Journal of Chromatography A, 1278 (2013) 181–183 Contents lists available at SciVerse ScienceDirect Journal of Chromatography A jou rn al h om epage: www.elsevier.com/locat e/chroma Short communication Quantitative criteria for needle trap device selection M. Kaczmarek a , A. Voelkel b,∗ , M. Pietrzy ´ nska b a Institute of Mechanics and Applied Computer Science, Kazimierz Wielki University, Kopernika 1, 85-074 Bydgoszcz, Poland b Pozna´ n University of Technology, Institute of Chemical Technology and Engineering, pl. M. Skłodowskiej-Curie 2, 60-965 Pozna´ n, Poland a r t i c l e i n f o Article history: Received 5 November 2012 Received in revised form 19 December 2012 Accepted 21 December 2012 Available online 10 January 2013 Keywords: Sampling Needle trap device Extraction method Parameters of NTD a b s t r a c t In this note the quantitative criteria for selection of parameters of the NTD system were derived. The conditions were formulated for the force exerted on syringe, the volume of tested solution, for the time of test and contact time of solution with the sorbent. The last two conditions allowed to establish limits for combinations of fundamental geometrical and macroscopic structural characteristics of the system. The practical reasons of testing and sampling effectiveness of the NTD systems were taken into account. © 2013 Elsevier B.V. All rights reserved. 1. Introduction The needle trap device (NTD) or in-needle extraction device is a useful miniaturized exhaustive technique for laboratory and on-site sampling from liquid or gas solutions [1]. The method has manual or automated realizations and can be coupled with standard analytical instrumentations.The needle trap device was described in literature very thoroughly [2–8]. The first reported use of a needle packed with a sorbent material comes from 1970s [9]. Over the years in-needle technique was used to prepare gaseous samples. Isolation of analytes from water samples was most often combined with head-space (HS) or purge and trap (P&T) techniques probably because of the high flow resistance produced by sorbent layer which was difficult to overcome. Moreover, only a portion of analytes is carried out through the sorbent bed, leading to prob- lems in quantitative analysis and possible loss of analytes.In 2012 Pietrzy ´ nska et al. [10] proposed the direct use of in-needle tech- nique for the preparation of liquid samples by direct passing water samples through the needle filled with sorbent material. The effec- tiveness of the NTD system was studied based on experimental data and chemometric evaluation. Due to the fact that the NTD technique has potentially large applicability some simple and general rules of selection of the parameters of the NTD system are needed to ensure its opti- mized and efficient use. In this note the quantitative criteria for ∗ Corresponding author. Tel.: +48 616653687; fax: +48 616653649. E-mail addresses: Adam.Voelkel@put.poznan.pl, adamvoelkel@wp.pl (A. Voelkel). selection of parameters of the NTD system, taking into account practical reasons and sampling effectiveness, are derived. The crite- ria derived contain only macroscopic characteristics of the NTD system without referring to any particular (not general) model relating macroscopic and microscopic structural properties of the sorbent as it was proposed in [10]. The results are valid assuming manual analysis and unidirectional flow, which are representative mostly for on-site extractions. Similar considerations could be done for automated and cyclic applications of NTD. 2. Analysis of criteria for NTD system Taking into account the fact that the needle trap device extrac- tion method is based on flow of a solution through a sorbent material during which sorption/desorption interactions take place the optimization of the system requires specification of appropriate conditions for simultaneous hydrodynamic (flow) and physico- chemical (sorption) processes. The processes undergo in a sorbent bed which is a porous material with present inter and intra granular pore spaces. The hydrodynamic conditions related to manual real- izability of the NTD test are constituted by limit for maximum force which can be exerted on the syringe and a maximum time which can be spent to make a single test. The physicochemical aspects of NTD extraction result from the fact that certain minimum volume of samples and minimum time for process of sorption or desorp- tion in a sorbent (dependent on the type of sorption kinetics) are required in order to perform extraction effectively. For the descrip- tion of flow the Darcy’s law is assumed neglecting friction with the needle’s wall as compared to internal friction within the sorbent bed. 0021-9673/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.chroma.2012.12.076