Whitford, Betty Lou, Phillip C. Schlechty, and Linda G. Shelor, Sustaining Action Research through Collaboration: Inquires for Invention, Peabody Journal of Education, 64(Spring, 1987), 151-169.

Discusses the need for cultural change in schools through collaborative action research

Conductometric Gradient Ion Exclusion Chromatography for Volatile Fatty Acids

We describe a fatty acid vapor extractor (FAVE) as a postcolumn device for sensitive detection following ion exclusion chromatographic (ICE) separation of weak acids. The device consists of a single length of a permselective membrane tube surrounded by a jacket that consists of two isolated sections. The separation column effluent flows through the lumen. A suitable strong acid is put in the upstream, short section of the jacket and permeates in, rendering the lumenal flow strongly acidic (pH ≤ 2) that suppresses eluite weak acid dissociation. A lipophilic polysiloxane membrane is selectively permeable to volatile fatty acids (VFAs). A small fraction of the VFAs transfer to a cocurrent receptor stream of water (or a weak base, e.g., dilute hydroxylamine), flowing through the second, longer section of the jacket. Even though the transferred amount of VFAs may be very small (0.5–5%), significantly better detection limits than conventional suppressed conductometric ICE (SCICE) is possible because of the low and stable background (noise <1 nS/cm). It also permits gradient elution, not possible in SCICE. The polysiloxane based FAVE device is highly selective for VFAs, it shows no response to dicarboxylic acids, hydroxycarboxylic acids, or aromatic acids. As such, trace detection of VFAs in the FAVE extractant is possible while other components can still be monitored conventionally in the FAVE lumenal effluent. Various parameters, related both to device design and operation were studied. The FAVE provides isolation from the eluent matrix and can be used for other detectors where the eluent matrix is incompatible with the detector

Automated Programmable Preparation of Carbonate-Bicarbonate Eluents for Ion Chromatography with Pressurized Carbon Dioxide

We introduce a novel carbonate–bicarbonate eluent generation system in which CO₂ is introduced using programmable CO₂ pressures across a membrane into a flowing solution of electrodialytically generated high purity KOH. Many different gradient types are possible, including situations where gradients are run both on the [KOH] and the CO₂ pressure. The system is more versatile than current electrodialytic carbonate eluent generators and can easily generate significantly higher eluent concentrations (at least to 40 mM carbonate), paving the way for future higher capacity columns. Demonstrably purer carbonate–bicarbonate eluent systems are possible compared to manually prepared carbonate–bicarbonate eluents and with considerable savings in time. Performance in different modes is examined. The dissolved CO₂ is removed by a carbon dioxide removal device prior to detection. Best case noise levels are within a factor of 2–3 of best case suppressed hydroxide eluent operation. The eluent system allows particular latitude in controlling elution order/time of polyprotic acid analytes. Although CO₂ introduction is possible prior to hydroxide eluent generation, this configuration causes complications because of electroreduction of CO₂ to formate

Water ICE: Ion Exclusion Chromatography of Very Weak Acids with a Pure Water Eluent

Separation of ions or ionizable compounds with pure water as eluent and detecting them in a simple fashion has been an elusive goal. It has been known for some time that carbonic acid can be separated from strong acids by ion chromatography in the exclusion mode (ICE) using only water as the eluent. The practice of water ICE was shown feasible for very weak acids like silicate and borate with a dedicated element specific detector like an inductively coupled plasma mass spectrometer (ICPMS), but this is rarely practical in most laboratories. Direct conductometric detection is possible for H₂CO₃ but because of its weak nature, not especially sensitive; complex multistep ion exchange methods do not markedly improve this LOD. It will clearly be impractical in acids that are weaker still. By using a permeative amine introduction device (PAID, Anal. Chem. 2016, 88, 2198–2204) as a conductometric developing agent, we demonstrate that a variety of weak acids (silicate, borate, arsenite, cyanide, carbonate, and sulfide) cannot only be separated on an ion exclusion column, they can be sensitively detected (LODs 0.2–0.4 μM). We observe that the elution order is essentially the same as that on a nonfunctionalized poly­(styrene-divinylbenzene) column using 1–10% acetonitrile as eluent and follows the reverse order of the polar surface area (PSA) of the analyte molecules. PSA values have been widely used to predict biological transport of pharmaceuticals across a membrane but never to predict chromatographic behavior. We demonstrate the application of the technique by measuring the silicate and borate depth profiles in the Pacific Ocean; the silicate results show an excellent match with results from a reference laboratory

Nonlinear Absorbance Amplification Using a Diffuse Reflectance Cell: Total Organic Carbon Monitoring at 214 nm

We present an absorption spectrometric method using a polytetrafluoroethylene (PTFE) cell as a diffuse reflector. The system was used for monitoring ultrapure water. All compounds absorb to some degree at low UV wavelengths, and the absorption at 214 nm from a zinc lamp source was monitored using a charge-coupled device (CCD) spectrometer. The absorption was interpreted in terms of total organic carbon present. The cell acts as a nonlinear absorbance amplifier, improving both the limit of detection (LOD) and the dynamic range. Potassium hydrogen phthalate (KHP) and glucose were used to evaluate the system and provided respective LODs of 46.5 ng/L and 4.5 mg/L as carbon. Although the physical path length was 25 cm, a maximum effective path length of 280 cm was observed at the lowest tested KHP concentrations. The system is intended for real-time monitoring of ultrapure water

