Question:
UV-Vis detector only detects the chemicals with chromophores absorbing wavelength between 400 nm to 700 nm
true or false
Answer
False
It should be rather between 400 – 800 nm. Thus, the statement is slightly wrong by the maximu range of absorption and again it is known that region scanned is normally from 200 to 400 nm, and on the other hand, the visible portion is from 400 to 800 nm
Explanation
What happens in this is that a beam of light from a visible and/or UV light source which is colored red and is separated into its component wavelengths by a prism or diffraction grating. Again, usually ultraviolet (UV) region scanned is normally from 200 to 400 nm, and on the other hand, the visible portion is from 400 to 800 nm and finally, the selection of a suitable solvent is influenced by the wavelength expected to be studied
Question:
In food analysis, the main source of systematic error comes from the random sampling
true or false
Answer
False
This is not true because whatever holds true as much as errors are concerned when evaluating a food sample for instance, is the sampling error which is rather the error caused by observing a sample instead of the whole population which in other words we can say arises from random sampling
Explanation
systematic error is rather a tendency to consistently underestimate or overestimate a true value which can be said to be consistent, repeatable error associated with faulty equipment or a flawed experiment design in the food analysis experiment for that matter. There are some ways which are used to minimize this type of error, for example, a good survey research methodology seeks to minimize systematic error through probability-based sample selection
Question:
1) Vitamin A is more suitable to be analyzed by the following instruments
a. ICP-MS
b. AAS
c. GC-ECD
d. HPLC-UV
e. DSC
What is the answer to this question?
Answer
a. ICP-MS
This is the best technique and commercially introduced in 1983 and has gained general acceptance in many types of laboratories where each antibody is usually labelled with a distinct combinations of lanthanides.
Explanation
Its advantages include
Extremely low detection limits
A large linear range
Possibilities to detect isotope composition of elements.
What happens is that rather than labelling antibodies (or other biological probes) with fluorochromes, each antibody is usually labelled with a distinct combinations of lanthanides. Generally, what will happen here is that the ICP source converts the atoms of the elements in the sample to ions that are then separated and detected by the mass spectrometer.
Question:
Which one of following gas chromatographic detectors is an universal and a non-destructive detector:
a. Flame ionization detector
b. Mass spectrometer
c. Thermal conductivity detector
d. Nitrogen Phosphorus detector
e. UV detector
Answer
c. Thermal conductivity detector
Thermal Conductivity Detector (TCD) is completely a universal detector and can be used to detect hydrogen, carbon monoxide, sulfur oxide, inorganic gases as well as many other compounds, the detector is also non-specific and non-destructive detector.
Explanation
There are reasons as to why the detector is considered universal and non-destructive, among them being the fact that it responds to all compunds. Also, since thermal conductivity of organic compounds are similar and very different from Helium, then a TCD will reespond the same way to similar concentration of analyte. This means that the detector can be applied without calibration and the concentration of a sample component can be estimated by the ratio of the analyte peak area to all components (peaks) in the sample.
Question:
Which one of following parameters will affect the retention index of an analyte in GC analysis:
a. Polarity of the column
b. Volume of the injection of the analyte
c. Length of the column
d. Detector connected to the column
e. Flow rate of the carrier gas
Answer
a. Polarity of the column
polar compounds have long retention times on polar stationary phases and shorter retention times on non-polar columns using the same temperature
Explanation
Mainly, in case the the polarity of the stationary phase and compound are similar, then what happens is that the retention time goes up since the compound can interact in a stronger manner with the stationary phase. Therefore, polar compounds have long retention times on polar stationary phases and shorter retention times on non-polar columns using the same temperature which is why it is said also that lower the boiling point, the higher the vapor pressure of the compound and the shorter retention time
