Examination of the insoluble residue

7 EXAMINATION OF THE INSOLUBLE RESIDUE It may well happen that after treating the sample with the various solvents, as described in Section V.6, some insoluble residue remains or the whole sample may prove to be insoluble. With this insoluble residue the preliminary tests, described in Section V.5, should be carried out these tests may supply valuable information as to the composition of the insoluble substance. In every case, the following methods of bringing the substance into solution for systematic analysis should be used. 

Lead silicate is insoluble in ammonium acetate solution it will be detected in 3. 

Removal of silver salts Warm the insoluble unknown or the residue from 1 (if lead salts are present) with a concentrated solution of potassium cyanide. (If it dissolves completely, only AgCl, AgBr, Agl, and AgCN are present.) Filter and reserve the residue, R, for subsequent treatment. Dilute the filtrate considerably and treat with hydrogen sulphide. Filter off any black precipitate (Ag2S), wash, dissolve in hot dilute nitric acid and add dilute hydrochloric acid. A white precipitate of silver chloride indicates the presence of silver. 

If silver is found, the halogen with which the metal was originally combined is identified by melting another portion of the insoluble substance, immersing it in dilute sulphuric acid, placing a piece of zinc in contact with the acid and the fused mass, warming and allowing to stand for a few minutes. The silver salt is reduced to metallic silver, whilst the anions are present in solution in the presence of zinc ions, i.e. as zinc salts. Filter. The filtrate is tested for chloride, bromide, and iodide in the usual manner the tests for mixtures of these anions are described in Section IV.45, and in Section V.18, Table V.30. 

Sodium carbonate fusion The residue left undissolved after operations 1 and 2 have been carried out, should be treated according to the scheme outlined inTableV.il. 

It may well happen that after treating the substanee with the solvents as described above, some insoluble material remains or the whole sample may prove to be insoluble. The most common insoluble substances, together with hints for their identification, are described below. 

Ag halides 1. Silver halides AgCl, AgBr, Agl and related compounds (AgCN). These 

Sulphates 2. Certain sulphates like SrS04, BaS04, PbS04. These white substances can 

Metal oxides 3. Refractory metal oxides like AI2O3, Cr203, Fe203, Sn02, the mixed anti- 

For the fusion it is best to start with placing 5 g analytical grade potassium hydrogen sulphate KHSO4 into a clean porcelain crucible. Heat gently over a Bunsen flame, when the hydrogen sulphate slowly decomposes to the pyrosulphate and water. Once foaming has abated, increase the temperature 

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Note 5. Insolubles are present when Klason lignin or wood meal is used. After a 40-min ozonation of wood meal, examination of the insoluble residue (in KBr) by FTIR showed the absence of characteristic lignin absorption bands. 

Larger filter sizes were used to retain degraded polymer with higher molecular weights and to examine the effect of the insoluble residues on filtration characteristics. 

Insoluble residues. Insoluble residue in the roots of peanuts accounted for 13.5X of the applied 48 hr after treatment with [ C]PCNB. This increased to 2lK after 33 days. The other plant systems examined also produced Insoluble residue after short-term treatment with [) C]PCNB (Figure 3). The values indicated for insoluble residues in systems other than peanut and peanut cell culture may be too high because these tissues were extracted with 70X acetone (IX) and acetone (2X) rather than with 80 l methanol (3X). 

Insoluble Matter.—20 grams of the substance are dissolved in at least 300 c.c. of water, the solution being filtered through a filter previously dried at 1050 and tared, and the insoluble residue thoroughly washed, dried at 105° and weighed. The residue is examined microscopically for starch. 

To distinguish catechu from gambier, the substance is treated with 30% acetic acid or with 10% soda solution and the insoluble residue examined under the microscope if this consists of fragments of woody fibre the product is catechu, whereas if it is formed of parenchymatous cells and hairs with curved and dotted base, i.e., of leaf elements, the product is gambier. 

Detection of Starch.—The colouring matter is treated in the cold with water or alcohol, the insoluble residue being examined microscopically. 

Detection of Glucose and Saccharose.—With colouring matters insoluble in water, these may be detected in the aqueous extract. Colours soluble in water and in alcohol may be treated in the cold with absolute alcohol (best mixed with a little ether) and the insoluble residue examined. 

