Clinical Chemistry -- Exam 1

Wavelengths of light are measured in _____ units.

Nanometer (nm)

Match the following approximate wavelength ranges to the correct region name:

180-380 nm

Ultraviolet

Match the following approximate wavelength ranges to the correct region name:

380-750 nm

Visible

Match the following approximate wavelength ranges to the correct region name:

750-1200 nm

Infrared

Match the common light source used for the following regions of wavelengths:

Deuterium

Ultraviolet

Match the common light source used for the following regions of wavelengths:

Tungsten

Visible

Match the common light source used for the following regions of wavelengths:

Hydrogen

Ultraviolet

Match the common light source used for the following regions of wavelengths:

Mercury arc

Ultraviolet

Which of the following curves can be used to determine the optimal wavelength to use for a

given spectrophotometric procedure:

Spectral absorbance curve, spectral transmission curve

The optimal wavelength of light of a test solution may be defined as the wavelength of light

that produces the ________ peak on a spectral absorbance curve.

Maximum absorbance

The optimal wavelength of light of a test solution may be defined as the wavelength of light

that produces the ________ peak on a spectral transmission curve.

Minimum %Transmission

The optimal wavelength of light is the wavelength of light producing the maximum absorbance peak

which is the same as the wavelength of light producing the minimum %Transmission peak.

True

If the %T value is 62.0%, the absorbance value may be calculated as ____.

0.208

When measuring the response of a test solution, the instrument detects the amount of incident light

that is absorbed by the compound of interest in the test solution.

False

The intensity of light being transmitted through a test solution (Is) is expected to be less than the

original incident light (Io) due to incident light being:

Absorbed by the compound of interest, absorbed by reagent or solvent molecules, reflected off the surface of the sample cell

Setting the baseline of the spectrophotometer to 100%T is the same as setting the baseline to

0.000ABS

True

Choose the correct relationship statement (choose all correct answers):

Absorbance and concentration are directly related, transmission and concentration are inversely and logarithmically related

By using a lightpath length of 2cm as compared to a standard 1cm lightpath, it is expected

the absorbance value will _______.

Double because there will be twice as many absorbing molecules for the light to pass

through

The maximum absorbance wavelength will be the same as the minimum %T wavelength.

True

A curvy line will result when plotting absorbance and concentration on linear graph paper.

False

Upper limit of linearity

Concentration of substance is at the highest

level where concentration and absorbance are still

directly related

Exceeds upper limit of linearity

Concentration of substance is too high and absorbance and concentration are no longer directly related

Lower limit of sensitivity

Concentration of substance is at the lowest level where concentration and absorbance are still directly related

Less than lower limit of sensitivity

Concentration of substance is too low and absorbance and concentration are no longer directly related

Beer’s Law states that:

Absorbance is directly related to concentration of substance in solution only to the upper

limit of linearity and above the lower limit of sensitivity.

Calculate the concentration of substance using the Beer’s Law equation and the following

data:

absorbance = 1.650

millimolar absorptivity constant = 0.235

light path length = 2cm

3.5

Evaluate the following data:

Limit of linearity: 1250 mg/dL

Limit of Sensitivity: 1.0 mg/dL

Specimen test result: 1500 mg/dL

The action that best correlates with this data is to:

Do not report; dilute specimen, repeat analysis, and correct for dilution.

Which component corresponds with A?

Light source

Which component corresponds with B?

Entrance slit

Which component corresponds with C?

Monochromator

Which component corresponds with D?

Exit slit

Which component corresponds with E?

Cuvet

Which component corresponds with F?

Detector

Which component corresponds with G?

Meter

Light source

provides polychromatic incident radiation (light)

Monochromator

separates or disperses polychromatic light into the individual wavelengths

Exit slit

isolates the desired wavelength to pass through the test solution

Cuvette

holds the test sample for light to beam through

Detector

measures the amount of light passing through the test cuvette (PMT)

Meter

readout device (Abs, %T, units)

What are the advantages of using a narrow bandpass instrument as compared to a wide bandpass instrument?

Increases sensitivity of the instrument (can detect lower concentration of substance), increases linearity of the instrument (can detect higher concentration of substance), increases resolution of substances in test solution (able to differentiate absorbance peaks from similar compounds; this means the specificity is improved.)

Explain how lipemic test samples will falsely affect spectrophotometric test results including how lipemia affects %T and absorbance values and if you expect the test result to be falsely increased or falsely decreased (or have no affect at all).

Lipemic test samples will cause the %T of light going through the test sample to be decreased. This equates to the ABS value being falsely increased.

The purpose of performing preventive maintenance on instruments is to:

All of the above are correct

After performing preventive maintenance, quality control specimens are analyzed to verify instrument performance has not been jeopardized by doing the maintenance.

