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This is the sentence which is assumingly wrong:

Solvent remains which could not have been evaporated were removed by [...].

The problem I have here is that the attempted evaporation of the solvent remains took place before the removal while the time at which the sentence takes place is in the past. I simply wanted to put which could not have been evaporated into the past perfect (while the remaining sentence is in the past simple) but since can is an auxiliary verb I do not know how to form it. The paraphrase able to is not really applicable to this problem either.

So how do I express this sentence properly?

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  • Could not have been done by me. But not: x could have been evaporated. Just: could not have evaporated. evaporate cannot be used in the passive form. – Lambie Jun 5 '19 at 18:11
  • It's not important whether you tried and failed to remove the solvent, as long as you got it out somehow. Thus, Solvent remains which had not evaporated were removed by [...] is sufficient. – John Lawler Jun 12 '20 at 1:30
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Although you say that the paraphrase 'able to' isn't applicable, paraphrasing with 'able to' is the only way to create perfect forms of 'can'. Using the past perfect, you would have:

Solvent remains which had not been able to be evaporated were removed by [...].
OR: Solvent remains which we had not been able to evaporate were removed by [...].

Unfortunately while the above is grammatically correct, it's quite awkward. This is therefore a good case for collapsing the tenses, avoiding perfect forms and using simple past for both clauses. In this case the sequence of events can be understood from context without using the past perfect:

Solvent remains which could not be evaporated were removed by [...].

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Your example sentence can be rephrased in the following way:

Solvent remains which had not evaporated were removed by [ . . .].

However, if you want to express the "could not have" piece, you can also phrase it this way:

Solvent remains which would not have evaporated were removed by [ . . .].

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The paraphrase able to is applicable here, if a past perfect form is absolutely required.

Solvent remains that we had not been able to evaporate were removed by...

but there are simpler ways that don't require such a long verb phrase:

(After evaporation,) any remaining solvent was removed by ...

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