Off-resin Analysis

Off-resin analysis is analysis of a compound cleaved off a polymeric carrier material, usually in solution. 

The loading of resin 60 and the success of each step of its synthesis was determined by an off-bead analysis involving the removal of the reaction products from the resin through an oxidative hydrolysis of the sulfoximine group at the S—N bond with formation of the corresponding sulfones by a method we have described recently [42]. 

Differential scanning calorimetry A Perkin-Elmer DSC-2 calorimeter with Thermal Analysis Data Station was used. The calorimeter was calibrated according to manufacturer s specifications. Heats of reaction were calculated from the peak areas using indium as a standard (AH=6.80 cal/g). Tg was taken as the onset of the endothermic deflection. The heating rate was set to 20 /min. For DSC analysis, samples were prepared by two techniques a) vacuum drying of varnish and b) by flaking off resin from prepreg. 

Off-line coupling of HPLC with FD-MS has been used by several authors [118-121] for the determination of oligomers, oligomeric antioxidants (such as poly-TMDQ), ozonation and vulcanisation products. Pausch [122] reported on rubbers, cyclic polyurethane oligomers, as well as on the determination of the molecular weight distribution (up to 5300 Da) and oligomer analysis of polystyrene. Also the components of an aniline-acetone resin were deduced from FD-MS molecular weights [122]. 

The use of HMDS as a derivatization reagent in the analysis of triterpenoid resins has been less explored. The TMS derivatives of triterpenoids bearing hydroxyl groups [a-amyrine, p-amyrine and hop-22(29)-en-3p-ol] have been identified in the triterpenic fraction of Burseraceae resins, thus demonstrating that HMDS combined with Py-GC/MS is effective in the derivatization of triterpenoid compounds [59]. However, the range of structures that can be fully derivatized and detected must be extended and, in order to get comprehensive results comparable with those coming from the well assessed off-line GC/MS procedures, general improvements in the on-line trimethylsilylation-pyrolysis method are needed. 

In a previous review of this topic (5), it was suggested that molecular distillation drying followed by resin embedding needed more work before it could be evaluated as a preparative technique for microanaly-tical work as there had only been one investigation that had used it (59). Unfortunately, as far as this author is aware, there has only been one more study (12) that has used the technique to prepare material for micro-analysis. It is possible that workers have been put off using it by the apparent fall from grace of the related freeze substitution technique or, more likely, by the expense of molecular distillation drying apparatus. 

The polymer-supported hydridoiron tetracarbonyl (33 mmol) is prepared by the addition ofFe(CO)5(6.46g, 33 mmol) to KOH (5.6 g, 0.1 mol) in aqueous EtOH (1 1 v/v, 100 ml) under N2. The mixture is heated with stirring under reflux for 2 h and Amberlyst A-26 resin (24 g) is then added and the mixture is stirred for a further 15 min. The resin is collected, washed with degassed H20 (to neutrality), MeOH and Et20, dried at room temperature under a flow of N2, and used immediately. The haloalkane (11 mmol) in THF (50 ml) is added to the resin and the mixture is stirred under reflux for ca. 4 h. When GLC analysis shows the reaction to be complete, the resin is removed by filtration, and the filtrate evaporated under reduced pressure to give the aliphatic aldehyde. 

Glass transition temperatures (Tg s) were detemined using a Dupont DSC 910 attached to a 9900 data analysis system. For off-stoichiometric studies, epoxy resin and diamine were cured in situ within a hermetically sealed DSC pan (sample tak from 25 C - 300 C at lO C/min), then cooled rapidly back to 25 C, and finally scanned from 40 C - 220 c to record the Tg. All samples were scanned under nitrogen atmosphere at a rate of 10 C/min. 

Urea-formaldehyde resins are generally prepared by condensation in aqueous basic medium. Depending on the intended application, a 50-100% excess of formaldehyde is used. All bases are suitable as catalysts provided they are partially soluble in water. The most commonly used catalysts are the alkali hydroxides. The pH value of the alkaline solution should not exceed 8-9, on account of the possible Cannizzaro reaction of formaldehyde. Since the alkalinity of the solution drops in the course of the reaction, it is necessary either to use a buffer solution or to keep the pH constant by repeated additions of aqueous alkali hydroxide. Under these conditions the reaction time is about 10-20 min at 50-60 C. The course of the condensation can be monitored by titration of the unused formaldehyde with sodium hydrogen sulfite or hydroxylamine hydrochloride. These determinations must, however, be carried out quickly and at as low temperature as possible (10-15 °C), otherwise elimination of formaldehyde from the hydroxymethyl compounds already formed can falsify the analysis. The isolation of the soluble condensation products is not possible without special precautions, on account of the facile back-reaction it can be done by pumping off the water in vacuum below 60 °C imder weakly alkaline conditions, or better by careful freeze-drying. However, the further condensation to crosslinked products is nearly always performed with the original aqueous solution. 

Resin-Bound 2-Methanesulfinyl-6-piperidinopyrimidine (9b) (R2NR2 = Piperidine) (lib). Resin 16 (500 mg, 0.50 mmol/ g loading, 0.25 mmol) is swollen in DMF (20 ml) for 30 min. The mixture is cooled to 0° and a solution of magnesium monoperoxyphthalate (MMPP, 212 mg, 0.34 mmol) in DMF (5 ml) is added dropwise and shaking continues for 2 h at 0°. After the resin is washed and dried in the usual manner, an aliquot of the resin (5 mg) is taken and cleaved off. RP-HPLC analysis indicates that approximately 6% starting material remained unreacted and a new oxidation cycle is performed with MMPP (0.14 mmol) for 1 h at 0°. Analysis confirmed the total conversion of resin 16 into a mixture of resin-bound sulfoxide (lib) ( 79%) and sulfone (11c) ( 15%). A theoretical loading of 0.50 mmol/g is assumed for subsequent work. 

Off-line dicarbamate solvent extraction and ICP-MS analysis [317] provided part-per-trillion detection limits Cd (0.2 ppt), Co (0.3 ppt), Cu (3 ppt), Fe (21 ppt), Ni (2 ppt), Pb (0.5 ppt), and Zn (2 ppt). Off-line matrix removal and preconcentration using cellulose-immobilized ethylenediaminetetraacetic acid (EDTA) have also been reported [318]. Transition metals and rare earth elements were preconcentrated and separated from the matrix using on-line ion chromatography with a NTA chelating resin [319]. Isotope-dilution-based concentration measurement has also been used after matrix separation with a Chelex ion-exchange resin [320]. The pH, flow rate, resin volume, elution volume, and time required for isotope equilibration were optimized. A controlled-pore glass immobilized iminodiacetate based automated on-line matrix separation system has also been described [321]. Recoveries for most metals were between 62% and 113%. 

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