The possibility of using thiocyanate to determine iron(II) and/or iron(III) in water-acetone mixturehas been re-examined as part of a systematic and comparative study involving metallic complexes ofpseudohalide ligands. Some parameters that affect the complete oxidation of the ferrous cations, theirsubsequent complexation and the system stability have been studied to optimize the experimental conditions.Our results show the viability and potentiality of this simply methodology as an alternative analytical procedureto determine iron cations with high sensitivity, precision and accuracy. Studies on the calibration, stability,precision, and effect of various different ions have been carried out by using absorbance values measured at480 nm. The analytical curve for the total iron determination obeys Beer’s law (r = 0.9993), showing a highersensitivity (molar absorptivity of 2.10x10 4 L cm -1 mol -1 ) when compared with other traditional systems (ligands)or even with the “similar” azide ion [1.53x10 4 L cm -1 mol -1 , for iron–III/azide complexes, in 70% (v/v)tetrahydrofuran/water, at 396 nm]. Under such optimized experimental conditions, it is possible to determineiron in the concentration range from 0.5 to 2 ppm (15-65% T for older equipments, quartz cells of 1.00 cm).

Neste estudo, procurou-se desenvolver e avaliar filmes para a captação e quantificação de vapores de amônia no ar, através de um sensor piezelétrico de quartzo. Muitas substâncias e suas misturas, em diferentes proporções, foram investigadas como possíveis filmes captores. Em etapas seguintes, verificaram-se alguns parâmetros importantes como o efeito da vazão do poluente, da temperatura de trabalho e da massa da película, otimizando-se as condições experimentais para a montagem do método. Concluiu-se que o filme mais promissor, sob as condições ajustadas, seria uma mistura 2:1 (v/v) de solução comercial (A) de ácido glicólico (70% m/m) em água, adicionada a tetrakis(hidroxietil)etilenodiamina - THEED (3:4 v/v), com uma solução saturada (B) de ácido tânico em acetona. Estudos de repetibilidade, do tempo de contacto (poluente-sensor) e de alguns possíveis interferentes completaram os trabalhos. As curvas analíticas resultantes mostraram faixas lineares na região de trabalho (2,0 a 11 ppmv ou 1,4 a 7,7 mg/m3 de NH3), para quatro diferentes tempos de exposição (0,5; 1; 2 e 3 min), com coeficientes de correlação (r) variando entre 0,9994 e 0,9980, e respectivas sensibilidades de 13,5 a 42,0 Hz/ppmv.

A simple, sensitive and alternative method for the spectrophotometric determination of iron(II or III) has been established. The procedure is based on the formation of iron-III/azide complexes, in 70% (v/v) tetrahydrofuran (THF)/water medium. Under these present experimental conditions, ferrous iron is rapidly oxidized and complexed. The high sensitivity obtained in this method is due to the use of an interesting absorption band caused by THF solvation.In the recommended conditions, absorbances for the ferric complexes are measured at 396 nm, where the molar absorptivity is 1.53 x 10(4) l mol(-1) cm(-1). The organic solvent utilized increases the sensitivity and the stability of the measurements. The reproducibility is shown by an average deviation about 0.15%. This system obeys the Beer's law and is suitable for iron determination in the concentration range from 0.6 to 2.8 ppm (15-65% T quartz cells of 1.00 cm). The optimal conditions for a faster iron-II oxidation were determined by studying the different factors involved. The influence of various diverse ions was also evaluated.Analytical applications have been tested for several different materials (iron-rocks), including pharmaceutical products for anemia, in which the results were compared with atomic absorption measurements. Very good concordances were obtained between these two different techniques, showing the potential of present spectrophotometric method in iron analysis. (C) 2000 Elsevier Science B.V. All rights reserved.

Three different methods to produce standardized vapors of mercury were tested and compared for posterior determination of metal, using a piezoelectric sensor (QCM). The generation techniques employed were: saturation, syringe dilution and permeation tube. Gold-coated piezoelectric crystals, without any substrate, were initially tested as sensor, based on the selective affinity of gold by mercury. Later, using a permeation tube as source of metal, some substances were investigated as possible substrates capable of interaction with mercury vapor. The best material found was a mixture (1:1 v/v) of palladium-II chloride solution (saturated in acetone) and tetrahydroxyethylethylenediamine (THEED) 50% v/v in acetone. The analytical curve is linear in the concentration range from 2.0 to 7.0ppm of Hg. Good linearities (r=0.9952 and 0.9979) and sensitivities (102 and 149Hz/ppm) were found for exposure times of 20 and 40s, respectively. It was shown that the technique has potential application as a small, rugged, sensible and portable mercury vapor sensor.

