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Speciation analysis calls for rapid, simple systems for minimizing errors made in the most troublesome of all steps in the analytical process: sample preparation. In this context, continuous-flow systems are of great help. The evolution in the different methodologies enabled solutions to the main shortcomings occurring from the lack of selectivity of using RP–C18as sorbent material. One solution was a shift to more sensitive and selective, but only partially automated, systems employing C60fullerene and Grignard’s reagent; another was a shift to completely automated systems employing sodium tetrapropylborate; and a final solution was to employ the simplest possible configuration by removing the reagent stream. The analytical methods developed allowed the identification and quantification of different organolead species at the pg/ml levels in rainwater samples, with precision (RSD) of about 5% and recoveries ranging from 92 to 100%.

We report a low cost selective analytical method based on inner filter effect (IFE) for citrate-silver nanoparticle (cit-AgNP) detection, in which fluorescent amine-derivatized carbon dots (a-CDs) act as the donor and aggregated cit-AgNPs as the energy receptor. Carbon dots (CDs) were chemically modified with ethylenediamine (EDA) moieties via amidic linkage displaying an emission band at 440 nm. The presence of cit-AgNPs produces a remarkably quenching of a-CD fluorescence via IFE, since the free amine groups at CD surface induce the aggregation of cit-AgNPs accompany by a red-shifting of their characteristic plasmon absorption wavelength, which resulted in “turn-on” of the IFE-decreased in CD fluorescence. The proposed method, which involves the use of chelating agents for removal of metal ions interferences, exhibits a good linear correlation for detection of cit-AgNPs from 1.23 × 10−5 to 6.19 × 10−5 mol L−1, with limits of detection (LOD) and quantification (LOQ) of 5.17 × 10−6 and 1.72 × 10−5 mol L−1, respectively. This method demonstrates to be efficient and selective for the determination of cit-AgNPs in complex matrices such as cosmetic creams and reveals many advantages such as low cost, reusability, high sensitivity and non time-consuming compared with other traditional methods.

A homogeneous liquid-liquid microextraction alternative, based on the use of switchable hydrophilicity solvents, is presented. The extraction technique makes use of 125 μL of a water-immiscible solvent (N,N-dimethylcyclohexylamine) that can be solubilized in the aqueous phase in 1:1 ratio using CO2 as a reagent. After the extraction, phase separation is induced by the addition of sodium hydroxide that produces a change on the ionization state of the amine, and centrifugation was not necessary. The extraction technique has been optimized and characterized using the determination of triazine herbicides by gas chromatography with mass spectrometry in water samples. The presence of metallic ions in environmental waters as interferents is easily avoided by the addition of ethylenediaminetetraacetic acid before the microextraction procedure. The proposed method allows the determination of the target analytes at the low microgram per liter range with good precision (relative standard deviation lower than 12.5%).

In this article, the easy synthesis of magnetic nanoparticles-nylon 6 composite is presented, characterized and applied in the microextraction field. The one-step synthesis of the composite is performed by a solvent changeover playing with the different solubility of the polymeric network in formic acid and water. The new material has been characterized by different techniques including infrared spectroscopy, transmission and scanning microscopy. The extraction performance of the composite under a dispersive micro solid phase extraction format has been evaluated by determining four polycyclic aromatic hydrocarbons (benzo[b]fluoranthene, fluoranthene, indeno[1,2,3-cd]pyrene and phenanthrene) in water using ultra performance liquid chromatography (UPLC) combined with photo diode array detection. The developed methodology allows the determination of the analytes with limits of detection in the range from 0.05 μg/L (benzo[b]fluoranthene) to 0.58 μg/L (phenanthrene). The repeatability of the method was better than 6.9% at the limit of quantification level. The relative recoveries varied in the interval 80-111%.

In situ chiral derivatization was used to obtain diastereomeric amides of ibuprofen for their subsequent extraction with supercritical carbon dioxide. For this purpose, ibuprofen [racemic 2-(4-isobutylphenyl)propionic acids] was previously extracted on a C-18 SPE device and quantitatively transferred into the supercritical fluid extraction (SFE) vessel for derivatization and extraction with ( R )-1-(naphthen-1-yl)ethylamine as chiral derivatizing base, and a mixture of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide and 1-hydroxybenzotriazole as reagents, in order to obtain and extract the corresponding diastereoisomeric amides, which were subsequently determined by liquid chromatography. The influence of different extraction and derivatization variables (pressure, temperature, extraction time in the static and dynamic extraction modes, and amount of chiral base) on the extraction efficiency was studied. Spiked and native urine samples containing ibuprofen were used to demonstrate the application of this method. The absolute recovery, selectivity, precision and accuracy of the combined solid-phase extraction (SPE)/SFE approach were compared to those provided by conventional liquid–liquid extraction. The results indicated that SFE seems to be an effective choice for in situ derivatization since analysis times and solvent consumption were dramatically reduced.

