A LAZAR LABORATORIES HANDBOOK MICRO pH …

1 A LAZAR LABORATORIES HANDBOOK MICRO pH measurement primer Answers to your basic MICRO pH measurement questions with helpful hints Copyright LAZAR Research LABORATORIES , Inc. 2000-2004 LAZAR Research LABORATORIES , Inc. MICRO pH measurement primer 2 About LAZAR Research LABORATORIES , Inc. LAZAR Research LABORATORIES , Inc., known as the MICRO measurement Experts have been coaching researchers on measuring small samples for over 27 years. Our knowledge has helped researchers in all scientific arenas including biotechnology, biomedical research, microchemistry, chemical engineering, environmental science, geology and more. Our family of MICRO pH electrodes are the premier product for measuring pH in samples smaller than 1 millilter. Free consultation For all your MICRO measurement questions Call us at 1-800-824-2066 (1-323-931-1204 international), fax us at 1-323-931-1204, or email us at and we will put our 27 years of experience in the MICRO measurement field at your disposal.

2 There is no cost or obligation for this service. Contact LAZAR Research LABORATORIES , Inc. Email: Website: Fax: 1-323-931-1434 Phone: 1-323-931-1204 1-800-824-2066 (toll free in the only) Address: LAZAR Research LABORATORIES , Inc. 731 North Labrea Avenue, Building 5 Los Angeles, California 90038 LAZAR Research LABORATORIES , Inc. MICRO pH measurement primer 3 TABLE OF CONTENTS 1. MICRO pH measurement Basics 2. MICRO measurement Hints 3. Recommended electrodes for measuring pH in various applications Standard pH Electrode NMR pH Electrode MICRO Surface pH Electrode MICRO Flow-Through pH Electrodes 4. Other Common MICRO Measurements Redox Measurements p02 & pC02 p02 in tissue samples 5. Measuring Ions in MICRO Samples Overview Hints MICRO electrodes for K, Na, Cl, and other Ions 6.

3 Placing an Order and Requesting Pricing Information LAZAR Research LABORATORIES , Inc. MICRO pH measurement primer 4 1. MICRO pH measurement BASICS MICRO volumes are generally considered those which are below 1 ml and all the way down to just a few microliters. Standard pH electrodes whose technology has been continuously improved over the last 60 years do not normally lend themselves to the measurement of MICRO volumes. This is due to the fact that glass pH technology normally precludes the manufacture of very small glass pH sensors which will function with the same accuracy, precision, and speed as standard size glass pH electrodes. The problems that are encountered when the glass pH membrane is miniaturized are as follows: 1. High resistance - A standard glass electrode already has a very high output resistance which is on the order of several hundred megohms.

4 The higher the resistance of the electrode the weaker the signal is to the pH meter. Using ohms law we see that for the same output voltage the higher the resistance the lower the current (signal strength) between the pH electrode and the reference electrode. The very low signal strength of a standard size pH electrode requires that the output cable be specially shielded and that the pH meter have an ultra high input resistance (normally 1 million megohms).The weak signal strength of the standard glass pH electrode is particularly problematic with the presence of electrical noise from electrical appliances or even fluorescent lights in the laboratory. The lower the signal strength the lower the signal to noise ratio. A low signal to noise ratio produces a signal which is unstable and difficult to read. Standard size pH have been optimized in the last several years giving very stable accurate signals even though the signal strength is relatively low.

5 When a glass pH electrode is miniaturized the resistance of the electrode goes up inversely proportional to the surface area of pH electrode. For example, if we take a standard size pH glass sensor (10 mm diameter) and reduce it to a MICRO pH electrode with a 1 mm glass sensor the resistance will increase by a factor of 100 (the surface area is related to the square of the diameter-10x10=100 1x1=1). The surface area of the 10 mm glass pH bulb is 100 times greater than the surface area of the 1 mm glass pH bulb. LAZAR Research LABORATORIES , Inc. has overcome the high resistance problem with small pH electrodes by producing a solid state pH sensor which has an output resistance which is significantly lower than any MICRO glass pH electrode. The lower resistance leads to a significantly higher signal strength. The higher signal strength gives a higher signal to noise ratio and a corresponding more stable and accurate pH reading.

