Table 2.

Techniques used for the extraction of antiviral drugs from biological matrices with their main advantages and drawbacks.

Extraction technique	Matrices	Advantages	Drawbacks
Protein precipitation (PP)	Plasma samples, seminal plasma, cell lysates, cerebrospinal fluid, mice vaginal lavage, saliva, urine and breast milk.	Fastest and simplest extraction technique. It can be used also as sample pre-treatment before applying other extraction techniques.	Low selectivity; it could induce analytes co-precipitation. It does not sufficiently remove endogenous compounds such as lipids, phospholipids and fatty acids.
Solid-phase extraction (SPE)	Plasma, cell lysates, cerebrospinal fluid, chicken tissue, poultry muscle.	It combines extraction, clean-up and concentration procedures in a single step. It ensures analytes extraction with high selectivity.	Slightly tedious and time-consuming extraction technique. In some cases, it could result in less intense chromatographic peaks if compared to liquid-liquid extraction.
Liquid-liquid extraction (LLE)	Plasma, urine, faeces, hairs, mice vaginal tissues, liver tissues, poultry muscles, peripheral blood mononuclear cells, and human placental choriocarcinoma trophobplast cells.	Faster and easier than SPE. It desalts samples very well, lessening the problem of source fouling in mass spectrometry analyses.	Time-consuming technique and a rather hazardous one, due to the use of large amounts of toxic organic solvents. It is less selective than solid-phase extraction; moreover, the possibility of emulsion formation prevents automation of this technique.
Ultrasound-assisted extraction (UAE)	Urine, chicken tissue, dried sample spots.	Ultrasound increases the rate of mass transfer of analytes from matrix in the solvent compared to the classic liquid-liquid extraction.	Technique not widespread for the extraction from biological matrices.
QuEChERS (Q)	Plasma, chicken muscle.	More suitable for the extraction of drugs from biological tissues compared to liquid-liquid extraction or solid-phase extraction. It is a quick, easy, cheap, effective, rugged and safe method, ensuring an high selectivity of the extraction.	The QuEChERS method yields final extracts less concentrated compared to the traditional extraction techniques.