Hardness screening of water using a flow-batch photometric system

A novel pH-sensitive method for the quantification of Ca2+ ions by complexometric titration with Na3HEDTA

A simple and accurate complexometric titration has been developed by the reaction between Ca2+ ions (pH 7) and Na3HEDTA (pH 11) solutions. Formation of a Ca-EDTA complex and release of H+ ions in the system were traced by a decrease in the pH. At the equivalence point of the titration, a sharp increase in the pH was observed. Looking at the working pH range (pH 6.2-7.5) of this method, another complexometric titration method has been developed by using bromothymol blue as a pH sensitive indicator. This is the first report of a complexometric titration by using an acid base indicator.

A 3D-printed robotic system for fully automated multiparameter analysis of drinkable water samples

This work describes a 3D-printed robotic system named RSAWA (robotic system for automatic water analysis) for fully automated water analysis. RSAWA consists of a robotic arm coupled to a syringe pump, temperature and conductivity sensors, a low-cost webcam as colorimetric detector, and a 96-well microplate placed on a 3D-printed platform. The robotic system is controlled by software and it performs all analytical procedures. RSAWA was applied to measure conductivity (CDT), pH, total alkalinity (TA), total hardness (TH), chloride (Cl^-), nitrite (NO₂^-), total dissolved phosphorus (TP), and total iron (TI) in drinkable water samples. A simple circuit was designed for conductivity determinations, while colorimetric pH determinations were carried out using Hue values extracted from digital images and a pH universal indicator. HSV histograms were used to calculate Pearson's correlation coefficients, allowing the construction of accurate titration curves. In addition to achieving sample throughputs of 112 h^-1 for TA and TH determinations and 92 h^-1 for Cl^- determinations, RSAWA produced 99.5% less waste than the corresponding reference methods during titrations. Colorimetric measurements were performed through RGB vector norms calculated from digital images were used as analytical signals. Limits of quantification (μg L^-1) were 6.83, 13.0 and 1.5 mg L^-1 for NO₂^-, TP, and TI determinations, respectively. Sample throughputs (samples h^-1) were 83 for NO₂^- and TP and 72 for TI with a 98.5% reduction in waste generation. Thus, RSAWA is a low-cost, feasible, and environmentally friendly alternative to quickly and accurately determine several chemical and physicochemical parameters in aqueous samples.

Complexometric titrations: new reagents and concepts to overcome old limitations

Chelators and end point indicators are the most important parts of complexometric titrations.

A real-time fluorescent sensor specific to Mg2+: crystallographic evidence, DFT calculation and its use for quantitative determination of magnesium in drinking water

An “off-the-shelf” fluorescence “turn-on” Mg²⁺ chemosensor BCSA has been developed for real-time quantitative monitoring of magnesium in drinking water.

Automatic flow-batch system for cold vapor atomic absorption spectroscopy determination of mercury in honey from Argentina using online sample treatment

An automatic flow-batch system that includes two borosilicate glass chambers to perform sample digestion and cold vapor atomic absorption spectroscopy determination of mercury in honey samples was designed. The sample digestion was performed by using a low-cost halogen lamp to obtain the optimum temperature. Optimization of the digestion procedure was done using a Box-Behnken experimental design. A linear response was observed from 2.30 to 11.20 μg Hg L(-1). The relative standard deviation was 3.20% (n = 11, 6.81 μg Hg L(-1)), the sample throughput was 4 sample h(-1), and the detection limit was 0.68 μg Hg L(-1). The obtained results with the flow-batch method are in good agreement with those obtained with the reference method. The flow-batch system is simple, allows the use of both chambers simultaneously, is seen as a promising methodology for achieving green chemistry goals, and is a good proposal to improving the quality control of honey.

Rapid screening of polycyclic aromatic hydrocarbons (PAHs) in waters by directly suspended droplet microextraction-microvolume fluorospectrometry

A rapid and simple screening method for polycyclic aromatic hydrocarbons (PAHs) in water samples is proposed. The method is based on the combination of a miniaturized sample preparation approach, namely, directly suspended droplet microextraction (DSDME), and microvolume fluorospectrometry. Benzo[a]pyrene (BaP) was used as the model compound for screening purposes. Under optimal conditions, a detection limit of 0.024 μg L(-1) and an enrichment factor of 159 were obtained for BaP in 5 min. The repeatability, expressed as relative standard deviation (RSD), was 4.9% (n=8). The unreliability region of the screening method was 0.54-0.67 μg L(-1), by using a cut-off value of 0.6 μg L(-1) of BaP. Finally, the proposed method was applied to the in situ achievement of the binary "yes/no" response for PAHs in different water samples and recovery studies were performed at three different levels, with BaP recoveries in the range of 93-104%.

A rapid, sensitive screening test for polycyclic aromatic hydrocarbons applied to Antarctic water

We describe a rapid, sensitive, fluorescence screening test for polycyclic aromatic hydrocarbons in water samples that avoids more costly time-consuming methods. The screening test works by detecting benzo[a]pyrene. It runs without the need for any pre-concentration step, thus rendering it suitable for routine use in water-quality-control laboratories. The test recognizes contaminated samples rapidly (150 s) and inexpensively with a cut-off level of 10 ng l(-1), which is the value that the European Union and World Health Organization (WHO) have laid down in its assessment of the quality of water for human consumption. This was first ascertained by analysing tap and waste-water samples before studying environmental water samples from the Antarctic region. The reliability of the screening test was 2% false positives and 4% false negatives in 200 samples of tap and waste-water. The applicability was confirmed by the fact that the predictions of the screening test coincided exactly with results obtained with gas chromatography-mass spectrometry assays. We also discuss the polluted Antarctic samples and the possible sources of the contamination involved.

Digital image-based titrations

The exploitation of digital images obtained from a CCD camera (WebCam) as a novel instrumental detection technique for titration is proposed for the first time. Named of digital image-based (DIB) titration, it also requires, as a traditional titration (for example, spectrophotometric, potentiometric, conductimetric), a discontinuity in titration curves where there is an end point, which is associated to the chemical equivalence condition. The monitored signal in the DIB titration is a RGB-based value that is calculated, for each digital image, by using a proposed procedure based on the red, green, and blue colour system. The DIB titration was applied to determine HCl and H3PO4 in aqueous solutions and total alkalinity in mineral and tap waters. Its results were compared to the spectrophotometric (SPEC) titration and, by applying the paired t-test, no statistic difference between the results of both methods was verified at the 95% confidence level. Identical standard deviations were obtained by both titrations in the determinations of HCl and H3PO4, with a slightly better precision for DIB titration in the determinations of total alkalinity. The DIB titration shows to be an efficient and promising tool for quantitative chemical analysis and, as it employs an inexpensive device (WebCam) as analytical detector, it offers an economically viable alternative to titrations that need instrumental detection.