Maximum sample capacity

The maximum sample capacity can be derived from the equations concerning the resolution. Under ideal conditions. 

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A conventional capillary column, 0.200mm x 12.5M with a 3 of 250 has a sample capacity of about 50 ng at k 10. In comparison, a 0.480 mm x 28M column with a 8 of 250 has a sample capacity of about 540 ng at a k - 10. These very low sample capacities affect the XCD requirements very severely since the minimum detectable quantity, l.e. the detectivity, approaches the maximum sample capacity of the column as the column diameter decreases. 

Loodability studies on a LIChrosorb DIOL column of 6 mm and 23.4 mm bore and 250 mm length, packed with 5 fim material, yielded maximum sample capacities of 0.1 mg of protein per g of packing, in conjunction with a 20% loss In plate number. A sample containing variously 25 mg of albumin (bovine), chymotryp-sinogen and lysozyme was separated on a large—bore LIChrosorb DIOL column in 5 minutes with high resolution. 

Instrument Specialists offers the iSeries TGA with a vertically oriented bottom-loading balance. With different configurations the temperature range is ambient to 1000 °C or 1500 °C with heating rates of <300°C/min, and with maximum sample capacities of 40 or 400 mg. Evolved gas analysis capability is optional. Upgrades to existing thermal analysis systems are available. For more information, see www.instrument-specialists.com. 

Seiko offers the EXSTAR6000 TGA/DTA series with dual-beam, horizontally oriented balance configuration. The TG/DTA6200 has an ambient-1100 °C range, and the TG/DTA6300 has an ambient-1500 °C range. Both systems have a maximum sample capacity of 200 mg, can heat from 0.01 to 100°C/min, and will cool from 1000 °C to 50 °C in less than 15 min. A 30-pan autosampler is optional. For more information, see wvw.sii.co.jp or the North American distributor RT Instruments at vww.rtinstruments.com. RT Instruments also sells previously owned, refurbished thermal analysis systems. 

Theta Industries offers the Gravitronic II—1600 0 TGA, a top-loading instrument with a maximum sample capacity of 100 g. This system will support a corrosive environment and vacuum of 10 torr. Also offered is the Gravitronic IV—1100°C DTA/TGA, a vertically oriented bottom-loading system with a maximum sample capacity of 5 g. For more information, see www.theta-us.com. 

The maximum sample capacity of a column is reached tifig falls below 90% for a critical pair. If too much sample material is applied to a column, the k value and the peak width are no longer independent of the size of the sample, which ultimately affects the identification and the quantitation of the results (Figure 2.116). 

Figure 7 shows voltage profiles, for the second cycle of most of the graphitic carbon samples listed in Table 1. The curves have been sequentially offset by 0.1 V for clarity. Most striking is a reduction of the maximum reversible capacity, or Q ,, (<2 =372-x ,3,), as P increases. 

The curves show that the peak capacity increases with the column efficiency, which is much as one would expect, however the major factor that influences peak capacity is clearly the capacity ratio of the last eluted peak. It follows that any aspect of the chromatographic system that might limit the value of (k ) for the last peak will also limit the peak capacity. Davis and Giddings [15] have pointed out that the theoretical peak capacity is an exaggerated value of the true peak capacity. They claim that the individual (k ) values for each solute in a realistic multi-component mixture will have a statistically irregular distribution. As they very adroitly point out, the solutes in a real sample do not array themselves conveniently along the chromatogram four standard deviations apart to provide the maximum peak capacity. 

Equation (33) shows that the maximum capacity ratio of the last eluted solute is inversely proportional to the detector sensitivity or minimum detectable concentration. Consequently, it is the detector sensitivity that determines the maximum peak capacity attainable from the column. Using equation (33), the peak capacity was calculated for three different detector sensitivities for a column having an efficiency of 10,000 theoretical plates, a dead volume of 6.7 ml and a sample concentration of l%v/v. The results are shown in Table 1, and it is seen that the limiting peak capacity is fairly large. 

Employing equation (1), curves relating maximum sample volume to the capacity ratio of the first eluted peak for different separation ratios were calculated and constructed and the results are shown in Figure 2. 

Figure 2. Curves Relating Maximum Sample Volume to the Capacity Ratio of the First Peak for Different Separation Ratios...

The capacity ratios, efficiencies and separation ratios are given in Table 1, together with the maximum sample volume as calculated from equation (1). Comparing the maximum sample volume used for benzene given in Table 1, with the actual sample volumes for benzene shown in Figure 3, it would appear that equation (1) can be used with confidence for calculating (Vl). In a similar manner, using the same... 

The technique of column overloading is only feasible if more than adequate resolution is possible between the solute of interest and its nearest neighbor. Many samples require a column to be constructed that will only just separate the solutes of interest and under these circumstances the loading capacity must be increased without overloading the column. It has been shown in earlier chapters that the maximum sample (mass or volume) that can be placed on a column is proportional to the plate volume of the column and the square root of its efficiency. Thus, the maximum sample mass (M) will be given by... 

The sample capacity Q, arbitrarily defined as the maximum amount of a component that can be injected on a column giving a limited (10%) increase in peak width, is given by... 

Efficiency or plate count (N)—an assessment of column performance. N should be fairly constant for a particular column and can be calculated from the retention time and the peak widths. Selectivity (a)—the ratio of retention k ) of two adjacent peaks. Sample capacity— the maximum mass of sample that can be loaded on the column without destroying peak resolution. Capacity factor k )—a measure of solute retention obtained by dividing the net retention time by the void time. 

As mentioned above, the most common multidimensional separations are performed by using 2D systems. A considerable increase in peak capacity of the 2D system can be achieved if the whole sample is subjected on-line to two independent displacement processes (comprehensive MD separation) with peak capacities of and Uy, respectively. If the two separations have different retention mechanisms (e.g., are orthogonal to each other), the maximum peak capacity 2d of the system is approximately equal to the product of the peak capacities and Hy [5] ... 

Theoretical performance in gas chromatography. As the inside radius of an open tubular gas chromatography column is decreased, the maximum possible column efficiency increases and sample capacity decreases. For a thin stationary phase that equilibrates rapidly with analyte, the minimum theoretical plate height is given by... 

The selection of materials used for the construction of passive samplers is based on a number of criteria, including price, mechanical strength, the maximum sampling rate, and accumulation capacity. 

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