We propose a new account of calibration according to which calibrating a technique shows that the technique does what it is supposed to do. To motivate our account, we examine an early twentieth-century debate about chlorophyll chemistry and Mikhail Tswett’s use of chromatographic adsorption analysis to study it. We argue that Tswett’s experiments established that his technique was reliable in the special case of chlorophyll without relying on either a theory or a standard calibration experiment. We suggest that Tswett broke (...) the experimenters’ regress by appealing to material facts in the common ground for chemists at the time. (shrink)

Herein, I discuss the enduring mystery of the receptor layout in the vertebrate olfactory system. Since the awarding of the 2004 Nobel Prize to Axel and Buck for their discovery of the gene family that encodes olfactory receptors, our field has enjoyed a golden era. Despite this Renaissance, an answer to one of the most fundamental questions for any sensory system—what is the anatomical logic of its receptor array?—eludes us, still, for olfaction! Indeed, the only widely debated hypothesis, finding its (...) origins in the musing of another Nobel laureate Sir Edgar Adrian, has it that the vertebrate nose organizes its receptors according to the “sorptive” properties of their ligands. This idea, known as the “sorption” or “chromatography” hypothesis, enjoys considerable support despite being controversial. Here, I review the history of the hypothesis—its rises and falls—and discuss the latest data and future prospects for this perennial idea whose history I liken to the mythical Phoenix. (shrink)

We demonstrate how different normalization techniques in GC‐MS analysis impart unique properties to the data, influencing any biological inference. Using simulations, and empirical data, we compare the most commonly used techniques (Total Sum Normalization ‘TSN’; Median Normalization ‘MN’; Probabilistic Quotient Normalization ‘PQN’; Internal Standard Normalization ‘ISN’; External Standard Normalization ‘ESN’; and a compositional data approach ‘CODA’). When differences between biological classes are pronounced, ESN and ISN provides good results, but are less reliable for more subtly differentiated groups. MN, TSN, and (...) CODA approaches produced variable results dependent on the structure of the data, and are prone to false positive biomarker identification. In contrast, PQN exhibits the lowest false positive rate, though with occasionally poor model performance. Because ESN requires extensive pre‐planning, and offers only mixed reliability, and ISN, TSN, MN, and CODA approaches are prone to introducing artefactual differences, we recommend the use of PQN in GC–MS research. (shrink)

The present paper claims that M. S. Tswett’s chromatographic adsorption analysis, which today is a ubiquitous and instrumentally sophisticated chemical technique, was either ignored or outright rejected by chemists and botanists in the first three decades of the twentieth century because it did not make sense in terms of accepted chemical theory or practice. Evidence for this claim is culled from consideration of the botanical and chemical context of Tswett’s technique as well as an analysis of the protracted debate over (...) Tswett’s chromatographic analysis of chlorophyll between him and Leon Marchlewski, a noted chlorophyll chemist of the period. In this way, the paper expands and amends what it calls the ‘textbook story’ of the early history of chromatography, examples of which may be found in historical notes in many textbooks of chemical instrumental analysis and numerous short articles in chemistry journals. The paper also provides an accessible introduction to the early history of chromatography for historians of science likely to know little or nothing about it. (shrink)

Immobilized Metal‐ion Affinity Chromatography, IMAC, has been gaining in popularity as the purification technique of choice for proteins and peptides. IMAC of proteins on transition metals (Co, Ni, Cu, Zn) can be rationalized in terms of the coordination of histidine residues. Brief accounts of the principles of IMAC, its anticipated development and plausible applications are presented. Metal Ion Transfer, MIT, may offer an efficient means to deplete a metal ion from a metalloprotein or, conversely, to charge its apo form (...) with a metal. (shrink)

