International Journal of Mass Spectrometry 299 (2011) 178–183 Contents lists available at ScienceDirect International Journal of Mass Spectrometry journal homepage: www.elsevier.com/locate/ijms Characterization of a capillary spray cell for easy analysis of extracts of biological samples Christian Janfelt ∗ , Frants R. Lauritsen Dept. of Pharmaceutics and Analytical Chemistry, University of Copenhagen, Universitetsparken 2, 2100 Copenhagen, Denmark article info Article history: Received 17 September 2010 Received in revised form 22 October 2010 Accepted 24 October 2010 Available online 3 November 2010 Keywords: Electrospray ionization New instrumentation Plant analysis Biological extracts Alkaloids abstract We present a very simple electrospray unit, a capillary spray cell, for easy analysis of small (10–50 L) sample aliquots. The sample, e.g., an unfiltered extract, is injected to a small sample cell, made of alumina and containing a short fused silica capillary mounted in its side. By the application of a 5 kV potential between the sample cell and the entrance orifice of a mass spectrometer with an atmospheric pressure interface, the sample is dragged out of the cell at a rate of a few L/min and an electrospray is generated at the tip of the silica capillary. The capillary spray cell benefits from a high internal diameter (up to 250 m) and very easy and inexpensive replacement of the capillary, which makes the sprayer well suited for analysis of unfiltered extracts. We demonstrate the direct analysis of extracts from plants and insects. In quantitative measurements using internal standards, a relatively high sensitivity (low ng/mL) is obtained together with good linearity (R 2 = 0.998) in the range of 10–1000 ng/mL. The capillary spray cell is also suited for use with field portable mass spectrometers, since no syringe pump or nebulizer gas is needed. Furthermore, the capillary spray cell is easily manufactured by most mechanical workshops. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Since its breakthrough in the 1980s electrospray ionization mass spectrometry [1] and later nanoelectrospray ionization mass spec- trometry [2] have played increasingly bigger roles in today’s work with mass spectrometry since they are particular well suited for the polar compounds which are found in most biological samples [3,4]. The majority of mass spectrometers today are sold with Elec- trospray ion sources built to work in the hyphenation with an HPLC system, thus accommodating liquid flows of up to 1 mL per minute. These sources are typically fed with sample solution from either an HPLC or a syringe pump, and gasses are used to various extents to assist in the nebulisation of the sample solution and subsequent desolvation of the analyte droplets [5]. At lower flow rates the neb- uliser gas is not needed as the charged droplets can be formed by the electrospray potential alone [6]. However, in most setups, even without nebuliser gas, a syringe pump is still needed to provide the necessary transport of sample solution to the spray. That changed with the introduction of the static nanospray source where the sample, typically 2–10 L total volume, is injected into a glass tube which has been pulled in one end to obtain a tip with an orifice of 2–5 m and coated with a gold film to enable electrical contact to the sample solution [2]. With ∗ Corresponding author. Tel.: +45 35 33 65 57; fax: +45 35 33 60 30. E-mail address: cja@farma.ku.dk (C. Janfelt). this setup a forced flow is not needed as the applied electric field is able to generate a flow by itself, controlled by the diameter of the capillary tip. The technique provides a stable signal for a long time from just a few microlitres of sample, however with relatively high expenses in consumables. Very simple ways to generate an electrospray from a droplet of sample solution have been demonstrated by Shiea et al., by deposi- tion of a droplet on an object onto which high voltage is applied. This object has been of various materials and shapes such as a copper ring [7], a copper coil [8] or a gold coated optical fiber [9], pro- viding simple ways to analyze tiny amounts of sample with low costs of consumables and no use of nebuliser gas or sample deliv- ery pumps. A variation of this is the so-called probe electrospray by Hiraoka et al. [10] where a solid needle picks up a droplet of sample in a motorized fashion and moves it to the proximity of the MS inlet orifice. Ionization then occurs from the needle simi- larly to the techniques describes above. This technique was later implemented in a new ambient imaging technique where the nee- dle systematically samples a whole area [11], similarly to other MS imaging techniques such as, e.g., DESI imaging [12]. An alternative solution is the microfabricated electrospray emit- ter presented by Sikanen et al. in 2008 which provides the options of free flow as well as forced flow electrospray [13]. Operated in free flow mode a sample amount of 20 L will give a very stable signal for nearly 30 min. It was successfully applied for analysis of phar- maceuticals, peptides and proteins. However, the construction of these microfabricated emitters is quite complicated, as it requires 1387-3806/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.ijms.2010.10.032