We describe novel cycloolefin polymer (COP)-based open tubular capillary ion exchange columns. COP capillaries (inner diameter of 19-28 μm) were successfully sulfonated at room temperature using a cocktail of ClSOH (85-95% w/w) and HOAc or HSO. The cation exchange capacity is controlled by the sulfonation time and the sulfonation solution composition and can be as high as 300 pequiv/mm. Following sulfonation, the capillaries were coated with 65-nm-diameter anion exchanger (AEX) latex nanoparticles that attach electrostatically. The typical anion exchange capacities were ∼20 pequiv/mm. The chromatographic behavior of the AEX latex-coated COP capillaries are greatly dependent on the degree of sulfonation. When the base is heavily sulfonated, neutrals elute after the anions. The position of the water dip varies with the degree of sulfonation; the elution order is normal (water dip appear before anions) only with lightly sulfonated columns. On silica (-SiOH) or poly(methyl methacrylate) (-COOH) surfaces, AEX latex attachment is not stable over long periods in significant concentrations of strong base (e.g., ≥10 mM NaOH). Latex attachment on sulfonated COP surfaces are much stronger; several types show sufficient binding to be used over long periods at practical eluent concentrations, paving the way for suppressed hydroxide eluent ion chromatography (IC), which is discussed in a companion paper. Another interesting feature of COP capillaries lies in their flexibility. If softened at modestly elevated temperatures (e.g., boiling water), they can be coiled down to <1 mm coil radii, revealing, for the first time, the beneficial effects, albeit small, of centrifugal force on mass transfer in open tubular columns.
Bioinspired materials have attracted attention in a wide range of fields. Among these materials, a polymer family containing 2-methacryloyloxyethyl phosphorylcholine (MPC), which has a zwitterionic phosphorylcholine headgroup inspired by the...
We developed an organic solvent-compatible
paper-based analytical
device (PAD) for the quantitative analysis of indole, which is an
indicator of shrimp freshness. Although indole is insoluble in water,
ethyl acetate is a suitable solvent to dissolve and extract indole
from shrimp. The PADs are fabricated using a cutting method that allows
the use of an organic solvent because no hydrophobic barrier is needed
to form fluidic channels. Ehrlich’s reagent consists of 4-(dimethylamino)benzaldehyde
and p-dimethylaminobenzaldehyde and was deposited
onto the reaction zone of the PAD followed by lamination to prevent
evaporation of the ethyl acetate. Samples are introduced into the
PAD via immersion in organic sample solutions. When the PAD is immersed
into an indole solution of ethyl acetate in a closed bottle, the sample
solution penetrates the channel of the PAD and successively flows
into the detection zone to form a hydrophilic colored product. The
PADs provide a linear relationship between the logarithm of the indole
concentration and the color intensity within a range of 1.0–20
ppm with correlation coefficients of r
2 > 0.99. The limits of detection and quantification are 0.36 and
0.71 ppm, respectively. Relative standard deviations for both the
intraday (n = 2) and interday (n = 3) precision were less than 2.5%. In the indole analysis of shrimp,
the PADs separated the interfering orange-colored astaxanthin in the
extract from the colored product of indole via the paper chromatographic
principle. We used the PADs to investigate the degradation of shrimp,
and the results showed a rapid increase in the indole level after
7 days. High-performance liquid chromatography verified the accuracy
of the PADs by showing good agreement with the obtained indole levels.
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