Maximum injection volume

Loading capacities in size exclusion chromatography are very low because all separation occurs within the liquid volume of the column. The small diffusion coefficients of macromolecules also contribute to bandspreading when loads are increased. The mass loading capacities for ovalbumin (MW 45,000) on various sizes of columns can be seen in Table 10.5. The maximum volume that can be injected in size exclusion chromatography before bandspreading occurs is about 2% of the liquid column volume. The maximum injection volumes for columns of different dimensions can also be seen in Table 10.5. 

Major advantages of LVI methods are higher sensitivity (compare the 100-1000 iL volume in LVI to the maximum injection volume of about 1 iL in conventional splitless or on-column injection), elimination of sample preparation steps (such as solvent evaporation) and use in hyphenated techniques (e.g. SPE-GC, LC-GC, GC-MS), which gives opportunities for greater automation, faster sample throughput, better data quality, improved quantitation, lower cost per analysis and fewer samples re-analysed. At-column is a very good reference technique for rapid LVI. Characteristics of LVI methods are summarised in Tables 4.19 and 4.20. Han-kemeier [100] has discussed automated sample preparation and LVI for GC with spectrometric detection. 

The maximum injection volume depends on the volume of the sample loop in the injection valve. The reproducibility of manual injection depends on the skill of the operator. The use of a small sample loop and an overflow injection of the sample solution so that the loop is fully flushed with sample are basic requirements for quantitative analysis. The highest injection reproducibility can be obtained by an auto-injector with a fixed sample loop. The smallest reasonable injection volume is 1 (A. A nl-scale injection valve can be constructed however, the memory effect at the surface of contact parts affects quantitative analysis compared with the use of a /d-scale injection valve. For a semi-micro system, a low hold-up volume injection valve is desired. The minimum injection volume is 80 nl. For a preparative-scale injection, the sample loop can be easily replaced with a larger-volume loop, such as a 200 jA, instead of the standard 20 /A loop. 

The maximum injected volume was 50 mL kg" [25]. LD50 was thus limited by the iodine concentration of the solution in the case of P743 and P840 and the NS-CA iobitridol. Thus, the intravenous acute systemic tolerance by the route intended for use in clinical practice was found to be satisfactory (Table 5). 

Equation 1 Estimation of maximum injection volume, Vjnj.max (ml), with capacity factors of the components, ki, and void volume, Vq (ml). 

Once the maximum injection volume is decided, the maximum sample load should be determined. In this example, the amount of the mono- and dicarboxylic acids was increased from 10 to 100 mg (of each acid) per injection in 1 mL of mobile phase. At first glance, the overlap between peaks suggested that the electronics of the refractive index detector were saturated... 

The injection is a critical factor in fast LC methods and must be considered to maintain column efficiency. Injection volumes that are too large can cause volume overload of the column, which results in broad, flat-top shaped peaks with low plate counts that are more pronounced for earlier eluting components. As injection volume is increased, peak height should increase however, peak width should remain the same. If peak width increases as well, this is indicative of volume overload. As column dimensions are reduced, the maximum injection volume must be reduced by the ratio of the column volumes [see equation (17-33) in Section 17.7.4], For example, reducing... 

The maximum injection volume depends from column size and packing pore volumes, and for high-efficiency 300 X 8-mm columns, it is generally recommended not to exceed 100 /xL per column. 

The sample can be injected ahead of the column, either on the suction side or on the pressure side of the pump. Injection on the suction side is performed by a three-way magnetic valve, which switches between the eluent and the feed. Some pumps have an additional pump head for the injection of the feed. If the sample is injected on the pressure side a switch valve is used. The sample is injected into a sample loop, which is connected to the six-port valve. The volume of the sample loop is adapted to the maximum injection volume of the process (see Tab. 5.1). 

Usually the injection quality can be assumed to correspond with K=2 but for excellent injection it is lower, thus allowing larger sample volumes. However, it is more important that the maximum injection volume depends on the retention volume of the solute therefore, for capillary columns with their extremely small retention volumes (since Ur decreases with the square of the capillary diameter), the allowed injection volume has values in the nanolitre range. 

In contrast to the concentration, the minimum detectable mass depends on the retention factor of the solute. The earlier a peak is eluted, the smaller is the maximum injection volume and, with the concentration of the sample solution being constant, the smaller is the absolute mass of solute injected. The same is true if the column inner diameter is reduced. 

One of the first steps in the formulation of a solution product is, therefore, to select the administration volume and concentration. This may be dictated primarily by physiological considerations, such as maximum injection volume as discussed above, or by pharmaceutical considerations. For example, if solubility is low, a larger volume/lower concentration formulation maybe required, whereas if stability is improved at higher concentrations, then the converse would be true. 

Ideally, the sample should be dissolved in the mobile phase and applied to the column in as small a volume as possible. The maximum injection volume without a loss in resolution is given by... 

Diazinon samples were analyzed with a Tracer 222 Gas Chromatograph equipped with a flame photometric detector in the phosphorous mode. The diazinon standard employed was obtained from EPA, Research Triangle Park. The limit of detection of the instrument was 0.3 ng with a maximum injection volume of 10 ul. since all environmental samples were extracted in 30 ml of solvent and were not concentrated, the sensitivity per sample was 900 ng. 

As mentioned before, when pressure-based sample injection is employed, the maximum injection volume must be less than the effective length of the capillary. At least 10% of the effective capillary length must remain available for separation. To inject a larger sample volume, electrokinetic injection must be employed. In most online sample preconcentration techniques, the maximum amount that can be injected without loss of separation efficiency is certainly less than the capillary volume. However, with a large volume sample injection under cathodic EOF conditions in SDS MEKC, a sample devoid of the micelle can be continuously electrokinetically injected for a volume equivalent to seven times the capillary volume without significant loss of separation efficiency under favorable... 

In principle, volume overload may be increased until the peaks begin to touch each other. This maximum injection volume, Vl can be calculated from the data given by the analytical chromatogram ... 

Equation (23) relates the maximum injection volume to the column dimensions, particle size d, mobile-... 

Molecular mass Concentration (w/v) Maximum injection volume... 

As the column diameter decreases, the loading capacity of the column also decreases, thus the maximum sample injection volume has to be reduced accordingly. The following equation describes the maximum injection volume that can be injected into a column ... 

Maximum injection volume without extra band broadening is given by... 

The maximum injection volume or swept volume is the product of the screw diameter and its maximum retraction stroke during plasticating. The value is expressed in cubic centimeters (cm ), cubic inches (in ), and sometimes as the weight in ounces (oz) or grams (gm) of plastic material that can be injected (Table 7.4). The weight rating is a less accurate measure and is relative to the density of the plastic material in question. The figure used to make the conversion should be the density in the melted state rather than in the solid state (Table 7.5). 

Injection-molding machines are generally characterized by two different parameters the maximum injection volume and the clamp force. The maximum injection volume determines the maximum volume of the object or of several objects in a single mold. The maximum clamp force is defined as the maximum force available to keep the mold closed without occurrence of leaking at the contact areas where the mold closes. 

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