| Significant advancements to a dynamic surface tension detector (DSTD) are reported, which facilitate coupling the DSTD with flow injection analysis (FIA) and size exclusion chromatography (SEC). By measuring differential pressure across the liquid-air interface of growing drops, rapid dynamic surface tension measurements of flowing liquids are possible. A calibration procedure is reported that utilizes differential pressure signals from three drops (water, standard, and analyte). This novel approach eliminates the need to optically image each growing drop as required by similar techniques. Growing drops are precisely detached with a controlled air burst in a regime were surface tension forces significantly dominate gravitational forces, thereby minimizing drop elongation effects and adhesion effects to the pressure response. The decrease in drop volume, to as low as 1 muL, results in excellent data density for rapid chemical analysis.; Model surfactant, protein and polymer systems are evaluated to demonstrate the significance of these improvements. In a FIA/DSTD configuration, instrument precision is demonstrated using 0.5 to 3.0 mM sodium dodecyl sulfate (SDS) solutions, with a precision of 0.2 dynes/cm routinely obtained. FIA/DSTD is then shown to be an effective tool for the rapid study of kinetically-hindered proteins, such as bovine serum albumin as well as surfactant mixtures. A reproducible method to perform stress-relaxation experiments of surfactant systems is also demonstrated using polyoxyethylene-20-cetyl ether (BrijRTM 58) solutions. Rapid characterization of polymeric surfactant solutions above the critical micelle concentration (CMC) is also demonstrated with FIA/DSTD, providing insight into the impact that micelles have on dynamic surface properties.; Polyethylene Oycol (PEG) samples are analyzed with the SEC/DSTD configuration to illustrate advantages the multi-dimensional technique provides over traditional single-channel detection methods. After illustrating the information rich, multi-dimensional data through the separation of PEG standards, the utility of SEC/DSTD in quality control applications is shown by readily identifying high a molecular weight impurity, based on its' surface activity. In addition, subtle changes in polydispersity index (PDI) between PEG mixtures are distinguished with SEC/DSTD. A quantitative assessment of the SEC/DATA data predicts the PDI of samples within approximately 1%, using first and second order partial least squares (PLS) algorithms. |