The use of a solid electrode in routine analytical work is proposed as a good alternative for electroanalytical detection. The performance of the electrode for oxidative voltammetry was studied for the model compound, catechol. Some theoretical aspects of the preparation and features of the PVC-graphite composite electrode are shown. A protocol has been described for its construction and general advice for the appropriate use. Quality control activities were designed to check the performance of the electrode.

A slurry electrothermal atomic absorption spectrometric technique was used to determine Ni and Cr in wheat flour and its by-products. Slurries (3%, w/v) were prepared in a mixture of 15% HNO3–10% H2O2 as suspended medium. Differences in Ni and Cr contents due to origin and texture of the wheat and to the effects of the milling process were studied. Ni and Cr levels were more markedly influenced by the geographical origin of the wheat than by its texture. Both metals were related to the amount of bran present in each milled fraction and varied over the ranges of 212–298 ng/g (Ni) and 34–85 ng/g (Cr) in flours (with minimal bran contents); 297–460 ng/g (Ni) and 67–118 ng/g (Cr) in shorts; and 424–723 ng/g (Ni) and 106–165 ng/g (Cr) in brans. The Ni and Cr contents were not significantly affected by the technological processes typically performed in a flour-producing factory.

A screening method has been developed for the determination of 23 organochlorine pesticides (OCPs) and 3-pyrethroid metabolities [cis- and trans-3-(2,2-dichlorovinyl)-2,2-dimethyl-(1-cyclopropane) carboxylic acid, cis-3-(2,2-dibromovinyl)-2,2-dimethyl-(1-cyclopropane) carboxylic acid and 3-phenoxybenzoic acid] from human urine. OCPs were directly detected in urine samples while pyrethroid metabolites required acid-induced hydrolysis to convert their conjugates into free acids; all compounds were then cleaned-up/preconcentrated using solid phase extraction. Determination and quantitation was achieved by gas chromatography with a mass spectrometer detector operating in selected ion monitoring mode. Limits of detection varied between 0.1 and 0.3 ng/mL with linear ranges from 0.3 to 700 ng/mL; the precision of the method was high (4.3-7.2%). Recoveries of all analytes from urine samples fortified at levels of 30 ng/mL for each OCP and 15 ng/mL for each pyrethroid metabolite ranged from 88 to 101% (captan gave the lowest recovery). The results obtained from the analysis of real urine samples show the suitability of the proposed method for monitoring people exposed to organochlorine and pyrethroid pesticides.

Two phenoxyacid herbicides (2,4-D and MCPA) and their six corresponding phenols were determined in soil by using gas chomatography with electron impact mass spectrometry (GC/MS) for confirmation/quantitation. An automatic extraction (leaching), preconcentration, and cleanup (sorption) module was developed to extract the eight compounds from soil. The average recovery of all species, spiked to soil at microg/kg-mg/kg levels, was 95% (average standard deviation +/- 5%). A plot of agricultural clayey soil (approximately 12 m2) was contaminated with both herbicides (approximately 96 g/m3, depth 10 cm, density 1.23 g/cm3) and irrigated with (17 mm) at variable time intervals. Both herbicides and their corresponding phenol compounds were monitored at different soil depths over a 50 day period. The degradation of both herbicides in the surface layer (t(1/2) approximately 5 days) is a result of photodecomposition and microbial action; in the deeper layers, the degradation products occur in lower proportions by effect of leaching and are also the result of microbial action. The six phenol metabolites are only detected in the surface layer as they form preferentially by photodecomposition. The main metabolites (viz. 2,4-DCP for 2,4-D and 4-C-2-MP for MCPA) are formed within 24 h after the soil is contaminated; their concentration peaks are at day 8 in the absence of irrigation.

A systematic approach to selectivity in chemical analysis is presented and discussed. The conventional definition of this property is completed by considering its relationships with analytical errors, other analytical properties, chemical measurement processes and sample composition. The different types of interferences as well as the parameters used for a mathematical description of selectivity and the strategies to increase it are also systematically described. The manipulation of selectivity for circumventing legal regulations is mentioned as representative of the importance of this feature.

