2-Electrochemistry

Atomic Absorption

measurment of the conc. of a specific atomic species

ICP-mass spec

ionization source: decompses sample into elements and transforms them into ions

Potentiometry

measures electrical potential difference between 2 electrodes in an electrochemical cell

What 2 electrodes does potentiometry need?

1. indicator: measuring; variable voltage

2. reference: constant voltage

How is an analyte measured with potentiometry?

Measure potential difference between reference and indicator electrode = log of the ion activity

Indicator electrodes

1. ISE #1: semi-permeable

2. Redox: chemical equilibria involving e- transfer

3. pCO2 gas sensing electrode: blood gas

Reference electrodes

1. Standard hydrogen: standardizes other reference electrodes

2. Saturated calomel

3. silver-silver chloride

Ion selective electrode (ISE)

electrodes that selectively interact with a single ionic species

How does ISE work?

potential produced at the membrane/sample solution interface is proprotional to the log of the ionic activity

What do ISE’s measure

ions (free, unbound)

What are ISE made of

-glass

-polymer

-solid state

-gas

-enzyme

The glass ISE electrode is mostly used to measure____.

hydrogen ion activity

What is the common ISE polymer electrode for K+ only

Valinomycin

Solid state electrodes are used to test ____

anions (Cl-)

The ISE enzyme electrode is commonly used to test____and_____

glucose and urea

The pCO2 is a type of____electrode

potentiometric

Direct vs Indirect method of measuring for ISEs

Direct (non-diluted)

-mesures electrolytes of plasma water

-Blood gas, POC

-results independent of solids in a sample

Indirect (diluted)

-measures electrolyte content of total plasma

-Larger chemistry analyzers

-reported results dependent of solids in a sample

How does pseudohyponatremia happen with indirect ISE?

sodium is in the aqueous phase of plasma so dilution in the indirect method can make it unbalanced if low/high proteins/lipids are present

*In the context of pseudohyponatremia, what samples should we be aware of?

-hemolyzed

-lipemic

How does Amperometry/Voltammetry work?

measures current flowing through an electrochemical cell when a constant potential is applied

Clark pO2 Electrode

primary electrode for amperometric measurment

How does Clark electrode measure

current is proportional to pO2 in sample

What is coulometry

measures electrical charge between 2 electrodes

How does coulometry work

-measures charge during electrochemical reaction (charge is proportional to oxidation or reduction of a substance)

-Titration: electrons are added until reaction reaches end. This time is measured

-Charge and titration time are plugged into Faradays law

Unit of measurment for coulometry

couloumbs / sec

What type of titrator is used for coulometry

amperometric titration

The Cotlove Titrator (chloride analysis) is the gold standard for the ___

sweat test (cystic fibrosis)

List normal, intermediate, and abnormal levels for chloride conc.

<40 mmol/L normal

40-60 mmol/L intermediate

> 60 mmol/L abnormal

What is IMT (Integrated Multisensory Technology)

self contained potentiometric chip to determine conc of electrolytes (K, Na, Cl)

How does IMT work

Using Potentiometry

-unknown sample voltage measured and compared to know voltage for a specific electrolyte

What value would tell us that IMT is not working?

Anion gap is too big

-QC issue