In a fluorimeter, the emitted light is measured at a right angle to the exciting beam. Why?

To keep the exciting light out of the detector

To increase the wavelength of the emitted light

To remove the need for an emission filter

To allow two samples to be read together

Laboratory instruments

24 Kerala PSC Lab Technician Gr II practice questions on Laboratory instruments, part of Biochemistry. The first 24 are below; the first 5 with answers and explanations (tap Show answer after you have chosen), the rest in Learn with a free account.

Question 1 · Hard
Glucose by GOD-POD is read against distilled water: reagent blank 0.05, standard (100 mg/dL) 0.45 and test 0.65. What is the glucose concentration?
1. A144 mg/dL
2. B67 mg/dL
3. C133 mg/dL
4. D150 mg/dL
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Answer: D · 150 mg/dL
Subtract the reagent blank from both readings: test 0.65 - 0.05 = 0.60 and standard 0.45 - 0.05 = 0.40. Glucose = (0.60 / 0.40) x 100 = 150 mg/dL. Leaving the blank in gives 144 mg/dL, and inverting the ratio gives 67 mg/dL. Setting the instrument to zero with the reagent blank instead of water removes this step.
- A: 144 mg/dL comes from not subtracting the blank (0.65/0.45 x 100).
- B: 67 mg/dL comes from inverting the ratio (0.40/0.60 x 100).
- C: 133 mg/dL comes from correcting only the test reading (0.60/0.45 x 100).
Question 2 · Medium
In a fluorimeter, the emitted light is measured at a right angle to the exciting beam. Why?
1. ATo increase the wavelength of the emitted light
2. BTo remove the need for an emission filter
3. CTo allow two samples to be read together
4. DTo keep the exciting light out of the detector
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Answer: D · To keep the exciting light out of the detector
Fluorescent molecules absorb light of one wavelength and emit light of a longer wavelength in all directions. With the detector at 90 degrees, the strong transmitted exciting beam does not reach it, so mainly emitted light is measured. An emission filter or monochromator removes any scattered exciting light. This arrangement gives fluorimetry much greater sensitivity than absorption photometry.
- A: The emission wavelength is set by the molecule, not by the detector angle.
- B: A fluorimeter still needs both an excitation and an emission filter or monochromator.
- C: The right-angle geometry serves one sample beam; it does not read two samples.
Question 3 · Easy
In a flame photometer, sodium emits light of which color?
1. ABrick red
2. BYellow
3. CCrimson red
4. DViolet
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Answer: B · Yellow
Excited sodium atoms emit light at 589 nm, which is yellow, and the instrument reads this line through a matching filter. Potassium gives a lilac (violet) flame and is read at 766 nm, lithium gives crimson red and calcium brick red. Flame photometers are used mainly for sodium and potassium in serum and urine, and many use lithium as an internal standard.
- A: Brick red is the flame color of calcium.
- C: Crimson red is the flame color of lithium.
- D: Violet (lilac) is the flame color of potassium.
Question 4 · Easy
In atomic absorption spectrophotometry, what is the cathode of the hollow cathode lamp made of?
1. ADeuterium for all elements
2. BMercury for all elements
3. CTungsten for all elements
4. DThe element being measured
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Answer: D · The element being measured
The lamp's cathode is made of, or coated with, the same metal that is to be measured, so it emits that element's exact resonance lines. Ground-state atoms of the element in the flame absorb these lines, and the absorbance is proportional to concentration. This gives AAS high specificity, but a separate lamp is needed for each element, such as calcium, magnesium, lead, zinc or copper.
- A: A deuterium lamp gives continuous ultraviolet light for UV spectrophotometry.
- B: A mercury vapor lamp gives mercury lines only and is used as a source in some fluorimeters.
- C: A tungsten lamp gives continuous visible light for colorimeters and spectrophotometers.
Question 5 · Medium
A colorimetric test gives a red solution. Which filter color should be selected to read it?
1. AGreen
2. BYellow
3. CRed
4. DOrange
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Answer: A · Green
A solution looks red because it transmits red light and absorbs its complementary color, green. The filter must pass the light that the solution absorbs most, so a green filter gives the greatest change in absorbance with concentration. Red, orange or yellow light passes through the solution, so readings change little and sensitivity is poor. In practice, the best filter is the one that gives the highest absorbance against the blank.
- B: Yellow light is also poorly absorbed by a red solution.
- C: A red solution transmits red light, so a red filter gives almost no absorbance.
- D: Orange light is largely transmitted by a red solution, giving poor sensitivity.
Question 6 · Medium
Atomic absorption spectrophotometry differs from flame emission photometry in that it measures light:
1. AScattered by suspended particles
2. BEmitted by fluorescent molecules
3. CAbsorbed by ground-state atoms
4. DEmitted by excited atoms
Answer and explanation in LearnFree account
