Abstract This study compares four sample dissolution methods for Boron determination in two National Institute of Standard and Technology (NIST) botanical Standard Reference Materials (SRMs) and three Agriculture Canada/NIST RMs, each having a reference (certified or best estimate) B concentration. The dissolution treatments consisted of: 1) dry ashing at 500° C, 2) wet digestion with HNO 3 + H 2 O 2 , 3) extraction with hot HNO 3 and 4) closed vessel microwave dissolution. The samples were spiked before and after imposing dissolution treatments to study B recovery by inductively coupled plasma mass spectro- metric (ICP-MS) analysis. Microwave digests of NIST SRM 1515 and some in-house RMs were also used to compare the B values of ICP-MS and ICP-AES (atomic emission spectrometry). While all three digestion methods (dry ash- ing, wet ashing and microwave) dissolved botanical sam- ples, only the microwave method worked well for animal tissues. In terms of B values in these materials, there was no significant difference among the three digestion treat- ments. Near 100% recovery of B spiked before and after the sample dissolution indicates that there may not be a significant loss of B during the dissolution process used in this study. Extraction with hot HNO 3 was as effective as the three digestion treatments, and B values for this method agreed well with reference values. For the botanical mate- rials studied, the B values determined by ICP-AES were not significantly different from ICP-MS values. This study shows that a simple, time and labor efficient hot HNO 3 ex- traction is as effective as other digestion/dissolution meth- ods for quantitative B recovery from biological materials. Introduction Boron is an essential element for plants [1] and its defi- ciency as well as toxicity threaten crop productivity in many areas [2]. Though the essentiality of B for animal is not yet fully established [3, 4], there is growing evidence that it may have a metabolic role in human and animal nu- trition [5, 6]. Excess of B in food products and drinking water is considered harmful for health [7]. Radiobiologi- cal destruction of tumor tissue by Boron Neutron Capture Therapy (BNCT) involves administering 10 B to diseased tissues followed by irradiation with slow neutrons [8]. This technique requires targeting of 10 B to appropriate tis- sues and precise monitoring of B concentrations in tumor and surrounding tissue samples. Therefore, a method with high precision and low detection limit is required to deter- mine the quantity and the isotope composition of B in bio- logical materials. Analyte introduction in an aqueous liquid phase is con- ventient for most analytical instruments. Boron present in biological materials is brought into the liquid phase either by destroying the sample matrix or extracting it with some solvents. The sample matrix may be destroyed by fusion, wet or dry ashing and microwave dissolution methods. The closed-vessel (high pressure) microwave dissolution method is fast and overcomes contamination and volatiliza- tion problems of open-vessel methods. However, high- pressure methods may be hazardous due to the danger of explosion [9, 10]. Boron contamination and leaching of B from borosilicate glass digestion vessels may increase the B values [9] which may explain the higher recovery of B in wet digestion compared to the microwave dissolution method found by Bañuelos et al. [11]. Boron extraction with dilute acids also overcomes contamination and vola- tilization problems without dealing with strong acids and high pressure. Boron may be analyzed colorimetrically or by absorp- tion, emission or mass spectrometry. Several colorimetric methods which make use of reagents such as azomethine- H, carminic acid, curcumin, dianthrimide, methylene blue or quinalizarine, have been used for B analysis [12]. All spectrophotometric methods however, have high limits of detection (LOD) and suffer from matrix interferences [13]. The azomethine-H method, which has been heavily used, may not be suitable for B determination in micro- A. M. S. Nyomora · R. N. Sah · P. H. Brown · R. O. Miller Boron determination in biological materials by inductively coupled plasma atomic emission and mass spectrometry: effects of sample dissolution methods Fresenius J Anal Chem (1997) 357 : 1185–1191 © Springer-Verlag 1997 Received: 13 June 1996 / Revised: 17 September 1996 / Accepted: 19 September 1996 ORIGINAL PAPER A. M. S. Nyomora · R. N. Sah () · P. H. Brown · R. O. Miller Department of Pomology, University of California, Davis, CA 95616, USA