6 2. Fragility - In order to try to compensate for the increase in resistance with decrease in pH electrode size, manufacturers have tried to decrease the thickness of the pH bulb which somewhat reduces the overall resistance. As we all know, standard size glass pH sensors are already quite fragile. When the pH bulb is made even thinner this results in significant loss of strength in the bulb and frequent pH bulb breakage and replacement. Besides the fragile pH bulb, the long thin glass stem of these MICRO glassp H electrodes makes them very fragile and prone to breakage by even the smallest mechanical stress. LAZAR Research LABORATORIES , Inc. MICRO pH measurement primer 5 LAZAR Research LABORATORIES , has overcome the fragility problem by not only using a solid state pH sensor which is unbreakable, but also using a totally flexible fluoropolymer pH stem which can be bent to 90 degrees and even dropped on the lab floor without breakage.

7 LAZAR is so confident that their MICRO pH electrode will not break, that it guarantees the electrode against breakage for the life of the electrode. LAZAR Research LABORATORIES , Inc. MICRO pH measurement primer 62. MICRO pH measurement HINTS 1. Solution carryover - Solution carryover from one sample to another is more critical for MICRO samples than macro type samples because of the small volumes that are being measured. One should exercise care in thoroughly rinsing the MICRO pH probe with liberal amounts of DI water and then wiping dry with a lab paper wiper in going from one sample to the next. 2. Reduction of Noise Pickup - In order to reduce noise pickup and thereby get the most accurate and stable results, MICRO pH measurements should be done in a lab environment where electrical noise is minimized. This is simply done by not operating any mechanical devices such as lab mixers, pumps, etc.

8 In the proximity of the sample during measurement and replacing any flickering (defective) fluorescent lights in the vicinity of thesample. 3. Stirring - Stirring of MICRO samples during measurement is often not feasible due to the small size of the samples. To get the most accurate results the pH buffer solutions that are used to calibrate the MICRO pH electrode should be placed in relatively small volume containers (2 to 10 ml) and should also not be stirred. 4. Ground loops - Occasionally users have tried to dip two different MICRO probes ( pH and ion electrodes) into the same sample using two separate pH meters at the same time. Unless one is very careful, the common circuit ground (same power outlet) that the two pH meters share can lead to a ground loop which may give an erroneous reading. If two electrodes need to be used in the same sample at one time with two different pH meters, it is best to use pH meters that are battery powered.

9 LAZAR Research LABORATORIES , Inc. MICRO pH measurement primer 73. RECOMMENDATIONS FOR MEASURING pH in VARIOUS APPLICATIONS MICRO COMBINATION pH ELECTRODE NMR MICRO pH ELECTRODE MICRO SURFACE pH ELECTRODE 96 well plates MICRO test tubes serum ups capillary tubes NMR tubes microcentrifuge tubes We recommend the Ultra M family of MICRO pH electrodes for these applications for the following reasons: MEASURE pH IN 1/10 OF A DROP. This electrode enables you to measure samples as small as 5 microliters (1/10 of a drop) EXTREMELY SMALL SENSOR SIZE. Tip diameter of the Ultra M electrode is only 1mm. LOW IMMERSION DEPTH. Immersion depth for the Ultra M microcombination electrode is 1 mm. For even lower immersion depths use the PHM-146 MICRO pH mono probe with an immersion depth of mm.

10 The Model PHR-146F MICRO flat surface pH probe is also applicable to low immersion depth measurements. GUARANTEED UNBREAKABLE. Electrode features solid state sensor and fluoropolymer capillary tube making it virtually unbreakable. Electrode is guaranteed against breakage for the life of the probe. Why settle for glass? MORE STABLE THAN GLASS ELECTRODES. The solid state design of the probe offers a much lower output resistance than glass probes of the same size giving a much more stable pH reading. BROAD pH RANGE. The pH range of the Ultra M combination pH probe is 1 to 12. COMPATIBLE WITH ALL LABORATORY pH METERS. The Ultra M MICRO comb. pH probe is compatible with all major brand pH meters including Orion(R), Beckman(R) Corning(R), Fisher(R), and Radiometer(R). Specify meter when ordering. MICRO NMR pH ELECTRODE A longer version of the standard MICRO combination pH electrode with same 1 mm pH sensor, same 2 mm stem diameter, but with longer 220 mm stem length.