Question 7 · Easy
A centrifuge rotor whose tube holders lie level during the spin, so the sediment packs flat at the tube bottom, is called a:
1. AVertical rotor
2. BZonal rotor
3. CFixed-angle rotor
4. DSwing-out rotor
Answer and explanation in LearnFree account
Question 8 · Easy
Firefly luciferase reacts with ATP and gives off light. Which instrument measures this light?
1. AFluorimeter
2. BLuminometer
3. CNephelometer
4. DFlame photometer
Answer and explanation in LearnFree account
Question 9 · Medium
A spectrophotometer is more specific than a filter colorimeter mainly because its prism or grating:
1. ASelects a narrow band of wavelengths
2. BIncreases the intensity of the light
3. CLengthens the light path in the cuvette
4. DRemoves the need for a reagent blank
Answer and explanation in LearnFree account
Question 10 · Hard
A pH meter is calibrated with pH 4.00 and 7.00 buffers and then used to adjust a carbonate-bicarbonate buffer to pH 10.0. The buffer later performs poorly. What should be done before the next batch?
1. ACalibrate with the pH 7.00 buffer alone
2. BRecalibrate with fresh 4.00 and 7.00 buffers
3. CCalibrate with pH 7.00 and 10.00 buffers
4. DCheck the pH with universal indicator paper
Answer and explanation in LearnFree account
Question 11 · Easy
A magnetic stirrer mixes a solution by:
1. ASpinning a coated magnetic bar inside the vessel
2. BShaking the tube in fast small circles
3. CTilting the flask slowly from side to side
4. DPassing ultrasound waves through the liquid
Answer and explanation in LearnFree account
Question 12 · Easy
In a colorimeter, the absorbance of a coloured solution in a fixed cuvette rises in a straight line with its concentration. This relationship is the:
1. AGraham's law
2. BBeer-Lambert law
3. CBoyle's law
4. DStokes law
Answer and explanation in LearnFree account
Question 13 · Medium
In fluorimetry, compared with the exciting light, the light emitted by the sample has:
1. AThe same wavelength
2. BA shorter wavelength
3. CNo fixed wavelength
4. DA longer wavelength
Answer and explanation in LearnFree account
Question 14 · Hard
A standard of 10 mg/dL reads 50% transmittance and a test reads 25% transmittance in the same colorimeter. What is the test concentration? (log 2 = 0.30)
1. A20 mg/dL
2. B40 mg/dL
3. C5 mg/dL
4. D15 mg/dL
Answer and explanation in LearnFree account
Question 15 · Easy
A nephelometer measures:
1. ALight given off by a chemical reaction
2. BLight scattered by particles in the solution
3. CLight absorbed by a coloured solution
4. DLight emitted by atoms in a flame
Answer and explanation in LearnFree account
Question 16 · Medium
Many flame photometers add lithium to every standard and sample as an internal standard. What does it correct for?
1. AHemolysis of the serum sample
2. BErrors in the lamp output
3. CChanges in flame and aspiration rate
4. DProtein in the serum sample
Answer and explanation in LearnFree account
Question 17 · Easy
In a laboratory pH meter, which electrode responds to the hydrogen ion concentration of the sample?
1. ASilver-silver chloride electrode
2. BPlatinum electrode
3. CCalomel electrode
4. DGlass electrode
Answer and explanation in LearnFree account
Question 18 · Medium
A test tube reads absorbance 1.9, far above the top standard, on a method that is linear only to 1.0. What should be done?
1. ADilute the sample and repeat the reading
2. BReport the result from the calculation
3. CRead the tube again against water
4. DChange to a filter of another colour
Answer and explanation in LearnFree account
Question 19 · Hard
During a run on a flame photometer, the readings of the standards, controls and patient sera all fall steadily, and the flame flickers unevenly when the sample is sucked in. The most likely cause is:
1. AExpired control material
2. BA partly blocked aspirator capillary
3. CWrong filter for the element
4. DHemolysis in the patient samples
Answer and explanation in LearnFree account
Question 20 · Hard
A serum sample is diluted 1 in 5 because its colour was too deep. The diluted sample reads absorbance 0.40 and a 50 mg/dL standard reads 0.50, both against a reagent blank. What is the result to report?
1. A312 mg/dL
2. B40 mg/dL
3. C200 mg/dL
4. D8 mg/dL
Answer and explanation in LearnFree account
Question 21 · Medium
Serum IgG, IgA, IgM and CRP are measured in many laboratories by which instrument?
1. AFluorimeter
2. BAtomic absorption spectrophotometer
3. CFlame photometer
4. DNephelometer
Answer and explanation in LearnFree account
Question 22 · Easy
Which lamp supplies ultraviolet light in a UV-visible spectrophotometer?
1. ASodium vapour lamp
2. BTungsten lamp
3. CDeuterium lamp
4. DHollow cathode lamp
Answer and explanation in LearnFree account
Question 23 · Medium
In atomic absorption measurement of serum calcium, lanthanum chloride is added to the diluent in order to:
1. AAct as the light source
2. BRaise the flame temperature
3. CRemove protein from the sample
4. DRelease calcium from phosphate
Answer and explanation in LearnFree account
Question 24 · Medium
Why must quartz or silica cuvettes be used for readings at 340 nm?
1. AQuartz removes stray visible light
2. BOrdinary glass absorbs ultraviolet light
3. CQuartz keeps the solution at 37 °C
4. DGlass reacts with NADH in the sample
Answer and explanation in LearnFree account

