You are measuring blood glucose level by glucose oxidase method. Following are the absorbance values that you got for the standard and the test sample. Determine the glucose concentration in the test sample:
sample                                Concentration                                          𝐴505
Standard 1                       0.4 mmol/L                                                  0.120
Standard 2                      0.6 mmol/L                                                   0.180
Standard 3                      0.8 mmol/L                                                   0.240
unknown                             ?                                                                     0.210

A. 0.65 mm
B. 0.70 MM
C. 0.725 MM
D. 0.75 mM

Understanding Glucose Measurement with Glucose Oxidase Method

Measuring blood glucose using the glucose oxidase method is a common biochemical assay. The absorbance values obtained from a spectrophotometer can be used to calculate the unknown glucose concentration by comparing it with standard solutions.

Problem:

You have the following absorbance data:

Step-by-Step Solution: Linear Interpolation

The relationship between absorbance and concentration is linear (Beer-Lambert Law). We’ll use the two closest standard values to interpolate.

Between 0.6 mmol/L (0.180 A) and 0.8 mmol/L (0.240 A):

We can use the formula:

C = C1 + [(A - A1) / (A2 - A1)] × (C2 - C1)

Where:

• C1 = 0.6 mmol/L, A1 = 0.180
• C2 = 0.8 mmol/L, A2 = 0.240
• A = 0.210 (absorbance of unknown)

Plug in the values:

C = 0.6 + [(0.210 - 0.180) / (0.240 - 0.180)] × (0.8 - 0.6)
C = 0.6 + [0.030 / 0.060] × 0.2
C = 0.6 + 0.5 × 0.2
C = 0.6 + 0.1 = 0.7 mmol/L

✅ Final Answer: 0.70 mM

Correct Option: B. 0.70 mM

Key Takeaways:

• The glucose oxidase method follows a linear relationship between absorbance and concentration.
• Use linear interpolation when the unknown absorbance falls between two standards.
• Double-check units (mmol/L = mM).