A gas extraction sampling device integrated in a continuous flow system (CFS) was coupled to a capillary electrophoresis equipment (CE) for the direct determination of trimethylamine (TMA) and related amines in fish sample. This arrangement allowed the direct introduction and treatment of these solid samples with a high level of automation. The amine compounds were extracted from fish samples in the sampling unit, then they were conditioned in the CFS and injected into the CE vials via a programmable arm. Methylamine, dimethylamine, trimethylamine, ethylamine, propylamine, diethylamine and triethylamine were separated and quantified. The concentration of trimethylamine (the major amine in fish) in the analysed real sample was ranged from 20 to 250 mg g−1.

Eosin has been used to generate the background signal for indirect fluorimetric detection of inorganic and organic ions, simultaneously separated by capillary zone electrophoresis (CZE). This reagent provides constant fluorescence over the pH range of 5–10 and is compatible with the excitation by an argon ion laser at 488 nm with emission at 520 nm. The use of esosine as fluorophore, H 3 BO 3 , and Na 2 B 4 O 7 as electrolyte and diethylentriamine as modifier of the electroosmotic flow in CZE were optimised. The analytical potential of the studied buffer was tested on a group of 12 anions, used as model compounds. Both, hydrodynamic and electrokinetic injection mode were optimised. The detection limits determined by the last injection mode, were in the range 0.008–0.037 mg l −1 . By using this method, the quantitation of the common anions in tap and mineral water has been carried out successfully.

This paper reports a fast, simple procedure for the direct screening of biological fluids by using a flow configuration coupled on-line to an evaporative light scattering detector with no chromatographic separation. The potential of this coupling was exemplified for paracetamol. The configuration adopted permits selective retention of paracetamol and its metabolites from dilute urine or serum samples on a LiChrolut®EN sorbent column located in the loop of a high pressure injection valve. Retained paracetamol is eluted with acetonitrile and driven directly to the evaporative light scattering detector. Some analytical features are: detection limit 0.3 μg ml−1, quantitation interval 1–100 μg ml−1, repeatability, as RSD, 1.0%. The reliability of the method was studied at three concentration levels of paracetamol spiked to urine or serum blanks (1, 2 and 4 times the detection limit) yielding 0% of false positives and negatives, thanks to the high precision of the method. Finally a comprehensive study of 50 real urine samples (paracetamol free) obtained from different individuals (healthy, drug addicts and patients from a hospital) provided 4% of false positives and 0% false negatives for the threshold limit established.

A new, automatic method for the clean-up, preconcentration, separation, and quantitation of nonsteroidal anti-inflammatory drugs (NSAIDs) in biological samples (human urine and serum) using solid-phase extraction coupled on-line to capillary electrophoresis is proposed. Automatic pretreatment is carried out by using a continuous flow system operating simultaneously with the capillary electrophoresis equipment, to which it is linked via a laboratory-made mechanical arm. This integrated system is controlled by an electronic interface governed via a program developed in GWBasic. Capillary electrophoresis is conducted by using a separation buffer consisting of 20 mM NaHPO4, 20 mM beta-cyclodextrin and 50 mM SDS at pH 9.0, an applied potential of 20 kV and a temperature of 20 degrees C. The analysis time is 10 min and the detection limits were between 0.88 and 1.71 microg mL(-1). Automatic clean-up and preconcentration is accomplished by using a C-18 minicolumn and 75% methanol as eluent. The limit of detection of NSAIDs can be up to 400-fold improved when using sample clean-up. The extraction efficiency for these compounds is between 71.1 and 109.7 microg mL(-1) (RSD 2.0-7.7%) for urine samples and from 77.2 to 107.1 microg mL(-1) (RSD 3.5-7.1%) for serum samples.

