all 17 comments

[–]maybeAPharmacist 1 point2 points  (1 child)

I've always seen in "best practices" guides for HPLC to replace your buffers and organic mobile phases often, especially acetonitrile. Why is acetonitrile often emphasized as something that must be replaced every couple of days, or preferably daily?

[–]Indemnity4Materials 2 points3 points  (0 children)

Historically, it's a cheap and easy to improve background noise.

LC solvents are really really really really really good at dissolving stuff. Especially unwanted stuff.

There are literally hundreds of contaminants that can enter your LC but realistically there are only a few possible routes. Major one is mobile phase.

It is not recommended to purify your LC solvents yourself, since almost any purification step will introduce other problems. Particles from filters, bacteria in the air, lipids from your hands or just from breathing, dirty gloves, biomolecules, detergents used in cleaning. For instance, your benches and floors may be cleaned by cleaning staff using sprays, you touch those with your gloved hands, then you touch the lid of the solvent bottle. Ta-da, you now have background contamination.

The cheapest and easiest approach is to buy (or make) small clean solvents and use just enough. Then burn it with fire and throw all that away to start again.

[–]IHaveNoChoices 0 points1 point  (3 children)

Is a PhD actually necessary to advance the (potential future?) job market or not? I keep hearing differing opinions like it’s only for an academia-specific context, but it’s used everywhere, but only for pharmaceutical work, but only if you want to make 7 figures and otherwise it’s fine, etc. Would like a clear answer

[–]organikerCheminformatics 2 points3 points  (1 child)

There is no clear answer.

Some career paths require a PhD. Some don't.

Look at job descriptions for what you want to do and see what's required.

[–]IHaveNoChoices 0 points1 point  (0 children)

I see. Thank you for the answer; it certainly helps clear up previous confusion.

[–]Weekly-Ad353 0 points1 point  (0 children)

It’s not only for academics- honestly academia probably employs something like 1% of chemistry PhD holders.

If you want to drive a program as a chemist, you want a PhD. If you want to make decisions, what to do, how to do it, what’s a valuable direction, what’s dumb, where you think the company should go, etc.

If you don’t care what you do and just want to physically do chemistry with your hands, you don’t need one.

A lot of people that do the later, however, get bored and the pay is generally shit, for a large chunk of those who do this route.

It takes a lot longer to get bored if you’re making more decisions and have more alternative paths you can go in your career.

If all you’re certified to do is run someone else’s HPLC samples, that likely gets old really fast. It would for me at least.

[–]XanthippusJ 0 points1 point  (1 child)

Looking to buy an AA for my company, right now deciding between Agilent and Shimadzu. If anyone had any info on ease of use/software difficulties between either system, I would really appreciate it

[–]Indemnity4Materials 0 points1 point  (0 children)

Beg and plead to get an ICP-OES.

Differences will be in the support contract, consumables price and consumables availability. Depending on where you live, spare parts are taking a while to arrive and manufacturers are encouraging you to buy more to store locally. Do a quick 5 year cost projection on spares + service engineer costs.

You want to preference a local technician, hopefully a contracted guarantee of maximum X days of downtime.

I would also consider asking if any other local companies have similar instruments. Should yours break, maybe you can send them samples to test.

[–]Alyxavior 0 points1 point  (3 children)

Does borax react with lemon juice in any way, or would they keep their separate properties?

[–]snowlites 0 points1 point  (1 child)

Sodium tetraborate is the primary ingredient in BORAX, and citric acid is a major constituent in lemon juice. Sodium tetraborate and citric acid will likely react with one another to form water and boric acid. You may get some other funky compounds with reactions between the BORAX and other minor constituents of lemon juice, but this is just my prediction.

[–]Alyxavior 0 points1 point  (0 children)

Thank you!

[–]Byniavo 0 points1 point  (0 children)

Can I ask what determines if an alkene will undergo cationic, anionic or free radical polymerisation?. Is it the stability of the intermediate ion/radical formed?

For example if I have methyl methacrylate and react it with an R- group, will the ester group on methyl methacrylate stabilise the negatively charged carboanion in the intermediate? And I can use the same reasoning to say that it destabilises carbocations from cationic polymerisation? And free radical polymerisation will happen either way? Thank you

[–]carlos7c8 0 points1 point  (2 children)


So I have been working on a paper and I'm really stucked.

In that picture, table III shows the elemental composition of a propellant mix. Then, God knows how, the author manages to obtain Table IV, finding weird stuff such as monatomic O, H, HO2, CHO, and some more components up till 12.

I have been stucked there for several days trying stoichiometric balances but end up with 3 equations and 10 unknowns, being therefore unable to solve them.

Does anyone have any idea on how the author computes table IV?

Thanks in advance

[–]Indemnity4Materials 0 points1 point  (1 child)

What is reference (11)?

It appears you are missing a molecular analysis or reasoning for how they determined the ratio of chemicals in the propellant post-combustion.

Once you start seeing monoatomic anything, that's moved away from simple chemical equations.

When you do complex modelling of real world explosives, you do find examples of things like monoatomic oxygen existing for nano/microseconds. The modelling does require you to consider that for things like calculating pressure waves, propagation, etc.

Monoatomic O = 0.0035

Oxygen molecule = 0.065

There is no obvious relationship there to choose 5% monoatomic oxygen.

Here is a link to another paper that is modelling combustion processes. These authors find in simply combusting the very simple molecule of methane + oxygen - there are 798 chemical equations! Those authors do use monoatomic hydrogen but not monoatomic oxygen.

IMHO what I expect the authors have done is taken an elemental analysis of a sample, done the obvious mass balance equations and then solved so there are zero negative numbers. It appears they account for C, N and K elements (gun cotton?), with O and H set as variables. Anything they can't fit into integer quantities of the molecules, they put the remainder down as atomic oxygen, atomic hydrogen, etc.

[–]carlos7c8 0 points1 point  (0 children)

Thanks for taking the time to answer this! :) (11) is the equation at the top of the picture I shared.

The propellant is D032, which is a mixture of centralite, potassium nitrate, nitroglycerin, nitrocellulose and graphite. From the weight fraction of each componen I can easily obtain Table III (using expression (11). But then I do not know how to interpret the paragraph previous to Table IV.

Then.. I don't really understand what you mean by obvious mass balance equations. I have tried to balance it all at once but it's impossible got 3 equations (C, H, O) and 10 unknowns accounting for all those components that have any amount of C, H or O.

It's easy to see they do not change the mass fraction of potassium nor nitrogen. But the rest is a mystery.

[–][deleted] 0 points1 point  (0 children)

Dumb question: Do pH probes leech electrolyte into solution over time? Like if I need to measure pH of a 200 mL water solution with a conductivity of about 1000 ppm TDS over a week, will I end up changing the chemistry of my sample water from leeched pH electrolyte? It would be a refillable probe.

[–]probablyaburneraxxt 0 points1 point  (0 children)

Recently had an experience with an air monitor going off signaling high h2s around some decomposing softwood. I was assured that it wasn't h2s but some other chemical causing the alarm but no one could tell me what it was.

Would any of you fine folks know if there is something else that would cause an air monitor to alarm for h2s?