Técnicas de preparo de amostras aplicadas à espectrometria de massas com ionização por paper spray

Abstract

Over the past few years, paper spray ionization mass spectrometry (PS-MS) has emerged as a very promising technique for applications in analytical chemistry. The low costs of the ionization source, the facility of use and no need for pneumatic assistance make PS-MS a very attractive tool in chemical analysis. Despite the good performance presented for complex samples analysis, PS also has matrix effects and ionization suppression, especially when the analyte is in a complex matrix at low concentrations. In order to improve selectivity and sensitivity of the technique, and to reduce matrix effects and ionic suppression, in this work PS-MS was associated with sample preparation techniques: (i) extraction assisted by electric field, (ii) evaporative concentration in paper based analytical devices and (iii) headspace solid phase extraction. The method that associated electric field assisted extraction with PS-MS was applied for cocaine and lidocaine in synthetic saliva, malachite green dye in tap water and bisphenol A in red wine. The obtained results indicated enrichment of the analytical signals varying from 14 to 110 times, according to each proposal developed. The method that combined evaporative concentration in paper based analytical devices with PS-MS promoted up to 12 times enrichment of azo and triarylmethane dye signals. In addition, the evaporative concentration in a paper device was a viable proposal for colorimetric determination of chromophor compounds. The proposed method was employed to determine Cu2+ in cachaça, through reaction with NaDDTC which produces the chromophore substance Cu(DDTC)2. The limit of detection obtained was 0.3 µg mL-1 and the limit of quantification was 1.0 µg mL-1, lower values than those described on literature for Cu(DDTC)2 on paper surface determination. Finally, the method that utilized headspace solid phase extraction was employed to pre-concentrate volatile compounds of cachaça and beer. Polydimethylsiloxane immobilized on paper and free chromatographic paper were used as extraction adsorbents and directly analyzed by PS-MS. In addition to sample clean up, the use of PDMS as an adsorbent was able to associate PS-MS signals with markers for aging of cachaça in oak barrels and beers with corn as an adjunct ingredient. In general, associating PS-MS with consolidated preparation techniques promoted advantages such as: sample clean-up; pre concentration of analytes; and sensitive and selective methods.