Filter paper changes

Vacuum filtering can be a bit tricky, as the filter paper clogs up very quickly and stalls the process. With this stuff it is particularly important to get rid of as much of the solids as possible or your distillation be will very messy. A way round that I have found (that isn t in any book) was to use loads of filter papers, throw them all into a big beaker and then rinse them with solvent, then filter the solvent. Filter tiny amounts at a time, as soon as the paper blocks - stop and change the paper. I normally run the filtrate through at least twice. Any way you can make sure that you have done two... 

Although precipitates which require ignition will usually be collected in porcelain or silica filtering crucibles, there may be some occasions where filter paper has been used, and it is therefore necessary to describe the method to be adopted in such cases. The exact technique will depend upon whether the precipitate may be safely ignited in contact with the filter paper or not. It must be remembered that some precipitates, such as barium sulphate, may be reduced or changed in contact with filter paper or its decomposition products. 

This filtration may be slow. Buchner funnels of 20-cm. diameter are best used the preparation is allowed to suck dry from a single filling and the filter paper then changed. 

The effect of storage of water samples before determination of nitrogen and carbon associated with particulate matter was investigated. Freezing of the samples, and storage at 5°C, both affected the results obtained, but changes were minimized if the samples were filtered immediately after collection and the particulate matter stored on the filter paper. It is recommended that samples for determination of particulate carbon and nitrogen should be filtered immediately, and analysed as soon as possible. 

Colorimetric field tests for TATP and HMTD were described in Section 5 dealing with peroxide-based explosives. This group contains Keinan s PEX [85] (E. Keinan, Personal Communication, February 2006) and the kit developed by Schulte-Ladbeck et al., which involves also a preliminary stage to avoid falsepositive responses by non-explosive peroxides [86]. The color change of molybdenum hydrogen bronze suspension upon reaction with TATP was recommended also as a field test. Exposure of filter paper strips which were soaked in butanol suspension of the molybdenum compound to TATP or hydrogen peroxide vapors rapidly bleaches the blue color [87, 88]. 

I. 4-methoxyacetophenone (30 //moles) was added as an internal standard. The reaction was stopped after 2 hours by partitioning the mixture between methylene chloride and saturated sodium bicarbonate solution. The aqueous layer was twice extracted with methylene chloride and the extracts combined. The products were analyzed by GC after acetylation with excess 1 1 acetic anhydride/pyridine for 24 hours at room temperature. The oxidations of anisyl alcohol, in the presence of veratryl alcohol or 1,4-dimethoxybenzene, were performed as indicated in Table III and IV in 6 ml of phosphate buffer (pH 3.0). Other conditions were the same as for the oxidation of veratryl alcohol described above. TDCSPPFeCl remaining after the reaction was estimated from its Soret band absorption before and after the reaction. For the decolorization of Poly B-411 (IV) by TDCSPPFeCl and mCPBA, 25 //moles of mCPBA were added to 25 ml 0.05% Poly B-411 containing 0.01 //moles TDCSPPFeCl, 25 //moles of manganese sulfate and 1.5 mmoles of lactic acid buffered at pH 4.5. The decolorization of Poly B-411 was followed by the decrease in absorption at 596 nm. For the electrochemical decolorization of Poly B-411 in the presence of veratryl alcohol, a two-compartment cell was used. A glassy carbon plate was used as the anode, a platinum plate as the auxiliary electrode, and a silver wire as the reference electrode. The potential was controlled at 0.900 V. Poly B-411 (50 ml, 0.005%) in pH 3 buffer was added to the anode compartment and pH 3 buffer was added to the cathode compartment to the same level. The decolorization of Poly B-411 was followed by the change in absorbance at 596 nm and the simultaneous oxidation of veratryl alcohol was followed at 310 nm. The same electrochemical apparatus was used for the decolorization of Poly B-411 adsorbed onto filter paper. Tetrabutylammonium perchlorate (TBAP) was used as supporting electrolyte when methylene chloride was the solvent. 

Save the filter paper with residue for Zr detn. Fill the volumetric flask to the mark and pipet a 50-ml aliquot into a 400-ml beaker for the chromate detn. Dilute to 250 ml, and add 10 ml of dilute sulfuric acid (1 4) and 10 ml of phosphoric acid (1 1). Add a measured excess consisting of ca 30 ml of standardized 0.05N ferrous ammonium sulfate soln and 6 to 8 drops of Na diphenylamine sulfonate indicator soln (0.2 g in 100 ml of w). Titrate the excess ferrous iron with 0.05N std K dichromate soln, adding the dichromate slowly with stirring, until the pure grn color changes to gray-grn. Then add the dichromate one drop at a time until the first tinge of purple or violet-blue appears... 

NaL -2 H2O (0.5 g, 1.7 mmol) is dissolved in water (100 mL). Concentrated aqueous HCl (11 M, 3 mL) is added dropwise with stirring. Immediately, a deep green crystalline solid separates, and the color of the solution changes from violet (A ax 550 nm) to red-violet (A ax 523 nm) on the formation in solution of HL, the 2-tricyanovinyl-3,4-dicyano-5-amino-17/-pyrrole. The solid (HL + HL) is then collected on filter paper, washed with water (3 x 10 mL), dried in air, and then heated in an oven at 70°C for 24 h. During this time the complete HL HL transformation occurs in the solid state, and pure HL is obtained (0.38 g, 95%). 

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