Time-based injection

The multi-commuted system (see Figure 2D) is one of the most versatile systems, and exploits loop-based injection, time-based injection, or binary sampling for introducing the samples, reagents, and diluents in a programmable fashion. With discrete operation of its components, several approaches such as random reagent access, computer-controlled... 

Carroll, M. K. Tyson, J. F. An Experiment Using Time-Based Detection in Flow Injection Analysis, /. Chem. Educ. 1993, 70, A210-A216. 

Dec, J. and Kelly-Zion, P, The Effect if Injection Timing and Diluent Addition on Late-Combustion Soot Burnout in a Dl Diesel Engine Based on Simultaneous 2-D Imaging of OH and Soot, SAE, 2000-01-0238,2000. 

Note that the initial slope of the adsorption isotherm can be easily obtained from the knowledge of the retention time associated to a small injection performed on a column, as this retention time is given by tR = t0 ji + 1 - -k where /0 = V/Q is tiie zero-retention time based on the external bed porosity e (commonly, e is about 0.36-0.4). 

FIGURE 16.2 Representative base peak electropherograms from CZE runs of RPLC fractions, (a) Fraction 15 (5 peptide identifications) and (b) fraction 20 (19 peptide identifications). Column, bare fused silica capillary, 60 cm x 180 pm ODx30pm i.d. separation voltage, 15 kV observed CZE current, 1.91 p.A running electrolyte, 200 mm acetic acid + 10% isopropanol temperature, 22°C injection time, 10 s at 2 psi ( 4 nL total injection volume) supplementary pressure, 2 psi flow rate, 25nL/min spray voltage, 1.5 kV (reprinted with permission from Electrophoresis). 

Figure 21.15 Transient system response to onset of control at time t = 0 in Case 3A (a) measured amplitude, (6) apparent frequency of pressure oscillations, and (c) fuel injection phase based on the controller frequency response... 

ARS Technologies is developing an injection method based on push technology, which would eliminate the need for well installations. This method would significantly reduce the time and cost of operations (D18642Z, p. 2). 

M. Burguera, J. L. Burguera, C. Rivas, P. Carrero, R. Brunetto and M. Gallignani, Time-based device used for the determination of tin by hydride generation flow injection atomic absorption techniques. Anal. Chim. Acta, 308(1-3), 1995, 339-348. 

Injection voltage is varied between +500 and + 2000 V and maintained for 5, 10, and 20 s. Separation is carried out by applying a voltage of +2000 V using a detection potential of +0.7 V and 50 mM Tris-based buffer pH 9.0. Choose optimal injection time/voltage taking into account of peak current (7P) and half-peak width (1U1/2). 

Sample introduction is a major hardware problem for SFC. The sample solvent composition and the injection pressure and temperature can all affect sample introduction. The high solute diffusion and lower viscosity which favor supercritical fluids over liquid mobile phases can cause problems in injection. Back-diffusion can occur, causing broad solvent peaks and poor solute peak shape. There can also be a complex phase behavior as well as a solubility phenomenon taking place due to the fact that one may have combinations of supercritical fluid (neat or mixed with sample solvent), a subcritical liquified gas, sample solvents, and solute present simultaneously in the injector and column head [2]. All of these can contribute individually to reproducibility problems in SFC. Both dynamic and timed split modes are used for sample introduction in capillary SFC. Dynamic split injectors have a microvalve and splitter assembly. The amount of injection is based on the size of a fused silica restrictor. In the timed split mode, the SFC column is directly connected to the injection valve. Highspeed pneumatics and electronics are used along with a standard injection valve and actuator. Rapid actuation of the valve from the load to the inject position and back occurs in milliseconds. In this mode, one can program the time of injection on a computer and thus control the amount of injection. In packed-column SFC, an injector similar to HPLC is used and whole loop is injected on the column. The valve is switched either manually or automatically through a remote injector port. The injection is done under pressure. 

Figure 4 Isolation of specific peaks from an APTS-labeled glucose ladder with collection timing based on velocity determination from the two-point detection scheme. Conditions injection 1 pL capillary 200 pm i.d. x 30 cm detection UV at 254 nm field 330 V/cm. Reinjected fractions electrokinetic injection, 10 s at 400 V/cm capillary, 50 pm i.d. x 25 cm, 20 cm to the detection LIF excitation, 488 nm emission, 524 nm detection field 330 V/cm. (Reprinted from Ref. 2 with permission.)...

Dynamic range extension in GD quadrupole/ion-trap MS based on selective ion-accumulation (e.g. by mass-selective instability, single-frequency resonance ejection, combined rf-dc and entrance end-cap dc methods) allows the selective accumulation of the analyte ions and enables the dynamic range to be increased by a factor of 105 [233]. The linearities and relative trapping efficiencies of the previous methods were assessed with respect to the injection time and the methods were used for the GD ion-trap MS determination of major and minor constituents in NIST SRM 1103 Free Cutting Brass. 

The microactivity test (MAT) based on the ASTM-D-3907 [11] standard was used to determine activity and product selectivity of catalysts. MAT runs were performed in a X)Uel automated equipment with 4.0 g of catalyst using the same VGO as in the pilot plant runs. Unless otherwise specified catalyst samples were previously calcined at 853 K for three hours. Operating conditions were 793 K, CTO ratio of 4, 75 s injection time and WHSV of 15.7 h. Product analysis and conversion and selectivity calculations were done as in the pilot plant. The relative error of data was 5%. We analyzed coke bum products in-situ by IR analysis using an HORIBA VIA-510 analyzer. Product distribution was expressed in terms of produet yield/ activity ratio as defined in Table 2 as currently used for interpreting MAT numbers in equilibrium catalysts. 

Two introduction methods are commonly employed in capillary electrophoresis. Hydrodynamic injection is based on siphoning, or gravity feeding the sample into the anodic end of the capillary. The anodic end is removed from the buffer reservoir and placed in the sample solution. The capillary end is then raised so that the liquid level in the sample vial is at a height Ah above the level of the cathodic buffer, and is held in this position for a fixed time t. This process has been automated for reproducibility, and the hydrodynamic flow rate has been shown to obey Eq. 12.9 ... 

F. Albertus, A. Cladera, E. Becerra, V. Cerda, A robust multi-syringe system for process flow analysis. Part 3. Time based injection applied to the spectrophotometric determination of nickel(II) and iron speciation, Analyst 126 (2001) 903. 

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