Introduction. The original conception of this work included a complete study of certain codimension three perfect ideals that arise naturally in a set-up, with the purpose of enriching the present collection of such ideals. The ones we consider are always radical and their syzygy-theoretic properties are relatively easy to describe. From the viewpoint of the theory of graded resolutions, they share common numerical features with (the projecting cones of) certain codimension two and three varieties in projective space. Their resolutions being seldom pure, they seemed largely convenient for testing the sharpness of some calculations made in the pure case (cf. [19], [25], [26]). Moreover, they yield a large class suited for testing recently developed concepts, such as the notion of strong obstruction, that have its natural place in the theory of linkage ([loc. cit.]) or the more general theory of residual intersection developed in [16]. The authors did not pursue this line of thought, but it seemed worthwhile pointing it out. A brief description of the present contents is as follows. In the first section one obtains the explicit free resolution of a large class of codimension three ideals that appear as presentation ideals of normal cones associated to determinantal ideals fixing a submatrix. As it turns out, the resolutions of these presentation ideals are given by a mapping cylinder of a suitable map to the resolution of the original determinantal ideals. The second section is concerned with deriving some ideal-theoretic results from the knowledge of the presentation given in section one. This procedure, by and large, follows the techniques developed by various authors ([17], [14], [23] and [24]). In the third section one gives the resolution of the determinantal ideal Jr associated to a map m ~ R (m > n), fixing r c m, in the case of the data r = n - 2 and m = n + 2. This case not only extends the previous known ones [1], [2], but mainly gives some genuine clue for the general situation. The construction follows closely the spirit of the scandinavian complex [9] in that one is led to tensor suitable complexes and then to cut down the resulting size by an use of trace maps. This method seems to generalize well in various contexts [21]. Last one establishes exact values for the codimension of the complete intersection locus of the ideals considered in the previous sections. The reason for doing so is that the known estimates to present [11], [27] would give no real grasp, in this case, of the locus.

Let M be a n×m matrix with entries in a noetherian ring R and let M′ be the submatrix of M consisting of the first r columns (r ⩽ n− 1). Consider the ideal Jr(M) of n×n minors of M involving the columns of M′. We obtain the primary decomposition and the homological dimension of Jr(M) in the generic case. The proofs rely heavily on the methods and the theory of weak d-sequences and straightening laws. As a byproduct we obtain exact conditions under which Jr(M) is generated by a d-sequence and also a complete picture of the blowing-up algebras of Jr(M) in that case. The latter proofs rely on recent methods developed by several authors such as those of sliding-depth, approximation complexes, Cohen-Macaulay residual intersections. To close the discussion we construct a free resolution of Jr(M) when m = n + 1 (the case r = n−1 had been treated before by the present authors). A side curiosity herein obtained is an example of a nonperfect radical 3-generated ideal of codimension 2 whose associated graded ring is a Cohen-Macaulay reduced ring that is not Gorenstein. Examples of this sort do not seem to abound.

An “additivity” formula is obtained for the grade of an ideal in a residue ring R/I, where I is a perfect ideal. This result is then applied to compute the grade of ideals of linear (inhomogeneous) polynomials. Further results on the homological rigidity of the conormal module I/I2 are pointed out. Finally, an elementary proof is given of a result of Buchsbaum concerning the grade of ideals of minors of a matrix.

Let A A be an n × m n \times m matrix ( m ⩾ n ) (m \geqslant n) with entries in a noetherian ring R R , let J J be the ideal of R R generated by the n × n n \times n minors that are formed with n − 1 n - 1 fixed columns of A A . Necessary and sufficient conditions are given in order that a suitably defined complex be a free resolution of the R R -module R / J R/J . The complex is closely related to the complexes of Buchsbaum-Rim [2, §2] and it is perhaps worthwhile mentioning that a special case of the present result was obtained by Buchsbaum-Eisenbud in a different context [1, Theorem 8.1].