Low Pressure Separations Using Automated Flow and Sequential Injection Analysis Coupled to Monolithic Columns

Abstract

Automation is a key demand in modern analytical chemistry. Automated analytical schemes facilitate samples handling, and enable effective processes such as dilution, extraction, derivatization, and preconcentration to be carried out. Flow (FI) and sequential injection (SI) analysis are well-established and mature automated analytical techniques with more than 18,000 publications so far in all areas of analytical science. FI and SI offer significant advantages such as low instrumental and operational cost, widely available instrumentation, and effective automation of critical steps in the analytical process. Until recently, the main disadvantage of FI and SI was the inability of simultaneous determinations of more than two analytes in a single run. Due to the low pressure operation of these techniques, it was impossible for them to be coupled to conventional particulate-based separation columns that enable chromatographic separations. This drawback was overcome by the introduction of monolithic stationary phases. Monolithic columns are prepared from organic and silica monomers. Silica-based monoliths have small-sized skeletons and a bimodal pore size distribution with microm-sized throughpores and nm-sized mesopores. This gives silica-based monoliths favorable properties for high-efficiency fast separations, such as low-pressure drop across the column, fast mass transfer kinetics and a high binding capacity. They consist of a single rigid porous rod, enabling higher flow rates than particulate columns at reasonable back-pressures. These unique features of monolithic columns enabled their incorporation in low/moderate pressure setups, such as FI and SI, expanding dramatically their possibilities.

Preparing titania aerogel monolithic chromatography columns using supercritical carbon dioxide

“…The powder XRD analysis results (see Supporting Information) show the presence of anatase, and the crystallite sizes in scCO 2 and heptanes were 10.3 and 12.2 nm, respectively, calculated from the most intense peak of (101) planes using the Scherrer equation. The high resolution TEM micrographs show that the electron reflection patterns spread uniformly on the linear nanostructures prepared in scCO 2 (Fig. 3G), suggesting a high crystallinity.…”

“…It should be pointed out that the N 2 physisorption technique cannot characterize the pores larger than 50 nm (macropores). Figure 2B shows the photograph of a TiO 2 aerogel monolith synthesized in scCO 2 , which was carefully pushed out of the view cell reactor to maintain the cylindered structure, with no observable shrinkage. Figure 2C shows the picture of the monolithic columns prepared in transparent Flexon HP tubes, where the quality of the monolithic TiO 2 can be compared.…”

“…Such control can provide higher permeability, better separation efficiency and enhanced mechanical stability compared to conventional micron sized particle packed columns. However, this technique so far has been limited to using SiO 2 or polymers as the stationary phase [1][2][3][4][5][6][7]. Recently, TiO 2 and ZrO 2 has been used for separation of phosphopeptides and proteins [8][9][10][11][12][13][14][15], partially due to its property of selective absorbance of water-soluble organic phosphates [16][17][18].…”

Flow Chemistry in Contemporary Chemical Sciences: A Real Variety of Its Applications

“…Some other materials used for this purpose may also induce some additional catalytic properties. It is worth mentioning that, since the late 1990s, monolithic columns were employed to carry out high-performance chromatographic separations in both low-pressure FIA and SIA systems [115].…”

Automated Quality Control of Pharmaceuticals using Sequential Injection Chromatography (SIC)

“…Fast separations and short analysis cycles are based on the short length of the monolithic columns, while chromatographic efficiency depends on the selection of the mobile phase and on the properties of the analytes. The interested reader can find useful information on SIC in two excellent review articles that have been published recently [10,11].…”