Constant Volume Injection

Overfilling the loop (vhth twice the loop volume) is recommended in order to keep good control of the actual injected amount. The actual injected volume is then determined by the loop size. 

---

Ultra-thick microfluidic stmctures (up to 1.5 mm high) were fabricated using SU-8 photoresist. Instead of using a spin-coater, a constant-volume injection method was used to apply thick photoresist for patterning [237]. 

In contrast to the IS method, external standardization may be used in which several standard solutions of varying concentrations of the sample are prepared. Following constant volume injection of each standard solution, a plot of peak area (or height) versus concentration is made, and unknown sample concentrations are obtained from interpolation of the calibration curve. The success of this technique, however, is dependent upon the precision of injection volume, readily accomplished with automatic injection but less so when manual microliter syringes are used. 

The constant volume injection (CVI) system uses a mechanical cam-operated device to time the injection of the hydrogen to each cylinder. The CVI block is shown on the far right of the photo with four fuel lines exiting on left side of the block (one fuel line for each cylinder). 

Once again, one can solve for the ERR that arises due to constant volume injection, using Equation 39.25 to calculate the volume for given pressure. In calculating the potential energy used in the ERR calculation, the second term (pressure times injected volume) is dropped. The result is... 

Under constant volume injection, the ERR again falls as the crack extends (i.e., L increases), implying stable crack extension under constant volume injection. 

A group of chemistry students have injected 46.2 g of a gas into an evacuated, constant-volume container at 27°C and atmospheric pressure. Now the students want to heat the gas at constant pressure by allowing some of the gas to escape during the heating. What mass of gas must be released if the temperature is raised to 327°C ... 

Fig. 2.7 ESI mass spectra of ligands present in CPC spin column eluates have a linear response with increasing concentration ESI (positive ionization mode) mass spectral analysis of the eluate from the CPC spin column titration ofWY252 (MW 457 Da) with MM P-1 where the molar ratios of MM P-1/ WY252 are constant at 1 5 while their individual concentrations linearly increase. The volume injected for each sample was...

The critical operational assumption that makes it possible to draw conclusions in a given comparison situation about the effect of plate and pore amount is that a constant volume and a constant absolute amount of solute was injected per column to normalize comparisons. If pore amount per column is constant, then increase in resolution with several columns of the same kind in series is due only to the increased amount of plates. Conversely, if plates of a column bank are the same, then differences in resolution are due to differences in the amount of pores of appropriate size. Also, all the other appropriate operating parameters are constant for each comparison. The following group of comparisons will illustrate different issues involving the interplay of pores, plates, and resolving power. The times on the figures are maximum values for total permeation volumes at a flow rate of 1 ml/min. 

The accuracy of the pressure and temperature measurements was verified by measuring the vapor pressure curves and critical points for pentane and for toluene. Vapor pressures were measured by observing the formation of a liquid phase as pentane or toluene was injected into the constant-volume view cell under isothermal conditions. The observation of critical opalescence was used to determine the critical point. The measured vapor pressures and critical points are given in Table I. Vapor pressures deviate from... 

External Standard. This method is usually performed graphically. Known amounts of the analyte of interest are chromatographed, the areas are measured, and a calibration curve like Figure 7.6 is plotted. If the standard solutions of analyte vary in concentration, a constant volume must be introduced to the column for each. This requires a reproducible method of sample introduction a valve is adequate, but syringe injection in GC is usually inadequate, particularly for syringes that contain sample in the needle. Errors around 10% are common. 

For simplicity, one can desorb the sample charcoal in a vial containing 0.5 milliliters of carbon disulfide and prepare all standard mixtures in 0.5 milliliters of carbon disulfide and inject a constant volume of 1 microliter of desorbed sample and standard into the gas chromatograph. Calibration curves are prepared by plotting concentration of solvent in ul/ml carbon disulfide versus peak area. 

The hydrogenation reactions were carried out in a 100-ml stainless-steel autoclave equipped with a 50-ml glass liner and PTFE cover to provide clean conditions. The reactor was magnetically stirred (n = 1000 min 1). The pressure was held at a constant value by a computerized constant volume - constant pressure equipment (Buchi BPC 9901). By monitoring the pressure inside the vessel and the injected pulses, the hydrogen uptake could be followed. Under standard conditions, 42 2 mg prereduced catalyst, 1.84 mmol substrate, 6.8 imol modifier and 5 ml solvent were used at 10 bar and room temperature. 

Reaction mixtures contained substrate (ALA) and buffer the reaction was started by the addition of lysate. TCA was added to terminate the reaction. The incubation solution was clarified by centrifugation, and a constant volume removed and mixed with the internal standard. A known volume was injected for analysis. Figure 9.59 compares the profiles of two samples after incubation with enzyme and with blank. The appearance of the reaction product PBG is observed in the test profile (Fig. 9.59A) only. 

