Glossary of Chloridometry
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- What are the 4 types of analysis used in chloridometry?
- 1. Manual titration
3. Ion selective electrodes
- what is manual titration?
- adding a definite amt of a known substance to another substance being assayed until an end point is reached.
- what is the reference method for chloride measurement?
What type of sample is measured?
- Schales and Schales method.
-Protein free patient sample filtrate.
- What reaction takes place?
- 2 Cl- + Hg++ -> HgCl2
-Excess mercury combines with the indicator and forms a color.
- what are the disadvantages of the schales and schales method?
- -Very sensitive endpoint to pH
-Halogens can cause false Pos.
-Pigment in serum masks the color change.
-Variability btwn techs.
- How does autoanalysis work for chloride measmnt?
- -with an autoanalyzer!!
-Requires a dialyzer, room temp.
- what are the disadvantages of the autoanalyzer for cl-?
- Only linear between 80-120 mM so it is not applicable for sweat or urine chloride msmt.
- What is coulometry?
- a titration in which the titrant is ELECTROCHEMICALLY generated.
- how does coulemetric titration work in a nutshell?
- titrant reacts with equivalent amounts of sample to produce product.
- what is faraday's law?
- 96487 coulombs generate one equivalent weight of element.
- How is the concentration of unknown found?
- X unknown X standard
---------- = --------------
T unknown T standard
- what are the major components of a coulometer?
- 1. Generator electrode
2. Auxiliary electrode
3. Conducting medium
- what takes place at the generator electrode?
- oxidation - this is the anode!
Ag wire -> Ag+ and e-
- what takes place at the auxiliary electrode?
- reduction - this is the cathode. Nitric acid provides the proton.
2H+ and 2e- -> H2
- What reaction takes place after generation of the titrant?
- Ag+ and Cl- make AgCl precipitate.
- How is the end point detected in coulometric titration?
- After all Cl- is precipitated, excess Ag+ increases the current in the conducting medium. Amperiometric electrodes detect that change in I.
- What stops the titration process?
- a pre-determined value of Ag+ excess; records the time at which it stops.
- what is a chloridometer?
- an instrument for determining Chloride by generating silver titrant coulometrically.
- what 3 things need to be considered in chloridometry?
- what is the blank?
- the time required for the indicator current to trip the relay circuit by rising 10 uA above the initial current after equiv point reached.
- why do you need to consider a blank?
- b/c otherwise the analyte measurement will be too high
- how do you use the blank to correct msmt?
- subtract the blank time from both the standard and unknown T
- one mo time, why run a blank?
- to find the time needed to generate a 10 mA current - that's the current that trips the switch to stop msmt.
- why must titration RATE be considered?
- because different analytes react at different rates. A POTENTIOMETER is used for adjustment.
- What photodecomposition occurs in chloridometry?
- the solid, AgCl, decomposes in light, so the chloridometer CAN'T BE IN DIRECT SUNLIGHT.
- what are the 2 advantages of chloridometry?
- 1. Accuracy - within 0.5%, whereas the other methods are 10% (manual) or 12-15% (colorim)
2. Precision - within 0.3%!
- What the 3 disadvantages of chloridometry?
- 1. Interference from other halides
2. Cyanate and Thiocyanate and Sulfhydryl ions come from the rubber stoppers, interfere w/ msmt.
3. Light sensitive
- how do you correct for those disadvantages?
- -Only use glass/plastic bottles and lids for reagents.
-Keep the chloridometer out of sunlight.
- What needs to be done to maintain and care for the chloridometer?
- -Replinish silver wire and polish it daily.
-Keep electrodes wet to prevent oxidation.
-Condition the electrodes before running the unknown
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