Breaking Bad | Season 4 | Episode 1 | “Box Cutter”
Breaking Bad returns after what feels like several years, bludgeoning aside any speculation about a slow, gentle opening to season four. Walt and Jesse get to go back to work, but not until Gus makes it clear just what kind of business they are in. In this post, I’ll be talking about gas chromatography and Walt’s pop quiz.
Gale mentions that he would need a gas chromatograph to confirm just how pure Walt’s product is. A gas chromatograph is an analytical instrument designed to separate the components of a chemical mixture – by running a sample of Walt’s methamphetamine and comparing it to standard solutions of known concentration, Gale could figure out exactly how much of the sample is meth and how much is contaminant.
Chromatography generally works by moving a stream of gas or liquid, called the mobile phase, through a column of solid material, called the stationary phase. The sample is dissolved in the mobile phase, and different components of the sample will travel faster or slower through the stationary phase depending on their chemical or physical properties. By analysing the output of the chromatograph over time, we can figure out how much of each component is present (we can also identify each component as it exits the instrument if we couple the chromatograph to something like a mass spectrometer).
Without access to analytical instrumentation, Gale might have had quite a hard time working out that Walt’s product is 99 % pure. He could have done a very accurate melting point determination (the melting point will change as the sample becomes less pure), a fractional distillation or some kind of specific chemical reaction followed by weighing of a precipitate. It would also help to have a pure (i.e. 100 % pure) sample to refer to, otherwise statistical methods may have to be used to infer how much is present.
Walt’s blustering is based on sound chemistry, as we might expect. Here are the answers to his impromptu test:
Catalytic hydrogenation, is it protic or aprotic? Because I forgot.
Possibly a trick question. Hydrogenation is the process of adding hydrogen to something, usually across a double or triple bond and usually in the presence of a catalyst (hence, catalytic). Walt is referring to his trademark reductive amination, which adds hydrogen across a C=N double bond. Protic and aprotic refer to proton-donating and non-proton-donating solvents respectively (a proton is equivalent to a hydrogen ion, H+). Victor might claim that as we are adding hydrogen, the reduction has to be protic.
And if our reduction is not stereospecific, then how can our product be enantiomerically pure?
Another trick question! A stereospecific reaction is one that gives us exclusively one stereoisomer (as opposed to a stereoselective one, which merely favours one stereoisomer, or a non-selective one, which gives roughly equal amounts of all stereoisomers). Stereoisomers are molecules that have the same chemical composition and arrangement of atoms, but differ in their three-dimensional structure.
However, Walt asks about enantiomeric purity. Enantiomers are molecules that have the same chemical composition and arrangement of atoms, but differ in their three-dimensional structure in that they are non-superimposable mirror images. They are a specific sub-class of stereoisomer.
Methamphetaime is chiral, as we have seen before. Walt is suggesting that if Victor does not control his reduction, he will get a mixture of the psychoactive and non-psychoactive versions and hence a much-diluted product. However, Victor should contemptuously reply that stereospecificity does not imply enantiospecificity.
For background information on this topic, see the primer on chirality.
I mean, it’s one phenyl, one hydroxy two methyl aminopropane, containing of course chiral centres at carbons number one and two on the propane chain. Then, reduction to methamphetamine eliminates which chiral centre is it again? Because I forgot.
1-phenyl-1-hydroxy-2-methylaminopropane is one possible systematic chemical name for pseudoephedrine, a precursor (along with ephedrine) for methamphetamine. Is this another trick question? Walt’s method does not use pseudoephedrine anymore (which is why the product is blue), and so Victor could just remind Walt of that. However, the actual answer is the chiral centre at carbon number one – chirality is lost when the hydroxy group is removed.
For all Walt’s posturing, Victor has a surprisingly accurate answer: It’s called a cook because everything comes down to following a recipe. This is true for many industrial processes – if you use the right starting materials and follow the steps correctly (steps, we might add, that have been arrived at through long hours of experimentation and analysis), you’ll get the product you want. Walt’s comeback is equally accurate – if anything goes wrong or you get some kind of contamination or a change in conditions, you’ll need a chemist to diagnose and fix things.
Pfizer and Merck (known as Merck Sharp & Dohme outside of the USA) are, as you probably know, gigantic pharmaceutical manufacturers. They are ranked first and third respectively in terms of annual revenue (the second is Novartis).
“We have our work cut out for us, so to speak.” Is that a drug reference, Gale? We miss you.
Good to see that Gale keeps an accurate notebook – absolutely essential in a professional lab.
Victor’s chemical-pouring technique isn’t that great (though he is only a short-order cook, according to Walt) – he should be using a funnel, siphon or some kind of pump to avoid spilling.
Hank is bidding on Canadian magnesite, a fairly common mineral. The brown colour is probably caused by iron impurities.
Gale’s brew-o-matic is still seeing use. Hopefully the spectacular coffee at Los Pollos Hermanos isn’t attracting suspicion.
Walt and Jesse use a plastic container for HF body-disposal this time. Lesson learned!
Elements in the credits
|StewArt A. Lyons||Argon|