The coated wafer was placed in a petri dish and enough tetrahydrofuran was added to completely cover the wafer. The tetrahydrofuran dissolved the MP2400 resist film and the resulting solution was collected in a 5 cc volumetric flask and brought to the mark with additional solvent. Prior to the solution addition, a known constant volume of benzene solution was pipetted into the volumetric flask. The benzene serves two purposes first it acts as a marker to correct for flow rate variations and secondly its calculated area serves to normalize injection variations. 

In this connection, a series of steady state displacement tests were conducted in a 170-200 mesh bead pack with a porosity of 0.4 and an absolute permeability of 7000 md. The experimental apparatus is shown in Figure 7. Two types of gas injection were employed - constant pressure injection and constant rate injection air was used in the former, nitrogen in the latter. The liquid phase was water plus surfactant (0.25% by volume Amphosal CA, Stepan Chemical Company) and was always injected under constant... 

What will happen if 1.000 mole per liter of N2 is suddenly injected into the system at constant volume We can answer this question by calculating the value of Q. The concentrations before the system adjusts are... 

HPLC was performed using Waters 600S solvent delivery system (Waters, Milford, MA, U.S.A.). 2487 UV dual channel detector of Waters was used and injector (20 fit sample loop) from Rheodyne. The data acquisition system was Millenium (Waters). Water filtered 1 Milipore ultra-pure water system (Milipore, Bedford, MA, USA). The wavelength was fixed at 254 nm and the experiment was performed at room temperature. The size of the analytical colunm packed by C g was lS0X4.6mm (Spm) (Alltech, USA). The mobile phase of 0.75% TFA in water and acetonitrile were used in this experiment. The flow rates of the mobile phase were fixed at I ml/min. The constant volume of 0(d, was injected. This experiment was implemented at room temperature. The gradient mode was employed to isolate peptides. The complete gradient condition was listed in Table I. 

Figure 1-3 shows two different types of batch reactors used for gas-phase reactions. Reactor A is a constant-volume (variable-pressure) reactor and Reactor B is a constant-pressure (variable-volume) reactor. At time r = 0, the reactants are injected into the reactor and the reaction is initiated. To see clearly the different forms the mole balance will take for eadi type of reactor, consider the follovring examples, in which the gas-phase decomposition of dimethyl ether is taking place to form methane, hydrogen, and carbon monoxide ... 

The influence of wake motion on bulk turbulence induced in the liquid is understood more clearly by inspecting oscillograms which show the fluctuation of local liquid velocity. Figure 43 shows such oscillograms taken by Kikuchi (K30) with a hot-wire probe. The bubble column is 8.0 cm in diameter, water-filled to a 170-cm height, with the probe 115 cm above the bottom gas distributor. In the column bubbles of constant volume (100 cc) are injected successively at constant time intervals, either at 2.1 sec (case a) or 0.50 sec (case b). Case c is an example of continuous bubbling at f/c = 6.45 cm/sec. 

A successful sampling valve is that due to Pratt and Purnell (Fig. 58) . A dead-space sample is first withdrawn, followed by a reacted sample. Cundall et claim a better valve is the push-pull type (Fig. 59), a variation of the valve used on some commercial glc instruments. For sample injections after fractionation, a constant volume and manometer is employed for gases, and precision microlitre syringes for liquids. 

Basically, the technique is as follows. A small (but constant) volume of sediment, soil or cuttings is placed into the mixer cell along with two ceramic or stainless steel ball-bearings, and water is added to bring the remaining headspace to 10 cc. The mill is sealed and placed in a SPEX/Mixer-Mill and agitated for about five minutes. The cell is then immersed into a hot-water bath at 90°C for three minutes. A 1 ml aliquot of gas-free water is injected into the cell through a septum-sealed side arm on the cell, and then a 1... 

The calibration method most often used in ion chromatography is direct comparison of the peak area in an unknown sample with that of a solution with a known content of the same substance. This method requires the injection of constant volumes under constant chromatographic conditions. Errors in the sample delivery, however, are almost excluded upon application of a sample loop valve. A prerequisite is the existence of reference compounds for all sample components to be analyzed. In practice, several different standard solutions in the investigated concentration range are prepared and chromatographed [8], When the resulting peak area is plotted versus the concentration of the standards, one obtains a substance-specific calibration function. 

The theory of simple waves applies to large-volume injections, i.e., to the profiles obtained upon injection of rectangular profiles which are so wide that the injection plateau has not been entirely eroded when the band elutes. Then, simplifications of the solution occur because there is a constant state, the concentration plateau. This solution is not valid in overloaded elution chromatography when the injection volume is sufficiently small that the injection plateau has eroded and disappeared by the time the band elutes from the column. It is important to discuss this solution, however, because it takes a finite time for the profile of even a narrow rectangular injection to decay, and the band profile during that period is given by the simple wave solution. Also, this solution is the basis for a method of determination of competitive equilibrium isotherms (Chapter 4, Section 4.2.4). 

---