the use of article

09:44 Nov 8, 2019 

I'd surmise the problem is that the poster is not looking at the translation with an English Native Speaker's eyes.

08:27 Nov 8, 2019 

I think you are over-thinking this!
If you just say 'chromatograph solutions A and B', it would normally not be assumed you were going to mix them! The default situation would simply be that you would do them separately.
If, however, it was required to combine them, then that non-default situation would be required to be specifically indicated in some way.
I would tend to avoid 'consecutively', which tends to have a temporal connotation that is not necessary here; if you really feel some adverb is necessary to make it completely explicit and remove all possibility of ambiguity, I would simply use 'separately'.

05:06 Nov 8, 2019 

It has just dawned on me I'd use "chromatograph consecutively sol. A and sol. B" instead of making a cocktail of the 2 solutions. Am I right?

12:51 Nov 7, 2019 

As I speak Polish, Russian, and English, I understand the difficulty of using the article system. BTW - the article system usage is also different in German and French. Other than in idiomatic expressions, the usage of articles follows grammatical rules.

12:28 Nov 7, 2019 

This issue of whether or not to use a definite article poses a problem for speakers of certain languages, including I believe RU, due to the different structure of their own language.
It's important to note, however, that it is not merely a question of "what sounds best"; certainly, the presence or not may make the sentence read better — but there is also an element that may change the sense: perhaps not the broader meaning, but certainly, the nuance of expression behind it.
Using 'the' implies there is something specific about what follows, whereas its absence implies a certain generality. See if these examples help:

"Add the solution [that we've just been talking about] to the mixture described"
"Dilute the [= specific] solution using [some] water"
"Measure out equal quantities of glycerine and nitric acid, then add the acid [that you've just measured out] to the glycerine [ditto]

Sometimes you can add or omit the def. article freely — but you always need to bear in mind this "rule of thumb" to decide whether its presence might be necessary / desirable.

11:55 Nov 7, 2019 

Yes, both "the" should be kept with a suitably modified sentence, as suggested below.

08:37 Nov 7, 2019 

Tony M. It looks almost as if you want to use "each" at all costs, but If you are open to good advice, take Tony's and replace your "each" with "both". And leave the second "the" in - it simply sounds better to the ENS ear.

07:18 Nov 7, 2019 

Either you have to use 'all' — which leaves little room for ambiguity, since you would be unlikely to make a "cocktail" of several solutions!
Or else you have to use 'each', but with one of the modified wordings suggested, like 'each of' etc., to make it idiomatic.

06:19 Nov 7, 2019 

The key point is that the solutions are to be chromatographed separately! But when the number of solutions is MT 2, how can I use "both" instead of "each"?

12:51 Nov 3, 2019 

In other words:
"Chromatograph XX μL of each, that is, the test solution and the YYYYYYYY RS solution."
"Chromatograph XX μL of both the test solution and the YYYYYYYY RS solution."

So, one can keep both "the" in the sentence.

10:21 Nov 3, 2019 

with Tony M's entry just below; IMO, the answer posted could be misleading.

09:19 Nov 3, 2019 

As M.A.B. highlights, 'each the test solution' is quite wrong here; however, I suspect in fact the problem is not 'the', but rather, your attempted use of 'each'. I think if you are trying to say "make 1 chromatograph of each of: the test solution + solution XYZ", then you need to express it like that; however, it may not necessaily be essential to spell it out quite so literally, as people would naturally expect the solutions to be chromatographed separately! Or you could say "make chromatographs of the test solution + solution XYZ"
Otherwise, the way you are trying to express it here would often be expressed by using 'both' in EN instead of 'each'.

07:45 Nov 3, 2019 

but certainly not "each the test solution"; either "each test solution" or "each of the test solutions"