Enigmatic Ion-Exchange Behavior of <i>myo</i>-Inositol Phosphates

The separation of <i>myo</i>-inositol mono-, di-, tri-, tetra-, pentakis-, and hexakisphosphate (InsP₁, InsP₂, InsP₃, InsP₄, InsP₅, InsP₆) was carried out using hydroxide eluent ion chromatography. Acid hydrolysis of InsP₆ (phytate) was used to prepare a distribution of InsPs, ranging from InsP₁ to InsP₅’s and including unhydrolyzed InsP₆. Counting all possible positional isomers (many of which have stereoisomers that will not be separable by conventional ion exchange), 40 chromatographically separable peaks are possible; up to 22 were separated and identified by mass spectrometry. InsPs show unusual ion-exchange behavior in two respects: (a) the retention order is not monotonically related with the charge on the ion and (b) at the same hydroxide eluent concentration, retention is greatly dependent on the eluent metal cation. The retention of InsP₃–InsP₆ was determined to be controlled by steric factors while elution was influenced by eluent cation complexation. These highly phosphorylated InsPs have a much greater affinity for alkali metals (Li⁺ > Na⁺ > K⁺) than quaternary ammonium ions. This difference in cation affinity was exploited to improve separation through the use of a tetramethylammonium hydroxide–sodium hydroxide gradient

Simultaneous Electrodialytic Preconcentration and Speciation of Chromium(III) and Chromium(VI)

Large amounts of chromium (Cr) compounds are used for manufacturing of various products and various chemical processes. Some inevitably find their way into the environment. Environmental Cr is dominantly inorganic and is either in the cationic +3 oxidation state or in the anionic oxochromium +6 oxidation state. The two differ dramatically in their implications; Cr­(III) is essential to human nutrition and even sold as a supplement, while Cr­(VI) is a potent carcinogen. Drinking water standards for chromium may be based on total Cr or Cr­(VI) only. Thus, Cr speciation analysis is very important. Despite their high sensitivity, atomic spectrometric techniques or induction coupled plasma–mass spectrometry (ICP-MS) cannot directly differentiate the oxidation states. We present here a new electrodialytic separation concept. Sample analyte ions are quantitatively transferred via appropriately ionically functionalized dialysis membranes into individual receptors that are introduced into the ICP-MS. There was no significant conversion of Cr­(VI) to Cr­(III) or vice versa during the very short (6 s) separation process. Effects of salinity (up to ∼20 mM NaCl) can be eliminated with proper membrane functionalization and receptor optimization. With the ICP-MS detector we used, the limits of detection for either form of Cr was 0.1 μg/L without preconcentration. Up to 10-fold preconcentration was readily possible by increasing the donor solution flow rate relative to the acceptor solution flow rates. The proposed approach permits simultaneous matrix isolation, preconcentration, and chromium speciation

Evaluation of Amount of Blood in Dry Blood Spots: Ring-Disk Electrode Conductometry

A fixed area punch in dried blood spot (DBS) analysis is assumed to contain a fixed amount of blood, but the amount actually depends on a number of factors. The presently preferred approach is to normalize the measurement with respect to the sodium level, measured by atomic spectrometry. Instead of sodium levels, we propose electrical conductivity of the extract as an equivalent nondestructive measure. A dip-type small diameter ring-disk electrode (RDE) is ideal for very small volumes. However, the conductance (<i>G</i>) measured by an RDE depends on the depth (<i>D</i>) of the liquid below the probe. There is no established way of computing the specific conductance (σ) of the solution from <i>G</i>. Using a COMSOL Multiphysics model, we were able to obtain excellent agreement between the measured and the model predicted conductance as a function of <i>D</i>. Using simulations over a large range of dimensions, we provide a spreadsheet-based calculator where the RDE dimensions are the input parameters and the procedure determines the 99% of the infinite depth conductance (<i>G</i>₉₉) and the depth <i>D</i>₉₉ at which this is reached. For typical small diameter probes (outer electrode diameter ∼ <2 mm), <i>D</i>₉₉ is small enough for dip-type measurements in extract volumes of ∼100 μL. We demonstrate the use of such probes with DBS extracts. In a small group of 12 volunteers (age 20–66), the specific conductance of 100 μL aqueous extracts of 2 μL of spotted blood showed a variance of 17.9%. For a given subject, methanol extracts of DBS spots nominally containing 8 and 4 μL of blood differed by a factor of 1.8–1.9 in the chromatographically determined values of sulfate and chloride (a minor and major constituent, respectively). The values normalized with respect to the conductance of the extracts differed by ∼1%. For serum associated analytes, normalization of the analyte value by the extract conductance can thus greatly reduce errors from variations in the spotted blood volume/unit area

Anion Composition of Açaı́ Extracts

Many products labeled açaı́ are presently marketed as natural supplements with various claimed health benefits. Authentic açaı́ is expensive; as a result, numerous products labeled as containing açaı́ are being sold that actually contain little or no açaı́. Authentic açaı́ samples from Brazil and Florida as well as several reputed açaı́ products were analyzed by suppressed conductometric anion chromatography. Columns with different selectivities were used to obtain a complete separation of all anions. Tandem mass spectrometry was used for confirmation of the less common ions. Quinate, lactate, acetate, formate, galacturonate, chloride, sulfate, malate, oxalate, phosphate, citrate, isocitrate, and <i>myo</i>-inositol hexakisphosphate (phytate) were found. Only the Florida açaı́ had detectable levels of hexanoate. No açaı́ sample had any detectable levels of tartrate, which is present in abundance in grape juice, the most common adulterant. The highly characteristic anion profile and in particular the absence of tartrate can readily be used to identify authentic açaı́ products. Açaı́ from Florida had a 6 times greater level of phytate. The present analytical approach for phytate may be superior to extant methods