True

Checks for changes in bandpass and the amount of light energy falling on the photocell ensuring a constant and stable ABS value is obtained

Photometric Accuracy

Checks for presence of extraneous light striking the detector

Stray Light Detection

Ensures light energy being emitted from the monochromator’s exit slit is the same wavelength as that set on the wavelength dial

Wavelength Accuracy

Ensures reaction temperature is accurate and stable

Temperature Calibration

Ensure the response (ABS) from various dilutions of a check solution are linear and proportional

Photometric Linearity

Ensures the blank reading when set at 100%T/0.000 ABS is stable over time

Baseline Stability

Colorimetry is best defined as the measurement of

Colored compounds in solution

A spectral absorbance curve is used to determine the

Optimal wavelength of a specific test solution

A reagent blank is used in spectrophotometric measurements to

Negate the effects of reagent absorption

Choose the correct relationship statement:

Maximum absorbance correlates to minimum %T

Plotting ______ and concentration on ____ graph paper will result in a ______ line.

Absorbance; linear; straight

The upper limit of linearity on a standard curve is defined as the:

Highest concentration of substance that follows Beer’s Law

Evaluate the following data:
     Limit of linearity: 500.0 mg/dL
     Limit of Sensitivity: 1.0 mg/dL
     Specimen test result: 0.5 mg/dL
The action that best correlates with this data is to report the specimen test result as:

Report the specimen test result as <1.0 mg/dL

The purpose of the ‘Wavelength Accuracy’ Performance Check on a spectrophotometer
is to:

Confirm exit slit is set at the specified wavelength

Potential

Expression of energy

Current

Flow of a charge

Measuring electrode

Where sample activity is measured

Reference electrode

Device that can maintain a constant potential under a variety of conditions

Salt bridge

Device that allows ionic movement between compartments of an electrochemical cell to maintain an electrical current

Most common reference electrode

Silver/Silver Chloride Electrode

Amperometry

Measurement of the current flowing between two electrodes and generally involves an oxidation/reduction type of reaction

Potentiometry

Measurement of electrical (potential) difference between the measuring and reference electrodes

When calibrating electrodes, a “two point” calibration is performed to correct for:

Changes in the slope of the calibration line

What type of membrane does the pH electrode have?

Glass

This amperometric electrode measures an analyte that passes through a membrane that has an enzyme immobilized its middle layer:

Glucose

The principle of measurement of the pCO₂ and pH electrodes is:

Potentiometry

The sodium ion-selective electrode has ____________ as its membrane.

Specially formulated glass

The co-oximeter is a spectrophotometer which requires samples to be?

Well-mixed whole blood

Which of the following should be performed daily on the blood gas analyzers for preventative maintenance?

Injecting a cleaning solution through the system

Which of the following statements does NOT apply to enzymes:

Enzymes are resistant to denaturation

Choose the FALSE statement about isoenzymes:

Are not helpful in diagnosis of disease

An advantage of the kinetic method for measuring enzyme activity versus an end-point method is that it:

It is easier to demonstrate linearity of the reaction sequence
Substrate depletion is observable
Is the most accurate method of measurement

Which of the following phases of an enzyme reaction is the most accurate phase to measure enzyme activity?

Linear phase

The linear phase of an enzyme reaction is defined as when

The amount of product formed is consistent per unit of time
The change in absorbance per unit of time is consistent

Activation energy is:

decreased by enzymes

Enzyme reaction rates are increased by increasing temperatures until they reach the point of denaturation at:

40° - 60°C

Competitive inhibition

Inhibitor binds to active site of enzyme (E-I); this complex competes with free enzyme for substrate binding sites and prevents product formation. Generally reversible by diluting patient sample (ie increasing substrate concentration and changing the substrate to sample ratio)

Noncompetitive inhibition

Inhibitor binds to regulatory or allosteric site of enzyme (E-I); this complex prevents product formation

Uncompetitive inhibition

Inhibitor binds to enzyme-substrate complex that has formed (ES-I), preventing product formation

The first step of the reaction is called the ___________ and the final step of the reaction is generally called the ___________ step.

rate-limiting / measuring

Which of the following co-enzymes shows an absorbance peak at 340 nm?

NADH

When a reaction is performed in zero-order kinetics the:

Rate of the reaction is independent of the substrate concentration

low substrate concentration

The velocity of the reaction is approximately proportional to the substrate concentration

first-order kinetics

The velocity of the reaction is approximately proportional to the substrate concentration

zero-order kinetics

The velocity of the reaction is independent of the substrate concentration

high substrate concentration

The velocity of the reaction is independent of the substrate concentration

Certain factors affect the rate of enzyme-catalyzed reactions and must be controlled during the analysis to ensure accurate test results. Factors that are controlled during analysis include all the following EXCEPT:

Enzyme concentration in patient sample

An enzyme may be defined as a:

Protein catalyst of biological origin

The general relationship among the principle ‘players’ in an enzyme catalyzed reaction may be represented as follows: S + E → ES → P + E, The ‘ES’ stands for which of the following:

Enzyme-substrate complex

The site at which an enzyme binds to its substrate is called the:

Active site

To obtain valid measurements, enzyme activity measurements must be made in:

Zero-order kinetics

The Michaelis-Menten constant (Km), can be defined as the:

Substrate concentrate required to achieve ½Vmax

Which of the following terms is best described by the statement:
The velocity of a kinetic enzyme reaction (i.e. the amount of product formed) is dependent upon the concentration of enzyme in the test sample

Zero order

The rate of an enzyme reaction approximately doubles for every ____°C rise in temperature.

10

Which of the following best describes a kinetic monitoring system for enzyme analysis:

The rate of product formation is monitored throughout the reaction period