Direct analysis of ethylenediaminetetraacetic acid (EDTA) on concrete by reactive-desorption electrospray ionization mass spectrometry

A screening method for heavy metals in consumer goods using reactive desorption electrospray ionization mass spectrometry

RATIONALE

Contamination of everyday goods with heavy metals such as nickel, cadmium, and lead known to be hazardous to the health of customers is an ongoing problem.

METHOD

Here, a mass spectrometric screening method based on reactive desorption electrospray ionization (DESI) is presented for the analysis of metals in consumer goods such as jewelry, tableware, and paintings. The method detects oxidized species of lead, nickel, cadmium, copper, and iron from the surface of objects without sample preparation. Positively charged metal ions form singly and doubly negatively charged complexes with ethylenediaminetetraacetic acid added to the DESI solvent, which are analyzed by a mass spectrometer.

RESULTS

Qualitative and quantitative performance of the method was elucidated with metal salt standards. Subsequently, authentic samples were analyzed qualitatively. Reactive DESI-MS was able to detect lead and cadmium in eight out of nine consumer goods. For tableware, these heavy metals were found to be localized in the print as determined by reactive DESI imaging. In addition, mockup paintings generated from modern and historical pigments of Pb, Cu, Cd, and Fe in various media (acrylic binder, egg tempera, and linseed oil) were measured to show the suitability of the method for art authentication and conservation.

CONCLUSION

The developed method expands the range of analytes accessible by DESI-MS to metal ions. Hence, DESI becomes a suitable ionization technique for an increasing number of analyte classes, which are of interest in chemical screening of consumer goods.

Carbon dots for specific "off-on" sensing of Co2+ and EDTA for in vivo bioimaging

Fluorescent carbon dots (CDs) were hydrothermally synthesized from a mixture of frozen tofu, ethylenediamine and phosphoric acid in an efficient 64% yield. The resulting CDs exhibit good water solubility, low cytotoxicity, high stability, and excellent biocompatibility. The CDs selectively and sensitively detect Co²⁺ through fluorescent quenching with a detection limit of 58 nM. Fluorescence can be restored through the introduction of EDTA, and this phenomenon can be used to quantify EDTA in solution with a detection limit of 98 nM. As both analytes are detected by the same CD platform, this is an "off-on" fluorescence sensor for Co²⁺ and EDTA. The technique's robustness for real-world samples was illustrated by quantifying cobalt in tap water and EDTA in contact lens solution. The CDs were also evaluated for in vivo imaging as they show low cytotoxicity and excellent cellular uptake. In a zebrafish model, the CDs are rapidly adsorbed from the intestine into the liver, and are essentially cleared from the body in 24 h with no appreciable bioaccumulation. Their simple and efficient synthesis, combined with excellent physical and chemical performance, renders these CDs attractive candidates for theranostic applications in targeted "smart" drug delivery and bioimaging.

Reactive Laser Ablation Electrospray Ionization Time-Resolved Mass Spectrometry of Click Reactions

Reactions in confined compartments like charged microdroplets are of increasing interest, notably because of their substantially increased reaction rates. When combined with ambient ionization mass spectrometry (MS), reactions in charged microdroplets can be used to improve the detection of analytes or to study the molecular details of the reactions in real time. Here, we introduce a reactive laser ablation electrospray ionization (reactive LAESI) time-resolved mass spectrometry (TRMS) method to perform and study reactions in charged microdroplets. We demonstrate this approach with a class of reactions new to reactive ambient ionization MS: so-called click chemistry reactions. Click reactions are high-yielding reactions with a high atom efficiency, and are currently drawing significant attention from fields ranging from bioconjugation to polymer modification. Although click reactions are typically at least moderately fast (time scale of minutes to a few hours), in a reactive LAESI approach a substantial increase of reaction time is required for these reactions to occur. This increase was achieved using microdroplet chemistry and followed by MS using the insertion of a reaction tube-up to 1 m in length-between the LAESI source and the MS inlet, leading to near complete conversions due to significantly extended microdroplet lifetime. This novel approach allowed for the collection of kinetic data for a model (strain-promoted) click reaction between a substituted tetrazine and a strained alkyne and showed in addition excellent instrument stability, improved sensitivity, and applicability to other click reactions. Finally, the methodology was also demonstrated in a mass spectrometry imaging setting to show its feasibility in future imaging experiments.