Afterchrome dyeing of wool. Part B zyx - character- isation of chromium-treated wool by secondary particle mass spectrometry zyxw J Goschnick? M Lippt and H-J Achet, H Thomas", R Kaufmann", R Peters" and H Hocker" zyxw tlnstitut fur Radiochemie Kernforschungszentrum, Karlsruhe, Germany *Deutsches Wollforschungsinstitut an der RWTH, Aachen, Germany Secondary particle mass spectrometry has been used for the first time to determine the oxidation state and depth distribution of chromium on and in wool fibres. Wool tops were dyed with zyxw 4% 0.w.f. CI Mordant Black 11 and aftertreated with 1% 0.w.f. potassium dichromate, and wool samples treated in a blankdyebath aftertreated with 6% 0.w.f. potassium dichromate were analysed. It could be shown that the absolute concentration of chromium in a surface layer 50 nm thick became enriched with chromium by a factor of two, compared with the bulk fibre. Chromium in the hexavalent oxidation state was found to be mainly present in the outermost part of the fibres, while trivalent chromium was dominant inside the fibres. INTRODUCTION It is often insufficient to know the overall elemental composition of samples. The chemical state and the spa- tial distribution of the elements are also of importance in evaluating chemical behaviour. In particular, for chro- mium-treated wool fibres, information is required about the concentration, depth distribution and chemical state of the metal within the outermost parts of the fibre. Hence, an in-depth analysis is needed in order to under- stand fully the oxidation state of chromium. Sensitive analytical methods that meet these require- ments include secondary particle mass spectrometry techniques, such as SNMS (secondary neutral mass spec- trometry) and SIMS (secondary ion mass spectrometry), which have now been used for the first time to inves- tigate wool fibres. This work not only provides chemical information about chromium in the surface of wool, but also demonstrates the capability of these advanced meth- ods to investigate such samples effectively. Wool tops treated with different potassium dichromate solutions were investigated for their chemical constitution within the near-surface region. PRINCIPLES OF ANALYSIS The analytical methods used are based on the mass analysis of the particle flux generated in the erosion of solids during bombardment with ions, commonly called sputtering. A schematic drawing is given in Figure 1. Time-resolved analysis of the erosion flux provides an image of the depth distribution within the solid. SNMS was used to characterise the neutral particles within the erosion flux, which are mainly neutral atoms of all ele- ments contained in the sample. The plasma-based ver- Primary ions Secondary particles e- Positive secondarv ions Secondary neutrals \ // Sample Figure 1 The sputter process sion of SNMS developed by Oechsner [l], which was employed for the present investigations, accelerates no- ble gas ions extracted from a high-frequency plasma towards the sample. The neutral species emitted from the sample are analysed by a quadrupole-based mass separa- tor after discrimination of plasma-generated thermal ions by an ion energy filter (Figure 2). SIMS, being the mass analysis of the ionic sputter flux, was performed with the same spectrometer. However, this technique works without the plasma, because no n z I longun h A Figure 2 Principle of analysis (plasma used for SNMS only) (SEM = secondary electron multiplier) JSDC VOLUME^^^ APRIL 1992 191