Efficient hydridoirida-ß-diketone-catalyzed hydrolysis of ammonia- or amine-boranes for hydrogen generation in air.

The dihydridoirida-ß-diketone [IrH2{(PPh2(o-C6H4CO))2H}] (2) has been used as a homogeneous catalyst for the hydrolysis of ammonia- or amine-boranes to generate up to 3 equivalents of hydrogen in the presence of air. When using 0.5 mol% loading of 2, dimethylamine-borane is hydrolysed completely within 8 min at 30 °C and maintains its activity in consecutive runs. Ammonia-borane or tert-butylamine-borane is hydrolysed completely within 32 or 25 min respectively. Triethylamine-borane fails to be hydrolysed. Kinetic studies suggest a sequence of two consecutive first-order reactions, in which an intermediate builds up and finally falls, with the first step being the rate controlling step. ΔH1(‡) are in the range 65-85 kJ mol(-1) and negative values of ΔS1(‡) are obtained. A multinuclear NMR study of the catalyzed reaction shows the formation of a resting state (A) of the active catalyst proposed to be of the hydridodiacyl type [IrH(PPh2(o-C6H4CO))2(solvent)] with a hydride trans to the acyl group. In the absence of substrate a dormant species (B) is formed. By the reaction of hydridoirida-ß-diketones with ammonia, the hydridoirida-ß-ketoimine [IrHCl{(PPh2(o-C6H4CO))(PPh2(o-C6H4CNH))H}] (3) and the hydridobis(acylphosphane)aminoiridium(III) complex [IrH(PPh2(o-C6H4CO))2(NH3)] (4), with a hydride trans to phosphane, are formed. Aromatic amines such as aniline or anisidines afford cationic [IrH{(PPh2(o-C6H4CO))2H}(C6H4RNH2)]ClO4 (R = H (6); p-MeO (7); o-MeO (8)) hydridoirida-ß-diketones with a coordinated amine group trans to the hydride. The dormant species B is proposed to be of the hydridobis(acylphosphine)aminoiridium(III) type with a hydride trans to the amine group.

Gas chromatography with flame ionization detection for determination of additives in an electrolytic Zn bath.

The monitoring of additives in electrolytic baths is a fundamental task for proper coatings. Among the additives used in zinc baths, benzylideneacetone (BDA), benzoic acid (BA) and polyethylene glycol 400 (PEG400) are easily found. This paper deals with the possibilities of handling the bath sample before it is taken to a gas chromatograph (GC) in order to follow the additives concentration along the bath life. The applied techniques include solid phase extraction (SPE), solvent extraction (SE), static headspace (SHS), direct injection (DI) and headspace solid phase microextraction (HS-SPME) recoveries up to 6:1, 14:1, 9:1, 1:1 and 80:1 respectively have been obtained. Internal standards have been found for every case. Advantages and disadvantages of the techniques are collected. In this paper DI and HS-SPME have finally been applied, though none of them is able for PEG400 determination. DI provides quantitative information for BA (limit of detection, LOD, 1.6 gL(-1)) and BDA (LOD, 0.09 gL(-1)); HS-SPME only provides quantitative information for BDA (LOD, 0.05 gL(-1)). Taking into account that PEG400 and BA do not practically change with the use of the bath, that DI is very quick and simple and that no significant differences with spectrophotometric results have been found, DI is recommended for the monitoring of BA and BDA along the zinc bath life. This should be considered a technique for process analysis for these additives.

Quantitative nuclear magnetic resonance for additives determination in an electrolytic nickel bath.

The use of proton nuclear magnetic resonance (¹H-NMR) for the quantitation of additives in a commercial electrolytic nickel bath (Supreme Plus Brilliant, Atotech formulation) is reported. A simple and quick method is described that needs only the separation of nickel ions by precipitation with NaOH. The four additives in the bath (A-5(2X), leveler; Supreme Plus Brightener (SPB); SA-1, leveler; NPA, wetting agent; all of them are commercial names from Atotech) can be quantified, whereas no other analytical methods have been found in the literature for SA-1 and NPA. Two calibration methods have been tried: integration of NMR signals with the use of a proper internal standard and partial least squares regression applied to the characteristic NMR peaks. The multivariate method was preferred because of accuracy and precision. Multivariate limits of detection of about 4 mL L⁻¹ A-5(2X), 0.4 mL L⁻¹ SPB, 0.2 mL L⁻¹ SA-1 and 0.6 mL L⁻¹ NPA were found. The dynamic ranges are suitable to follow the concentration of additives in the bath along electrodeposition. ¹H-NMR spectra provide evidence for SPB and SA-1 consumption (A-5(2X) and NPA keep unchanged along the process) and the growth of some products from SA-1 degradation can be followed. The method can, probably, be extended to other electrolytic nickel baths.

Determination of additives in an electrolytic zinc bath by q1H-NMR spectroscopy.

