A new and accessible instrumentation to determine urea in UHT milk using digital image analysis.

This research demonstrates the development, optimization and application of a new low-cost detection system, based on digital image analysis, for the detection of urea in ultra-high-temperature (UHT) milk samples. The apparatus built in the laboratory, allows the capture of images through a simple system built by polyvinyl chloride (PVC) tubes, a digital microscope and a peristaltic mini-pump, after the colorimetric reaction between urea and diacetylmonoxime (butane-2,3-dionammonoxime). The red, green and blue (RGB) and hue, saturation and value (HSV) color systems were studied, with the saturation channel of the HSV color system selected as the analytical signal. Subsequently, the experimental chemical conditions were evaluated through multivariate experimental designs and the optimal conditions were defined. The proposed method was validated, and the detection and quantification limits presented by the method were 0.35 mg L-1 and 0.52 mg L-1, respectively; precision, ranged between 1.6  and 2.8 %. The results were compared with those obtained using the mid-infrared technique and no statistically significant differences were observed at a 95 % confidence level. The proposed method was applied to eight UHT milk samples that presented urea content ranging from 187 to 386 mg L-1. The mean values obtained are in agreement with values presented in other studies for the determination of urea in milk. The results indicated that the system described and validated here is promising and can be applied to assess the authenticity and quality of milk.

Homogeneity and stability assessment of a candidate to pumpkin seed flour reference material by means of computer vision based chemometrics assisted approach.

This study proposes a preliminary assessment of the homogeneity and stability through digital image acquisition of a candidate for mechanically processed pumpkin seed meal reference material, exploring the concepts of homogeneity curve and the analysis of texture characteristics by Continuous-Level Moving Block through Robust Principal Component Analysis. This innovative methodology allowed us to examine the percentage of homogeneity in a set of samples, revealing an average of 41% with only one outlier in relation to the entire sample, indicating low homogeneity. In the stability study carried out after storing samples for 12 months at different temperatures, 83% of the samples were considered regular and 17% were outlier, which means that most of them were considered stable. Therefore, this methodology is useful for screening samples for homogeneity, by textural analysis, and detected non-homogeneity can be corrected in advance for quantification by standard protocols.

Mineral content in mustard leaves according to the cooking method.

This work evaluated the influence of the cooking methods (cooked in a water bath, in a stove, and in a microwave oven) on the mineral composition of mustard leaves (Sinapis alba). So, raw and cooked samples were digested and afterward the elements calcium, magnesium, potassium, sodium, iron, zinc, phosphor, barium and sulfur were determined using inductively coupled plasma optical emission spectrometry (ICP OES). The experimental work involved a set of five samples from different locations, processed in triplicates. The results were evaluated employing Principal Component Analysis (PCA), Hierarchical Cluster Analysis (HCA) and Linear Discriminate Analysis (LDA). All techniques showed that the mineral content of the raw and cooked samples in a water bath is different from the samples cooked in stove and microwave oven. Especially for potassium, whose content is strictly controlled for chronic renal patients, this study showed that cooking using microwave oven has the greatest efficiency for reduction.

Homogeneity study of a corn flour laboratory reference material candidate for inorganic analysis.

In this work, a homogeneity study of a corn flour reference material candidate for inorganic analysis is presented. Seven kilograms of corn flour were used to prepare the material, which was distributed among 100 bottles. The elements Ca, K, Mg, P, Zn, Cu, Fe, Mn and Mo were quantified by inductively coupled plasma optical emission spectrometry (ICP OES) after acid digestion procedure. The method accuracy was confirmed by analyzing the rice flour certified reference material, NIST 1568a. All results were evaluated by analysis of variance (ANOVA) and principal component analysis (PCA). In the study, a sample mass of 400mg was established as the minimum mass required for analysis, according to the PCA. The between-bottle test was performed by analyzing 9 bottles of the material. Subsamples of a single bottle were analyzed for the within-bottle test. No significant differences were observed for the results obtained through the application of both statistical methods. This fact demonstrates that the material is homogeneous for use as a laboratory reference material.

A new method for preconcentration and determination of mercury in fish, shellfish and saliva by cold vapour atomic absorption spectrometry.

The development of a method using solid phase extraction for preconcentration and determination of mercury by cold vapour atomic absorption spectrometry is described. Hg (II) ions are sorbed on a minicolumn packed with Amberlite XAD-4 sorbent functionalised with 2-(2'-benzothiazolylazo)-p-cresol (BTAC). Then, a reducing solution was used for desorption and the transport of the analyte for subsequent detection. The assay presented a limit of detection of 0.011 µg L⁻¹ (0.011 µg g⁻¹, for solid samples), a limit of quantification of 0.038 µg L⁻¹ (0.038 µg g⁻¹, for solid samples), a precision of 0.50% (1.000 µg L⁻¹ Hg solution) and an enrichment factor of 46. The proposed method was applied to the determination of mercury in human saliva (0.055-0.200 µg L⁻¹). The following seafood collected in Todos os Santos Bay, Brazil was also analysed: bass (0.169-0.195 µg g⁻¹), mullet (0.043-0.361 µg g⁻¹), shrimp (0.075-0.374 µg g⁻¹) and mussel (0.206-0.397 µg g⁻¹).

Spectrophotometric determination of mercury in water samples after preconcentration using dispersive liquid-liquid microextraction.

A simple method for the determination of mercury in water samples after preconcentration using dispersive liquid-liquid microextraction is described. The procedure is based on the extraction of mercury in the form of a complex and its subsequent determination by spectrophotometry. The complex is formed between Hg(II) and 2-(2-benzothiazolylazo)-p-cresol. The detection at 650 nm is performed directly in the metal-rich phase, which is spread on a triacetylcellulose membrane. The method eliminates the need to use a cuvet or large quantities of samples and reagents. The parameters that influence the preconcentration were studied, and the analytical characteristics were determined. The enrichment factor and the consumptive index for this method were 64 and 0.16 mL, respectively. The LOD (3.3 microg/L) and LOQ (11.1 microg/L) were also determined. The accuracy of the method was tested by the determination of mercury in certified reference materials BCR 397 (Human Hair) and SRM 2781 (Domestic Sludge). The method was applied to the determination of mercury in samples of drinking water, sea water, and river water.