Zero dead volume

The contribution of the equipment between injection unit and detector cell should be negligable in relation to the column for a sufficient column characterization short connections with narrow capillaries and zero dead volume unions are the precondition for reliable plate numbers. Every end fitting of a column causes additional band broadening. In the past a column type was offered that could be directly combined without any capillary links unfortunately, it has disappeared from the market. 

The Waters company recommends a system check of the chromatographic equipment that is used for plate number determination and analyses (2) the columns in the GPC unit used are replaced by a zero dead volume union. Then the test sample is injected under the same conditions such as a plate number determination. The 5a peak width measured on a suitable recorded peak is evaluated this 5or width of a 20-/a1 injection should be lower than 150 /a1. 

SafeChem, a subsidiary of Dow, has developed a handling system for chlorinated solvents that allows them to be used in closed-loop degreasing systems. The Safe-Tainer system uses two dedicated double wall containers one to hold fresh solvent and the other used solvent. The containers are connected to the cleaning equipment with zero dead volume, leak-free connections that prevent spills, leaks or vapour emissions during use. Used solvent is collected for recycling and professional disposal of any residues. The system minimises solvent use and release to the environment. A study carried out by Dow during a trial in... 

II- Zero dead volume SSI Flow-Through Back-Pressure Regulator maintaining in the reactor pressure about 4 bars, 12- container for products. 

Figure 9 Schematic depiction of the zero-dead-volume CL detection system for liquid chromatography. (From Ref. 48.)...

In summary, this zero-dead-volume integrated CL detection approach provides two major advantages, namely ... 

First, disconnect the column and replace it with a zero-dead-volume union. 

Figure 4.20.A shows a more recent cell reported by Cobben et al. It consists of three Perspex blocks, of which two (A) are identical and the third (B) different. Part A is a Perspex block (1) furnished with two pairs of resilient hooks (3) for electrical contact. With the aid of a spring, the hooks press at the surface of the sensor contact pads (4), the back side of which rests on the Perspex siuface, so the sensor gate is positioned in the centre of the block, which is marked by an engraved cross as in the above-described wall-jet cell. Part B is a prismatic Perspex block (2) (85 x 24 x 10 mm ) into which a Z-shaped flow channel of 0.5 mm diameter is drilled. Each of the wedges of the Z reaches the outside of the block. The Z-shaped flow-cell thus built has a zero dead volume. As a result, the solution volume held between the two CHEMFETs is very small (3 pL). The cell is sealed by gently pushing block A to B with a lever. The inherent plasticity of the PVC membrane ensures water-tight closure of the cell. The closeness between the two electrodes enables differential measurements with no interference from the liquid junction potential. The differential signal provided by a potassium-selective and a sodium-selective CHEMFET exhibits a Nemstian behaviour and is selective towards potassium in the presence of a (fixed) excess concentration of sodium. The combined use of a highly lead-selective CHEMFET and a potassium-selective CHEMFET in this type of cell also provides excellent results.

Figure 2. Graphs of percent recoveries for pyrene, perylene, benzo[ghi]-perylene, and coronene using 1 8 sorbent bed geometries, one containing ca. 70% dead volume (light shading) versus one with zero dead volume (dark shading).

The scheme in Figure 9.19 shows a simplification of the separation unit, using a 2-position valve to reverse the flow through the column for load/wash and elute steps, and an additional 2-position valve as a detector diverter valve. The system also incorporated several zero-dead volume syringe pumps and several additional valves to route sample and reagents through the system. 

FIGURE 9.19 Simplified schematic diagram illustrating sample preparation, separation, and detection for an on-line analyzer for the continuous monitoring of the total "Tc content of nuclear-waste process streams. A number of zero-dead volume syringe pumps and valves are not shown. 

Figure 3.1 Compression fittings, (a) Male fitting (b) female fitting (c) zero dead volume union.

Zero Dead Volume—Fittings designed to leave no extra column volumes that might cause band spreading or remixing of peaks. 

Figure 6.8 Diagram of instrumental configuration of the LC/MS system used for characterization of crude fermentation extracts. The system consists of the following components (1) HPLC (2) loop injector (3) guard column (4) 5pm C18 HPLC column (4.6mm x 25cm) (5) zero dead volume tee (6) UV detector (7) fraction collector (8) triple quadrupole mass spectrometer equipped with ESI interface (9) ESI power supply and gas manifold and (10) syringe pump. (Reprinted with permission from Ackermann et al., 1996a. Copyright 1996 Elsevier.)...

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