Four levels of pattern recognition

Problems of pattern recognition in chemistry and other subjects can be divided conveniently into four different types depending on the level of scope of the problem.(1) Classification into one of a number of defined classes. As an example blood samples taken from persons known to be either controls or welders are considered. The problem is whether trace element concentrations in these samples contain information on whether or not a person is a welder.(2) Level 1 plus the possibility that an object is an outlier, i.e. does not belong to any of the defined classes. As an example, the üse of ¹³C-n.m.r. data to decide whether 2-substituted norbornanes have the exo or endo structure is discussed. (2A) Level 2, asymmetric. This situation occurs when one class does not have a systematic structure, but another class is homogeneous and can be described by a level 2 model. This occurs in the classification of materials or compounds as good or bad, active or inactive, and in binary classifications. As an example the use of trace element data to classify steel samples as having good or poor properties of strength is discussed.(3) Level 2 plus the ability to relate the variables measured to external properties of continuous character. As an example, the classification of a series of chemical compounds as β -receptor blockers, β -receptor stimulants, or neither, on the basis of their structural variables is discussed. In addition, relations between these structural variables and the measured biological activity are sought within each of the two classes.(4) Level 3 with the difference that several external property variables in the objects are measured. It may be desirable to use variables of the objects both for classification and for relations to several property variables: such examples are numerous in analytical chemistry.     

Studies of copper(II) sulphide ion-selective electrodes

Changes in liquid junction potentials in copper(II) solutions were measured when different reference electrodes were used. The slope and intercept of a calibration curve for a copper-selective electrode will depend on the selection of reference electrode. The condition of the electrode surface of an Orion copper-selective electrode was studied microscopically and the influence of redox potential on stability of the electrode against corrosion is discussed. Oxidizing solutions will produce pits at dislocations in the material and there will be a mixed electrode potential. The slope, stability, and speed of response are much lower when the surface contains pits. Diamond-polishing was shown to improve the electrode significantly.     

Phenylated polyimides via bifunctional monomers

The synthesis of two phenylated bifunctional monomers, dimethyl 4-(4-(p-aminophenoxy)phenyl)-3,5,6-triphenylphthalate and dimethyl 4-(4-(4-(p-aminophenoxy)phenoxy)phenyl)-3,5,6-triphenylphthlate, was accomplished. Polymerization in solution or by a bulk polymerization procedure yielded a series of low molecular weight phenylated polyimides. The polymers were soluble in chlorinated hydrocarbons and exhibited thermal stabilities comparable to other polyimide systems.     

Extraction of Polonium from Aqueous Lactic Acid Solutions Using Dioctyl Sulphide, Cyanex 272, Cyanex 301 or Cyanex 302 in Toluene

The extraction of polonium from lactic acid (HLac) solutions has been studied with di-n-octyl sulphide (DOS), Cyanex 272, Cyanex 301 and Cyanex 302 extractants dissolved in toluene. For the extraction with DOS, the extracted species is most likely PoO(Lac)₂·3DOS. The results for Cyanex 272 also indicate extraction via a solvation mechanism rather than cation exchange. The extracted species is probably PoO(Lac)₂·2HA. The major species extracted with Cyanex 301 or Cyanex 302 do not contain any lactate molecules. The extracted species is most likely PoOA₂ at low extractant concentrations, while at higher concentrations an adduct complex of the type PoOA₂·2HA is formed. The extraction of polonium increases in the order Cyanex 272 < Cyanex 302 < DOS < Cyanex 301, which is the same order as the increase of the number of sulphur atoms in the reagents.     

