(CSMLS) ELECTROCHEMISTY & ELECTROLYTES

Question 1

Define “activity” in electrochemsitry

Answer 1

Concentration of an electrolyte measured in an electrochemical cell (used in Nernst equation)

Question 2

Define “activity coefficient”

Answer 2

Activity of an electrolyte divided by molar concentration
- measurement of the interaction of selected electrolytes with other species in the solution

Question 3

Define “potentiometry”

Answer 3

Measures electric potential (E) between two electrodes under equilibrium conditions

Question 4

Components of a potentiometric ion-selective electrode (ISE)

Answer 4

(Ref)erence electrode: stable/ constant potential relative to sample solution
- has a junction (frit) to allow electrical, ionic conductivity (E jxn) between sample and internal chloride sol’n while preventing large convective mixing of sol’ns

(Ind)icator electrode: has an ion selective membrane
- potential occurs when there is a difference in activity of ions on either side of membrane

Question 5

Physical vs Chemical Properties of an Electrochemical cell

Question 6

What equation describes the selectivity of an ISE ?

Answer 6

Nicolsky-Eisenman

Question 7

List 6 general sources of error/ limitations for ISE

Answer 7

1. Temperature dependent
2. Ionic strength affects activity coefficient
3. pH - inadequate conversion of analyte to one form ie. calcium
4. Biofouling - protein buildup on membrane
5. Cross-reacting ions
6. Electrolyte exclusion effect

Question 8

What is an anion gap ?

Answer 8

The gap between measured cations and anions due to unmeasured anions (proteins, sulphates, phosphates…) and unmeasured cations (calcium, magnesium)

Question 9

__ is a common reference electrode

Answer 9

Ag/Ag electrode

Question 10

Normal plasma sample is __% water and _% lipid

Answer 10

Normal plasma sample is 92% water and 8% lipid

Question 11

Describe pH ISE, including specimen type, and sources of error

Answer 11

glass membrane
ion-exchange along membrane alters electrical potential
change in potential is correlated to H+ activity
Sources of Error:
- temperature dependent; as T increases, pH decreases
- exposure to air decreases CO2 and increases pH

Question 12

Lipemia plasma sample is __% water and __% lipid

Answer 12

Lipemia plasma sample is 75% water and 25% lipid

Question 13

What is an ionophore ?

Answer 13

neutral ion carrier
reversibly bind ions at membrane surface while counter-ions remain in solution = electric potential
Eg. valinomycin binds potassium

Question 14

Describe principle of CO2 ISE

Answer 14

• gas permeable membrane; Teflon or silicon rubber
• CO2 passes membrane and dissolves within inner electrolyte sol’n
• bicarbonate and H+ form
• H+ is detected by interior pH ISE; change in membrane potential is proportional to pCO2

Question 15

Sources of error for CO2 ISE

Answer 15

• Air exposure decreases [CO2]; false increase in pH
• Biofouling
• Temperature, barometric pressure, incorrect calibration

Question 16

Sources of error for ISEs

Answer 16

1. Fist pumping = increased Ca2+, K+
2. Hemolysis = increased K+, phosphorus, Mg+
3. Icterus = falsely increased phosphorus
4. Lipemia (Na+ falsely decreased in indirect ISE)

Question 17

Describe the electrolyte exclusion effect

Answer 17

• Exclusion of electrolyte from the fraction of total plasma volume that is occupied by solids
• Electrolytes are accounted for in the water content of sample, not solid
• Sodium concentration is falsely decreased in samples with increased proportions of solids

Question 18

Causes of increased anion gap

Answer 18

• diabetic ketoacidosis
• lactic acidosis
• renal failure
• renal tubular acidosis
• diarrhea, starvation
• decreased renal tubular reabsorption of bicarbonate
• intoxication (ethanol, methanol, ethylene glycol)
• metabolic alkalosis; proteins gain negative charges = increased unmeasured anions

Question 19

Causes of decreased anion gap

Answer 19

• hypoalbuminemia (primary unmeasured anion)
• increased cations; hypercalcemia and hypermagnesemia
• hypergammaglobulinemia; paraproteins (ie. IgG) have a positive charge
• laboratory error

Question 20

How is sodium regulated ?

Answer 20

By the kidneys and renin angiotensin aldosterone system:
- DROP IN BLOOD PRESSURE AND FLUIDS causes kidneys to release renin
- liver releases angiotensin = activated by renin
- angiotensin II stimulates adrenal grand to release aldosterone
- aldosterone = KIDNEYS REABSORB SALT and WATER

Question 21

How is chloride regulated ?

Answer 21

• by the kidney and the renin angiotensin aldosterone system (same as sodium)
• excess chloride is excreted in sweat and urine

Question 22

How is potassium regulated ?

Answer 22

By the kidney, aldosterone and insulin

Question 23

How is bicarbonate regulated ?

Answer 23

The kidneys and lungs regulate bicarbonate and CO2 levels

Question 24

What is metabolic alkalosis associated with ?

