8
mass spectrometer working in SRM mode. This step allows the determination of the
free fraction of the alcohols. In the second step, the polar fraction is submitted to a
simple hydrolytic step in a microwave oven under standardized conditions and
strong acidic conditions; the resulting reaction mixture containing the amount of
alcohols released by the esters, together with the free content, is submitted to the
HPLC-ESI-SRM experiment. Combining the data of the two steps, it is possible to
calculate the amount of phenols as requested by the regulation. In this way, the
drawback of the absence of appropriate internal standards is overcome by the hydrolytic reaction step.
1.2.4 Application of PS-MSMS for the Determination
of Quality Markers in Foodstuff
A new interesting approach for the determination of quality markers in food is based
on the use of paper spray tandem mass spectrometry (PS-MS/MS). The main advantage of this relatively new type of ionization source is the possibility to avoid tedious
purification steps prior the mass spectrometric analysis. PS source is rather easy to
set-up: it consists of a stainless steel clip on which a high voltage of some kV is
applied; the clip is connected to a triangular piece of porous paper (usually filter
paper) soaked with the dried sample. By spotting few microliters of a polar solvent,
usually methanol, the ions are generated at the tip of the paper and directed towards
the analyzer. The main drawback of this methodology is the poor reproducibility of
the signal, due to the presence of a high background ions level. Tandem mass spectrometry in SRM mode lowers strongly the noise providing good analytical performances. On the other hand, the use of isotopic standards surely increases either the
accuracy and LOQ and LOD values. PS-MS/MS has been applied with good results
for the determination of vitamin E in extra virgin olive oil [18], resveratrol in wine
[15] and methylxanthines alkaloids in coffee, cocoa products and drugs [19, 20], but
also for the determination of phenylethanoids in olive oil [21]. All the above methodologies are very rapid, having time of analysis reduced to two/four minutes only.
1.3 Conclusions
Tandem mass spectrometry is a powerful tool for the determination of molecular
quality markers in food. The superior capacity of MS/MS is due to the high specificity of analysis achieved. When used in conjunction with stable isotope dilution
analysis, it becomes the landmark between the analytical techniques used in food
analysis. The criticism usually reported, which describes the technique as too
expensive is, in effect, groundless if one considers that usually the samples analyzed
belongs to large production batches, and the cost of a single analysis is diluted in the
price of the final product.
G. Sindona and L. Di Donna
mass spectrometer working in SRM mode. This step allows the determination of the
free fraction of the alcohols. In the second step, the polar fraction is submitted to a
simple hydrolytic step in a microwave oven under standardized conditions and
strong acidic conditions; the resulting reaction mixture containing the amount of
alcohols released by the esters, together with the free content, is submitted to the
HPLC-ESI-SRM experiment. Combining the data of the two steps, it is possible to
calculate the amount of phenols as requested by the regulation. In this way, the
drawback of the absence of appropriate internal standards is overcome by the hydrolytic reaction step.
1.2.4 Application of PS-MSMS for the Determination
of Quality Markers in Foodstuff
A new interesting approach for the determination of quality markers in food is based
on the use of paper spray tandem mass spectrometry (PS-MS/MS). The main advantage of this relatively new type of ionization source is the possibility to avoid tedious
purification steps prior the mass spectrometric analysis. PS source is rather easy to
set-up: it consists of a stainless steel clip on which a high voltage of some kV is
applied; the clip is connected to a triangular piece of porous paper (usually filter
paper) soaked with the dried sample. By spotting few microliters of a polar solvent,
usually methanol, the ions are generated at the tip of the paper and directed towards
the analyzer. The main drawback of this methodology is the poor reproducibility of
the signal, due to the presence of a high background ions level. Tandem mass spectrometry in SRM mode lowers strongly the noise providing good analytical performances. On the other hand, the use of isotopic standards surely increases either the
accuracy and LOQ and LOD values. PS-MS/MS has been applied with good results
for the determination of vitamin E in extra virgin olive oil [18], resveratrol in wine
[15] and methylxanthines alkaloids in coffee, cocoa products and drugs [19, 20], but
also for the determination of phenylethanoids in olive oil [21]. All the above methodologies are very rapid, having time of analysis reduced to two/four minutes only.
1.3 Conclusions
Tandem mass spectrometry is a powerful tool for the determination of molecular
quality markers in food. The superior capacity of MS/MS is due to the high specificity of analysis achieved. When used in conjunction with stable isotope dilution
analysis, it becomes the landmark between the analytical techniques used in food
analysis. The criticism usually reported, which describes the technique as too
expensive is, in effect, groundless if one considers that usually the samples analyzed
belongs to large production batches, and the cost of a single analysis is diluted in the
price of the final product.
G. Sindona and L. Di Donna