Axis BTA 2100D Manual do Operador descarregar pdf (Página 439)

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programs a new, wider peak width. Although it is rarely necessary, the software

is also able to automatically program narrower peak width settings.

Instead of letting the software automatically program peak width settings as

needed, you can manually program your own peak width setting. The act of

manually programming a peak width event disables automatic peak width

programming. In the vast majority of cases, automatic peak width determination

is all that is needed.

Adjusting the Signal To Noise Ratio

The Signal to Noise Ratio (S/N ratio) also affects the peak detection process.

When you lower the S/N ratio, more small noise peaks are detected. Conversely,

increasing the S/N ratio causes fewer small peaks to be detected. In the extreme

case, a high S/N ratio may cause some larger peaks of interest to remain

undetected, particularly if you have manually programmed peak width value that

is too low. Another effect of a high S/N ratio value is that peak start and end

events tend to be closer to the peak apex, especially when there is a lot of tailing,

or a sloping baseline. This can result in valley separated peaks incorrectly

considered baseline resolved.

The optimal setting for this value depends on your analyses. You want to set this

value low enough so that all the peaks in which you are interested are detected,

but high enough so that extraneous noise “peaks” are not detected. If you want

small peaks to be detected in one part of the chromatogram, but not in another,

you can program different S/N ratio values at different times in the

chromatogram.

Rejecting Solvent Peaks

In many types of chromatographic analyses, you will have a large, essentially

unretained solvent peak elute at the beginning of your run. This represents the

solvent in which your sample is contained, and is not pertinent to your results.

You have two options for removing the peak from your results—using the Inhibit

Integrate or the Solvent Reject event. Generally you will use Inhibit Integrate

unless an analyte of interest is a shoulder peak or is tangent to the solvent peak.

Remember that Inhibit Integrate occurs at the first step of peak processing,

during the peak detection phase. Its effect is to remove the section of the

chromatogram specified by the event from consideration while peak detection is

in progress. With the Inhibit Integrate event, regardless of the specific location

where the event ended, the next detected peak always starts a new baseline.

This is why a Solvent Reject event is used if your analyte of interest is a shoulder

peak or is tangent to the solvent peak. This allows the peak detection algorithms

to correctly determine the baseline points for the shoulder or tangent peak, while

still removing the solvent peak from your final results calculations.

Skimming Fused Peaks

Fused peaks are peaks that elute next to each other and are not baseline

resolved. The peak detection software treats fused peaks as either valley

separated peaks, tangent peaks, or as fused tangent peaks. The Tangent

Percentage value affects which peaks are considered valley separated peaks

and which are tangent peaks. The Tangent Percentage value represents the

percentage of the peak height of the second peak to the first fused peak. If the

peak height of the second peak is a lower percentage than the Tangent

Percentage value relative to the first peak, then the peak is considered a tangent,

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