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Constant-volume injection method

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]. [Pg.39]

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. [Pg.474]

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. [Pg.209]

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. [Pg.337]

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). [Pg.389]

Detector response factors need to be accurately determined for good reproducible quantitative analyses [60]. They may be conveniently obtained by the constant volume method, that is, approximately 10 repeatable volumes of a sample containing an equal amount of the analytes are injected and the mean determined. Drf values are calculated hy normalising each peak area to that of the peak to be used as the reference. [Pg.232]

The second method consists of injecting constant volumes of sample saturated vapours into the column at various temperatures and plotting the peak height versus 1/T [96, 97]. If the detector employed has a linear response then the peak height is proportional to the saturated vapom pressure so that from the slope of the resulting line the heat of vaporization may be calculated. The results are close to those given by the ebuUioscopic method [98, 99], as demonstrated in Table 4.9. [Pg.117]

Sample Injection. For every quantitative HPLC analysis, especially in the external standard mode, a constant volume of injected sample solution is essential. This can be achieved only by using sample loops (5, 10. 20 pL. etc.) or automatic sample introduction system (see Section 12.2.4). The constancy in injection volume of these systems has to be checked from time to time. This is done by injecting the same sample several times and comparing the peak areas and peak heights generated. If a constant injected sample volume cannot be ensured, the internal standard method should be applied to compensate for these variations. A variation of the peak area can also result from short-time pulsation of the pump. [Pg.300]

However, unlike SFA, the sample is not inserted by continuous aspiration rather, a constant volume of sample is inserted into a stream of carrier liquid via an injection valve (Figure 1.4) for merging with the reagents used by the analytical method applied. [Pg.7]

The study on the spray combustion characteristics of 10% CPO blended with diesel fuel was conducted in a constant-volume combustion chamber. With the fixed experimental conditions such as spray ambient pressure and injection events, the effects of 10% CPO diesel at the injection line pressure of 100 MPa on spray combustion and flame stmcture were investigated using a photo diode and ICCD camera. Two-color method was also employed to predict combustion flame temperatures and KL factors. [Pg.701]

In this study, a mercury intrusion experiment was performed with a constant injection rate by regulating the intrusion pressure [58]. This is different from the conventional mercury intrusion experiment where the intrusion pressure is initially kept constant to record the mercury intrusion volume, then incremented to record the resultant incremental intrusion. In our experiment, the injection rate was kept extremely low so that the pressure loss due to flow was negligible compared with the capillary pressure. The data from this constant-rate mercury intrusion (CRMI) method, also called APEX [58], was collected through the pressure fluctuations as a function of intrusion volume, shown in Figure 3.7.4. [Pg.349]

Since the peak size is directly proportional to concentration, one may think that one could prepare a series of standard solutions and obtain peak sizes to be used for a standard curve of peak size vs. concentration, a method similar to Beer s law in spectrophotometry, for example. But since peak size also varies with amount injected, there can be considerable error due to the difficulty in injecting consistent volumes, as discussed above and in Section 12.3. A method that does away with this problem is the internal standard method. In this method, all standards and samples are spiked with a constant known amount of a substance to act as what is called an internal standard. The purpose of the internal standard is to serve as a reference for the peak size measurements, so that slight variations in injection... [Pg.354]

A dry packed column with porous material was used for the characterization according to size of the PVAc latex samples. The packing employed was CPG (Controlled Pore Glass), 2000 A, 200-400 mesh size. Deionized water with 0.8 gr/lit Aerosol O.T. (dioctyl sodium sulphosuccinate), 0.8 gr/lit sodium nitrate and 0.4 gr/lit sodium azide served as the carrier fluid under a constant flowrate. The sample loop volume was 10 pC A Beckman UV detector operating at 254 nm was connected at the column outlet to monitor particle size. A particle size-mean retention volume calibration curve was constructed from commercially available polystyrene standards. For reasons of comparison, the samples previously characterized by turbidity spectra were also characterized by SEC. A number of injections were repeated to check for the reproducibility of the method. [Pg.252]

An external standard method is used when the standard is analyzed on a separate chromatogram from the sample. Quantitation is based on a comparison of the peak area/height (HPLC or GC) of the sample to that of the reference standard for the analyte of interest. The external standard method is more appropriate for samples with a single target analyte and narrow concentration range, where there is a simple sampling procedure, and for the analysis of hydrocarbon fractions. The calculation requires an accurate extract final volume and constant injection size. The peak area of an analyte is compared with that from a standard or standard curve and corrected for volume ... [Pg.128]


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