Coupling methods between supercritical fluid extraction (SFE) and various chromatographic techniques have been reviewed. Developments using supercritical fluids in chromatography have been tremendous and a confirmation of the usefulness of this technique (called supercritical fluid chromatography (SFC)) has been evidenced by many scientists. Another field using supercritical fluids in analytical processes is SFE. Since SFE has many advantages compared to conventional solvent extraction method, such as faster and better controllability of conditions, no requirements for solvent waste and lower cost, popularity has been recently increasing. The most promising and favorable advantage of SFE is, however, the possibility to directly combine the extraction process to additional separation processes. The combination of SFE and various chromatographic techniques can be established more easily than the conventional solvent extraction technique. This review will mainly describe the potential of SFE, especially focusing on the coupling of SFE with chromatographic techniques. The review on SFC is also included since SFC is the major technique in which supercritical fluids are effectively used and no discussion concerning SFE is possible without knowledge about SFC.

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Theoretical expressions are presented for the potential step chronoamperometry, normal pulse voltammetry and cyclic voltammetry of the ion-transfer at an ion-selective microelectrode in which a polarizable nitrobenzene/water interface is formed at the tip of a micropipet of μm-order diameter with the nitrobenzene phase inside the micropipet. Experiment includes the ion transfer voltammetry of acetylcholine at the microelectrode. The experimental results are well explained by the theoretical predictions. Stripping voltammetry with the microelectrode is also studied; this proved to be promising for determination of acetylcholine at micromolar concentration levels.

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In order to compare the extractions of platinum(IV) and palladium(II) complex acids with trioctylphosphine oxide (TOPO) to those of other inorganic acids, the distribution ratio of these metals between o-xylene containing TOPO and 4.0mol/dm³ (Na, H)(Cl, HSO₄) has been measured at 298K. The extraction curves can be explained by the assumption that the dominant extracted species ratio of either platinum(IV) or palladium(II) would be 2:1:4 for proton:chlorocomplex anion:TOPO, at least in 4.0mol/dm³ chloride media. The extraction constants have been determined to be 10^5.01 for platinum(IV) and 10^4.04 for Palladium(II).

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The stoichiometries, stability constants and deprotonation constants of the complexes formed between iron(II) and either of two heterocyclic hydrazones, di-2-pyridylmethanone 2-pyridylhydrazone (DPPH) or di-2-pyridylmethanone 2-quinolylhydrazone (DPQH), have been determined spectrophotometrically at 25°C and, μ=0.2. Iron(II) reacts with DPPH and DPQH in acidic media to form a dipositively charged bis complex, Fe(HL)₂²⁺, which undergoes successive deprotonation to monocationic (Fe(HL)L⁺) and neutral bis (FeL₂) complexes, along with a decrease in the solution acidity. The acid-strengthening effect of coordinated metal on the imino group of the ligand is briefly discussed. There was no evidence for the formation of mono complexes. The logarithmic stability constants of the neutral complexes, FeL₂, were 36.8 and 33.0 for the DPPH and DPQH complexes, respectively.

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Normal pulse voltammetry with a stationary unshielded disk electrode can be used for determining the diffusion coefficients of electroactive species in an electrolyte solution if the pulse interval is sufficiently long to eliminate the effects of the preceding pulse. Two experimental examples are presented: (1) hexacyanoferrate(III) ions in 1mol dm^-3 KCl solution and (2) thallium(I) ions in 0.5mol dm^-3 KNO₃ solution. In the former example, the determined diffusion coefficient agreed with the reference value within 1%. In the latter, the agreement was less satisfactory, presumably due to the fact that the reduced form was deposited on the electrode surface.

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A sensitive flow-injection spectrophotometric method has been developed for the determination of sodium nitroprusside (SNP). The method is based on the catalytic effect of SNP on the reaction between titanium(III) chloride and an azo dye. The azo dye is formed in a 200-cm reaction coil (0.5mm i.d.) by diazotizing sulfanilamide and coupling with N-(1-naphthyl)ethylenediamine and then mixing with an SNP solution. Titanium(III) chloride solution is injected into a stream of water and merged with an SNP-dye mixture. A decolorizing reaction takes place in a 50cm coil (0.8mm i.d.) and the decrease in absorbance (ΔA), which is proportional to the SNP concentration is measured continuously at 530nm. The RSD is 0.45% (n=10) and 0.6% (n=10) for 5×10^-7M and 1×10^-6M SNP solutions, respectively. The limit of detection (twice the blank standard deviation) is 5×10^-8M (14.9ng ml^-1) SNP. EDTA interferes even at 1μg ml^-1 level on the determination of SNP.

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In order to select the matrix modifier for graphite furnace atomic absorption spectrometry, the reactions of the analyte elements with modifiers at high temperature of ashing and atomization were studied. For Se, As, Te, Cd and so forth, which have low vapor pressure and higher excitation energy, Ni, Pd or Pt modifier can be effectively applied under optimum ashing and atomization conditions. Then phase diagrams of those elements with these modifiers can be applied to consider the process of ashing and atomization.

