Residual solvents analysis standard preparation

In terms of residues in food, stability is an important parameter as it relates to (1) residues in biological matrices during storage, (2) analytical reference standards, (3) analytes in specified solvents, (4) samples prepared for residue analysis in an interrupted assay run such as might occur with the breakdown of an analytical instrument, and... 

The procedure of sample preparation for faecal BA analysis and derivatisation is an adaptation of the method of Czubayko et al. [17]. The internal standard (125 pg HDCA) is added to the aqueous phase of extraction. The sample is saponified with 200 pi 10 mol/1 sodium hydroxide at 120°C for 120 min and then acidified to pH 1 with hydrochloric acid. After extraction of BAs with diethyl ether (4 x 1 ml), the solvent phases are pooled and evaporated under a stream of nitrogen. The residue is... 

Determinative and confirmatory methods of analysis for PIR residue in bovine milk and liver have been developed, based on HPLC-TS-MS (209). Milk sample preparation consisted of precipitating the milk proteins with acidified MeCN followed by partitioning with a mixture of -butylchloride and hexane, LLE of PIR from aqueous phase into methylene chloride, and SPE cleanup. The dry residue after methylene chloride extraction was dissolved in ammonium hydroxide, and this basic solution was transferred to the top of Cl8 SPE column. The PIR elution was accomplished with TEA in MeOH. For liver, the samples were extracted with trifluoroacetic acid (TFA) in MeCN. The aqueous component was released from the organic solvent with n-butyl chloride. The aqueous solution was reduced in volume by evaporation, basified with ammonium hydroxide, and then extracted with methylene chloride. The organic solvent was evaporated to dryness, and the residue was dissolved in ammonium acetate. The overall recovery of PIR in milk was 94.5%, RSD of 8.7%, for liver 97.6%, RSD of 5.1 %. A chromatographically resolved stereoisomer of PIR with TS-MS response characteristics identical to PIR was used as an internal standard for the quantitative analysis of the ratio of peak areas of PIR and internal standard in the pro-tonated molecular-ion chromatogram at m/z 411.2. The mass spectrometer was set for an 8 min SIM-MS acquisition. Six samples can be processed and analyzed in approximately 3 hours. 

Three standard solutions were prepared—one containing 1 mg. of DDT and 1 mg. of DDD per 10 ml. of solvent the second containing 1 mg. of diazinon per 10 ml. of solvent and the other containing 1 mg. of ethion per 10 ml. of solvent (benzene). The retention time (time required after injection of the sample for the component to reach its maximum peak height) was used as a qualitative measure to identify the component. Quantitative information was obtained from the direct relationship of the concentration of insecticide to the maximum peak height. Standards were analyzed periodically during the analysis of the residues. 

First, consider the overall stability of the sample in the preparation solvent Note that this solvent may or may not be identical to the mobile phase (although it is generally recommended that the preparation solvent and mobile phase be the same so as to avoid system peak generation, etc.) Sanqjles (this includes standards) spend a large amount of time interacting with the preparation solvent. The time from completion of the preparation to the actual analysis is often hours. In some instances this has been shown to be crucial in cases of protein denatuiation in solvents [31] and on columns [32] decomposition of derivatized analytes [33] time, temperature, and light effects in the case of ascorbic acid [34] and pesticide residue decomposition on support media such as graphitized carbon and C,g silica [35]. 

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