Analysis time volume

Procedure. Select a volume of sample requiring less than 15 mL of titrant to keep the analysis time under 5 min and, if necessary, dilute the sample to 50 mL with distilled water. Adjust the pH by adding 1-2 mL of a pH 10 buffer containing a small amount of Mg +-EDTA. Add 1-2 drops of indicator, and titrate with a standard solution of EDTA until the red-to-blue end point is reached. 

From this equation we see that increasing k leads to a shorter analysis time. For this reason controlled-potential coulometry is carried out in small-volume electrochemical cells, using electrodes with large surface areas and with high stirring rates. A quantitative electrolysis typically requires approximately 30-60 min, although shorter or longer times are possible. 

Sediment Volume. If the dispersion is unstable, the sediment bed will be quite deep and sedimenting particles will stick together where they first strike the sediment bed, thus forming an open stmcture with considerable occluded Hquid. If the dispersion is stable to reagglomeration, the particles will move freely past one another to avoid contact as long as possible. The result is a thin sediment bed with maximum soHds packing and minimum occluded hquid (12). Since dispersed particles setde more slowly than docs, centrifugation maybe needed to force sedimentation of small particles within a reasonable analysis time. 

Small particle size resins provide higher resolution, as demonstrated in Fig. 4.41. Low molecular weight polystyrene standards are better separated on a GIOOOHxl column packed with 5 /u,m resin than a GlOOOHg column packed with 10 /Ltm resin when compared in the same analysis time. Therefore, smaller particle size resins generally attain a better required resolution in a shorter time. In this context, SuperH columns are best, and Hhr and Hxl columns are second best. Most analyses have been carried out on these three series of H type columns. However, the performance of columns packed with smaller particle size resins is susceptible to some experimental conditions such as the sample concentration of solution, injection volume, and detector cell volume. They must be kept as low as possible to obtain the maximum resolution. Chain scissions of polymer molecules are also easier to occur in columns packed with smaller particle size resins. The flow rate should be kept low in order to prevent this problem, particularly in the analyses of high molecular weight polymers. 

The Shodex GPC KF-600 series is packed with 3- im styrene-divinylbenzene copolymer gels in a column having a volume of about one-third compared to standard-types of columns, which are best suited for reducing the organie solvents eonsumption, shortening the analysis time, and lowering the detection limit (Table 6.5). 

An important parameter in LC-LC is the transfer volume, i.e. the time that C-1 is coupled to C-2, since the selectivity is highly dependent on this. In environmental samples, it is important to remove early-eluting interference in order to ensure selective analysis. A short analysis time is important for routine analysis of environmental samples. 

Ion chromatography permits the determination of both inorganic and organic ionic species, often in concentrations of 50 g L"1 (ppb) or less. Since analysis time is short (frequently less than 20 minutes) and sample volumes may be less than 1 mL, IC is a fast and economical technique. It has found increasing application in a number of different areas of chemical analysis and particularly for the quantitative determination of anions. The state-of-the-art has been reviewed.26... 

Methyl esterification When prohexadione was treated with methanolic HCl (3%, w/v) or sulfuric acid-methanol (1 %, v/v) under reflux at 75 °C for 60 min, or with BFs-methanol (14%, w/v) under reflux at 75 °C for 30 min, the yield of the methyl ester of prohexadione was 95,93 and 82%, respectively (prohexadione, 10 qg, volume 2 mL of methanolic HCl, 2 mL of sulfuric acid-methanol and 1 mL of BFs-methanol). A solution of 1% (v/v) sulfuric acid in methanol was chosen for ease of preparation. Even if prohexadione was treated with 1% sulfuric acid in methanol at room temperature for 12h, the yield of prohexadione methyl ester was not different from that under reflux conditions as described in Section 6.3. The conditions for methyl esteriflcation in Section 6.3 were chosen because of shortening of the analysis time and the reproducibility of the reaction yield in residue analysis samples which could contain large quantities of contaminants. 

