Human biomarkers in breath by photoacoustic spectroscopy.

Photoacoustic spectrometry provides a novel approach to the analysis of human breath biomarkers. This unique methodology has specific applications for determination of ethylene oxide, nitrous oxide, ammonia as well as other compounds of interest including sevoflurane, halothane, isoflurane, methane, ethane and propofol. The advantages and disadvantages of photoacoustic spectrometry for this purpose are evaluated.

Intra-laboratory testing of method accuracy from recovery assays.

A revision on intra-laboratory testing of accuracy of analytical methods from recovery assays is given. Procedures based on spiked matrices and spiked samples are presented and discussed.

Inorganic indicators of the origin of edible salts marketed in Spain from a chemometric approach.

Twenty edible salts marketed in Spain were studied for content of inorganic constituents in order to identify one or more indicators of the origins of salts. In Spain the principal source of salt is seawater, either from the Mediterranean coast or from the Atlantic coast. In addition, some manufactured salts in the dietary category were also considered. Five "Atlantic," 12 "Mediterranean," and 3 dietary salts were analyzed for potassium, magnesium, calcium, strontium, manganese, zinc, and sulfate contents and for alkalinity. Salt samples were first dried for moisture determination. Metals were determined by inductively coupled plasma atomic emission spectrometry, sulfate was determined by turbidimetry, and alkalinity was determined by titration with hydrochloric acid. All the results were expressed as the means for triplicate experiments, as mg of analyte per kg of salt on a dry basis. From these results and by application of chemometric strategies (principal component analysis, variable-variable plots, and cluster analysis) it was found that the potassium content distinguishes sea salts from dietary salts very well, and the contents of strontium and manganese discriminate salts of Atlantic origin versus salts of Mediterranean origin. Dietary salts showed levels of potassium higher than the sea salts, and salts of Atlantic origin had greater strontium and manganese content values than salts of Mediterranean origin.

Estimation of pH and autoprotolysis constants in mixtures of aliphatic amides with water: Medium effect on the 4-aminoazobenzene system.

Correction factors to the glass electrode and autoprotolysis constants of mixtures of aliphatic amides with water: N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMA), N-methylformamide (NMF), N-methylacetamide (NMA), formamide (F) and acetamide (A), have been determined. The acidity constants of 4-aminoazobenzene referred to the standard state of the mixtures of these aliphatic amides with water as well as the medium effect on the 4-aminoazobenzene system have been evaluated from spectrophotometric measurements.

Spectrophotometric determination of copper in foods, feedingstuffs and plants: a comparison between the glyoxal bis(4-phenyl-3-thiosemicarbazone) and bathocuproine disulphonate methods.

In this paper, both glyoxal bis(4-phenyl-3-thiosemicarbazone) (GBPT) and bathocuproine disulphonate (BCDS) methods for copper have been applied to the spectrophotometric determination of copper in foods, feedingstuffs and plants. Results obtained in both cases are typical of those expected for good spectrophotometric procedures. However, the GBPT method affords the distinct advantage of direct use in acidic solution without the necessity of neutralization and pH adjustment, being thus more satisfactory for unskilled usage.

Determination of the optimum working range in spectrophotometric procedures.

A brief introduction to the topics of covariance and variance is given in this paper. An abstract vectorial space, the "precision pattern space" is introduced in order to find the general expression for the law of random error propagation. A new approach to the determination of the optimum working range in spectrophotometric procedures has been developed. The method involves the use of the calibration curve and the application of the Laplacian operator to concentration. The general expression reported for the relative error in concentration tends towards the classical photometric error expression in limiting cases.

Mathematical treatment of absorbance versus pH graphs of polybasic acids.

Mathematical relationships determining the shape of absorbance vs. pH graphs of polybasic acids are derived, and new graphical and numerical techniques for evaluating the acidity constants of two-step overlapping equilibria are examined.

Spectrophotometric methods for the evaluation of acidity constants--II: Numerical methods for two-step overlapping equilibria.

A brief review of the numerical methods employed in the evaluation of acidity constants of two step overlapping equilibria is given. A new alternative to the method of three equations developed by Thamer is also proposed in this paper. Taking into account the Gauss-elimination method, several variants to the original method of Thamer are devised.

Spectrophotometric methods for the evaluation of acidity constants-I Numerical methods for single equilibria.

The spectrophotometric methods applicable to the numerical evaluation of acidity constants of monobasic acids are briefly reviewed. The equations are presented in a form suitable for easy calculation with a programmable pocket calculator. The aim of this paper is to cover a gap in the education analytical literature.