I am looking for a robust way to measure a high presumed concentration of Ca2+ (up to 2 mg/mL) in a sample. So far, I have come across several kits for Ca-measurements in cells, however, they don't allow for these high concentrations to be measured. Does anyone know of a method that can be used? Sadly, I don't have access to a flame spectophotometer.
I can't tell from your question if you are trying to assay Ca in a cell or a solution.
If a cell, 2 mg/ml is on the order of 10 mM. That's not a very happy cell. One can measure calcium with fluorescent indicators, but I agree this is higher than most indicators work. You would need a super-low affinity one, and hope to squeeze out signal at the upper end. Even mag-fura-2 wouldn't work, I expect.
If a solution, you can use a calcium sensitive electrode. I did this ages ago, and Fisher still sells these. You plug it into your pH meter, and record the voltage for different standard solutions. Then you put the probe in your sample, measure the voltage and calculate the calcium concentration. I just looked at the Orion one, and it says it is linear up to about 1 M, and they recommend dilution if you are above that.
Maybe dilution of sample to text so that it could be within range of your kits
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