Qualitative HPLC methods, using area percent, are used to monitor the disappearance of starting material and the formation of byproduct. Without the inclusion of an internal standard and the calculation of response factors, it is not possible to establish with certainty whether all of the starting material can be accounted for. An internal standard must be stable in the reaction mixture, must not co-elute with any of the components, and must be stable in the mobile phase. Ideally, the internal standard has a retention time about half that of the total analysis time. Internal standardization is extremely useful for kinetic studies. Added to the reaction vessel, samples that are withdrawn at various times will contain identical concentrations of internal standard, and chromatograms can be directly compared or adjusted to identical scales to correct for variation in injection volume. 

In the last decade, capillary electrophoresis (CE) has become one of the most powerful and conceptually simple separation techniques for the analysis of complex mixtures. The main reasons are its high resolution, relatively short analysis times, and low operational cost when compared to high-performance liquid chromatography (HPLC). The ability to analyze ultrasmall volume samples in the picoliter-to-nanoliter ranges makes it an ideal analytical method for extremely volume-limited biological microenvironments. 

Modern methods of sample handling for determination of surfactants in aqueous samples are practically all based on SPE and modifications thereof. Substantial reductions in analysis time, solvent consumption, sample volume required, and number of off-line steps have thus been achieved. This has not only increased the analysts capacity and analysis price per sample, but also decreased the risk of both analyte loss and contamination during sample handling. Whether or not this has indeed resulted in an increased quality of analytical results still needs to be validated through, e.g. intercalibration exercises. This aspect is discussed in more detail in Chapter 4. 

This limitation is offset by the high efficiencies and rapid analysis times of high-performance SEC. It should be evident that as support pore diameter and pore volume increase, the amount of solid material in the particle will be reduced, compromising the mechanical strength of the support matrix. 

As the name implies, CE separates sample components within the lumen of a narrow-bore capillary (20 to 150 pm) filled with a buffered electrolyte. High electric fields (hundreds of volts/centimeters in practice, but sometimes in excess of 1000 V/cm) can be used in CE because the capillary contains a small volume of electrolyte and a relatively large surface area to dissipate the heat generated by the electric current (Joule heat). High-voltage applications result in reduced analysis time and therefore less diffusion. 

FIGURE 21 Two HPLC gradient chromatograms (tryptic maps of lysozyme) illustrating the dramatic effect of flow rate (F), gradient time (t ), and void volume (Vg) on analysis time. Figure reprinted with permission from Reference 22. 

Raman microspectroscopy is readily performed on multiple locations inside each well. As in other instances, the results might not be representative of the whole sample because of the small sample volume probed. Polarization effects can be pronounced, but may be mitigated by averaging the results from additional locations. An alternative is rotating the sample, but this usually is not practical for multiwell plates. Both options increase analysis time. Such problems appear to be minimized when handling bulk powders [222,223,230], Several vendors sell systems preconfigured for automated analysis of microtiter plates and are typically integrated with optical microscopy. 

Disadvantages Large sample volume required Lorrg analysis time (60 s)... 

To help reduce these Influences, various data normalization techniques may be applied. Analysis of deposition (concentration times volume) rather than concentration alone may help avoid variability associated with precipitation amount. Another approach which was previously applied to aerosol measurements In Sweden ( )... 

Figure 3.29.A shows a flow-cell of 20 iL inner volume used to hold immobilized anti-mouse IgG bound to a rigid beaded support (activated Pierce trisacryl GF-2000). The cell was used to develop a two-site immunoassay for mouse IgG by consecutive injection of the sample, acridinium ester-labelled antibody and alkaline hydrogen peroxide to initiate the chemiluminescence, which started the reaction sequence shown in Fig. 3.29.B. Regenerating the sensor entailed subsequent injection of an acid solution, which resulted in a determination time of ca. 12 min (this varied as a fimction of the flow-rate used, which also determined the detection limit achieved, viz. 50 amol for an overall analysis time of 18 min) [218]. The sensor was used for at least one week with an inter-assay RSD of 5.9%. Attempts at automating the hydrodynamic system for use in routine analyses are currently under way.

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