The micellar electrokinetic capillary chromatographic method for the determination of monoterpenes such as camphene, α-pinene, β-pinene, γ-terpinene, α-terpinene, terpinolene and p-cymene was established. Addition of cyclodextrins (CDs) to the buffer solution permits the separation of these monoterpenes. The separation is dependent on the type of CD, and gamma-CD was the most effective cyclodextrin, in the method here developed. The method permits low concentrations of monoterpenes to be separated and detected. The addition of an organic solvent (acetonitrile) as modifier in the buffer (10 mM NaH2PO4, 6 mM Na2B4O7, 50 mM SDS, 7 mM de γ-CD) allowed this separation. The analysis was performed with a positive power supply of 20 kV at a temperature of 25°C. The samples were hydrostatically (5 s) introduced into the anodic end of the capillary and electropherograms were recorded at 200 nm. This method could be highly suitable for the separation and determination of monoterpenes in essential oils of leaves, and the flowers of marjoram and oregano among other real samples. © 2001 John Wiley & Sons, Inc. J Micro Sep 13: 293–299, 2001

The paper establishes a distinction between “screening” and “analysis”, as well as between “analyte screening” and “sample screening” in the context of analytical sciences. The paper then deals with the main relationships between screening and chromatography; analyte screening using chromatographic techniques, sample screening before the implementation of chromatographic and electrophoretic separation and the use of such techniques to confirm and expand the binary information provided by sample screening systems.

The principal aim of this article is to emphasize the need to systematically consider analytical chemistry as an information discipline on the basis of two essential ingredients of analytical quality, namely: chemical metrology and fitness for purpose. To this end, five different types of analytical information (true, referential, delivered, required and perceived) are defined, and binary and ternary relationships among them are discussed. In so doing, crucial analytical facets are precisely placed within the framework of analytical information. The role of the `client' (viz. the person or body requiring the analytical information) is also systematically considered.

Two spectrophotometric methods, a photochemical and a non-photochemical, for the determination of ascorbic acid in soft drinks and beer using a flow-injection system are proposed. The non-photochemical method is based on the redox reaction that takes place between ascorbic acid and Fe(III), yielding dehydroascorbic acid and Fe(II). Fe(II) reacts with 1,10-phenantroline, originating the reddish orange Fe(phen)3(2+) complex (ferroin). This complex is spectrophotometrically monitored at 512 nm, and the signal is directly related to the concentration of ascorbic acid in the sample. The photochemical method has the same basis, nevertheless, uses the irradiation with visible light to enhance the redox reaction and so achieve higher sensitivities in the analysis. The non-photochemical method shows a linear range between 5 and 80 microg mL(-1), with a relative standard deviation of 1.6% (n = 11), a detection limit of 2.7 microg mL(-1) and a sample throughput of 60 samples h(-1). The photochemical method shows a linear range between 1 and 80 microg mL(-1), with a relative standard deviation of 1.0% (n = 11 ), a detection limit of 0.5 microg mL(-1) and a sample throughput of 40 samples h(-1).

A supported liquid membrane system has been developed for the extraction of vanillin from food samples. A porous PTFE membrane is impregnated with an organic solvent, which forms a barrier between two aqueous phases. The analyte is extracted from a donor phase into the hydrophobic membrane and then back extracted into a second aqueous solution, the acceptor. The determination (100–1400 μg ml−1 vanillin) was performed using a PVC-graphite composite electrode versus Ag/AgCl/3MKCl at +0.850 V placed in a wall-jet flow cell as amperometric detector. The solid sample is directly placed in the membrane unit without any treatment, and the analyte was extracted from the sample, passes through the membrane and conduced to the flow cell by the acceptor stream. The limit of detection (3σ) was 44 μg ml−1. The method was applied to the determination of vanillin (9–606 μg g−1) in food samples.

An on-line supercritical fluid extraction-piezoelectric detection system was developed and applied to the quantitative gravimetric determination of total fat in food samples (skimmed milk and cocoa). The proposed assembly provides all the advantages of an on-line system as regards automation, in addition to acceptable sensitivity and precision. Its strength lies in the design of the interface between the supercritical fluid extractor and the piezoelectric detector. Samples of skimmed milk and cocoa are weighed in the extraction thimble, previously loaded with 1 g of diatomaceous earth. A temperature of 100°C and a CO 2 fluid density of 0.60 mg/ml are used for extraction. The linear calibration range thus achieved is 0.005–0.07% w/w total fat, and the relative standard deviation is ±2.3% ( n =11; P =0.05). The throughput is six samples h −1 (for the overall process). The proposed method was used to determine the total fat in food samples (milk, cocoa), the results being competitive with those of the Soxhlet methods for the same purpose.

