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Potentiometric Enzyme Electrodes
Published in Loïc J. Blum, Pierre R. Coulet, Biosensor Principles and Applications, 2019
Jean-Michel Kauffmann, George G. Guilbault
The presence of pesticides in river waters induced a proportional pH increase; the probe was reactivated by 2-pyridine aldoxime. Detections of pesticides as low as 10 nM have been reported. Other automated systems have advantageously combined multienzyme layers over a fluoride-selective electrode for the assay of maltose, glucose, and lactose (96). Coimmobilized peroxidase catalyzes the liberation of fluoride ions from a suitable reagent present in the analyzed solution (hydrogen peroxide being liberated by the substrate-enzyme reaction): R−Fn+H2O2→HRPR−F(n−1)+F−+H2O
Polymers
Published in Bryan Ellis, Ray Smith, Polymers, 2008
Amorph. fluoroelastomer has globular struct; same struct. both in films and bulk. It is resistant to corrosive liqs., milling, and unchanged by vulcanisation and is altered only by high pressure [42]. Ms studies of microstruct. reveal comonomers linked by intermediate -CH2CFCl- and -CF2CF2- units [45]. Far ir measurements have been used to investigate degree of ordering/ chain conform.; order reduced by increasing amounts of CTFE [13]. X-ray measurements show struct. is similar to that of PVDF (Form II) [13]. Typical commercially available copolymer, e.g. CTFE:VDF (75:25) is partially crystalline. The extent of crystal- linity depends on thermal history. Annealing at temps. Tg < T < Tm (also under strain) produces slow crystallisation resulting in a rather low ultimate degree of crystallinity, as randomly distributed ribbon-like lamellae. Thermal and mechanical (tensile) behaviour following annealing have also been reported [15]. The crystallisation rate is also dependent on processing history; DSC studies have revealed 'memory effect' in some copolymer systems [34]. X-ray diffraction anal. of semi- crystalline polymer shows unusually large crystallites (less than 500A) depending on processing conditions; apparent crystallite size can be regarded as measure of crystalline perfection [16]. Molecular motions of copolymer have been investigated by esr spectroscopy and fluorescence polarisation experiments [55]. Motions of graft (VDF on CTFE) copolymer have been studied by pulsed pmr spectroscopy; the struct. consists of a ribbon-like (mobile) component and a crystalline (immobile) component; motions correlate with mechanical props. [33]. Commercial elastomer is amorph. at temps. down to -40°, but partially crystallises at 300% elongation [58]. Small amounts of CTFE reduce crystallinity of polyvinylidene fluoride. Greater than 30 mol% vinylidene fluoride can be incorporated into helical struct. of CTFE homopolymer before crystallinity and struct. are significantly affected. 50/50 Compositions have a fair amount of disorder along chain direction and are of random struct. with low degree of alternation, head-to-head, head-to-tail [51] Identification: Fluorine determined by burning in presence of urethane rubber, PE and NaNO3, using distilled water as absorbing soln.; fluoride ions in solns. containing urotropin (pH 5-5.2) are titrated with La(NO3)3 soln., using a fluoride-selective electrode [18]. Controlled pyrolysis- electron impact mass spectrometry has been reported as diagnostic method for identifying commercial material [54]. Atom ion emission- ms anal. for qualitative and quantitative evaluation has the particular advantages of high accuracy, efficiency and the need for only small sample sizes [39]. H-1 nmr and C-13 nmr spectroscopy is used for identification/anal. of impurities in copolymer resin and its lacquers: F-19 nmr is used to identify impurities and emulsifiers (e.g. perfluorodecanoates) from polymerisation process [57]. Anal. of esca data gives compositional results to within 2% of those obtained from elemental anal. [43]. CTFE content in copolymers can be monitored by the intensity of the 840 cm-1 band in the vibrational (ir) spectrum; intensity decreases with increasing CTFE content [56]
In vitro abrasivity and chemical properties of charcoal-containing dentifrices
Published in Biomaterial Investigations in Dentistry, 2020
Foteini Machla, Aida Mulic, Ellen Bruzell, Håkon Valen, Ida Sofia Refsholt Stenhagen
A solution of fluoride (10 mg/L) was prepared from a standard solution (100 mg/L F-, Thermo Scientific, Waltham, MA) using deionized water as solvent. Firstly, a baseline measurement of the fluoride concentration was conducted using an ion analyzer (ION 450, Meter Lab, Lyon, France) and a fluoride-selective electrode (Radiometer Analytical, Lyon, France). NAO, COCO and activated charcoal for laboratory use (positive control) was subsequently added (1 g/mL) and stirred at a speed of 150 RPM. Measurements were performed after 1, 3, 6, 12 and 24 h. During each measurement, a 5 ml aliquot was removed and filtered through a paper filter (White ribbon, 5892, Schleicher & Schuell, Dassel, Germany) and a syringe filter (0.45 µm, Millex, Millipore, Bedford, MA) to remove the charcoal powder from the sample solution. After adding an equal amount of total ionic strength adjustment buffer for fluoride (TISAB-F, Radiometer Analytical, Krefeld, Germany) to the filtered aliquot, the fluoride concentration was measured. Each aliquot was measured three times, the mean of which was calculated. Three experiments were performed.
Fluoride exchange by glass-ionomer dental cements and its clinical effects: a review
Published in Biomaterial Investigations in Dentistry, 2023
John W. Nicholson, Sharanbir K. Sidhu, Beata Czarnecka
Another feature, which has been reported in the literature but is largely ignored, is that in acidic conditions, more of the fluoride is released as complexes rather than as free F– ions [27,32]. The two types of fluoride may be distinguished using a fluoride-selective electrode [32]. This device is able to determine F– ions only, and fluoride in any other form, for example combined into a complex ion, is not detected. The overwhelming majority of studies forcibly decomplex all of the fluoride present by adding total ionic solubility acid buffer (TISAB) solution prior to measuring fluoride in the storage solutions.