H. van Vliet

On-line trace enrichment in high-performance liquid chromatography using a pre-column

Abstract The potential of on-line trace enrichment on a pre-column in high-performance liquid chromatography is demonstrated using phthalate esters as model compounds. The esters are concentrated onto a very shortr, i.e.,ca. 2 mm long, plug of an apolar chemical bonded stationary phase (5-μm LiChrosorb RP-18). Analysis is performed on LiChrosorb RP-18 with a methanol step gradient as mobile phase; detection is done by UV absorption measurement at 233 nm. Phthalate ester recoveries are 95-100% even after enrichment from sample volumes of 500–1000 ml, with pumping speeds varying between 5 and 25 ml min-1. The single-column and the column-to-column reproductivity of the technique are usually 4–6% (relative standard deviation); band broadening due to the insertion of the pre-column is negligible. As an application, the determination of two esters in tap, distilled, mineral and river water, and in soft drinks, is reported. The trace enrichment of mixtures of polychlorinated biphenyls, and of chloroanilines, is also described.

Building up and Exploiting Architectural Knowledge

Architectural knowledge consists of architecture design as well as the design decisions, assumptions, context, and other factors that together determine why a particular solution is the way it is. Except for the architecture design part, most of the architectural knowledge usually remains hidden, tacit in the heads of the architects. We conjecture that an explicit representation of architectural knowledge is helpful for building and evolving systems. If we had a repository of architectural knowledge for a system, what would it ideally contain, how would we build it, and exploit it in practice? In this paper we describe a use case model for an architectural knowledge system.

Towards a broader view on software architecture analysis of flexibility

Software architecture analysis helps us assess the quality of a software system at an early stage. We describe a case study of software architecture analysis that we have performed to assess the flexibility of a large administrative system. Our analysis was based on scenarios, representing possible changes to the requirements of the system and its environment. Assessing the effect of these scenarios provides insight into the flexibility of the system. One of the problems is to express the effect of a scenario in such a way that it provides insight into the complexity of the necessary changes. Part of our research is directed at developing an instrument for doing just that. This instrument is applied in the analysis presented.

The performance of some cell designs for laser-induced fluorescence detection in open-tubular liquid chromatography

Abstract The applicability of fluorescence detection in miniaturized cells using a helium—cadmium laser as the excitation source at 325 nm to open-tubular liquid chromatography has been studied. The investigated cells were fused-silica capillaries of 25 and 10 μm I.D., comprising part of the column or being coupled separately to it, and a sheath flow cell. The volume standard deviation of the various cells was found to be 0.1–2 nl which makes them suitable for the above purpose. The mass detection limits were found to be in the attogram range. However, the concentration detection limits, were found to be one to two orders of magnitude higher than those obtainable with conventional sized fluorescence detectors. This is mainly caused by the instability of the laser.

Studies on external peak broadening in open-tubular liquid chromatography systems using the exponentially modified Gaussian model

SummaryTo optimize performance in Open-Tubular Liquid Chromatography (OTLC) it is necessary to minimize external peak broadening. To see how to reduce the external broadening an insight into its origins is required. This can be obtained by careful evaluation of experimental results with peak deconvolution methods based on the exponentially modified Gaussian model and comparison with theoretical predictions. It is assumed that the column response is Gaussian and that the responses due to the external effects are exponential.For peak deconvolution the algorithm described by Yau was used. Simulations were carried out to check the performance of the algorithm in calculating the standard deviation and the time constant. The effects of the presence of more than one time constant and of the number of data points and their position were investigated. The limits within which reliable results can be obtained are reported.Experimental results were obtained with laser-induced fluorescence and mass spectrometric detection. It is shown that the Yau algorithm can be used to obtain physically realistic estimates of the contribution to peak distortion in the various system components. By suitable design external effects can be reduced to the order of 1 nl and in some cases even lower limits can be reached.

Assessing a Multi-Site Development Organization for Architectural Compliance

Multi-site development organizations require coordination and communication efforts between different sites to ensure successful distributed development. These efforts need to be guided by a set of principles and statements on the software architecture that must be complied with throughout the organization: architectural rules. It is of paramount importance that multi-site development organizations incorporate measures in the architecting process to secure compliance with these rules throughout the organization. We describe a method to assess the degree to which compliance measures are secured in multi-site development organizations. We share our experience in applying this method in a large development organization in the consumer electronics domain.

Prerequisites for Successful Architectural Knowledge Sharing

Sharing knowledge pertaining to software architectures becomes increasingly important. If this knowledge is not explicitly stored or communicated, valuable knowledge dissipates. However, stakeholders will only share knowledge with each other if they are motivated to do so, or in other words if the necessary incentives are created. In this paper we identify three incentives for architectural knowledge sharing: the establishment of social ties, more efficient decision making, and knowledge internalization. Next, we discuss our experiences on how architectural knowledge is shared in a large software development organization. Based on these experiences we propose a set of prerequisites that need to be met to foster successful architectural knowledge sharing. The importance of these prerequisites is motivated by demonstrating that they create the identified incentives.

Tool support for traceable product evolution

In software product families, the full benefit of reuse can only be achieved if traceability of requirements to architecture, components and further down to source code is supported. This requires automated tool support for tracing from the abstract features of the product family to a set of concrete features and source code of family members. We extended a commercial software tool to support top-down as well as bottom-up traceability in product families, from the family feature map all the way down to implementation files. At the code level, both newly developed and commercial-off-the-shelf components are accommodated. The tool has been validated by (bottom-up) filling the tools reuse base with features, components, documentation files, etc. from six related products in the next generation network service domain, and next deriving a seventh product from this reuse base.

Risks and Risk Management in Software Architecture Evolution: An Industrial Survey

The effort that has been made to study risk management in the context of software architecture and its evolution, has so far focused on output from structured evaluations. However, earlier research shows that formal, structured evaluation is not commonly used in industry. We have performed a survey among software architects, in order to capture a more complete picture of the risk and management issues in software architecture evolution. Our survey is specifically about their current knowledge of actual challenges they have anticipated and experienced, as well as strategies they have employed in response. We received completely filled questionnaires from 82 respondents out of a total distribution of 511 architects from the software industry in Norway. While many of the risks we have identified can be aligned with results from earlier studies, we have also identified several risks which appear not to fit these risk categories. Additionally, we found a direct link to business risks, as well as a relatively low level of awareness that lack of software architecture evaluation represents a potential risk.

Post-column reaction detection for open-tubular liquidchromatography using laser-induced fluorescence

Abstract The applicability of post-column reaction detection to open-tubular liquid chromatography is investigated, using the o -phthalaldehyde—amino acid reaction and laser-induced fluorescence detection. Two mixing devices were designed and evaluated in terms of external peak broadening on the nanolitre scale. It was found that mixing devices having a volume of about 10 nl resulted in an acceptable loss in plate numbers for unretained peaks using 25 μm I.D. fused-silica columns. A method was developed for determining the flow-rates and residence times in the various parts of the system, based on the correlation of observed total residence times and the pressures on the column and the reagent delivery system.