Which of the following instruments should be used when analyzing for a mixture of traces of chlorinated hydrocarbon pesticides?

Gas chromatography is the appropriate instrument for analyzing a mixture of traces of chlorinated hydrocarbon pesticides due to its ability to separate volatile compounds in a mixture. The technique works by vaporizing the sample and passing it through a column filled with a stationary phase. Different components of the mixture interact with this phase to varying degrees, resulting in separation as they elute at different times.

Chlorinated hydrocarbon pesticides are often present in low concentrations and are volatile, making gas chromatography particularly effective for their analysis. It allows for the identification and quantification of these compounds as they are detected by an appropriate detector, often coupled with mass spectrometry for enhanced identification.

While mass spectrometry is a powerful technique for detecting and identifying compounds based on their mass-to-charge ratios, it is often used in conjunction with gas chromatography to provide detailed information about the compounds after they have been separated. Spectrophotometry is useful for measuring absorbance or transmittance of light at specific wavelengths but is not typically effective for complex mixtures of volatile compounds. Liquid chromatography, while also a valid separation technique, is more suited for non-volatile or thermally unstable compounds, which is not the case with many chlorinated hydrocarbons.

Thus, gas chromatography is the best choice for the