PASCO Specialty & Mfg. CI-6734 User Manual download pdf (Page 11)

012–06615A Sodium Ion Selective Electrode

Figure 3

Typical sodium electrode calibration curve

6. To a clean, dry 150 ml beaker, add 100 ml of sample and 2 ml of ISA. Place the beaker on the magnetic

stirrer and begin stirring. After rinsing the electrode tip with electrode rinse solution, blot dry and place

the electrode tip in the solution. When the reading has stabilized, record the Voltage reading in the Digits

Display. Using the calibration curve, determine the sample concentration.

7. The calibration should be checked every two hours. Assuming no change in ambient temperature, place

the electrode tip in the mid-range standard. After the reading has stabilized, compare it to the original

reading recorded in step 3 above. A reading difference by more than 0.5 mV or a change in the ambient

temperature will necessitate the repetition of steps 2-5 above. A new calibration curve should be prepared

daily.

Low Level Sodium Determination

This procedure is recommended for solutions with ionic strength less than 1.0x10

-2

M and a sodium concentration

less than lxl0

-5

M or 1 ppm. If the solution is high in ionic strength, but low in sodium, use the same procedure, but

prepare a calibration solution with a composition similar to the sample. Use plastic lab-ware for low sodium

measurements.

1. Using 20 ml of standard ISA, dilute to 100 ml with distilled water.

2. Dilute 20 ml of the outer chamber filling solution to 100 ml with distilled water and fill the reference

electrode if using a double junction reference electrode.

3. Dilute 1 ml of the 0.l M standard to 100 ml to prepare a 1.0Xl0

-3

M standard solution for measurements

in moles per liter. Dilute 10 ml of the 1000 ppm standard solution to 100 ml to prepare a 100 ppm standard

solution for measurements in ppm. Add 1 ml of low level ISA to each 100 ml of standard. Standards should

be prepared fresh daily.

4. Using a 150 ml plastic beaker, add 100 ml of distilled water and 1 ml of low level ISA. Add NH

OH, if

necessary, to adjust the pH above 9. Place the beaker on the magnetic stirrer and begin stirring at a constant

rate.

5. Place the electrode tip in the solution. Assure that ScienceWorkshop is operating.

-60

-6

-5

- 4

-3

-2

~59 mV

10-fold change

0.1 1 10

(ppm)

100 1,000

-20

+20

+60

+100

+140

-1

electrode

potential

(mV)

concentration (M)

1 2 ... 6 7 8 9 10 11 12 13 14 15 16 ... 21 22

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PASCO Specialty & Mfg. CI-6734 User Manual Page 11

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