The use of proton nuclear magnetic resonance ((1)H-NMR) for the quantification of additives in an electrolytic Zn bath is reported. A simple and quick method is described that does not need any prior sample preparation. Contrary to other analytical methods, the three additives in the bath, benzylidene acetone (BDA), benzoic acid (BA) and poly(ethylene glycol) (PE400), can be quantified. Two calibration methods were tried: integration of NMR signals with the use of an internal standard and partial least squares (PLS) regression applied to the characteristic NMR peaks. Both methods are compared and the univariate method was preferred because of simplicity, accuracy and precision. The following limits of detection were found: 0.30 g L(-1) BA, 0.08 g L(-1) BDA and 0.7 g L(-1) PE400 with dynamic ranges of at least 1.0-6.0, 0.1-0.6 and 3.0-18.0 g L(-1) respectively. Those concentration ranges are suitable to follow the concentration of additives in the bath in real time. (1)H-NMR spectra provide evidence for the BDA degradation pattern.

CCD detectors for molecular absorption spectrophotometry. A theoretical and experimental study on characteristics and performance.

Uncertainty in charge-coupled devices (CCDs) as UV-vis spectrophotometric detectors is studied here considering that it highly affects the limit of detection of analytical methods. Opposite to photomultiplier-type detectors (PMDs) and diode-array detectors (DADs), where uncertainty is mainly dependent on the photonic signal (shot noise), in CCD detectors uncertainty may come from both independent and dependent effects upon the photonic signal. Shot noise is specially important for high photonic signals in the detector (those for low absorbances) while the uncertainty that is independent of the signal is specially important for low photonic signals in the detector (those for high absorbances). That is, the main source of uncertainty is different depending on the value of the experimental measurement. On the other hand, temperature does not practically affect absorbance measurements, though it is very important for emission measurements (fluorescence, Raman, scattering, etc.). Mathematical equations for uncertainty are proposed with excellent fittings to the experimental data. The equation parameters can be experimentally determined from non-linear regression analysis and used to characterize spectrometers or to test their performance. In order to help buyers and users, some recommendations are finally given considering, among others, cooling, slit, attenuator or fiber optic assemblies.

Detection limit estimator for multivariate calibration by an extension of the IUPAC recommendations for univariate methods.

A methodology is proposed to estimate the limit of detection (LOD) of analytical methods when multivariate calibration is applied. It tries to follow the same premises as the IUPAC methodology for univariate calibration. The mathematical support is given and algorithms such as partial least squares (PLS) regression, PLS2 and principal component regression (PCR) are used. Only multivariate raw data are used; that is, no surrogate univariate signal is deduced. Non-linearities are allowed. Near infrared (NIR) data of 5 component pseudo-gasoline samples together with simulated fluorescence synchronous spectra of binary mixtures (first order data) are used for evaluation. Experimental verification is performed using different kinds of data, namely: binary mixtures of bentazone and fenamiphos (very overlapped spectra, second order data) obtained by sequential injection (SI), and kinetic data of the reaction between the Fenton's reagent (FR) and pesticides such as atrazine, bentazone and alachlor (individual or binary mixtures, second order data). Results are always compared with independent methods previously proposed in the literature, based in the use of surrogate univariate signals. In general, similar results are found and no statistically significant differences seem to be present, except in a few cases when complex chemical systems are involved.

Interference modelling, experimental design and pre-concentration steps in validation of the Fenton's reagent for pesticides determination.

The determination of atrazine in real samples (commercial pesticide preparations and water matrices) shows how the Fenton's reagent can be used with analytical purposes when kinetic methodology and multivariate calibration methods are applied. Also, binary mixtures of atrazine-alachlor and atrazine-bentazone in pesticide preparations have been resolved. The work shows the way in which interferences and the matrix effect can be modelled. Experimental design has been used to optimize experimental conditions, including the effect of solvent (methanol) used for extraction of atrazine from the sample. The determination of pesticides in commercial preparations was accomplished without any pre-treatment of sample apart from evaporation of solvent; the calibration model was developed for concentration ranges between 0.46 and 11.6 x 10(-5) mol L(-1) with mean relative errors under 4%. Solid-phase extraction is used for pre-concentration of atrazine in water samples through C(18) disks, and the concentration range for determination was established between 4 and 115 microg L(-1) approximately. Satisfactory results for recuperation of atrazine were always obtained.

Uncertainty due to the quantification step in analytical methods.

The quantification step is an important source of uncertainty in analytical methods, but it is frequently misunderstood and disregarded. In this paper, it is shown how this uncertainty is closely related to the linear response range of a method, and to the Pearson correlation coefficient of the calibration line. So, if there is a need for a pre-fixed quantification uncertainty, the linear response range will be affected. Some practical cases are given showing the quantification uncertainty significance. The theoretical equation giving the value of the quantification uncertainty is deduced from which new conclusions can be taken out. Because of that, the quantification uncertainty can easily be calculated and the parameters that really affect its value are shown along the paper. Some final considerations about detection limits and two-point calibration lines are also given. The paper can also be considered a reflection on uncertainty owed to calibration and on their consequences on the analytical methodology.

The acetylsalicylic acid-bromine system for multicomponent kinetic determinations.

