Unit 3: Quantitative Tests - Practice Quiz

1 Which reagent is commonly used in the Dubois method for carbohydrate estimation?

2 What is the main purpose of concentrated sulfuric acid in the Dubois method?

3 Which instrument is used to measure the color intensity in the Dubois method?

4 The color developed in the Dubois method is generally measured at approximately which wavelength?

5 Which substance is commonly used to prepare the carbohydrate standard curve?

6 In the Dubois method, a higher absorbance usually indicates a higher concentration of:

7 What is the role of a reagent blank in the Dubois method?

8 Which protein is commonly used as the standard in Lowry's method?

9 Which reagent provides the biuret reaction in Lowry's method?

10 Which reagent is added in the second step of the Lowry method to increase color development?

11 What is measured in the Lowry method to estimate protein concentration?

12 The absorbance in the Lowry method is commonly measured near which wavelength?

13 The Lowry method primarily estimates the concentration of:

14 Why is a standard curve used in the Lowry method?

15 Which enzyme is central to the glucose oxidase method?

16 What product is formed when glucose is oxidized by glucose oxidase?

17 Which enzyme commonly reacts with hydrogen peroxide in the color-producing step?

18 In the glucose oxidase method, the intensity of the color is related to the concentration of:

19 Which instrument is commonly used to measure the colored product in the glucose oxidase method?

20 Why is a fasting blood sample often used for glucose estimation?

21 What is the main purpose of adding concentrated sulfuric acid in the Dubois method?

22 A carbohydrate sample gives an absorbance of 0.42. The standard curve indicates that an absorbance of 0.42 corresponds to 60 μg of glucose in the assay tube. If 0.5 mL of sample was used, what is the concentration of carbohydrate in the sample?

23 Why is a reagent blank used in the Dubois carbohydrate assay?

24 A test sample produces an absorbance above the highest point of the glucose standard curve. What should be done before calculating its concentration?

25 A 1:5 dilution of a carbohydrate sample gives a calculated concentration of 18 μg/mL. What is the concentration in the original sample?

26 In the Dubois method, why must the reaction mixture be mixed carefully after adding sulfuric acid?

27 A standard curve for the Dubois assay is linear between 10 and 100 μg/mL. A diluted sample is estimated as 65 μg/mL, and the sample had been diluted fivefold. Which result should be reported for the original sample?

28 Which sequence best describes the chemical basis of the Lowry protein assay?

29 A protein sample has an absorbance corresponding to 40 μg of protein in the assay tube. If 0.2 mL of a 1:10 diluted sample was added, what was the protein concentration in the original sample?

30 Why is an appropriate protein standard, such as bovine serum albumin, used to construct the Lowry calibration curve?

31 A protein extract contains a high concentration of detergent that produces an unexpectedly high absorbance in the Lowry assay. What is the most appropriate response?

32 Why should the Folin–Ciocalteu reagent be added after the alkaline copper incubation in the Lowry assay?

33 A sample gives an absorbance of 0.30, while the reagent blank gives 0.08. What absorbance should be used for interpolation from the protein standard curve?

34 If a protein sample has an absorbance above the linear range of the Lowry standard curve, why is direct extrapolation undesirable?

35 Which reaction product is directly generated when glucose oxidase acts on β-D-glucose?

36 In a glucose oxidase–peroxidase assay, the intensity of the colored product is primarily related to the amount of:

37 A glucose standard has a concentration of 100 mg/dL and an absorbance of 0.50. An unknown sample has a blank-corrected absorbance of 0.35. Assuming linearity, what is the glucose concentration of the sample?

38 Why should blood samples for glucose estimation be separated from cells promptly when analysis is delayed?

39 A reducing substance in a blood sample consumes hydrogen peroxide during the glucose oxidase assay. What result is most likely obtained?

40 A blood sample is diluted twofold before analysis and gives a calculated glucose concentration of 82 mg/dL from the diluted solution. What is the glucose concentration in the original sample?

41 A carbohydrate standard curve is described by , where is in . A diluted unknown gives . If the sample was diluted tenfold before analysis, what is the carbohydrate concentration in the original sample?

42 In the Dubois assay, the reagent blank has an absorbance of , whereas an unknown has an absorbance of . If the calibration equation based on blank-corrected readings is , what concentration should be used for the unknown?

43 A sample gives absorbances of , , and after being diluted 2-, 4-, and 8-fold, respectively. The standard curve is linear only up to . Which result provides the most defensible estimate of the original concentration?

44 Two samples contain equal masses of glucose and starch, but the assay is calibrated with glucose. Which interpretation is most appropriate?

45 A carbohydrate assay is performed with concentrated sulfuric acid added to a phenol-containing mixture. The absorbance is unusually low in every tube, including standards, but the blank is normal. Which procedural error most plausibly explains this pattern?

46 A diluted unknown gives a measured absorbance of . Its matrix-matched sample blank is , while the reagent blank is . If the calibration curve uses reagent-blank-corrected values, which absorbance should be used for quantification?

47 A sample analyzed in triplicate gives concentrations of , , and , but a spiked aliquot expected to increase the concentration by gives . What is the best conclusion?

48 A Lowry calibration equation is , with in . A diluted sample gives an absorbance of and was prepared by diluting of serum to . What is the protein concentration in the original serum?

49 A Lowry assay gives for an unknown and for the reagent blank. The standard curve was generated using blank-corrected absorbances with slope . What is the concentration of the measured solution?

50 A protein extract contains sodium dodecyl sulfate, and its Lowry result is much higher than expected. Which explanation is most scientifically justified?

51 Why can two proteins at the same mass concentration produce different Lowry absorbances when bovine serum albumin is used as the standard?

52 A set of Lowry standards is linear through but becomes curved above that concentration. An unknown gives a reading corresponding to on the curved portion. What is the best next action?

53 Which change would most directly compromise comparability among Lowry tubes even if all tubes contain the correct protein concentrations?

54 A protein sample contains a high concentration of ammonium sulfate after precipitation. The measured Lowry protein concentration is substantially elevated. Which control is most useful for diagnosing this bias?

55 In the glucose oxidase-peroxidase method, which sequence best represents the analytical chemistry?

56 A blood sample contains a high concentration of ascorbate. In a glucose oxidase-peroxidase color assay, what bias is most likely if no interference correction is used?

57 Whole blood is left at room temperature before glucose analysis. The glucose result is lower than expected, although the assay reagents and calibration are valid. What is the most likely cause?

58 A glucose assay has a standard absorbance of for and an unknown absorbance of . The sample was diluted 1:5 before testing. Assuming a linear zero-intercept response, what is the original glucose concentration?

59 Two glucose samples have identical glucose concentrations, but one is markedly hemolyzed. In a peroxidase-based colorimetric glucose oxidase assay, which issue should be considered first?

60 A patient sample gives a glucose value above the highest calibrator. Which response best preserves quantitative validity?