Imaging in the modern age

This report of the 2011 James L. Waters Symposium at Pittcon 2011 highlights the powerful imaging technologies of electron microscopy (EM) and ion microscopy (IM). The four speakers each provided a window into a specific subset of the field:

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David Bell described the history, development, application, and commercialization of transmission EM (TEM) and scanning TEM (STEM);

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David Martin presented the challenges and methodologies of imaging ordered polymers and biomaterials with TEM;

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Joseph Michael explained the history of the commercialization of scanning EM (SEM) and its modern applications; and,

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David Joy, who submitted his talk in absentia, provided a history of EM and a summary of the advantages of IM versus EM.

     

Detecting “bad” regression models: multicriteria fitness functions in regression analysis

Regression models with good fitting but no predictive ability are sometimes chance correlations and often show some pathological features such as multicollinearity, overfitting, and inclusion of noisy/spurious variables. This problem is well known and of the utmost importance. The present paper proposes some criteria that are to be fulfilled as conditions for model acceptability, the aim being to recognize linear regression models with pathology. These criteria have been thought of in order to face the following problems:

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model instability due to outliers and influential objects;

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predictor multicollinearity;

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redundancy in explanatory variables;

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overfitting due to chance factors.

A multicriteria fitness function based on the maximization of the Q² statistics under a set of tests is proposed here. This new fitness function can also be used in model searching by variable selection approaches in order to obtain a final optimal population of models. Computations on the Selwood data set are reported to illustrate the use of this multicriteria fitness function in model searching.     

Lab-on-valve in the miniaturization of analytical systems and sample processing for metal analysis

In the past decade, the lab-on-valve (LOV) system, as the third-generation of the flow-injection analysis technique, has exhibited powerful capability in instrument miniaturization and on-line sample pretreatment.This review presents and discusses the state of the art in the progress of the LOV system in the determination of metal species in two parts:

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miniaturization of analytical instrumentations; and,

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sample-processing front-ends.

As a miniaturized analytical set-up, LOV incorporates detection techniques for the determination of metal species (e.g., spectrophotometry, electrochemical detection and atomic spectrometry). However, coupling LOV sample pretreatment with atomic or mass spectrometric detectors provides high-sensitivity determination or speciation of metal species.We also discuss future perspectives of the LOV system in metal determination and/or speciation.     

Second-order and higher-order multivariate calibration methods applied to non-multilinear data using different algorithms

We discuss and evaluate the current state of second-order and higher-order multivariate calibration methods devoted to the determination of compounds in non-multilinear data systems. We examine possible causes of multilinearity deviations:

(1)

a non-linear relationship between signal and analyte concentration;

(2)

a signal for a given sample that is non-multilinear; and,

(3)

component profiles that are not constant across the different samples.

We discuss the advantages and the limitations of the algorithms available to cope with these different situations.The review covers relevant analytical problems found in samples of environmental and biological interest, highlighting some significant examples, and evaluating the advantages and the limitations of the different algorithms available.     

Challenging applications offered by direct analysis in real time (DART) in food-quality and safety analysis

Direct analysis in real time (DART) is an ambient ionization technique undergoing rapid development. With minimal sample pre-treatment, ionization of analyte molecules outside the mass spectrometry (MS) instrument in the ordinary atmosphere is feasible. This ionization approach relies upon the fundamental principles of atmospheric pressure chemical ionization.The current review highlights and critically assesses application of DART (and some related desorption/ionization techniques) coupled to various types of MS analyzers for both target and non-target analysis of complex food matrices. Based on existing studies, DART-MS is presented as a simple, high-throughput tool for:

(i)

qualitative confirmation of chemical identity;

(ii)

metabolomic fingerprinting/profiling; and,

(iii)

quantification of low-molecular-weight food components, including some trace organic contaminants.

With regard to regulatory requirements, we mention practical aspects of DART-MS use, as well as performance characteristics that can be attained.     

Measurement of VLE (TPx or TPxy data) for hydrogen sulfide + (dimethylsulfide or ethylmethylsulfide or carbon disulfide) and methane solubilities in (dimethylsulfide or ethylmethylsulfide or methylmercaptan or ethylmercaptan)

VLE data (gas solubilities (TPx data) or complete TPxy data) were measured for the following systems:

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hydrogen sulfide (H₂S) + dimethylsulfide (DMS) at 278, 293, 313, and 333 K.     

Synthesis of 5,6-dihydrobenz[c]acridines: a comparative study

5,6-Dihydrobenz[c]acridines were synthesized by the reaction of 1-chloro-3,4-dihydro-2-naphthaldehyde with aromatic amines under three different conditions:

a.

Thermolysis of 1-chlorovinyl-(N-aryl)imines prepared from 1-chloro-3,4-dihydro-2-naphthaldehyde.

b.

Acid catalyzed cyclization of 1-(N-aryl)amino-3,4-dihydro-2-naphthaldehydes.

c.

Thermolysis of N-arylenaminoimine hydrochlorides derived from 1-chloro-3,4-dihydro-2-naphthaldehyde in DMF medium.

All the three approaches exclusively yielded only 5,6-dihydrobenz[c]acridines and not the isomeric 7,8-dihydrobenzo[k]phenanthridines.The structures of these products have been unambiguously established by detailed NMR spectral study and by independent synthesis as well as by single crystal XRD study.     

Use of inorganic, complex-forming ions for selectivity enhancement in capillary electrophoretic separation of organic compounds

Capillary electrophoresis (CE) is a powerful separation method based on the migration of charged species under the influence of electric field. The main merits of CE are high separation efficiency, short analysis time and small consumption of solvents and samples. However, the main drawbacks of CE are generally lower sensitivity compared to classical column-chromatographic methods.Selectivity and/or sensitivity of CE separation can be improved by forming complexes between analytes and a complex-forming reagent present as an additive in the background electrolyte (BGE). We focus this review primarily on the application of inorganic complex-forming reagents added to the BGE to separate organic ligands. We briefly mention common CE separations of inorganic analytes (mainly metal ions) using BGEs with organic ligands (e.g., hydroxycarboxylic or aminopolycarboxylic acids) as selectors.The review involves brief theoretical consideration of the significance of the effect of complex formation on separation selectivity and/or sensitivity in CE, but the major topic is critical evaluation of different inorganic complex-forming reagents used recently in the CE analysis of organic compounds, including:

(i)

borate, tungstate and molybdate in separating organic compounds possessing vicinal -OH groups;

(ii)

ligand-exchange CE and capillary electrochromatography in chiral analysis; and,

(iii)

the role of metal ions as central ions employed for selectivity enhancement of CE separation of various classes of organic compounds, including biopolymers.

     

NdHO, a novel oxyhydride

A new metal oxyhydride; neodymium oxyhydride, NdHO, has been synthesized from a reactant mixture of metal hydride (CaH₂ or NdH₃) and neodymium oxide (Nd₂O₃). The unit cell dimensions decrease smoothly in the series from LaHO, CeHO, PrHO to NdHO, in line with the lanthanide contraction. The crystal structure of NdHO is described on the basis of Rietveld refinement on neutron powder diffraction data:

Space group: P4/nmm (no. 129, D_4h⁷).

Axis lengths: a=7.8480(5) Å, c=5.5601(8) Å.

Volume: V=342.46(6) Å³.

The tetragonal structure is derived from the fluorite structure, showing complete ordering of hydride and oxide ions over the anion sublatttice. The formation of NdHO was further substantiated by Raman spectroscopy.