护手霜中pH的测定

pHofHand CreamspH ofHand Creams pH ofHand Creams Calibration and Analysis 1. Allow all the standards and the samples to attain room temperature for precise measurements since themeasurement is temperature sensitive. 2C.alibrate the meter using the pH7.00 buffer followed by the pH 4.01 buffer， stirring the standards ata uniform rate. 3. Place electrode， ATC probe and Orion stirrer into beaker with pH 7.00 buffer standard with theelectrode tip fully immersed in the solution. The stirrer should be positioned slightly below the tip ofthe electrode. Press the STIRRER key on the meter to turn the stirrer on. Press the CALIBRATE key. 4.Wait for stable reading (1-2 minutes). Enter standard value of 7.00 using the UP and DOWN arrowkeys and the DECIMAL /DIGIT key. 5. Press CALIBRATE key to accept 7.00 standard and press the STIRRER key to turn the stirrer off. 6.Rinse electrode， ATC probe， and stirrer thoroughly with deionized water. Gently remove excesssolution from the outer sleeve of the electrode by dabbing with a clean paper tissue. Do not wipe orrub the sensing element of the electrode. 7.Place the electrode and stirrer into beaker with the pH 4.01 buffer standard with the electrode tip fullyimmersed in the solution. The stirrer should be positioned slightly below the tip of the electrode. Pressthe STIRRER key on the meter to turn the stirrer on. 8.Wait for a stable reading (1-2 minutes). Enter standard of 4.01 using the UP and DOWN arrow keysand the DECIMAL /DIGIT key. 9.Press MEASURE key to accept 4.01 standard and to move to the measure mode of the meter. Pressthe STIRRER key to turn the stirrer off. 10. Rinse the electrode， ATC probe and stirrer thoroughly with deionized water. Gently remove excesssolution from the outer sleeve of the electrode by dabbing with a clean paper tissue. Do not wipe orrub the sensing element. 11. Place the electrode， ATC probe and stirrer into prepared sample with the electrode tip fully immersedin the solution. Press the MEASURE key on the meter； the stirrer will turn on. The pH icon will flashas the measurement is being made. The pH icon will become solid and the display value will freezewhen a stable reading is achieved. This value is logged and printed automatically and the stirrer turnsoff automatically. 12. Repeat steps 10 and 11 for additional samples. Remember to rinse the electrode with deionized waterbetween measurements. Upon completion of samples， rinse the electrode with deionized water andstore the electrode according to instructions in the Electrode Storage section of this method note. Introduction This method describes a procedure for the determination of the pH of Hand Cream. Orion ROss"Sure-Flowelectrodes offer stable， fast results regardless of sample composition. 3. Stainless Steel ATC probe 927007MD 4. Orion benchtop stirrer (or magnetic stir plate and bar) 096019 5. Orion benchtop electrode stand 1110001 6.Beakers (50 mL) 7. Beaker watch glass Required Solutions Cat. No. 1. pH 4.01 buffer (color coded pink) 910104 2. pH 7.00 buffer (color coded yellow) 910107 3. pH 10.01 buffer (color coded blue) 910110 4. ROSS Reference filling solution 810007 5. pH electrode storage solution 910001 6. Deionized water Calibration Standard Preparation 1. Ensure that the buffers are well conditioned to room temperature. 2.Select two buffers which bracket the expected sample pH. The first should be near the electrodeisopotential point (pH 7) and the second near the expected sample pH. 3. Using a graduated cylinder， transfer 30 mL of the pH 7.00 buffer into a 50 mL beaker. 4. Using a graduated cylinder， transfer 30 mL of the pH 4.01 buffer into a 50 mL beaker. Sample Preparation 1. Ensure that the test sample is well conditioned to room temperature. 2. Prepare 10 % aqueous solution of the hand cream by diluting 30 g of sample in 300 mL of deionized water. 3.Dispense approximately 30 mL of prepared solution into a beaker. Cover the beaker with a watch glass. 4. Repeat this procedure for additional measurements. Results Five aliquots of the 10 % (weight/volume) hand cream solution were measured and the results demonstrategood repeatability between replicate tests. Hand Cream pH Sample #1： 6.72 Sample # 2： 6.71Sample #3： 6.69Sample#4： 6.74 Sample # 5： 6.68 Mean： 6.71 Standard Deviation： 0.020.36 %CV： Electrode Storage To ensure a quick response and free-flowing liquid junction， the sensing element and reference junction mustremain wet and not be allowed to dry out. For short-term storage (up to one week)， soak electrode in Orion pHelectrode storage solution. If not available， as a temporary substitute， use about 200 mL of Orion pH 7 bufferwith 1 gm KCl added. For prolonged storage， the reference chamber should be filled with the fill hole cover in place. Cover thesensing element and reference junction with the protective cap containing a few drops of pH storage solution.After prolonged storage， prepare the electrode as described in the Electrode Setup section of this method. There are no specific ATC storage requirements. Equipment Setup Electrode Setup-ROSS Sure-Flow° 1.Remove the protective shipping cap from sensing element and save cap for storage. 2.Clean any salt deposits from the exterior by rinsing with deionized water. 3. Uncover fill hole by removing plastic sleeve， and add ROSS internal filling solution to the electrode. Tomaintain an adequate flow rate， the level of filling solution must cover the coil and be at least one inchabove the sample level when immersed. 4. Thoroughly wet the junction by pressing down on the electrode cap and allowing some of the ROSS fillingsolution to flow out of the electrode through the junction. Replenish lost filling solution. 5.Shake down the electrode to remove air bubbles. 6.Soak electrode in pH electrode storage solution for one hour. For initial meter setup， follow the steps in the Quick Reference Guide attached to the meter itself. TheQuick-Start Guide also contains a layout of the meter keypad for reference. The words in this methodrepresented in all capital letters， such as POWER， indicate a key on the meter， and words in quotations such as“Unit”indicate information on the meter display. 1.Connect the electrode to the meter. Connect the ATC stirrer and probe to the meter. 3P.ress the POWER key on the meter to turn the meter on. 4N.ote that the arrow on the left of the screen indicates the active line. If the top line is not active， press theLINE SELECTION key to change the selected line to the top line. Then press the UP or DOWN arrowkeys to change the measurement mode of the top line to pH. 5P.ress the SETUP key to enter pH setup. Press the LINE SELECTION key to select the middle line. Pressthe UP or DOWN arrow keys to select“rES”which is resolution. 6.Press the LINE SELECTION key to select the bottom line. Press the UP or DOWN arrow keys to select“0.001”for "rES” which is an abbreviation for resolution or number of significant digits. Press the LINESELECTIONkey to accept value. 7.Press the LINE SELECTION key to select the middle line， and press the UP or DOWN arrow key toselect“bUF”which is pH buffer. 8.Press the LINE SELECTION key to select the bottom line， and press the UP or DOWN arrow key toselect“USA”which is US/Orion buffers. 9 Press the LINE SELECTION key to accept and select the pH setup Menu line (top Line). 10. Press the MEASURE key to return to the measurement mode. If all steps were followed correctly the meter display will show three digits in the top line and "ISE： mg/L" tothe right of the top line. The meter and electrode are now ready for calibration. Note： The Orion Benchtop Stirrer must be turned on in General Instrument setup before analysis，please see the Quickstart guide for instructions. www.thermo.comof of of of