Characteristics of Picoliter Droplet Dried Residues as Standards for Direct Analysis Techniques

Abstract

The characteristics of dried residues of picodroplets of single-, two-, and three-element aqueous solutions, which qualify these as reference materials in the direct analysis of single particles, single cells, and other microscopic objects using, e.g., laser ablation inductively coupled plasma time-of-flight mass spectrometry (LA-ICP-TOF-MS) and micro-X-ray fluorescence (MXRF), were evaluated. Different single-, two-, and three-element solutions (0.01-1 g/L) were prepared in picoliter volume (around 130 pL) with a thermal inkjet printing technique. An achievable dosing precision of 4-15% was calculated by total reflection X-ray fluorescence (TXRF) determination of the transferred elemental mass of an array of 100 droplets. The size of the dried residues was determined by optical microscopy to be 5-20 microm in diameter depending on the concentration and the surface material. The elemental distribution of the dried residues was determined with synchrotron micro-X-ray fluorescence (SR-MXRF) analyses. The MXRF results show high uniformity for element deposition of every single droplet with an RSTD of 4-6% depending on the concentration of spotted solution. The shape and height profile of dried residues from picoliter droplets were studied using atomic force microscopy (AFM). It was found that these dry to give symmetrical spherical segments with maximum heights of 1.7 microm. The potential of this technique for direct LA-ICP-TOF-MS analysis is shown.

Statistical Data Analyses of Trace Chemical, Biochemical, and Physical Analytical Signatures

“…More recently, aerosols have been tailored for use in drug delivery (Jain et al 1998;Hauschild et al 2005), Raman spectroscopy of levitated droplets (Trunk et al 1994), maskless lithography for microelectromechanical system (MEMS) fabrication (Wang et al 2004), and as particle standards containing trace levels of molecules for ion mobility spectroscopy (Fletcher et al 2008) and trace levels of elements for X--ray fluorescence spectrometry and laser ablation inductively coupled plasma mass spectrometry (Fittschen et al 2006;Fittschen et al 2008). …”

Elemental Analysis of Glass and Ink by Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) and Laser Induced Breakdown Spectroscopy (LIBS)

“…Other types of inks have been analyzed and characterized based on their elemental composition [51][52][53][54][55] and thus initially provided some insight as to the types of elements that may be found gel ink samples, with the assumption that the same raw materials are used in their respective formulations. In addition, it is unfair to only present elemental compositions of inks because in the case of a forensic document, the paper itself may provide additional discrimination potential (though that is not the work that will be presented in this chapter).…”

“…XRF, an elemental analysis technique, was solely used to identify the colorant (pigment) used in the associated pen set and with respect to the analysis of gel inks, good discrimination was reported using a combination of Raman and FTIR [53]. In a recent article by Fittschen et al, picoliter droplets (HNO 3 spiked with As, Co, Fe, and Ti) were delivered from an ink-jet printer onto acrylic glass, allowed to dry, and then analyzed by LA-ICP-MS [54]. Fairly linear calibration curves were generated from the dried picoliter drops [54], the work offers a potential quantification approach for ink analysis, provided that a matrix-matched standard can be produced.…”

“…In a recent article by Fittschen et al, picoliter droplets (HNO 3 spiked with As, Co, Fe, and Ti) were delivered from an ink-jet printer onto acrylic glass, allowed to dry, and then analyzed by LA-ICP-MS [54]. Fairly linear calibration curves were generated from the dried picoliter drops [54], the work offers a potential quantification approach for ink analysis, provided that a matrix-matched standard can be produced. Spence et al used dissolution ICP-MS to study document paper wherein Na, Mg, Al, Mn, Sr, Y, Ba, La, and Ce (from a starting list of 23 elements) were used to discriminate 17 different paper sources (Australian document paper) by t-test at the 95% confidence interval [55].…”

“…The initial element list was gathered by first looking through the scientific literature which detailed the elemental analysis of ink by various techniques [51][52][53][54][55].…”