A simple and novel screening method for lead compounds in environmental waters is proposed. The analytes, in an acetic medium, are sorbed on a C 60 fullerene column as diethyldithiocarbamate complexes and subsequently eluted with isobutyl methyl ketone (IBMK), the lead being determined by flame atomic absorption spectrometry. The screening method acts as filter and indicates whether the target analytes are present above or below the detection limit of the method (0.5 ng/mL), giving no false positives. Positive samples were speciated by GC/MS, using a flow system similar to that of the screening method. Lead(II) and ionic di- and trialkyllead are derivatized with a Grignard reagent. Both methods use similar chemical and flow variables except for the eluent, IBMK in the screening method and n-hexane in the speciation method. The GC/ MS speciation method is very sensitive; it exhibits a linear range of 0.02-5 ng/mL, and detection limits of 1-4 ng/L are achieved. Also, its repeatibility, as RSD, is less than 6%. The method was applied to the speciation of Pb 2+ and di- and trialkyllead in positive prescreened rainwater samples from three different urban areas.

In this work, the analytical potential of C60 fullerene as a sorbent for organic and organometallic compounds from aqueous solutions was studied for the first time. Fullerene adsorbs many types of organic substances (e.g., N-methylcarbamates, phenols, polycyclic aromatic hydrocarbons, amines) with efficiencies that depend on the nature of the compound concerned and never exceed 60%. Conventional sorbents such as XAD-2 or polyurethane foam are more efficient than C60 for this purpose. Organometallic compounds (viz. metalocenes and organoleads) are quantitatively adsorbed on C60 via the formation of neutral complexes or chelates; the adsorption constant is dramatically increased by the use of classical reagents such as pyrrolidinedithiocarbamate or diethyldithiocarbamate. A complementary comparative study on the adsorption of organometallic complexes on RP-C18 and silica gel 100, among others, showed C60 to be superior as sorbent. All experiments in this work were carried out by using continuous flow configurations and gas chromatography-atomic absorption spectrometry techniques.

A fully automated urinary screening system for paracetamol and its metabolites is proposed. The method comprises on-line acid microwave assisted hydrolysis of the drug to p-aminophenol followed by reaction with o-cresol in alkaline medium. The indophenol blue dye formed can be continuously monitored at 620 nm. The detection limit achieved, 0.1 μg ml−1, allows a high dilution of the samples, thus reducing potential interferences from the sample matrix (mainly protein degradation during urine hydrolysis). The proposed screening system also possesses an adequate selectivity, as the major interferent, epinephrine, is tolerated at concentrations higher than those that could be found in the positive urine samples. The reproducibility, expressed as relative standard deviation, was 3.0% and the sample frequency 20 h−1. The reliability of the method was established at five concentrations (between 0.5 and 4 times the detection limit). Finally, it was applied to the screening of several human urine samples. The results obtained were compared with those provided by batch acid hydrolysis, and were similar in all instances.

A simple, rapid method for the spectrophotometric discrimination of monosaccharides from the oligosaccharide fraction of fruit juice, jam, syrup and honey samples is proposed. The sample, in alkaline medium, is directly introduced into a flow system and passed through an activated carbon column for its decolourization; then, a volume of 200 μl is injected into the derivatising reagent stream to start the analytical reaction, which takes place at 85°C. The two fractions are discriminated on the basis of the different colours of the derivatives formed; thus, the derivatives of the monosaccharides are yellow while those of the di- and trisaccharides are violet-carmine. The two fractions are monitored at 400 and 540 nm, respectively. Sucrose gives no reaction as it is a non-reducing sugar. The proposed method allows reducing sugars contents from 0.01% to 0.80% w/v to be determined with an average relative standard deviation of 4.5% and a sampling frequency of 10 h−1. The proposed method was validated by applying it to two milk-based and sugar candidate artificial CRMs, with good correlation. The detection limits achieved (0.01% w/v for maltose, lactose and maltotriose at 540 nm) allow adulteration of fruit juices with high fructose syrup from starch at the 4% level to be detected.

A simple flow injection system for the on-line preconcentration of metal dithiocarbamates (fungicides) by sorption on a C60 fullerene column was developed. Neither the acid hydrolysis needed by the conventional method to release CS2 nor derivatization is required as the fungicides are directly retained on the sorbent column and subsequently eluted from it with dilute HNO3. The eluted fraction is directly fed into a flame atomic absorption spectrometer. Group speciation can be done according to the metals present in the dithiocarbamate (viz., dithiocarbamates of Zn2+, Mn2+, or Fe3+) but no within-group discrimination is possible (ziram, zineb and propineb provide a global response). The analytical figures of merit of the proposed method are as follows: limits of detection (3ς) from 1 to 5 ng ml−1; precision (RSD) ca. 2.5%; and preconcentration factor 45 (using 10 ml of sample). No interference from metals such as Zn, Mn or Fe, as inorganic salts, was observed. The method was applied to the resolution of synthetic mixtures as well as to the speciation/determination of ziram, maneb and ferbam in spiked grain samples, all with acceptable recoveries.

