A cryogenically cooled ablation cell enables the direct analysis of thin sections from fresh soft tissue samples, such as liver or kidney, for trace elements using laser ablation ICP-MS. We show here, for the first time, that reproducibilities of about 2-6% can be achieved if the tissue sample can be ablated at a temperature below 260 uC. All ablation and detection parameters, such as energy, spot size, focus, fire frequency and integration time at the ICP-TOF-MS, were optimised. A calibration method using three different tissue samples (sheep kidney, pig liver and sheep liver), from which the bulk element concentrations were determined, was validated with CRM Pig Liver (LGC 7112), which was pressed and frozen in the form of a thin slice. Good recoveries (86-124% for the certified values) were achieved for Cd (0.31 mg kg 21 ; 0.25 ¡ 0.04 certified), Cu (101 mg kg 21 ; 117 ¡ 8 certified), Zn (43.0 mg kg 21 ; 43.0 ¡ 2.7 certified) and Mo (1.8 mg kg 21 ; y1 indicative value). Therefore this CRM can be used for the quantification of other tissues with similar C-content using a one-point calibration. Detection limits in the lower mg kg 21 range (Cd: 15 mg kg 21 , Cu: 50 mg kg 21 , Zn: 20 mg kg 21 , Mo: 10 mg kg 21 and Pb: 2 mg kg 21 ) were determined based on 3s of the blank signal with a spatial resolution of less than 200 mm. Using the CRM Pig Liver, it was shown that the use of an internal standard ( 13 C) can account for fluctuations in the ablated material during a line scan. Instead of 12% RSD without internal standard, the stability of the signal was improved using the normalized signal (5.2%) compared to 2.5-3.5% precision when a NIST 610 Glass standard was ablated. Hence, LA coupled to ICP-MS with a cryogenically cooled ablation chamber is the ideal technique for 2D mapping of trace elements in soft tissues. Depending on the concentration of element present, it may be possible to determine trace elements directly in tissue samples at a spatial resolution of v20 mm.

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Understanding the detailed dissolution behavior is of importance when novel glasses are designed for different clinical applications. The goal of this work was to develop a sensitive on-line analysis method to study the dissolution of bioactive glasses. An inductively coupled plasma optical emission spectrometer together with a flow-through microvolume pH electrode were utilized to continuously measure the concentration profile of the ions dissolving from glass particles into aqueous solutions. The method was tested with the bioactive glass 1-98 consisting of seven oxides: 6Na 2 O, 11K 2 O, 5MgO, 22CaO, 1B 2 O 3 , 2P 2 O 5 , and 53SiO 2 (wt%). The influence of flow rate and temperature on the dissolution profile and kinetics of 1-98 was studied in ultrapure water. In addition, the influence of the solution composition was studied using ultrapure water and with tris(hydroxymethyl)aminomethane (TRIS) buffer. The strength of the method is that the initial dissolution can be accurately determined simultaneously both qualitatively and quantitatively. When using the highest flow rates, the dissolution rate changed from a diffusion-controlled toward a surfacecontrolled mechanism. As a result of the temperature increase, the overall dissolution increased according to Arrhenian behavior and led more rapidly to steady-state dissolution. The change of solution from unbuffered (ultrapure water) to TRIS changed the dissolution mechanism from uniform to preferential. In addition, higher concentrations of all ions were measured in TRIS than in pure water. The method develop is promising for fast screening of the dissolution mechanism of glasses in different experimental conditions. II. Experimental ProcedureThe effect of surface area, flow rate, temperature, and solution composition on the dissolution behavior of bioactive glass 1-98 was measured using a flow-through cell connected to an inductively coupled plasma optical emission spectrometer, ICP-OES (Optima 5300 DV; Perkin Elmer, Waltham, MA). The ion concentrations of the solution were measured on-line every 12 s (one replicate per measurement). The pH values were C. Jantzen-contributing editor Manuscript No. 31143.

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