When acetylsalicylic acid (ASA) is added to a bromine solution, slow decay of the bromine concentration occurs. Hydrolysis of ASA yields salicylic acid (SA) slowly, and bromine reacts rapidly with SA but not with ASA. Simulated reaction profiles based on a two-step reaction scheme agree closely with the experimental profiles. This behaviour can be used to develop kinetic methods for resolution of mixtures of ASA and a second component that reacts rapidly with bromine. A remarkable practical feature of these methods is that the faster the reaction between bromine and the second component, the simpler and easier the analytical method. The reaction between hydroquinone (HQ) and bromine is rapid and a very simple analytical method is proposed. Mean validation errors of 2.8% for HQ and 7.2% for ASA have been found with concentration ratios [ASA]:[HQ] ranging between 0.32 and 19.4. The reaction between paracetamol (AAP) and bromine is not so fast and more complicated calibration methods are required. After use of a calibration plane mean validation errors of 2.7% for AAP and 8.1% for ASA have been found with concentration ratios ranging between 1.28 and 77.5. Similar kinetic approaches should be possible with many other mixtures of ASA and a second fast-reacting component, because bromine reacts with many inorganic and organic species by oxidation-reduction, substitution, and addition reactions.

The bromination of acetone. application to multicomponent kinetic determinations.

A very simple kinetic method is proposed for the resolution of mixtures of acetone and a second component. It is based on the reaction, at constant temperature, between bromine and acetone. This reaction can be regarded, under certain conditions, as pseudo-zero-order on the bromine concentration. To show the possibilities of the method, mixtures of acetone (between 2 and 20 x 10(-4) mol L(-1)) and either hydroquinone (between 0.4 and 2.2 x 10(-4) mol L(-1)) or resorcinol (between 0.1 and 10.7 x 10(-4) mol L(-1)) have been used with the concentration ratios [acetone]:[hydroquinone] ranging between 0.5 and 50 and [acetone]:[resorcinol] ranging between 2.8 and 200. No systematic errors were found to exist (90% confidence level) and random errors were mainly under 5%. The method can be extended to mixtures of acetone and a second component whose reaction with bromine is fast (phenols, aromatic amines, etc.).

Study of a fluorometric-enzymatic method for bilirubin based on chemically modified bilirubin-oxidase and multivariate calibration.

The chemical derivatization of bilirubin oxidase (BOx) with a fluorescein derivative (FS) yields a chemically modified enzyme (BOx-FS), with excitation and emission maxima at 487 and 520 nm, respectively. During the oxygen oxidation reaction of bilirubins, in the presence of the modified enzyme, the change in the fluorescence of the modified enzyme depends on the concentration and type of bilirubin. This effect can be used for analytical purposes. Firstly, a theoretical-experimental study of the analytical system was carried out. The mechanism responsible for the fluorescence variation was clarified, a mathematical model developed and the variables affecting the fluorescence changes optimized. The concentration ranges in which the model can be applied (up to 12 mg bilirubin l(-1)), and the precision of the measurement (about 4%) were established for the three bilirubins. The application of the methodology to the simultaneous determination of direct and total bilirubins were studied by applying multivariate calibration methods to the whole kinetic profiles. A reduced calibration matrix (derived from a 5(3) base matrix) is proposed for calibration and different numerical methods were tested: Principal Components Regression (PCR), Partial Least Squares Regression (PLS) and Artificial Neural Networks (ANN). The simultaneous determination of direct and total bilirubin (average validation errors of about 9 and 10%, respectively) can be carried out from a single run. Furthermore, a semi-quantitative speciation of the three bilirubins (free, conjugated and albumin-bonded bilirubin) may be simultaneously obtained.

Multicomponent determinations by partial least-squares regression analysis of fast-reaction multiwavelength profiles obtained by continuous addition of a reagent.

Partial least-squares regression (PLS) analysis of multiwavelength reaction profiles, obtained by continuous addition of a reagent to a binary mixture of analytes, giving fast reactions, is presented. The methodology has proved to be useful for the simultaneous determination of the mixture components. Octacyanomolibdate(V) (Mo(V)) has been used as a reagent for mixtures of hydroquinone (HQ) and pyrogallol (PG) in acidic medium. When the reaction profiles are followed spectrophotometrically at several wavelengths, and they are handled with PLS, the mixture can be resolved. The final spectrum of the mixture, after reaction with Mo(V), is enough to predict the HQ concentration, but in the case of PG successive spectra along the reaction are necessary to predict properly the concentration. The concentrations for HQ in the calibration set ranged between 1.8x10(-6) and 1.7x10(-5) M and for PG between 2.5x10(-6) and 2.5x10(-5) M. The concentration ratio, [HQ]:[PG], in the validation set ranged between 0.17 and 4.10. Mean validation errors of 1.6% for HQ and 4.2% for PG were found. Satisfactory results were obtained when independent studies of accuracy and precision were accomplished. The effect of p-phenylenediamine and aminophenols was studied as interferences and, in general, hydroquinone is more affected than pyrogallol. The tolerated concentration of interferences ranged between 10(-6) and 10(-4) M.