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highly refined and purified mineral oil fractions are widely used for elaboration of consumer products such as foods and cosmetics. these mineral oils (mo) are called “white oils” and must meet very strict criteria in terms of residual levels of mineral oil aromatic hydrocarbons (moah). reliable methods for detecting and monitoring the total moah levels in mo are needed to optimize the moah removal processes in white oil production.
a novel detector has been introduced, the vacuum ultraviolet (vuv) detector. this detector is used in combination with a gas chromatograph (gc) and measures the absorbance of gas phase compounds in the far uv wavelength range from 120 to 430 nm. at low wavelengths, all aliphatic and aromatic compounds are detected, and at higher wavelengths, only the aromatic and unsaturated compounds are detected. given that the vuv spectra of compounds can differ significantly depending on the different functional groups present in the molecule, the detector is able to quantify moah levels in mineral oil without requiring prior separation from mineral oil saturated hydrocarbons (mosh), which makes the vuv an improvement upon earlier detection methods. figure 1 shows vuv absorbance spectra of select aliphatic and aromatic compounds containing the typical structural elements of mosh and moah compounds, respectively.
figure 1
study 1
to study the spectral differences between actual mosh and moah fractions, eight different mineral oil samples were separated using the traditional solid phase extraction (spe) method. figure 2 shows the overall averaged vuv absorbance spectra obtained for the mosh and moah fractions from these 8 oils.
figure 2
study 2
to determine the practical application limits of the newly proposed rapid vuv method for moah analysis, a series of starting samples and intermediates of white oil production of different origins and moah levels were analyzed and compared with data from two standard detection methods: solid phase extraction (spe) and liquid chromatography (lc). the vuv and lc methods were used in conjunction with gas chromatography. figure 3 shows the moah content obtained from 18 different mineral oil samples.
figure 3
suppose the vuv spectrum of an unknown mineral oil is obtained and displays significant absorbance only above 200 nm. based on the information provided, the unknown mineral oil would have contained
title
moah and vuv
your result
correct
difficulty
medium
your pace
0:04
others' pace
0:57
text explanation
the correct answer is (b).
from the mosh graph in figure 2, we can see that mosh compounds have absorbance from 100 nm to 180 nm. since mosh compounds exhibit no absorbance at 200 nm. because this unknown mineral oil only shows absorbance above 200 nm, and no absorbance below 200 nm, this unknown mineral oil cannot contain mosh compounds.
on the other hand, from the two moah graphs in figure 2, we can see significant absorption at 200 nm, so we can conclude the unknown mineral oil contains moah compounds.
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