Newborn screening consists of taking a few drops of blood from a baby's heel in the first week of life and testing it for a list of disorders. In the United States and most countries in Europe, newborn screening programs began in the 1960s and 1970s with screening for phenylketonuria (PKU), a rare metabolic disease that causes severe and irreversible mental retardation unless treated before problems arise. As knowledge about rare diseases expanded and new screening technologies were introduced—such as the (...) tandem mass spectrometer and high‐performance liquid chromatography—the same blood sample could be used to test for a whole list of disorders. In general, screening programs in most countries have tended to expand, but in different countries they have expanded in different ways. Regulation also varies. In some states, screening is mandatory, whereas in others—Wyoming and Maryland—parents are asked for their informed consent. Germany and France have adopted an explicit informed consent procedure, whereas other European countries have a more informal “opt‐out” procedure that does not require signing an informed consent form. Whether newborn screening requires informed consent is an ongoing issue in bioethics. In this article, we will focus on the tension between informed consent and the problem of compliance in newborn screening. Asking for informed consent—allowing parents to opt out—is often thought to pose a threat to compliance. Building on the work of Onora O'Neill on informed consent and trust, however, as well as on work she coauthored with Neil Manson, we will argue that informed consent procedures may actually help maintain trust in newborn screening and may therefore support compliance. (shrink)

Early life stress precedes alterations to neuro-immune activation, which may mediate an increased risk for stress-related psychiatric disorders, potentially through alterations of central kynurenine pathway metabolites, the latter being relatively unexplored. We hypothesized that ELS in a non-human primate model would lead to a reduction of neuroprotective and increases of neurotoxic KP metabolites. Twelve adult female bonnet macaques reared under conditions of maternal variable foraging demand were compared to 27 age- and weight-matched non-VFD-exposed female controls. Baseline behavioral observations of social (...) affiliation were taken over a 12-week period followed by the first cerebrospinal fluid sample. Subjects were then either exposed to a 12-week repeated separation paradigm or assigned to a “no-RSP” condition followed by a second CSF. We used high-performance liquid chromatography for kynurenine, tryptophan, 5-hydroxyindoleacetic acid, kynurenic acid, and anthranilic acid as a proxy for quinolinic acid determination. At baseline, social affiliation scores were reduced in VFD-reared versus control subjects. CSF log KYNA and log KYNA/KYN ratio were lower in VFD-reared versus control subjects. CSF log KYNA/KYN was positively correlated with CSF log ANTH in VFD only. Controlling for log KYNA/KYN, log ANTH was elevated in VFD-reared subjects versus controls. CSF log KYNA/KYN obtained post-RSP was positively correlated with mean social affiliation scores during RSP, specifically in VFD. ELS is associated with a reduced neuroprotective and increased neurotoxic pathway products. That the two contrasting processes are paradoxically correlated following ELS suggests a cross-talk between two opposing KP enzymatic systems. (shrink)

RésuméLe dosage de traces de molécules organiques dans les matrices biologiques fait appel à des techniques analytiques physico‐chimiques dont la chromatographie en phase gazeuse couplée à la spectrumétrie de masse est une des plus puissantes. Des possibilityés nouvelles pour augmenter la sensibilityé de la détection de ces substances sont presentees et mises en relation avec la signification physiologique des résultats obtenus.SummaryGas chromatography‐mass spectrometry is the method of choice for the quantitative determination of organic traces in biological systems. New technical (...) developments allow higher sensitivity and greater specificity which are discussed together with the physiological meaning of the data thus obtained.ZusammenfassungDie Dosierung der Spuren von organischen Molekülen in den biologischen Matrizen erfordert physico‐chemische analytische Techniken, deren Chromatographie in gasförmiger Phase ver‐bunden mit der Massenspektrometrie eine der mächtigsten ist. Es werden neue Möglichkeiten zur Steigerung der Empfindlichkeit der Aufweisung dieser Substanzen vorgelegt, und mit der physio‐logischen Bedeutung der erhaltenen Ergebnisse in Beziehung gesetzt. (shrink)

Recombinant adeno‐associated viruses (rAAVs) are promising vectors for the delivery of various genetic constructs into eukaryotic cells. rAAVs have a number of properties that make it possible to successfully use them both in vitro and in vivo. Purification and concentration of rAAV vectors are critical for achieving high viral titer, stability, efficiency, and purity. This review systematically analyses all available purification approaches. The purification methods described in this work differ substantially from each other in mechanisms, efficiency, labor time, and cost. (...) Researchers have to choose a purification algorithm depending on the purpose of their work. We strive to simplify the choice of the necessary and sufficient technique based on the experimental needs and available resources of the laboratory. (shrink)