The behavior of arsenite (AsIII), arsenate (AsV), monomethylarsonate (MMA), dimethylarsinate (DMA), arsenobetaine (AsB) and arsenocholine (AsC) in pyrolytic graphite coated graphite (pyrocoated) tubes was studied. The influence of a tungsten carbide coating on the thermal pretreatment losses of the analytes and on the anal. signals in aq. and methanolic solns. was studied. Inorg. species, MMA and DMA are less volatile in pyrocoated tubes; a tungsten carbide coating produces a good thermal stabilization, but a marked 'dip' in the pyrolysis curves is obsd. in aq. solns. No pronounced stabilizing effect for the highly volatile AsB and AsC was obsd. in tungsten-treated tubes or in the presence of palladium chloride. The detn. of these species requires the addn. of palladium nitrate in both pyrocoated and tungsten-treated tubes. A comparison of the stabilizing action of palladium as its chloride and nitrate was made. Palladium nitrate exhibits efficient stabilizing action for each of the species studied, whereas palladium chloride is efficient only for inorg. As species in pyrocoated tubes. The tungsten treatment of the tube and addn. of palladium nitrate leads to a further increase in the pyrolysis temp. and better sensitivity for the As species. Tungsten treatment plays an important role in improving the performance of palladium chloride, particularly in the detn. of organically bound species. The effective stabilization and relative 'leveling-off' of the signal for each of the As species (except for AsC) in methanolic soln. was obsd. in the presence of a palladium modifier in tungsten-treated tubes. The in situ sepn. and detn. of AsIII and AsB in tungsten-treated tubes was attempted. However, because of the presence of significant amts. of AsB under the conditions used for AsIII detn., complete sepn. of these species was not possible. [on SciFinder (R)]