Polylactide/Montmorillonite Hybrid Latex as a Barrier Coating for Paper Applications.

We developed a paper coating for the potential application in food packaging based on polylactide and montmorillonite. It is applied to the paper in the form of a stable, water-based latex with a solid content of 25⁻28 wt %. The latex is prepared from a commercially available polylactide, surfactants, montmorillonite, a plasticizer, chloroform (to be removed later) and water by an emulsion/solvent evaporation procedure. This coating formulation is applied to the paper substrate by bar-coating, followed by hot-pressing at 150 °C. The coated papers achieved up to an 85% improvement in water vapor transmission rates when compared to the pristine papers. The coating latex is prepared from inexpensive materials and can be used for a solvent-free coating process. In addition, the ingredients of the latex are non-toxic; thus, the coated papers can be safely used for food packaging.

Embroidered electrode with silver/titanium coating for long-term ECG monitoring.

For the long-time monitoring of electrocardiograms, electrodes must be skin-friendly and non-irritating, but in addition they must deliver leads without artifacts even if the skin is dry and the body is moving. Today's adhesive conducting gel electrodes are not suitable for such applications. We have developed an embroidered textile electrode from polyethylene terephthalate yarn which is plasma-coated with silver for electrical conductivity and with an ultra-thin titanium layer on top for passivation. Two of these electrodes are embedded into a breast belt. They are moisturized with a very low amount of water vapor from an integrated reservoir. The combination of silver, titanium and water vapor results in an excellent electrode chemistry. With this belt the long-time monitoring of electrocardiography (ECG) is possible at rest as well as when the patient is moving.

The uncertainty of purity of reference materials must be known.

Quantitative chromatographic analyses do not belong to the class of primary methods, but the analyst needs to calibrate the obtained signals with well-known solutions made of high-purity reference materials. Every analyte, to be quantified by a non-primary method, needs the chemically identical compound as its reference. It is not necessary that the content of the reference is 100.0%, but it is crucial that its purity is known, together with the uncertainty of this value (e.g., 99.9±0.05%). Any high-quality analytical result should include information about the associated measurement uncertainty, and the purity uncertainty of the reference is a parameter which always appears in the overall measurement uncertainty calculation of the measurand (such as the concentration or content of an analyte). Our general postulation is that the purity and the uncertainty of all reference materials must be known. It concerns all types of reference materials although we focus our discussion on the analysis of drug products. Unfortunately, at present only a few pharmaceutical reference materials are commercially available from regulatory bodies with a certificate confirming their purity with the related uncertainty. In contrast, such well-characterized materials, traceable to the International System of Units (SI), are available from various commercial suppliers.

Minimum required signal-to-noise ratio for optimal precision in HPLC and CE.

In a survey, results of more than 100 assay determinations of various analytes (active pharmaceutical ingredients, methylparabene, chlorthalidone, and proteins) at different concentration levels were collected with signal-to-noise ratio (S/N) levels between 2 and higher than 10 000. It must be concluded that without having a S/N of at least 50, repeatabilities (combination of injection, separation process, and integration) of 2% cannot be achieved, in contrast to the general assumption that a S/N of 10 is sufficient for analytical HPLC. These data now confirm an earlier assumption with a much broader fundamental of measurements. The empirical functions %RSD = 58/(S/N) + 0.30 (for HPLC data) and %RSD = 73/(S/N) + 1.07 (for CE data) could be derived. It was shown that a S/N of greater than 100 is necessary for optimal precision. Before optimizing HPLC or CE methods, for example, for sample pretreatment, S/N > 100 should be the prerequisite, else optimal precision will not be achieved. Only after the detection-related scatter is sufficiently reduced, other sources of variation can be successfully tackled.

A simple HPLC-MS method for the quantitative determination of the composition of bacterial medium chain-length polyhydroxyalkanoates.

Bacterial poly(hydroxyalkanoates) (PHAs) vary in the composition of their monomeric units. Besides saturated side-chains, unsaturated ones can also be found. The latter leads to unwanted by-products (THF ester, secondary alcohols) during acidic cleavage of the polymer backbone in the conventional analytical assays. To prevent these problems, we developed a new method for the reductive depolymerization of medium chain-length PHAs, leading to monomeric diols that can be separated and quantified by HPLC/MS. Reduction is performed at room temperature with lithium aluminum hydride within 5-15 min. The new method is faster and simpler than the previous ones and is quantitative. The results are consistent with the ones obtained by quantitative (1)H NMR.

