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Multivariate curve resolution techniques try to estimate physically and/or chemically meaningful profiles underlying a set of chemical or related measurements. However, the estimation of profiles is not generally unique and it is often complicated by intensity and rotational ambiguities. Constraints as further information of chemical entities can be imposed to reduce the extent of ambiguities. Not only a long list of constraints has been introduced but also some of them can be applied in different ways. Either investigating constraint effects on the extent of rotational ambiguity or how they can be applied during curve resolution can shed light on curve resolution studies. The motivation behind this contribution is to pave the way to a clarification about the closure constraint. Considering simulated equilibrium and kinetic spectrophotometric data sets, different approaches to closure implementation were applied to demonstrate the geometrical explanation of closure constraint and its effect on multivariate curve resolution‐alternating least squares results. Besides, the closure constraint is compared with normalization and it is proved that the closure constraint is a Borgen norm and has the same effect as other Borgen norms in multivariate curve resolution. Finally, to further examine the closure constraint, a real data set was investigated. Investigating constraint effects on the extent of rotational ambiguity or how they can be applied during curve resolution can shed light on the curve resolution studies. The motivation behind this contribution is to pave the way to a clarification about closure constraint. Different approaches to closure implementation were applied to demonstrate the geometrical explanation of closure constraint. Additionally, the closure constraint is compared with normalization, and it is proved that the closure constraint is a Borgen norm. [ABSTRACT FROM AUTHOR]

• A method was developed to distinguishing bovine bone from skin gelatins for the first time. • Full scan LC/MS spectra were acquired from trypsin-digest gelatin samples. • PLS-DA method were used to build a stable and reliable model for classification. • An entry-level LC/MS instrument was used, eliminating the need for more complex equipment. • The strategy was used to accurately identify tissue origin of gelatin in commercial products. Gelatin, as a by-product of the meat industry, is extracted from bone and skin of mainly bovine and porcine origins. It is used widely in the food, drug, and cosmetic industries. Authenticity testing methods can be used to confirm whether labelled ingredients are present in the product. Generally, studies on gelatin are concerned mainly with determining species, but detecting tissue origin is also important from religious, health, and commercial perspectives. In the present study, for the first time, liquid chromatography/mass spectrometry (HPLC/MS) was used to differentiate bovine bone gelatin from gelatin derived from bovine skin. Tryptic-digested gelatins were measured using HPLC/MS and, subsequently, two powerful chemometrics approaches (i.e., PCA and PLS-DA) were used to classify samples as either skin or bone gelatins. Origin of bovine gelatins in different test samples were predicted accurately using this method. The results showed both the stability and reliability of the proposed procedure. [ABSTRACT FROM AUTHOR]

The utilization of entomological specimens such as larvae (maggots) for the estimation of time since oviposition (i.e., egg laying) for post mortem interval determination, or for estimation of time since tissue infestation (in investigations of elder or child care neglect and animal abuse cases), requires accurate determination of insect species identity. Because the larvae of multiple species are visually highly similar and difficult to distinguish, it is customary for species determination of maggots to be made by rearing them to maturity so that the gross morphological features of the adult can be used to accurately identify the species. This is a time-consuming and resource-intensive process which also requires that the sample be viable. The situation is further complicated when the maggot mass being sampled is comprised of multiple species. Therefore, a method for accurate species identification, particularly for mixtures, is needed. It is demonstrated here that direct analysis in real time-high resolution mass spectrometric (DART-HRMS) analysis of ethanol suspensions containing combinations of maggots representing Calliphora vicina , Chrysomya rufifacies , Lucilia coeruleiviridis , L. sericata , Phormia regina , and Phoridae exhibit highly reproducible chemical signatures. An aggregated hierarchical conformal predictor applied to a hierarchical classification tree that was trained against the DART-HRMS data enabled, for the first time, multispecies identification of maggots in mixtures of two, three, four, five, and six species. The conformal predictor provided label specific regions with confidence limits between 80 and 99% for species identification. The study demonstrates a novel, rapid, facile, and powerful approach for identification of maggot species in field-derived samples.