Laboratory instruments

Glucose by GOD-POD is read against distilled water: reagent blank 0.05, standard (100 mg/dL) 0.45 and test 0.65. What is the glucose concentration?

In a fluorimeter, the emitted light is measured at a right angle to the exciting beam. Why?

In a flame photometer, sodium emits light of which color?

In atomic absorption spectrophotometry, what is the cathode of the hollow cathode lamp made of?

A colorimetric test gives a red solution. Which filter color should be selected to read it?

Atomic absorption spectrophotometry differs from flame emission photometry in that it measures light:

A centrifuge rotor whose tube holders lie level during the spin, so the sediment packs flat at the tube bottom, is called a:

Firefly luciferase reacts with ATP and gives off light. Which instrument measures this light?

A spectrophotometer is more specific than a filter colorimeter mainly because its prism or grating:

A pH meter is calibrated with pH 4.00 and 7.00 buffers and then used to adjust a carbonate-bicarbonate buffer to pH 10.0. The buffer later performs poorly. What should be done before the next batch?

A magnetic stirrer mixes a solution by:

In a colorimeter, the absorbance of a coloured solution in a fixed cuvette rises in a straight line with its concentration. This relationship is the:

In fluorimetry, compared with the exciting light, the light emitted by the sample has:

A standard of 10 mg/dL reads 50% transmittance and a test reads 25% transmittance in the same colorimeter. What is the test concentration? (log 2 = 0.30)

A nephelometer measures:

Many flame photometers add lithium to every standard and sample as an internal standard. What does it correct for?

In a laboratory pH meter, which electrode responds to the hydrogen ion concentration of the sample?

A test tube reads absorbance 1.9, far above the top standard, on a method that is linear only to 1.0. What should be done?

During a run on a flame photometer, the readings of the standards, controls and patient sera all fall steadily, and the flame flickers unevenly when the sample is sucked in. The most likely cause is:

A serum sample is diluted 1 in 5 because its colour was too deep. The diluted sample reads absorbance 0.40 and a 50 mg/dL standard reads 0.50, both against a reagent blank. What is the result to report?

Serum IgG, IgA, IgM and CRP are measured in many laboratories by which instrument?

Which lamp supplies ultraviolet light in a UV-visible spectrophotometer?

In atomic absorption measurement of serum calcium, lanthanum chloride is added to the diluent in order to:

Why must quartz or silica cuvettes be used for readings at 340 nm?