Calculating Peak Area

5.12 Calculating Peak Area

For a spectrum displayed at present, you can obtain the peak area value by integration in the specified range. Click the button on the Data Process toolbar (or select the Calculation Area command from the Data menu). A window as shown in Fig. 5-33 will appear.

Fig. 5-33

5.12.1 Setting of Calculation Range

The range for area calculation is settable in the following two ways.

(1) Setting by Moving Cursor

1) Click the Start button (refer to (1) in Fig. 5-34). Move the trace cursor to a desired start wavelength on the spectrum (refer to (2) in Fig. 5-34), and then click the right button of the mouse.

2) Click the End button (refer to (3) in Fig. 5-34). Move the trace cursor to a desired end wavelength on the spectrum (refer to (4) in Fig. 5-34), and then click the right button of the mouse.

3) Click the Calculate button (refer to (5) in Fig. 5-34). The result of calculation will be displayed.

Fig. 5-34

(2) Setting by Entering Numerical Value

1) Enter a desired start wavelength in the Start input box from the keyboard.

2) Enter a desired end wavelength in the End input box from the keyboard.

3) Click the Calculate button. The result of calculation will be displayed.

(3) The principle of calculation is shown below.

D n-1 D 1

Section end Section start wavelength

Specified range

wavelength

WL 1 WL 2 WL 1 WL 2

Fig. 5-35 Principle of Calculation

5.12 Calculating Peak Area

The peak area is calculated using the spectral elements (D 1

to D n ) as follows. S 3 =S 1 +S 2 =S a +S c +S d

= {D 2 +D 3 + ... D n-2 +D n-1 + (D 1 +D n )/2}* ∆λ

S 2 =S b +S d = [(D 1 +D n )*{ ∆λ*(n – 1)}]/2

= [(D 1 +D n )*{section start wavelength (WL 2 )–

section end wavelength (WL 1 )}]/2 S 1 =S 3 –S 2

D 1 : Spectral data at section start wavelength

D n : Spectral data at section end wavelength ∆λ: Sampling interval

For the time scan mode, change as follows.

Start wavelength (WL 2 )

End time (T 2 )

End wavelength (WL 1 )

Start time (T 1 )

5.12.2 Printing of Calculation Result

The result of area calculation can be printed out.

(1) For printing both the spectrum and calculation result, put a check mark at “Print spectrum” (refer to (1) in Fig. 5-36). To avoid spectrum printing, remove the check mark.

(2) Click the Print button to start printing (refer to (2) in Fig. 5-36). Upon execution of printing, the Area window will close. The same window can be called up by clicking the

(Area) button on the Data Process toolbar.

Fig. 5-36

Fig. 5-37 Example of Printout (with “Print spectrum” selected)

(3) After calculation, click the OK button (refer to (3) in Fig. 5-36). The Area window will close with the result saved.

(4) The calculation result is reset by clicking the (Reset

Data) button on the Data Process toolbar with the data processing window displayed. Upon calling up the Area window again, therefore, “*****” will be indicated in each result box.

NOTE: Upon execution of file saving after area calculation, the result is also saved in a file. So a numerical value is indicated in each result box when the Area window is called up. These values cannot be erased by clicking the reset button, because they are saved in the computer.

5.12 Calculating Peak Area

5.12.3 Expansion of Scale

For expanding the scale in the Area window, use the left button of the mouse.

(1) To specify the area to be expanded, draw a rectangle on the spectrum by moving the mouse with its left button held down as shown in Fig. 5-38.

Fig. 5-38

(2) Then release the left button. The specified area will be

expanded as shown in Fig. 5-39.

Fig. 5-39

(3) For returning to the original scale, double-click the left

button on the spectrum.

5.13