How to generate peak capacity in column liquid chromatography. The Halász nomograms revised.

For the separation of complex samples it is necessary to run the analyses on a chromatographic set-up with high peak capacity. The concept of peak capacity is broader than the one of the theoretical plate numbers because it covers both the column characteristics and the run time of the separation. Therefore, a desired peak capacity can be obtained with many combinations of particle diameter, column length, pressure, and analysis time: either with a short column, small-diameter packing, short analysis time, and high pressure; or with less pressure at the expense of a longer column, larger-diameter packing, and longer analysis time. These combinations can be presented in the form of nomograms with the analysis time as x-axis and the peak capacity as y-axis and including particle diameter, column length, and pressure as parameters. The practical limits of the peak capacity are given by the maximum pressure delivered by the pump in use. These considerations are valid for isocratic and gradient separations as well. They are based on a 1982 paper by Halász and Görlitz and apply the concept of HPLC columns used at their Van Deemter optimum.

Measurement uncertainty.

Measurement uncertainty is a statistical parameter which describes the possible fluctuations of the result of a measurement. It is not a mere repeatability but it is at least as high as the intra-laboratory reproducibility. If it is an attribute of a general analytical test procedure it is at least as high as the inter-laboratory reproducibility. Measurement uncertainty can be determined by the addition of the variances of the individual steps of the test procedure or by an approach which starts with one of the above-mentioned reproducibilities. Any measurement uncertainty should be kept low but it is objectionable to state too low a value, e.g. by falsely reporting mere repeatability data instead of properly determined uncertainty data. Some good working principles can help to obtain low measurement uncertainties.

Measurement uncertainty of liquid chromatographic analyses visualized by Ishikawa diagrams.

Ishikawa, or cause-and-effect diagrams, help to visualize the parameters that influence a chromatographic analysis. Therefore, they facilitate the set up of the uncertainty budget of the analysis, which can then be expressed in mathematical form. If the uncertainty is calculated as the Gaussian sum of all uncertainty parameters, it is necessary to quantitate them all, a task that is usually not practical. The other possible approach is to use the intermediate precision as a base for the uncertainty calculation. In this case, it is at least necessary to consider the uncertainty of the purity of the reference material in addition to the precision data. The Ishikawa diagram is then very simple, and so is the uncertainty calculation. This advantage is given by the loss of information about the parameters that influence the measurement uncertainty.

The uncertainty of atomic mass fractions in a molecule.

The mass fraction of a certain atom species in a molecule is needed for the calculation of the result of some chemical analyses. Common examples are gravimetric determinations (e.g., the sulfur concentration in a sample that can be obtained from the mass of precipitated barium sulfate). A similar problem is encountered when a reference solution of an ion is prepared by dissolution of a salt. This paper presents how the uncertainty of the mass fraction is calculated from the uncertainties of the atomic weights as published by IUPAC. The value is needed for the determination of the combined standard uncertainty of the analysis. Some calculated examples illustrate the mathematical considerations presented in the paper.

The purity of laboratory chemicals with regard to measurement uncertainty.

The purity P of laboratory chemicals is often declared in the form P > or = xy% (e.g., P > or = 97%). With a randomly chosen set of 40 compounds we found that their purity is generally closer to 100% than to the lower limit. The distribution of the purity data as found in the laboratory depends on the analytical technique used. Whereas purities determined by chromatography do not exceed 100% (because the sum of all observed peak areas is set to 100%), the purities obtained by titration can exceed 100% (because the functionality of the compound is measured). Therefore, the data for these two groups need to be dealt with in different ways. For purities based on titration we propose to use a rectangular distribution with a range from Pmin to 101%, an expected purity value which is the mean and a standard uncertainty of the purity u(P) of 29% of the range. Purities determined by chromatography can be described with a triangular distribution (ramp function). One leg of the triangle represents the range from Pmin to 100% and the right-angle is located at 100%. The expected value is the median and the uncertainty u(P) is 24% of the range. These proposals match the experimental data well.