Recent reports on using bio-active paper and bio-active thread to determine human blood type have shown a tremendous potential of using these low-cost materials to build bio-sensors for blood diagnosis. In this work we focus on understanding the mechanisms of red blood cell agglutination in the antibody-loaded paper. We semi-quantitatively evaluate the percentage of antibody molecules that are adsorbed on cellulose fibres and can potentially immobilize red blood cells on the fibre surface, and the percentage of the molecules that can desorb from the cellulose fibre surface into the blood sample and cause haemagglutination reaction in the bulk of a blood sample. Our results show that 34 to 42% of antibody molecules in the papers treated with commercial blood grouping antibodies can desorb from the fibre surface. When specific antibody molecules are released into the blood sample via desorption, haemagglutination reaction occurs in the blood sample. The reaction bridges the red cells in the blood sample bulk to the layer of red cells immobilized on the fibre surface by the adsorbed antibody molecules. The desorbed antibody also causes agglutinated lumps of red blood cells to form. These lumps cannot pass through the pores of the filter paper. The immobilization and filtration of agglutinated red cells give reproducible identification of positive haemagglutination reaction. Results from this study provide information for designing new bio-active paper-based devices for human blood typing with improved sensitivity and specificity.

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A continuous-flow extraction system was developed to speed up, facilitate, and improve the accuracy of the chemical fractionation of metals in solid materials. A three-step sequential extraction scheme was used to evaluate the novel system by analyzing calcium (Ca), iron (Fe), manganese (Mn), copper (Cu), and zinc (Zn) in a soil certified reference material (National Institute of Standards and Technology [NIST] SRM 2710). In the proposed system, extraction occurred in a closed chamber through which extractants were passed sequentially. The extracts were collected in a number of subfractions for subsequent name atomic absorption analysis. Apart from the advantages of simplicity, speed, and less risk of the contamination that flow analysis systems usually possess, the continuous-flow system can improve the accuracy of chemical fractionation of metals by sequential extraction. The system ensures that extraction is performed at designated pH values without any need of adjustment. Variation of sample weight to chamber volume ratios from 1:12 to 1:40 had no effect on the extractability of the metals studied. In the extraction of the acid soluble fraction, concentrations of acetic acid in the range 0.11 to 0.5 mol L(-1) had no significant effect on the amounts of metals extracted, except Fe. Increasing the concentration of hydroxylamine in the reducible fraction step from 0.04 to 0.5 mol L(-1) affected the extraction efficiency for Fe, Mn, and Zn. The extraction profile, rather than a single value of extracted concentration, of each element offers additional information about the kinetics of leaching processes and chemical associations between elements in the solid materials.

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ABSTRACTthat because As and P form similar oxyanions in the ϩ5 oxidation state in soils (O'Neill, 1990), soil extraction Batch sequential extraction techniques for fractionating metals orschemes that have long been employed for P fractionmetalloids in soils are time consuming and subject to several potential ation are more suitable for As (Jacobs et al., 1970; Wool-errors. The development of a continuous-flow sequential extraction method for soil As is described and assessed, having the benefits of son et al., 1971; McLaren et al., 1998). simplicity, rapidity, less risk of contamination, and less vulnerabilityChemical fractionation (operationally defined chemito changes in extraction conditions compared with traditional batch cal speciation by sequential extraction) has been widely methods. The validated method was used to fractionate soil As using accepted and applied. However, the technique has been water, NaHCO 3 , NaOH, and HCl, followed by digestion of the residue questioned because of poor selectivity of reagents towith HNO 3 and HF acids. The extracts and digests were analyzed ward the targeted solid materials. Therefore, it is impor- 1993; Tu et al., 1994; Raksasataya et al., 1996; generally support previous suggestions of the likely forms or associaLo and Yang, 1998).tions of As present in the different soil fractions.Our previous work on development of a continuousflow extraction system for sequential extraction has manifested many advantages compared with using a M inerals, metals, or metalloids, toxic or essential, batch method (Shiowatana et al., 2001). For example, are present in soils or sediments in various forms the flow system has the benefits of simplicity, rapidity, with varying bioavailability, toxicity, and mobility. Deless risk of contamination, and less vulnerability to termination of total concentrations of these elements in changes in extraction conditions. In a continuous-flow solid materials is therefore considered to be of limited system, because elements brought into solution are conuse in assessing potential environmental impacts. In ortinuously being removed from the system, there should der to assess their actual behavior, role, and impact, a be less opportunity for readsorption to occur. The sysgood understanding of the chemical forms of the eletem also has an additional advantage in that the exments of interest is required. The use of sequential extractograms obtained can provide useful information on traction techniques to fractionate metals in solid materithe association of elements in each solid phase. In this als, and evaluate their potential effects, has become study, the continuous-flow extraction system was apwidely used and well recognized (Tessier et al., 1979).plied to the sequential extraction of As using an extracHowever, there are relatively few reports on the fraction scheme modified from the work of McLaren et al. tionation of metalloids such as As. Some reports have (1998). This scheme was selected because it was develemployed the extraction schemes original...