The separation of seven pesticides by micellar electrokinetic capillary chromatography in spiked water samples is described, allowing the analysis of pesticides mixtures down to a concentration of 50 μg l−1 in less than 13 min. Calibration, pre-concentration, elution and injection into the sample vial was carried out automatically by a continuous flow system (CFS) coupled to a capillary electrophoresis system via a programmable arm. The whole system was electronically coupled by a micro-processor and completely controlled by a computer. A C18 solid-phase mini-column was used for the pre-concentration, allowing a 12-fold enrichment (as an average value) of the pesticides from fortified water samples. Under the optimal extraction conditions, recoveries between 90 and 114% for most of the pesticides were obtained.

Although capillary electrophoresis (CE) with photometric detection is a well-established technique for the determination of various inorganic ions, its limited sensitivity has hindered greater development in this area. In this work, we used a mixture of metals consisting of Co(II), Ni(II), Zn(II) and Mn(II) to demonstrate that the sensitivity of CE with ultraviolet-visible (UV-vis) detection can be improved by using chromogenic reagents such as porphyrins. To this end, the metals were reacted with 5,10,15,20-tetrakis(4-sulphophenyl)-porphine dodecahydrate (TPPS(4)) to obtain their respective porphyrinato complexes, which were then separated by CE with a citrate buffer and detected at 410 nm. The ensuing electrophoretic method has a limit of detection (LOD) of 3 x 10(-6) M (180 microg L(-1)) for Co(II), 2 x 10(-10) M (0.012 microg L(-1)) for Ni(II), 4 x 10(-6) M (260 microg L(-1)) for Zn(II) and 4 x 10(-9) M (0.219 microg L(-1)) for Mn(II). The method is a highly promising choice for the ultratrace determination of Ni(II) and Mn(II).

A new method for the speciation of inorganic lead and trialkyllead compounds involving the selective separation of the analytes in a continuous system and their subsequent introduction into a flame atomic absorption spectrometer was developed. The proposed flow system consists of two units. In the first unit, total inorganic lead at concentrations from 8 to 200 ng ml−1 is continuously precipitated as lead chromate and the filtrate, containing trialkyllead cations, is collected in a vessel, the precipitate then being dissolved in diluted acid and driven to the instrument. In the second unit, trimethyllead (TML+) and triethyllead (TEL+) cations at ng ml−1 levels are complexed with sodium diethyldithiocarbamate and retained on a C60 pre-conditioned fullerene column; the mixture of both species was resolved by conditioning the sorbent column with n-hexane or isobutyl methyl ketone solvents. Detection limits of 1–2 ng ml−1 can be achieved by using a sample volume of 50 ml. Special attention was given to the reliability and robustness of the global flow injection method in assessing its applicability to both types of organolead compounds and inorganic lead present in different proportions. Trimethyllead provides the poorest results as consequence of its low adsorption constant on C60; however, the three different types of species (Pb2+/TML+/TEL+) can be effectively determined in proportions from 1:1:1 to 30:12:1 with relative errors less than 10%.

Continuous flow systems have easily been coupled to a evaporative light scattering detector for screening purposes. The interface was constructed by means of a high pressure line consisting of a high pressure pump and a high pressure six-port injection valve. This design allows sample preparation (clean-up and preconcentration) and separation to be done automatically. The universal response provided by the detector permits the screening of a variety of analytes in different samples.

One of the most relevant bottlenecks of the progress of analytical sciences is the existence of adequate references in general and, in particular, of measurement standards for analytical processes and their proper use in the context of metrology in chemistry. Keywords such as traceability, uncertainty, calibration, etc. are crucial to characterise the analytical information. All of them can be summarised by using reliability as an overall analytical attribute. The main aim of this paper is the systematic consideration of this basic approach among the trends in Analytical Chemistry, particularly in qualitative analysis.

