Bandwidth IBW

FIGURE IS Comparative chromatograms showing the deleterious effect of instrumentai bandwidth to the performance of a Fast LC separation of four paraben anti-microbiais. HPLC conditions coiumn CIS (33x4.6 mm, 3fun), mobile phase 50% acetonitriie/water, 2mL/min, detection at 254 nm. 

Alliance with an 996 detector with a standard 8-jiL, 10-mm flowcell 

FIGURE 16 The chromatogram of an injection of a caffeine solution without the column showing the instrumental bandwidth of a Waters Alliance HPLC system with a 966 PDA detector with a standard flow cell. 

FIGURE I 7 Chart showing the efficiency loss at various k of 100-mm long 3- lm columns of various diameters from an HPLC with IBW of 60 jlL. Note that while column efficiency is mostly retained for the 4.6mm at high k, substantial losses are experienced with that of smaller i.d. columns. 

The IBW of a standard system can be reduced to 30-40 jL by using shorter lengths of 0.005-0.007 i.d. tubing and a semi-micro flow cell (2-3 tL).i° Further reduction might involve a low dispersion micro-injector or a redesign of the autosampler. Table 4 summarizes the typical IBW and other instrumental requirements of various column types from conventional (4.6 mm), Fast TC, minibore (3 mm), narrowbore (2 mm) and microbore (1mm) to micro TC ( 0.5mm) columns. Note that the dispersion 

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This effect of system bandwidth can be calculated using the additive relationship of variances where the total variance of the observed peak is equal to the sum of the true column peak variances plus the variance of the IBW ... 

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