Mem. Ist. ital. Idrobiol.,56: 157-161, 1997 The routine use of Anodisc ™ filters with automatic CHN analysers Roberto BERTONI C.N.R. Istituto Italiano di Idrobiologia, 28922 Verbania Pallanza, Italy ABSTRACT There are certain drawbacks involved in the routine use of Anodisc filters (0.2 μm pore size) in the analysis of particulate organic carbon (POC) from environmental samples. These filters are hard and brittle and consequently difficult to use in the autosampler of CHN ana- lysers. This paper describes a technique for grinding Anodisc filters with their organic load and for quantitatively recovering the resultant fragments in the sample carrier capsules used in the CHN autosamplers. Key words: Anodisc, CHN analysis, particulate organic matter, POC 1. INTRODUCTION The first step in measuring particulate organic matter in waters with CHN ele- mental analysers is the separation and concentration of particles from liquid sam- ples. In environmental research this is normally done by filtration. The common practice is to concentrate particles on inorganic filters to be analyzed with their or- ganic load, as the quantitative recovery of particles from organic filters is almost impossible. Thus the choice of inorganic filter sets the lower limit of the particle size range. The most commonly used inorganic filters are made of glass fiber and are able to retain particles with a maximum dimension of 1.2 μm (Whatman GF/C) or 0.7 μm (Whatman GF/F). This nominal cut off size claimed by the manufacturer is widely questioned by researchers. One important reason for this lies in the sponge- like structure of glass fiber filters and in the pre-combustion treatment necessary to remove organic contaminants from them. The sponge-like structure of glass fiber filters can be altered by the pre-combustion treatment, depending on the temperature and duration of the treatment and on the characteristics of any particular batch of filters. Particles smaller than the nominal cut off size can be trapped between glass fibers and larger soft particles can be squeezed through the fibers (Johnson & Wang- ersky 1985). As a result, the difference in retention of GF/C and GF/F filters is questioned (Prepas et al. 1988). Silver filters with a minimum nominal cut-off size of 0.45 μm have been proved to have better retention characteristics (Landry et al. 1992) but they have never been widely used because they are relatively expensive. By the end of the eighties a new type of inorganic filter became commercially available. It is made of anodically oxidized aluminium (Anopore™ membrane) (Furneaux et al. 1989); it has a sieve-like structure with regular pores of 0.2 μm.