The state of the art and the potential of sample screening systems (SSS) for the expeditious, reliable selection of samples to meet the requirements of customers and legislation is presented and discussed. The underlying procedures use simple equipment and operations and provide a yes/no binary response that occasionally requires confirmation. After a brief discussion of the distinction between `screening' and `analysis' and the principal features of analytical screening systems, the main aims and features of SSS are presented. Several classifications of these allow one to offer a general view of the topic. Representative examples are classified according to the complexity of the sample pretreatment required, and are used to demonstrate the impact SSS may have on analytical chemistry in the next century.

A systematic procedure to check the performance of the PVC-graphite composite electrodes used in routine amperometric and voltammetric measurements is proposed. After careful preparation of the composite material and packing it in the appropriate electrode body, a list of tests is proposed (background signal characteristics, reversibility, baseline restoration, sensitivity and precision) for the rapid checking of the quality of the electrode built. Some quality control strategies were designed in order to assure that the validation conditions were fulfilled for long-term analytical work. Thus, a final protocol can be suggested for this kind of electroanalytical work, as well as some final recommendation from a quality point of view.

A method for the determination of caffeine in coffee and tea samples based on the use of supported liquid membranes coupled to a flow system has been developed. The sample may be analysed both as solid and slurry. In the case of solid sample, this is directly placed in the membrane unit, and when the sample is slurry, this is continuously pumped to the membrane unit. In both cases, the caffeine released from the sample passes through the membrane (PTFE/ n -undecane:hexyl ether) into an acidic acceptor stream. This stream flows through a spectrophotometric detector allowing the measurement of the absorbance of caffeine at 274 nm. The method shows a linear range between 0.5 and 15 g l −1 , with a relative standard deviation of ±3.7% and a sample throughput of 7–8 samples h −1 .

A new method was developed and validated for the determination of chlorophenols in human urine by using micellar electrokinetic chromatography (MEKC) coupled via a mechanic arm to an on-line automatic clean-up and preconcentration unit for urine samples. Separation is accomplished by using a selective buffer consisting of 15 mM borate, 25 mM phosphate and 100 mM sodium dodecyl sulfate (SDS) at pH 9.1 in addition to a positive power supply of 25 kV at 18 degrees C. The proposed capillary electrophoresis (CE) method allows the separation of 11 chlorophenols within 7 min with a reproducibility as relative standard deviation (RSD) between 2.6% and 7.2%, and limits of detection (LODs) between 0.08 and 0.46 microg/mL for all chlorophenols. Urine samples were previously hydrolyzed with 37% HCl at 80 degrees C for 60 min and then cleaned on a C-18 mini-column. Recoveries ranged from 58% to 103%. The preconcentration treatment affords limits of determination between 4 and 12 ng/mL for all chlorophenols except pentachlorophenol and 4-chlorophenol, which could not be determined. The overall analysis time, including on-line clean-up, preconcentration and electrophoretic separation is 20 min per sample.

Traceability is the foundation of any metrological science. Traditionally this term has been associated with the results of a particular measure as synonymous with the accuracy or reliability of such results (i.e., a certain level of quality). It ensures a clear (unbroken) relationship between results and the corresponding samples by using appropriate standards and calibrated equipment. This simple principle can be easily implemented in physical measurements, in which – commonly – the measurement process is mainly performed by the simple use of a (single) calibrated equipment. The case of chemical measurements is quite different because only the measurement step of the analytical process can be calibrated, but not the other steps. As measurements have a clear sample dependence, standards are not available in many situations. Therefore, the term metrology in chemistry needs to relate to a wider meaning of traceability, more addressed to a practical approach which is useful for end users (chemists and clients). Some adaptations are needed if a rational use of the term is to be applied to routine analytical work. In this article we propose a more practical and flexible view of term, `traceability' in the field of metrology in chemistry.

Whereas the concept of quality control and quality assurance is well understood by modern laboratories (either commercial or with national responsibilities) which are accredited in various analytical sectors, there is an enormous gap in the transfer of knowledge to smaller laboratories. A strong and urgent need has been highlighted for improving the measurement infrastructure in Europe, particularly in less favoured regions or countries. This article gives a summary of needs expressed in the course of five workshops funded by the Standards, Measurements and Testing Programme (European Commission) and held, respectively, in Greece, Ireland, Italy, Portugal and Spain.

