Hydrodynamic chromatography (HDC) has experienced a resurgence in recent years for particle and polymer characterization, principally because of its coupling to a multiplicity of physical detection methods. When coupled to light scattering (both multiangle static and quasi-elastic), viscometric, and refractometric detectors, HDC can determine the molar mass, size, shape, and structure of colloidal analytes continuously and as a function of one another, all in a single analysis. In so doing, it exposes the analytes to less shear force (and, hence, less potential for flow-induced degradation) than in, for instance, size-exclusion chromatography. In this review, we discuss the fundamental chromatographic underpinnings of this technique in terms of retention, band broadening, and resolution, and we describe the power of multidetector HDC with examples from the recent literature.

A detailed quantitative description of particle size, shape, and their distributions is essential for understanding and optimization of the solid-, solution-, and melt-state properties of materials. Here, we employ quadruple-detector hydrodynamic chromatography (HDC) with multi-angle static light scattering, quasi-elastic light scattering, differential viscometry, and differential refractometry detection as a method for characterizing three important physical properties of materials, namely the molar mass, size, and shape of a polydisperse, non-spherical colloidal silica sample. These properties and their distributions were measured continuously across the HDC elution profile of the sample. By combining information from the various parameters determined, we were also able to obtain quantitative knowledge regarding the compactness or denseness of the sample. The applicability of multi-detector HDC to characterize polydisperse, non-spherical analytes was shown to be rapid, accurate, and precise. An advantage over traditional characterization methods is the ability of multi-detector HDC to determine particle size, shape, compactness, and their distributions simultaneously in a single analysis.

Particle size and shape and their distribution directly influence a variety of end-use material properties related to packing, mixing, and transport of powders, solutions, and suspensions. Many of the techniques currently employed for particle size characterization have found limited applicability for broadly polydisperse and/or nonspherical particles. Here, we introduce a quadruple-detector hydrodynamic chromatography (HDC) method utilizing static multiangle light scattering (MALS), quasi-elastic light scattering (QELS), differential viscometry (VISC), and differential refractometry (DRI), and apply the technique to characterizing a series of solid and hollow polystyrene latexes with diameters in the approximate range of 40-400 nm. Using HDC/MALS/QELS/VISC/DRI, we were able to determine a multiplicity of size parameters and their polydispersity and to monitor the size of the particles across the elution profile of each sample. Using self-similarity scaling relationships between the molar mass and the various particle radii, we were also able to ascertain the shape of the latexes and the shape constancy as a function of particle size. The particle shape for each latex was confirmed by the dimensionless ratio rho identical with R (G,z )/R (H,z ) which, in addition, provided information on the structure (compactness) of the latexes as a function of particle size. Solid and hollow polystyrene latex samples were also differentiable using these methods. Extension of this method to nonspherical, fractal objects should be possible.

Alternan is an ultrahigh molar mass polysaccharide composed of alternating α-(1→3) and α-(1→6) repeat units and that also possesses long-chain branching. Its molar mass distribution (MMD) can extend into the hundreds of millions of grams per mole. Characterizing alternan by means of size exclusion chromatography (SEC) is a lengthy process and an incomplete one because even under the best possible experimental conditions, the polysaccharide appears to degrade during its passage through the SEC columns. As an alternative to SEC, we have investigated the use of hydrodynamic chromatography (HDC) as a possible characterization technique for alternan. Results from packed-column HDC with multiangle static light scattering (MALS) detection compare favorably to results from off-line MALS analysis, and HDC results are obtained in a fraction of the time needed for SEC. The largest molar mass alternan did appear to undergo some degradation during HDC as a result of interstitial stresses in the column bed. This could be remedied by the use of columns with larger packing particles. Evidence of long-chain branching in alternan is provided via a comparison of the intrinsic viscosities and viscometric radii of the polysaccharide to those of a pullulan standard and of a theoretical pullulan of molar mass equal to those of the alternans examined.

The ability to characterize the size and shape distributions of broadly polydisperse analytes is a driving force in particle size analysis. Multi-detector hydrodynamic chromatography (HDC), which has previously shown promise in its ability to characterize the size and shape of monodisperse, spherical polystyrene latex standards, is applied here to include the characterization of bi-, tri-, and tetramodal latex blends and their constituents varying in size, chemistry, and compactness. The ability of multi-detector HDC to distinguish between similar-sized particles of different chemistry is realized by the coupling of a concentration-sensitive detector and two different types of light scattering detectors. The use of both multi-angle static and quasi-elastic light scattering permits for determination of two different size parameters across the elution profiles of the blends. Combining the size information obtained from both light scattering methods provides a measure of how particle compactness changes as a function of size in a latex blend. Multi-detector HDC was shown to be a rapid and precise method for characterizing particle size, shape, and their distributions of broadly polydisperse analytes.