Under the auspices of the Organic Analysis Working Group (OAWG) of the Comité Consultatif pour la Quantité de Matière (CCQM) a key comparison, CCQM K55.b, was coordinated by the Bureau International des Poids et Mesures (BIPM) in 2010/2011. Nineteen national measurement institutes and the BIPM participated. Participants were required to assign the mass fraction of aldrin present as the main component in the comparison sample for CCQM-K55.b which consisted of technical grade aldrin obtained from the National Measurement Institute Australia that had been subject to serial recrystallization and drying prior to sub-division into the units supplied for the comparison.Aldrin was selected to be representative of the performance of a laboratory's measurement capability for the purity assignment of organic compounds of medium structural complexity [molar mass range 300 Da to 500 Da] and low polarity (pKOW < −2) for which related structure impurities can be quantified by capillary gas phase chromatography (GC).The key comparison reference value (KCRV) for the aldrin content of the material was 950.8 mg/g with a combined standard uncertainty of 0.85 mg/g. The KCRV was assigned by combination of KCRVs assigned by consensus from participant results for each orthogonal impurity class. The relative expanded uncertainties reported by laboratories having results consistent with the KCRV ranged from 0.3% to 0.6% using a mass balance approach and 0.5% to 1% using a qNMR method.The major analytical challenge posed by the material proved to be the detection and quantification of a significant amount of oligomeric organic material within the sample and most participants relying on a mass balance approach displayed a positive bias relative to the KCRV (overestimation of aldrin content) in excess of 10 mg/g due to not having adequate procedures in place to detect and quantify the non-volatile content—specifically the non-volatile organics content—of the comparison sample.There was in general excellent agreement between participants in the identification and the quantification of the total and individual related structure impurities, water content and the residual solvent content of the sample.The comparison demonstrated the utility of 1H NMR as an independent method for quantitative analysis of high purity compounds. In discussion of the participant results it was noted that while several had access to qNMR estimates for the aldrin content that were inconsistent with their mass balance determination they decided to accept the mass balance result and assumed a hidden bias in their NMR data. By contrast, laboratories that placed greater confidence in their qNMR result were able to resolve the discrepancy through additional studies that provided evidence of the presence of non-volatile organic impurity at the requisite level to bring their mass balance and qNMR estimates into agreement.Main text. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison ...
Under the auspices of the Organic Analysis Working Group (OAWG) of the Comité Consultatif pour la Quantité de Matière (CCQM) a laboratory comparison, CCQM-P20.f, was coordinated by the Bureau International des Poids et Mesures (BIPM) in 2007/2008. Nine national measurement institutes, four expert laboratories and the BIPM participated in the comparison. Participants were required to assign the mass fraction of digoxin present as the main component in the comparison sample (CCQM-P20.f) which consisted of digoxin material obtained from a commercial supplier stated to comply with USP requirements.In addition to assigning the mass fraction content of digoxin for the material, participants were requested, but not obliged, to provide mass fraction estimates for the minor components they identified in each sample.In contrast with the previous round of the CCQM-P20 series, in which the mass fraction content of theophylline in two comparison samples (CCQM-P20.e.1 and CCQM-P20.e.2) was determined, a wider range of results were reported for the mass fraction content of digoxin in the CCQM-P20.f comparison.A minority of participants did not appear to use conditions capable of fully resolving and/or quantifying the major related structure impurities present in the comparison sample. Among those that did achieve suitable separations, there was further variation in their reported quantifications of the individual and total related substance content which reflected in part the limited availability of reference standards for these materials and the resulting assumptions that had to be made regarding the structure and response factors relative to digoxin for each individual impurity. This was particularly relevant because of the span of molecular masses of the impurities present in the sample, which ranged from aglycones to glycones with tetrameric carbohydrate chains, relative to that of digoxin.A significant additional factor also contributed to the observed variation of results. Unlike the CCQM-P20.e samples, in which the major impurities were solely related structure organic compounds, the CCQM-P20.f study material contained significant levels of residual organic solvents (ethanol, dichloromethane and to a lesser extent toluene). The majority of participants failed to detect and allow for the presence of this class of impurity, introducing a bias towards overestimation of digoxin content in most of the individual results.However, the uncertainty budgets produced by several participants were sufficiently conservative such that their reported results were nevertheless consistent with the reference value for digoxin content assigned using a consensus mass balance approach. The results of the comparison reinforce the conclusion from previous rounds of the CCQM-P20 study that care in developing and validating the suitability of the chromatographic separation method used to resolve the main component from the related structure impurities present is essential to obtaining reliable, comparable results when using the mass balance approa...
