Column temperature as an active variable in the isocratic, normal-phase high-performance liquid chromatography separation of lipophilic metabolites of nonylphenol ethoxylates.
Normal-phase separation of technical grade nonylphenol (t-NP, about 90% 4-nonylphenol), 4-nonylphenol mono-ethoxylate (4-NP1EO) and 4-nonylphenol di-ethoxylate (4-NP2EO) was assessed, with the inclusion of column temperature as an active variable. The compound 2,4,6-trimethylphenol was evaluated for use as internal standard. Isocratic elution with 2-propanol/hexanes mixtures from an amino-silica column and spectrometric UV detection at 277 nm were employed. Technical nonylphenol presented a significant contribution from unknown substances that eluted with retention times similar to that of 4-NP1EO. GC-MS analysis of the unknowns allowed to identify them as isomers of 2-NP. The response of the system to joint variations in flow rate, eluent composition and column temperature was investigated by means of Doehlert statistical experimental design. A model for retention of the analytes as a function of the experimental variables was proposed, and separation selectivity was studied. Selection of the optimal working zone was made through desirability function (D) calculations. Potential co-elution of 2-NP isomers with 4-NP1EO was considered when optimizing the separation. The occurrence of a restricted region of the experimental space where baseline resolution of analytes, associated impurities and internal standard results feasible (D not equal to 0) is apparent.
Babay
Paola A
PA
Unidad de Actividad Química, Centro Atómico Constituyentes, Comisión Nacional de Energía Atómica, Av. General Paz 1499, (B1650KNA) San Martín, Provincia de Buenos Aires, Argentina. babay@cnea.gov.ar
Gettar
Raquel T
RT
Magallanes
Jorge F
JF
Becquart
Elena T
ET
Thiele
Björn
B
Batistoni
Daniel A
DA
D002851:Chromatography, High Pressure Liquid / Q000295:instrumentation*; D005026:Ethylene Glycols / Q000302:isolation & purification* / Q000378:metabolism; D012680:Sensitivity and Specificity; D013056:Spectrophotometry, Ultraviolet; D013696:Temperature
D005026:Ethylene Glycols; C021754:terics