Compaq Aero 2150 Betriebsanweisung PDF herunterladen (Seite 38)

Configure an Experiment Method for Concentration

The absorbance of a solution is related to the concentration of the species within it. The relationship, known

as Beer’s Law , is:

where

is the absorbance at wavelength

is the extinction coefficient of the absorbing species

at wavelength

, c is the concentration and

is the optical pathlength.

Concentration is the amount of a specified substance in a solution. Graphs of absorbance vs. concentration

are known as Beer’s Law plots or concentration calibration curves. These are prepared by measuring the

light absorbed by a series of solutions with different known concentrations. The length of the sample --

such as the path length of your cuvette -- and the wavelength chosen for monitoring the amount of light

absorbed are constants. A plot from taking scans of these standard solutions with known concentrations is

then obtained. This plot is used to determine the unknown concentrations of substances in solutions.

Before you begin, we suggest you place a blank in the sampling region, store a reference and a

dark, and then place your sample with the highest known concentration in the sample holder of

the Palm-SPEC. Make sure you are in absorbance mode. Find the wavelength of the highest

peak. Note this wavelength.

1. Select

Method | Create

from the menu. You receive a

Create Method

dialog box where you must

name the method you are about to create. After naming the file, click

. The method you now create

is saved under this file name.

2. An empty

Edit Method

dialog box opens. You now need to select and insert the software events you

need for your experiment method. Select the

Insert

button in the right side of the dialog box to view

all 104 possible software events.

3. The

Edit Method Step

dialog box opens. Under

Method Action

, click on the down arrow to reveal

104 software events. You have to insert one event at a time. The events recommended to insert for a

concentration experiment and the order that they should appear are the following:

0: Display cursor value on main screen

This step is optional. Selecting this step allows you to see the absorbance values of your solutions with different

known concentrations, which helps to verify that the experiment is working correctly.

1: Set cursor location

This step allows you put the cursor at a specific wavelength for the absorbance measurements of your

samples with known concentrations. One option is to place the cursor on the wavelength noted in the

message above. Another option is to select a wavelength that you know is in a non-absorbing region of

the samples.

2: Set acquisition parameters

This step is also optional. However, if you do not set acquisition

parameters for your method, then the software will use the acquisition

parameters already in use, which are set by selecting

Spectra | Configure

| Data Acquisition

from the menu. For details on selecting values for

integration time, averages, and boxcar width, see page 17.

3: Store reference and dark spectra

You must select this step as storing a reference and a dark is requisite

before the software can calculate absorbance. This command merely

stores a reference and a dark. If you want to save the reference and dark,

insert the

Save reference spectrum

and

Save dark spectrum

method steps.

4: View Data in absorbance mode

This step is mandatory. It assures that you are in absorbance mode while the Palm-SPEC analyzes your

solutions with known concentrations.

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