The optimum conditions for forming the acid and ammoniacal sulfide precipitates were also studied. Whether a moderate or a large excess of thioacetamide is added appears to have little or no effect on the completeness of precipitation. Precipitation of the acid-insoluble sulfides occurs slowly at room temperature however, precipitation may be hastened by heating the solution to just below boiling. To ensure complete precipitation and an easily filtered precipitate, the solution should be filtered only after the residue has settled foir several hours or overnight. An examination of the filtrate showed complete removal of antimony, arsenic, bismuth, cadmium, copper, and lead only molybdenum was not completely removed. 

The residue insoluble in HCI should also be examined. This can most simply be done by dissolving away the calcareous matter with monochloro acetic acid or formic acid, followed by X-ray examination of the residual material. Furthermore, the distribution of dolomite can be investigated by means of staining... 

This problem is encountered when testing materials used as pigments and in the examination of the so-called insoluble residue in qualitative inorganic analysis. An appropriate quick method of meeting this situation consists of fusing small quantities of the sample with sodium formate. If the temperature is maintained at about 240-250 (glycerol bath) only black elemental lead is formed in the colorless mass. The probable reaction is... 

For additives extracted from polyolefins, usually with diethyl ether, the extract is refluxed with ethanol and the solution is decanted from the insoluble residual polymer. On cooling, additives such as dilauryl and distearyl thiodipropionate separate out and are identified by infrmed examination. A 30 ul volume of the ethanolic solution is then spotted on to a thin Kieselgel 60 TLC plate and eluted with a suitable solvent, usually 98.5 + 1.5 toluene-ethyl acetate. The eluted plate is dried and sprayed with colour-developing reagents and the spots are examined. If the spots are to be submitted to mass spectrometric examination, methanolic iodine is used as the colour-developing reagent as this does not over-complicate the mass spectrometry. 

Torpex. Place 0.2 gram of the explosive in a five milliliter beaker and extract with three, 3 milliliter portions of acetone. Dry the insoluble residue and examine under a microscope. Note if the residue has the characteristic appearance of metallic aluminum. Place 0.2 gram of the explosive in a 5 milliliter beaker and digest with two, 3 milliliter portions of benzene, decanting the benzene into a small evaporating dish. Evaporate the benzene solution to dryness and test for TNT as indicated in table 13-1. Dry the insoluble residue from the benzene extraction and test for RDX as described in (1) above. 

Reduction of a nitro compound to a primary amine. In a 50 ml. round-bottomed or conical flask fitted with a reflux condenser, place 1 g. of the nitro compound and 2 g. of granulated tin. Measure out 10 ml. of concentrated hydrochloric acid and add it in three equal portions to the mixtiue shake thoroughly after each addition. When the vigorous reaction subsides, heat under reflux on a water bath until the nitro compound has completely reacted (20-30 minutes). Shake the reaction mixture from time to time if the nitro compound appears to be very insoluble, add 5 ml. of alcohol. Cool the reaction mixture, and add 20-40 per cent, sodium hydroxide solution imtil the precipitate of tin hydroxide dissolves. Extract the resulting amine from the cooled solution with ether, and remove the ether by distillation. Examine the residue with regard to its solubility in 5 per cent, hydrochloric acid and its reaction with acetyl chloride or benzene-sulphonyl chloride. 

Sulfur Polymer Cement. SPC has been proven effective in reducing leach rates of reactive heavy metals to the extent that some wastes can be managed solely as low level waste (LLW). When SPC is combined with mercury and lead oxides (both toxic metals), it interacts chemically to form mercury sulfide, HgS, and lead sulfide, PbS, both of which are insoluble in water. A dried sulfur residue from petroleum refining that contained 600-ppm vanadium (a carcinogen) was chemically modified using dicyclopentadiene and oligomer of cyclopentadiene and used to make SC (58). This material was examined by the California Department of Health Services (Cal EPA) and the leachable level of vanadium had been reduced to 8.3 ppm, well below the soluble threshold limit concentration of 24 ppm (59). 

Preliminary structural studies of cutin and suberin breakdown involved examination of 13C NMR spectra for insoluble residues that were resistant to chemical depolymerization. In cutin samples, flexible CH2 moieties in particular were removed by such treatments, but CHOCOR crosslinks and polysaccharide impurities were retained preferentially. A concomitant narrowing of NMR spectral lines suggested that the treatments produced more homogeneous polyester structures in both cases. Our current studies of cu-ticular breakdown also employ selective depolymerization strategies with appropriate enzymes (1,28). 

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