Development of Karl Fischer Reagents
Development of Karl Fischer Reagents
Development of Karl Fischer Reagents
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Chapter I: Basic Knowledge<br />
Na2S2O5+I2+CH3OH � 2NaI+SO2+HSO4CH3<br />
Sodium tetraborate (Na2B4O7) and sodium metaarsenite<br />
react in approximately the same quantities as shown in (d).<br />
The following are examples <strong>of</strong> salts that cause nonquantitative<br />
reactions with <strong>Karl</strong> <strong>Fischer</strong> reagent, and salts<br />
for which the reaction mechanism is not fully understood.<br />
Na2CrO4 � H2O, Mg(NH4)2(CrO4)2 � 6H2O, (NH4)2Cr2O7, Na2S �<br />
9H2O, 20MoO3 � 2H3PO4 � 48H2O, ZrOCl2 � 8H2O, ZrO(NO3) �<br />
2H2O, Al2O(OOCCH3)2 � 4H2O<br />
(g) Reducing agents<br />
When strong reducing agents are titrated, the amount <strong>of</strong><br />
moisture will be higher. Stannous chloride and sodium<br />
thiosulfate react with <strong>Karl</strong> <strong>Fischer</strong> in approximately constant<br />
quantities.<br />
SnCl2 � 2H2O+3I2+2SO2+2CH3OH �<br />
SnI4+2HCl+2HI+2HSO4CH3<br />
2Na2S2O3 � 5H2O+11I2+10SO2+10CH3OH �<br />
2NaI+Na2S4O6+20HI+10HSO4CH3<br />
Sodium sulfide also reacts with iodine.<br />
Na2S+I2 � 2NaI+S<br />
(2) Substances that produce iodine (oxidation reactions) and cause a<br />
negative error<br />
(2.1) Organic compounds<br />
(a) Dichloroisocyanuric acid<br />
Iodine is freed through the oxidation <strong>of</strong> hydriodic acid.<br />
(b) Quinone<br />
Iodine is freed through the oxidation <strong>of</strong> hydriodic acid.<br />
(c) Peroxy acid<br />
Iodine is freed through the oxidation <strong>of</strong> hydriodic acid.<br />
RC(O)OOH+2HI � I2+H2O+CH3COOH<br />
(d) Peroxides (diasyl)<br />
Iodine is freed through the oxidation <strong>of</strong> hydriodic acid<br />
(C6H5COO)2+2HI � I2+2C6H5COOH<br />
(2.2) Inorganic compounds<br />
(a) Chlorine<br />
Iodine is freed through the oxidation <strong>of</strong> hydriodic acid<br />
Cl2+2HI � I2+2HCl<br />
(b) Oxidizing agents<br />
Moisture content appears lower when strong oxidizing are<br />
measured.<br />
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