Micro fractionating capillary

Wettstein PJ, Strausbauch ALA. Fraction collection in micro-preparative capillary electrophoresis. In ... 

New concepts presented in this edition include monolithic columns, bonded stationary phases, micro-HPLC, two-dimensional comprehensive liquid chromatography, gradient elution mode, and capillary electromigration techniques. The book also discusses LC-MS interfaces, nonlinear chromatography, displacement chromatography of peptides and proteins, field-flow fractionation, retention models for ions, and polymer HPLC. 

As a rule, a separation method should be used for both purification and concentration of the sample. The classic method for peptides and proteins is a reverse-phase liquid chromatography preparation of the sample, followed by a concentration step (often lyophiliza-tion) of the fraction of interest. During those steps performed on very small quantities of sample, loss on the sample can occur if care is not taken to avoid it. Lyophilization, for instance, can lead to the loss of the sample absorbed on the walls of the vial. The use of separation methods on-line with the mass spectrometer often are preferred. Micro- or nano-HPLC [32,33] and capillary electrophoresis [34], both coupled mainly to electrospray ionization/mass spectrometry (ESI-MS), are used more and more. 

The fourth soil fraction is known as the soil solution, which consists of moisture held by capillary action in the soil particles. The soil solution may be separated by centrifugation. The soil solution contains the ions, which are mobile in soils and is thought to be the main nutrient medium for sustaining plant roots and micro-organisms. The soil is in dynamic equilibrium with the soil solution and the exchange time is of the order of seconds. The movement of the soil solution through the soil after rainfall is responsible for the layered structure of soils. 

Altria, K.D. Dave, Y.K. Peak homogeneity determination and micro-preparative fraction collection by capillary... 

The gas-phase tram-alkylation reaction was performed in an automated micro-flow apparatus containing a quartz fixed-bed reactor (i d. 10 mm) at lO Pa [16 vol% benzene (1, p.a., dried on molsieve), 3.2 vol% diethylbenzene (2, consisting of 25% ortho, 73% meta, 2% para isomers, dried on molsieve), N2 balance (50 mL/min), WHSV =1.5 h ] with 2.0 mL of the tube reactor filled with catalyst particles (500-850 pm sieve fraction, typically 1.4 g). Two separate saturators were connected to the inlet of the reactor for the supply of 1 and 2. The partial vapor pressure of 1 and 2 was controlled by adjusting the temperature of the saturator-condensers and the N2 flow rate. After equilibration for 30 min at the applied reaction temperatures (473 K and 673 K, heating rate 10 K/min) within a dry N2 flow (50 mL/min), benzene (1) and diethylbenzene (2) were passed throu the reactor. To prevent condensation of both reactants and products prior to GC analysis [Hewlet Packard 5710 A, column CP-sil 5CB capillary liquid-phase siloxane polymer (100% methyl) 25 m x 0.25 mm, 323 K, carrier gas N2, FID, sample-loop volume 1.01 pL], tubes were heat-traced (398 K). FID sensitivity factors and retention times were determined using ethene (99.5 %, dried over molsieve) and standard solutions of 1, 2, and ethylbenzene (3, 99%) in methanol (p.a.). The conversion of 2 was measured as a function of time [8]. 

To obtain micro flow rates (for example, 1 pL/min), necessary for a packed capillary column, the same pumps are used, though with the addition at the outlet of a bypass which divides the flow into two fractions of which only the smaller is directed towards the column. To resist the low pHs of many elution mixtures, which can be more corrosive when pressure is high, the components and surfaces that come into contact with the mobile phase need to be inert. The pistons and valves of the pumps are made of sapphire, agate. Teflon or special alloys. 

The sample is loaded at atmospheric pressure into an external or internal loop, or groove in the valve core and introduced into the mobile phase stream by a short rotation of the valve. The volume of sample injected is normally varied by changing the volume of the sample loop or by partially filling a sample loop with a fraction of its nominal volume. External sample loops have volumes from about 5 p.1 up to about 5 ml, although typical injection volumes for conventional diameter columns are 10-50 xl. Injections from 1 p,l to about 40 nl require micro-injection valves equipped with replaceable internal loops [7,32-34]. Injection volumes less than about 40 nl are performed by positioning a split vent between the injector and the column. Typical injection volumes that preserve column efficiency for packed columns of different internal diameters are summarized in Table 5.1. For packed capillary columns with internal diameters < 0.2 mm direct injection will usually require the use of a split vent to minimize volume overload unless on-column focusing is possible. Injection volumes about 5 times larger than those indicated in Table 5.1 are sometimes used to increase sample detectability but with some decrease in the column separation power. 

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