Please could you give me an idea of how to measure pH in a volume ~100 µl if I don't have an appropriate pH meter?
I had an idea to use fluorescent ph-sensitive tags.
I would also use a pH sensitive fluorophore in the situation. I have previously used Carboxy SNARF (http://tools.lifetechnologies.com/content/sfs/manuals/mp01270.pdf). It has the advantage that its emission spectrum is more sensitive to pH than its excitation spectrum. Thus one can use a single laser line (in this case 488 nm) for excitation and measure the ration of emission intensities at two wavelength. This makes it convenient for florescence microscopy. If you can measure fluorescence excitation spectra as well (ration of emission intensities for two different excitation wavelength) you have more fluorophores to choose from (including ordinary fluorescein - though I'm sure there are better dyes available). See e.g. http://www.lifetechnologies.com/sg/en/home/references/molecular-probes-the-handbook/ph-indicators.html
Use pH sensitive fluorophore like norharmane (NHM). it is highly sensitive to pH.
Had to deal with this problem today. In case somebody encounter it I copy here a link to fluorophores info: https://www.thermofisher.com/content/dam/LifeTech/global/technical-reference-library/Molecular%20Probes%20Handbook/chapter-pdfs/Ch-20-pH-Indicators.pdf?icid=WE216841
Also, medical/veterinarian equipment is capable of measuring pH in the volume of 0.1 mL. They are called blood gas analyzers. They measure pH as well. The older machines use non-disposable probes, so the owners might mind you using it for chemicals. The newer machines have disposable probes (cartridges), so testing chemicals should be OK. They do measure just static condition. The cost of a cartridge is about $25 US.
Vasily, have you tried finally in your experiments some fluorophores? What is your opinion to use them for pH measurements of microvolumes?
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