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Serious methodological defects of the internal referencing method are revealed by quantitative studies using the bulbed capillary external referencing method. Entirely new quantitative data on solute-solvent effects fatally affecting the internal referencing method are presented and discussed. Possibilities of new solute-solvent effect studies are also suggested.

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Two fluorescence labeling reagents, 3- and 4-(2-phthalimidyl)benzoyl azide, were designed for primary and secondary alcohols for high performance liquid chromatography. These reagents, prepared from orthophthalaldehyde and aminobenzoic acid in several steps, react with alcohols at 125°C for 30min to produce the fluorescent derivatives, which can be separated on a reversed-phase column ERC-ODS-1161 with acetonitrile/water (70:30) or acetonitrile/ethanol (70:30) as eluent. The extent of conversion of cholesterol into fluorescent derivative was 100%. The detection limit for the alcohols labeled with 3-(2-phthalimidyl)benzoyl azide was 0.1-0.4pmol per injection (10μl). 3-(2-Phthalimidyl)-benzoyl azide was applied for the determination of cholesterol in human serum by high performance liquid chromatography with fluorescence detection. The values of cholesterol in normal human sera were 4.8-9.4μmol/ml.

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A newly developed surface ionization detector for gas chromatography is described. The principle of this detector is based on the surface ionization of a suitable substance to positive ions on a platinum emitter (platinum filament) which is electrically heated in an oxygen-containing atmosphere, e.g., air. The important factors that influence the creation of positive ions include the work function, temperature and atmospheric environment of the platinum emitter, as well as the ionization potential of the chemical species that are eluted from the column and contact the platinum emitter. The detector has a highly selective sensitivity to compounds having a low ionization potential. This report also refers to the analysis of compounds to which the detector has high selectivity and sensitivity.

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The separation and identification of aflatoxins and trichothecenes in submicrogram quantity by thin-layer chromatography/fast atom bombardment (TLC/FAB) mass spectrometry is reported. Separated TLC spots (R_f values given) were put directly to an FAB probe tip along with a glycerol matrix. Two dimensional TLC in the solvent systems used could separate a mixture of aflatoxins (M1, M2, B2, G1, G2) and trichothecenes (HT-2, T-2). FAB mass spectral data are characteristic in identifying individual components.

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The isolation of caffeine from coffee powder was performed using supercritical fluid extraction (SFE) and preparative supercritical fluid chromatography (SFC). Two grams of roasted coffee bean powder gave 0.49g of extract using supercritical carbon dioxide (40°C, 200kg/cm2) as an extractant. This extract was mixed with 0.6ml of methanol and after decantation, 0.2ml of the supernatant was subjected to preparative SFC. Fractionation was carried out with referring to the retention time of the standard caffeine. After evaporation of ethanol added as a modifier from the collected fraction, a 7-8mg of needle-like crystals was obtained. This crystal was identified to be caffeine by FTIR and by FT-NMR, respectively.

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Polytetrafluoroethylene (PTFE) was used as a fluorinating agent in order to facilitate a direct analysis of Cr in biological materials by electrothermal vaporization-inductively coupled plasma atomic emission spectrometry. The electrothermal vaporization parameters and the PTFE amount were optimized experimentally. The effects of different matrices on the emission signal of Cr were investigated in detail. Under the optimal conditions, the detection limit of Cr is 1.4ng ml-1 and RSD 3.8% at 0.03μg ml-1. The proposed method has advantages of sensitivity, simplicity, rapidity and no-chemical pretreatment, and has been applied to a direct determination of trace Cr in serum.

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A novel method for the fluorometric assay of horseradish peroxidase and microperoxidase activities is described based on their catalytic reactions between 1, 2-diarylethylenediamines and catechol compounds as fluorogenic substrates in the presence of hydrogen peroxide. meso-1, 2-Diphenylethylenediamine and epinephrine as a couple of substrates are most recommendable in practical use. This method is highly sensitive: the detection limits (S/N=2) are 10μU tube-1 for horseradish peroxidase and 500fmol tube-1 for microperoxidase.

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Sensitive and convenient methods for the spectrophotometric determination of nickel(II) with N, N′-bis(salicylaldehyde)ethylenediamine, N, N′-bis(salicylaldehyde)O-phenylenediamine and N, N′-bis(2-hydroxy-1-naphthaldehyde)O- phenylenediamine have been developed. The optimum concentration range evaluated by Ringbom′s method and the effect of diverse ions on the determination were also investigated. Themolar absorptivity and the Sandell sensitivity of the complexes were obtained. The present methods have been applied for the analysis of standard samples of nickel(II) in tap water and in industrial wastewater.

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Trace tellurium in urine was determined by hydride generation atomic absorption spectrometry. The urine was digested with HNO₃-HclO₄ and evaporated to dryness. Tellurium(VI) in the urine was reduced to tellurium(IV) by hydrochloric acid during the drying step. The residue was dissolved into 6M hydrochloric acid, and introduced into a hydride generation atomic absorption spectrometer. Recoveries of tellurium added to urine samples ranged from 90 to 95%, the relative standard deviation was 9% at the 0.1μg level. The tellurium contents in urine ranged from 0.02 to 1.63μg l-1.

