Application of Ion-Pair Methods to Drug Extraction from Biological Fluids II: Quantitative Determination of Biguanides in Biological Fluids and Comparison of Protein Binding Estimates

Physicochemical Properties, Solubility, and Protein Binding of Δ9 -Tetrahydrocannabinol

“…The details of these procedures were reported previously (15,16). In both cases, isotonic phosphate buffer (pH 7.4) was used as a reference solution and drug concentrations of 0.05, 0.1. and 1.0 pg/ml were investigated.…”

Determination of metformin in biological samples.

“…By this technique the halflife would appear to be shorter than previously suggested by gas chromatographic assay. Garrett, Tsau & Hinderling (1972) found negligible extraction of metformin into polar organic solvents even at high alkalinities and attributed this to a low degree of molecular association of dialkylated compared to mono-substituted biguanides. In our hands, extraction of metformin from alkaline solutions using methylene chloride, as described by Matin et al (1975), was not sufficiently reproducible when using buformin as internal standard.…”

“…In our hands, extraction of metformin from alkaline solutions using methylene chloride, as described by Matin et al (1975), was not sufficiently reproducible when using buformin as internal standard. One solution to this problem is based upon protein precipitation with trichloroacetic acid followed by extraction of a 1:1 bromothymol blue-biguanide ion-pair from the supernatant into methylene chloride (Garrett et al, 1972 standard and 5.0 ml acetonitrile. After shaking and centrifuging the supernatant was removed and evaporated to dryness using a vortex-evaporator (Buchler).…”

Determination of metformin in human plasma by high-performance liquid chromatography

“…Numerous chromatographic methods are now available for metformin [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20]. Extraction and clean-up of drugs from biological fluids are usually the first and most difficult step in bioanalysis due to the need to selectively remove interferences without significant analyte loss.…”