theory is accurate without repeating the experiment with no acid added - but unfortunately that's not possible at this stage. Any ideas?

Naturally and normally speaking a person cannot be brought back to life once brain activity has stopped for a substantial amount of time (about 10 minutes) but there have been several documented cases of people being in this state for much longer and still coming back without any problems. Those are the few and far between bizarre cases though!

Hi all I need to determine the amount of acid in guacamole at different pH levels. Our autotitrator has broken so I must do it manually. Problem is I've not done a titration in the last 5 years or so and also, as it's with guacamole, I'm not sure how much to dilute it or what to use as an indicator. Could anyone give me some guidance on the best way of going about this please? Thanks very much:)

I need to grow up Listeria monocytogenes and have been instructed to use Tryptone Soya Agar as the growth medium, however I would have thought Heart Brain infusion would be better. Can anyone please tell me how I must decide which is best? Should I not use HIB cos it would grow absolutely everything and TSA is more selective? Will TSA grow ALL the listeria present? Cheers:)

Ok, thanks for your reply. I've started to write up the protocol. However I have a few more questions now! How do I know how what inoculum level to use and when do I take the L.m for inoculation - at lag, log or stationary phase? How many repetitions must I use? What should the intervals of testing be for a product of 30 days shelf-life? I'm sure there must be articles with information out there but I've been looking for 3 days now and can't find anything on the lag/log/sta... and everyone seems to say 'use 3 reps minimum' but I need a little more info than that. Unfortunately I must present the final plan before I can do any testing so there's not much room for error here! Thanks again:)

I need to do a challenge test on L.Monocytogenes in guacamole. I'm to reduce the CFU/g through changing temperature and pH (the primary focus is on pH). Only problem is - I've never done a challenge test before. Can anyone help me out and point me to a list of steps I need to take to do the tests please? I've searched the net for quite some time but the information isn't terribly relevant. Thanks:)

Hah, I would but I don't know all the details of everything yet;) It's ok as a starting point, but should never be used for reference. It's not that I think it's rubbish in every aspect, but considering I could just go in there and change it with no knowledge on a subject...I think that says a lot about it's reliability:) Anyway, thanks for advice everyone. Yes the question was about why it dissolves in acid and bases and not water. I think acids, bases and pH7 of water is a hint. Maybe it's because it's zwitterionic and needs a definite electron acceptor/donator. I think. The structure must have something to do with it, but I'm not entirely sure what...

Erm, first of all NEVER use wikipedia, it's a pile of poo! And monkeys probably write half the stuff on there;) Second, it is classed as poorly water soluble, this is because it takes around 2000ml of water to dissolve 1g of Theobromine. It's called water-insoluble 'cos that's far above the amount it would require if it were water-soluble, however it's not technically 'insoluble'. Thanks for the response tho, I reckon it is something to do with pH...

I'm sure this is simple enough but for some reason my brain is not willing to work with me! Theobromine (a structural analogue of caffeine) dissolves easily in acids and bases, but is poorly soluble in water. Why is that?? Thanks for any advice offered:)

Hi, I need to draw a cubic and triclinic unit cell and label the axes and angles...how do I know how to correctly label the axes and angles? Are there any good sites I can look at for beginning x-ray crystallography studies? Ta!

Thanks, very helpful!

Ok, thanks for reply. How do I know what will be substituted/added for other questions tho? Are there some general rules for this?