Under the auspices of the Organic Analysis Working Group (OAWG) of the Comité Consultatif pour la Quantité de Matière (CCQM) a laboratory comparison, CCQM-P20.e, was coordinated by the Bureau International de Poids et Mesures (BIPM) in 2006/2007. Nine national measurement institutes, two expert laboratories and the BIPM participated in the comparison. Participants were required to assign the mass fraction of theophylline present as the main component in two separate study samples (CCQM-P20.e.1 and CCQM-P20.e.2).CCQM-P20.e.1 consisted of a high-purity theophylline material obtained from a commercial supplier. CCQM-P20.e.2 consisted of theophylline to which known amounts of the related structure compounds theobromine and caffeine were added in a homogenous, gravimetrically controlled fashion. For the CCQM-P20.e.2 sample it was possible to estimate gravimetric reference values both for the main component and for the two spiked impurities.In addition to assigning the mass fraction content of theophylline for both materials, participants were requested but not obliged to provide mass fraction estimates for the minor components they identified in each sample.The results reported by the study participants for the mass fraction content of theophylline in both materials showed good levels of agreement both with each other and with the gravimetric reference value assigned to the CCQM-P20.e.2 material. There was also satisfactory agreement overall, albeit at higher levels of uncertainty, in the quantification data reported for the minor components present in both samples. In the few cases where a significant deviation was observed from the consensus values reported by the comparison participants or gravimetric reference values where these where available, they appeared to arise from the use of non-optimal chromatographic separation conditions.The results demonstrate the feasibility for laboratories to assign mass fraction content with associated absolute expanded uncertainties in the range 0.05% to 0.5% for solid organic compounds of high purity (mass fraction of main component >995 mg/g) and in the range 0.1% to 1% for compounds of lower purity (mass fraction of main component >980 mg/g).Main text. To reach the main text of this paper, click on Final Report.The final report has been peer-reviewed and approved for publication by the CCQM Working Group on Organic Analysis.
Resonance-enhanced multiphoton ionization time-of-flight mass spectrometry (REMPI-TOFMS) is a powerful technique for the on-line analysis of aromatic compounds with unique features regarding selectivity and sensitivity. Aliphatic compounds, however, are difficult to address by REMPI due to their unfavorable photo ionization properties. This paper describes the proof of concept for an on-line derivatization approach for converting nonaromatic target analytes into specific, photoionizable aromatic derivatives that are readily detectable by REMPI-TOFMS. A multichannel silicone trap or poly(dimethylsiloxane) (PDMS) open tubular capillary was used as a reaction medium for the derivatization of volatile alkyl aldehydes and alkylamines with aromatic "photoionization labels"and to concentrate the resulting aromatic derivatives. The aldehydes formaldehyde, acetaldehyde, acrolein, and crotonal, which when underivatized are poorly detectable by REMPI, were converted into their easily photoionizable phenylhydrazone derivatives by the on-line reaction with phenylhydrazine as reagent. Similarly, the methyl-, ethyl-, propyl-, and butylamines were converted into their REMPI-ionizable benzaldehyde alkylimine derivatives by the on-line reaction with benzaldehyde as reagent. The derivatives were thermally desorbed from the PDMS matrix and transferred into the REMPI-TOFMS for detection. The REMPI-TOFMS detection limits obtained for acetaldehyde; acrolein; crotonal; and methyl-, ethyl-, propyl-, and butylamine using this photo ionization labeling method were in the sub-parts-per-million range and, thus, readily below the permissible exposure limits set by OSHA.
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