Comparison of denuder and impinger sampling for determination of gaseous toluene diisocyanate (TDI)

An air-sampling method employing denuders coated inside with a chemisorptive stationary phase has been evaluated for analysis of the hazardous gaseous 2,4 and 2,6 isomers of toluene diisocyanate (TDI). The denuder stationary phase consisted of polydimethylsiloxane (SE-30) to which dibutylamine (DBA) was added as a reagent for derivatization of TDI. The accuracy and precision of sampling by means of denuders were shown to differ only slightly from those of the established impinger method. The denuder method was, however, also shown to be suitable for long-term measurements (up to 8 h). The limit of determination (LOD) of the method, including LC-APCI-MS-MS analysis, was found to be 1.9 microg m(-3) and 1.2 microg m(-3) for 2,4- and 2,6-TDI, respectively, for short-term measurements (15 min). Significant lower LOD was obtained for long-term measurements. This is well below the Occupational Safety and Health Administration (OSHA) 8-h TWA (time-weighted average) exposure limit, which is 40 microg m(-3) for the sum of the TDI isomers. The denuder method was also found to be robust and easy to handle. The samplers can be prepared several days before sampling with no loss in performance. The contents of denuders should, on the other hand, be extracted immediately after sampling to prevent degradation of the isocyanate derivatives formed.     

Deoxygenation of supporting electrolytes in stripping voltammetry by glocuse and co-immobilized glocuse oxidase and catalase in a flow system

Carrier solutions for stripping voltammetry in flow systems are deoxygenated by reaction with glucose added to the carrier. The reaction was catalyzed by glocuse oxidase and catalase co-immobilized in an enzyme reactor which was inserted before the injector. The oxygenated was removed at least as efficiently as with nitrogen purging and the voltametric behaviour of cadmium(II), lead(II) and zinc(II) was unaffected by the glucose/gluconic acid system. A particular advantage is the rapid start-up compared to the lengthy purging of carrier solution when nitrogen degassing is used. The enzyme reactor made from porous glass was effective for several months.     

Simultaneous liquid chromatographic determination of seventeen of the major monoamine neurotransmitters, precursors and metabolites. I. Optimization of the mobile phase using factorial designs and a computer program to predict chromatograms

Utilizing reversed-phase high-performance liquid chromatography (HPLC) with electrochemical detection and optimization of the mobile phase using factorial designs and a constructed computer program to predict chromatograms, it has been possible to obtain a satisfactory resolution of seventeen of the major monoamine neurotransmitters, precursors and metabolites. A rapid (less than 25 min) isocratic system for the simultaneous determination of 3,4-dihydroxyphenylalanine, dopamine, dihydroxyphenylacetic acid, 3-methoxytyramine, homovanillic acid, norepinephrine, normetanephrine, 3,4-dihydroxyphenylethylene glycol, 3-methoxy-4-hydroxyphenylethylene glycol, epinephrine, metanephrine, vanillylmandelic acid, 5-hydroxytryptophan, serotonin, 5-hydroxytryptophol and 5-hydroxyindoleacetic acid in addition to the internal standard isoproterenol is presented. The optimization strategy included selection of variables to optimize by a reduced factorial design a detailed study of these variables by a complete factorial design, theoretical predictions of chromatograms by a constructed computer program and test on the HPLC system. This optimization strategy can easily be applied to any problem of solute separation by liquid chromatography.     

An intercomparison of sampling techniques for measurements of radiocaesium in upland pasture and soil

An intercomparison of sampling procedures used by five laboratories for the determination of radiocaesium in vegetation and peaty soil was carried out at two locations in Cumbria. The multiple sampling has given information on the homogeneity of the parameters studied at each location. The parameters comprise soil bulk densities, total deposition of¹³⁷Cs, deposition of¹³⁷Cs in three soil layers, biomass densities, concentrations of¹³⁷Cs in pasture, and activity ratios (¹³⁴Cs/¹³⁷Cs) in soil and vegetation. The determination of total deposition of¹³⁷Cs gave no indication of differences between the laboratories. The results from the soil profiles do indicate significant differences between laboratories. One laboratory using a coring technique observed difficulties during sampling due to compression of the soil. The coring technique should thus be avoided or applied with extreme care for the sampling of depth profiles in peaty soil. The results from the sampling of pasture show no indication of differences between the laboratories. For the parameters studied the observed variabilities across soil depths and locations range from 10% to 81% in terms of relative standard deviations. A comparison across all results at the two locations indicate a 50% higher field variability at one of the sites relative to the other.