Axis BTA 2100D Manuel de l'opérateur télécharger pdf (Page 443)

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Internal Standard Calibration

When you use the Internal Standard calibration type, you calibrate with regular

calibration standards but you also add a known amount of another analyte, the

internal standard, to each calibration standard and sample. When you make an

injection, any variation in the injection volume will be reflected by a detectable

variation in the amount of the internal standard. Fluctuations may also be caused

by the process used to prepare the samples. In this case, adding the internal

standards before sample preparation corrects for recoveries. Your Peak Table

may contain as many as eight internal standard peaks. Each non-standard peak

refers to the internal standard peak to use for calculations. Having multiple

internal standards allows you to match each peak to a standard with similar

chemical properties, which should have a similar recovery.

In generating the curve for an Internal Standard Calibration, you plot ratios: the

peak size divided by the standard peak size on the y axis and amount of

standard divided by the amount of internal standard on the x axis. Even if your

injection volume varies slightly, the ratio of the sample to the internal standard

will remain constant.

Normalized Percent Calibration

The Normalize Percent calibration type gives a percentage amount of each

analyte relative to the total amount of all analytes in the sample, adjusted for

varying detector response to the different analytes. It is analogous to a regular

percentage calculation, except that the percentages are based on actual

amounts of sample components rather than on peak size. It is also analogous to

the Internal Standard calibration type in that the amounts are determined using a

calibration curve based on ratios of sample to internal standard. An alternative

method of generating ratios of amounts is to use either Internal Standard or

External Standard calibration types and choose Normalize Results in the

Integration Parameters window in the Data Handling section of the Method.

Choosing a Calibration Type

Your choice of which calibration type to use depends on your regulatory

requirements and sample workup techniques. If you can very accurately

measure your standard amounts, using an external standard calibration type is

the easiest. The Internal Standard calibration type accurately accounts for

variances in injection volume. You would also choose Internal Standard

calibration if you have varying loss during sample preparation. In this case you

would add a known amount of your Internal Standard compound before sample

preparation, and sample loss during preparation will be accounted for.

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Axis BTA 2100D Manuel de l'opérateur Page 443