Question

A student, when using the gas chromatograph, was concerned that \(\mathrm{CO}_{2}\) in the exhaust sample may be interfering in the detection of CO. Which of the following procedures would best help the student investigate this problem? A. Filling the bag with \(\mathrm{CO}_{2}\) before collecting the exhaust B. Collecting exhaust from additional cars C. Injecting a sample of air into the gas chromatograph D. Testing a sample with known amounts of \(\mathrm{CO}\) and \(\mathrm{CO}_{2}\)

Short answer

The best procedure to investigate the interference is D. Testing a sample with known amounts of \(\mathrm{CO}\) and \(\mathrm{CO}_{2}\), as it allows the student to directly observe and compare the gas chromatograph's response with expected results.

Step-by-step solution

Procedure A: Filling the bag with \(\mathrm{CO}_{2}\)

Filling the bag with \(\mathrm{CO}_{2}\) before collecting the exhaust would not specifically address the interference issue, as it actually saturates the bag with the interfering compound. Therefore, this procedure may introduce more error.

Procedure B: Collecting exhaust from additional cars

Collecting exhaust from additional cars might reveal trends or differences in CO detection but would not directly address the interference issue. This procedure is not sufficient to investigate the main concern, which is the interference of \(\mathrm{CO}_{2}\) with CO detection.

Procedure C: Injecting a sample of air into the gas chromatograph

Injecting a sample of air into the gas chromatograph can act as a control sample. However, a typical air sample might not contain enough CO and \(\mathrm{CO}_{2}\) quantities to reveal any definite interference. Therefore, this procedure would not be the best way to address the interference concern.

Procedure D: Testing a sample with known amounts of \(\mathrm{CO}\) and \(\mathrm{CO}_{2}\)

Testing a sample with known amounts of \(\mathrm{CO}\) and \(\mathrm{CO}_{2}\) would allow the student to observe the gas chromatograph's response and compare it with the expected results. If there is any significant discrepancy, the student can determine if the \(\mathrm{CO}_{2}\) is interfering with the CO detection. This procedure directly addresses the interference issue, making it the best choice among the given procedures. Based on the analysis of each procedure, the correct answer is: D. Testing a sample with known amounts of \(\mathrm{CO}\) and \(\mathrm{CO}_{2}\).

Key concepts

Understanding the Scientific Method

The scientific method is a systematic approach used by scientists to explore phenomena, acquire new knowledge, or correct and integrate previous knowledge. To be termed scientific, a method of inquiry must be based on empirical and measurable evidence subject to specific principles of reasoning. In the context of the gas chromatography exercise, the scientific method is used to make an educated decision on which procedure would best investigate the problem of potential interference in detection of CO by CO2.

Following the steps of the scientific method, the student starts with an observation: CO detection might be affected by CO2. The student then formulates a question and proposes several hypotheses, represented by each of the suggested procedures (A, B, C, and D). They then conduct an experiment, choosing one procedure to test the hypothesis. Procedure D is the experimental design that allows for testing the hypothesis under controlled conditions, by adding known amounts of CO and CO2 and observing the chromatograph's response. This aligns with the hypothesis testing step in the scientific method, leading to the conclusion that Procedure D is indeed the best approach to determine if there is interference.

Role of Analytical Chemistry

Analytical chemistry is a field of chemistry involved with the analysis of substances; it is about separating, identifying, and quantifying matter. In the gas chromatography exercise, analytical chemistry principles are applied to solve the problem of separating CO from CO2 in an exhaust sample. This is a typical analytical task, where precise detection and quantitation of substances are crucial.

When the student suggests testing a sample with known amounts of CO and CO2 (Procedure D), they are essentially looking to create a calibration curve, a common tool in analytical chemistry. This curve helps relate the concentration of a substance in a sample to the response of the analytical instrument. By using a calibrated response, the student can identify and quantify the CO in the presence of CO2, effectively managing any interference. This illustrates the core analytical chemistry principle: to understand and manage the chemical components of a sample using appropriate tools and methods.

Utilizing Laboratory Techniques

Laboratory techniques encompass the set of procedures used to conduct experiments, measurements, or gather data in a controlled environment. In our example of gas chromatography, laboratory techniques are illustrated by how the student decides to test the CO and CO2 sample. Gas chromatography itself is a laboratory technique for separating and analyzing compounds that can be vaporized without decomposition.

The improvement of the exercise lies in applying a suitable laboratory technique (Procedure D) that specifically addresses the problem at hand - the interference of CO2 with CO detection. By ensuring that a known concentration of each gas is tested, the student can observe the individual peaks in the chromatogram, determine their retention times, and form a conclusion on interference. This is a clear demonstration of laboratory techniques: utilizing scientific tools to systematically obtain results and answer questions. The precision and methodology are critical, exemplifying the high value of well-chosen laboratory procedures.