Question

1. Some special GC detectors, such NPD and FPD, are often used to analyzed nitrogen containing and phosphorus containing pesticides, respectively, because these detectors have higher sensitivity than FID for the above-mentioned chemicals (T or F);
2. UV spectra always give sharp peaks that reflect the maximal absorption of chromophores (T or F);

Answer 1

1. Some special GC detectors, such as NPD and FPD are often used to analyze Nitrogen containing and Phosphorus containing pesticides, respectively because these detectors have higher sensitivity than FID for the above mentioned chemicals.

Answer : The above given statement is TRUE.

Explanation: Gas Chromatography is used for the analysis of organic materials. It is based on the principle that when a mixture of volatile materials transported by a carrier gas is led through a column containing an absorbent solid phase or more commonly an absorbing liquid phase coated on a solid material ,each volatile component will be partitioned between the carrier gas and the solid or liquid. Depending on the retention times in the column the volatile component will emerge for the column at different times and finally be detected by the suitable detector.

The flame ionization detectors (​FID) is extremely sensitive for the detection of organic compounds. Halogens, nitrogen or oxygen, if present in the organic compounds, decrease the sensitivity of the detector. The FID is sensitive to very low levels of hydrocarbons.

On the contrary, FPD-Flame Photometric Detector and NPD- Nitrogen Phosphorus Detector are used widely for the analysis of Amines.

2. UV spectra always give sharp peaks that reflect the maximal absorption of Chromophores.

Answer: The above given statement is also TRUE.

​​​​Groups in a molecule which absorb light are known as Chromophores. In these molecules more delocalization is present that results in the lowering of energy between bonding and antibonding orbitals or smaller gap between lowest energy pi-antibonding orbital to promote an electron easily. Therefore, sharp maximal peak is observed.