Answer 24

Increase in bicarbonate

Question 25

What is metabolic acidosis associated with ?

Answer 25

decrease in bicarbonate

Question 26

How is calcium regulated ?

Answer 26

1. parathyroid hormone (PTH): - directly increases Ca2+ levels by increasing calcium reabsorption in the distal convoluted tube - indirectly increases calcium by inducing 1 α-hydrolase activity = production of calcitrol - directly increases bone resorption 2. Calcitrol: - synthesized from vitamin D by actions of liver and kidney (1 α-hydrolase) - increases Ca2+ levels by increasing vitamin D absorption and increasing bone resorption

Question 27

How is phosphate regulated ?

Answer 27

Regulated by PTH and calcitrol - PTH decreases blood phosphate by decreasing phosphate reabsorption in the PCT - calcitrol increases blood phosphate by increasing phosphate absorption in the intestines; at high levels = bone resorption

Question 28

How is magnesium regulated ?

Answer 28

NONE - but magnesium does influence PTH secretion

Question 29

What is Conn’s syndrome ?

Answer 29

- a type of hyperadrenalism - primary hyperaldosteronism; hypersecretion of aldosterone by adrenal adenoma - electrolyte imbalance = increased plasma Na+, decreased plasma K+

Question 29

What is Cushing’s syndrome ?

Answer 29

- a type of hyperadrenalism - increased plasma cortisol; can suppress ADH - linked to pituitary tumors - electrolyte imbalance = increased plasma Na+, decreased plasma K+

Question 30

What is Secondary Hyperaldosteronism ?

Answer 30

- a type of hyperadrenalism - caused by decreased blood flow to kidney (ie. CHF, nephorotic syndrome, stenosis) - electrolyte imbalance = increased plasma Na+, decreased plasma K+

Question 31

What is Addison’s disease ?

Answer 31

- a type of hypoadrenalism - primary adrenal disease affecting entire adrenal cortex - decreased cortisol and aldosterone - increased ACTH; by pituitary to compensate for decreased adrenal hormones - electrolyte imbalance = decreased plasma Na+, increased plasma K+ - also associated to hypoglycemia

Question 32

What is SIADH ?

Answer 32

- syndrome of inappropriate antidiuretic hormone - ectopic overproduction of ADH; associated with lung cancer - electrolyte imbalance = decreased plasma Na+, increased plasma K+ - increased urine osmolality

Question 33

What is Rhabdomyolysis ?

Answer 33

- breakdown of skeletal muscle (after trauma) - myoglobinuria - electrolyte imbalance = hyperkalemia

Question 34

What is Fanconi’s Syndrome ?

Answer 34

- renal tubular defects - electrolyte imbalance = hypophosphatemia

Question 35

What are Rickets and Osteomalacia ?

Answer 35

- metabolic bone disorders; imbalanced bone formation and resorption - defective mineralization of bone due to vitamin D deficiency OR phosphate depletion - electrolyte imbalance = hypophosphatemia

Question 36

Which of the following can increase the electrolyte detection limits of a polymer ISE? a. decreasing the concentration of electrolyte in the electrode internal solution b. increasing the size of the frit c. recharging the electrode in an acidic buffer between samples d. substituting polystyrene for polyvinylchloride

Answer 36

a. decreasing the concentration of electrolyte in the electrode internal solution

Question 37

Membrane potential is proportional to the __ of the ion concentration

Answer 37

Membrane potential is proportional to the LOGARITHM of the ion concentration

Question 38

Which of the following chemicals is a main component of glass ISE membranes? a. tellurium dioxide b. lead (II) oxide c. silicon dioxide d. sodium carbonate

Answer 38

c. silicon dioxide

Question 39

Where is the majority of the body's magnesium and phosphate located ?

Answer 39

bones

Question 40

T or F: If the arm tourniquet is not released before the beginning of the draw, the plasma total calcium concentrations will be falsely decreased.

Answer 40

FALSE; If the arm tourniquet is not released before the beginning of the draw, the plasma IONIZED calcium concentrations will be falsely INCREASED.

Question 41

Which condition could be associated with a sodium of 151 mmol/L? a. normal health b. mannitol therapy c. Conn syndrome d. electrolyte exclusion effect

Answer 41

c. Conn syndrome Reference Interval: 133-146 mmol/L Critical Value: <125 or > 155

Question 42

T or F: Hemolysis will cause falsely elevated sodium concentrations.

Answer 42

FALSE; hemolysis and icterus DOES NOT cause interference in sodium levels

Question 43

T or F: Icterus does NOT interfere with the ammonium molybdate method (340 nm) for measuring phosphate.

Answer 43

FALSE; Icterus DOES interfere with the ammonium molybdate method (340 nm) for measuring phosphate.

Question 44

Which of the following indices is routinely measured using conductometry? a. hematocrit b. anion gap c. TIBC d. osmolal gap

Answer 44

a. hematocrit