[Himik_1982]

Dear chemists!
Please help me to solve a problem.
There is a solution for zinc coatings: appr. 100 g/l NaOH, 10 g/l ZnO. I need to determine free NaOH (by HCl titration) and mask Na₂CO₃ by BaCl₂. They advise to mask Zn by K₄[Fe(CN)₆], but precipitation of Zn₃K₂[Fe(CN)₆]₂ may not occur cause of its good solubility in NaOH. Are there any other ways of simple Zn masking in my system?
Thanks.

[Himik_1982]

I speak Russian, so may be word "masking'' is out of date (or unfamiliar) in modern analytical chemistry? To mask means to hide an ion that can cause errors.

[AWK]

Probably no masking of Zn is needed. Just use a proper indicator

[Himik_1982]

Probably no masking of Zn is needed. Just use a proper indicator

2 AWK
Well, phenolphthalein is proper one. I can't use methyl red (and others changing their colour at low pH) because of BaCO3 dissolution. As far as I understood, Zn masking prevents lower results. Zn(OH)2, Zn(OH)3- still exist when phenolphthalein looses its colour (appr. at 8,2). So Zn binding plays a role of OH- liberation.