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A new sensitive chromogenic reagent, 2-[(5-nitro-2-pyridyl)azo]-5-dimethylaminobenzoic acid (5-NO₂-PAMB), was synthesized and applied to the determination of nickel in aqueous solutions. This sensitive chromogenic reagent has a molar absorptivity (ε) of 1.64×10⁵l mol^-1 cm^-1 to nickel, and has excellent solubility in water. The reaction requires no heat or organic solvent. The reagent can react immediately with nickel at room temperature to form a blue complex with maximum wavelength of 631.2nm. The concentration of the linear range was 0.008-0.88μg/ml. Using this new reagent to determine nickel in a low-alloy steel sample, we obtained satisfactory results.

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In this study, a two-step preconcentration procedure is proposed to be used in conjunction with ICP-AES for the determination of trace metals in seawater. The two-step preconcentration involves extraction of trace metals from seawater with dithiocarbamate (DTC) into chloroform followed by back-extraction with a Pd²⁺ solution. The extraction could concentrate the trace metals by forming a chelate with DTC with a high enrichment factor obtained with the large phase volume ratio. The back-extraction agent Pd²⁺ is selected because the extraction constant of Pd(DTC)₂ is the largest and much higher than most of the other metal dithiocarbamates. The enrichment factor could be further enhanced at the back-extraction step with a large phase volume ratio. Finally, the aqueous solution containing simply the enriched metals and some of the nonreacted Pd²⁺ was taken for ICP-AES.

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1-(2-Pyridyl)-3-phenyl-5-anthryl formazan (PAnthPF), 1-(2-quinolyl)-3-phenyl-5-anthryl formazan (QAnthPF) and 1-(2-quinolyl)-3, 5-Biphenyl formazan (QPPF) were prepared and their acid dissociation constants and metal complex stability constants were investigated. The investigation involved the following metal ions: copper(II), zinc(II) and cadmium(II). QAnthPF reacts with metal ions to form complexes with intense color. The zinc(II) complex is red whereas the cadmium(II) complex is bluish green, the difference in their absorption maximum wavelength (Δλmax) is remarkably large (110nm).

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Chelating polymer bearing 2-(2-diazolylazo)phenol moiety was synthesized and its metal adsorption properties for 6 divalent heavy metal ions (M²⁺): Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Cd²⁺ and Pb²⁺ were investigated. The polymer changed color from orange yellow to blue or to red violet with its chelation to Cu²⁺ or to Ni²⁺, respectively. The maximum capacity of the polymer for Cu²⁺ was found to be 1.35meq/g in pH 5.71 solution. The degrees of saturation of the capacity of the polymer after shaking for 30min were 71.3 and 83.6% for the adsorptions of Zn²⁺ and Cu²⁺, respectively. The capacity of the polymer for M²⁺ hardly varied with the presence of alkali or alkaline earth metal ions. The elimination of metals from the polymer-M²⁺ chelates was achieved with 4mol/l HCl or 4mol/l H₂SO₄ solution.

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A method for the kinetic determination of nanogram amounts of nitrite based on its acceleration of the rate of bromination of pyridine-2-aldehyde 2-pyridylhydrazone in acidic medium has been developed. The reaction is followed by fluorometry while monitoring the formation of a fluorescent product using an excitation wavelength of 291nm and an emission wavelength of 432nm. The kinetic methods of the initial rate and induction period have been assessed regarding their analytical performance, the latter showing improved capabilities. This method has been applied to drinking water analysis, with a detection limit of 4.6ng/ml and recoveries of 92-105%. The relative standard deviation of the method is 2.4%. The major advantages of this method are simplicity, absence of a reagent blank, selectivity and sensitivity.

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A microamount of bulk oxygen in ultra-pure iron was determined separately from surface-contaminated oxygen by a surface-area-variation method. In this method, the total oxygen values (μg/g) for specimens with different specific surface areas were determined by means of a vacuum fusion analysis, and were plotted against the specific surface areas (cm²/g); the quantity of oxygen in the bulk (μg/g) was determined from the intercept of the regression line and the oxygen quantity per unit area of surface (μg/cm²) from the slope. A surface treatment method capable of controlling the depth of the surface oxygen layer at an atomic level was developed in order to prevent scattered bulk oxygen values caused by an irregular surface oxygen layer. Specimens were etched in a mixed solution of hydrogen peroxide, hydrofluoric acid and de-ionized water (volume ratio 17:1:2) under an argon atmosphere. A high sensitivity vacuum fusion gas analyzer with a Pirani gauge was used in this experiment. Bulk oxygen over 0.03μg/g in ultra-pure iron could be analyzed independently from the influence of surface oxygen. Bulk oxygen in an electrolytic pure iron sample was determined as 0.08±0.004μg/g with surface oxygen of 0.31±0.001μg/cm².

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