A spectrophotometric method for the determination of lactic acid in milk samples based on the use of a photochemical reaction carried out in a Flow Injection System is proposed. Determination is based on the reaction between lactic acid and Fe(III), which is reduced to Fe(II) in the presence of UV light, being the latter made to react with o -phenanthroline. The complex formed between Fe(II) and o -phenanthroline, Fe( o -phen) 3 2+ (ferroin) is a coloured compound and it can be spectrophotometrically monitored at 512 nm. The method shows a linear range between 0.5 and 50 μg ml −1 with a limit of detection of 0.16 μg ml −1 . The precision was ±2.15 expressed as relative standard deviation ( n =11) and the sample throughput of 30 samples h −1 . Also non-linear adjustments have been made and validated by ANOVA. The proposed method has been applied to the determination of lactic acid in both synthetic and milk samples.

A partially automated gas chromatographic method for the simultaneous determination of antioxidants (tert.-butyl-4-hydroxyanisole, 2,6-di-tert.-butyl-p-hydroxytoluene, tert.-butylhydroquinone, alpha-tocopherol and alpha-tocopheryl acetate) and preservatives (sorbic acid, benzoic acid and their esters) in fatty foods without derivatization is reported. About 95% of triglycerides from lipid material are avoided by manually extracting the samples with a mixture of solvents and the remaining by using a continuous solid-phase extraction system. By using aqueous sample solutions (in 0.1 M HNO3), XAD-2 sorbent and selective elution with 200 microliters of 2-propanol, only ca. 0.03% of total triglycerides present in the original sample remains in the final extract. Manual injection of the extract into a GC-flame ionization detection allows the additives to be determine at concentrations in the range 0.5-100 micrograms/ml with a high precision (ca. 3%). Mass spectrometry in the conventional electron impact mode, in conjunction with library search, permits the unequivocal identification of all the additives. Margarine, oil, cheese, pâté and sauce samples were analysed in this way, all with good results.

A module for the continuous extraction and preconcentration of phenol compounds from soils was developed which comprised a soil extraction unit, a preconcentration unit, and an interface between th...

Software that implements the SIMPLEX optimisation method and the quality requirements of laboratories working on various tasks was developed. The program presents the users with different optimum experimental conditions according to preselected quality criteria, these variables being subsequently subjected to robustness test. This methodology is based on the development of a special response function from the area of a polygon constructed from four main variables, viz. sensitivity, precision, cost and throughput, each of which is weighted by a `quality coefficient'. In this way, the principal parameters that define overall analytical quality are integrated and weighted in order to obtain information on the quality parameters on which the quality policy of a given laboratory relies. The system was used to optimise the flow injection method for the determination of furfural with aniline. The results obtained are discussed, and the design of the apparatus and software is commented on.

The slurry technique was applied to the determination of Ni, Cr and Co in wheat flour by electrothermal atomic absorption spectrometry (ETAAS). The influence of the graphite furnace temperature programme was optimized. Optimum sensitivity was obtained by using a mixture of 15% HNO(3)-10% H(2)O(2) as suspended medium for a 3% w/v slurry in the determination of Ni; lower concentrations of HNO(3) were necessary for the determination of Co and Cr (viz. 5 and 10%). The precision of direct analyses of the slurries was improved by using mechanical agitation between measurements; thus, the RSD of the measurements was ca. 5% for repeatability. The direct slurry sampling (SS) technique is suitable for the determination of Ni and Cr in wheat flour samples at levels of 150-450 and 30-72 ng g(-1), respectively, as it provides results similar to those obtained by ashing the sample. However, the typically low level of Co in these samples precluded its determination by the proposed method (the study was made in an SRM spiked wholemeal flour), at least in those samples that were contaminated with elevated concentrations of the metal (viz. more than 90 ng of Co per g of flour). The method provides a relative standard deviation of 6, 8, and 4% for Ni, Cr, and Co, respectively.

On-line ion-exchange preconcentration, performed in a flow injection analysis system, has been integrated with capillary electrophoresis via a specially designed interface, and a sensitive and selective method for the determination of nitrite, nitrate, bromide and iodide using direct UV absorbance detection has been developed. Fivefold enrichment of these aforementioned anions can be realised. Separation conditions such as carrier electrolyte and concentration of electroosmotic modifier were investigated. Limits of detection were ca. 10 ng ml−1 for nitrite and nitrate in aqueous samples, and the overall relative standard deviation was about 5%.

A method for the evaluation of the amount of nicotine released from Swedish snuff based on the use of supported liquid membranes has been developed. The solid sample is directly placed, with minimal pre-treatment, in the membrane unit and the nicotine released from the sample passes through the membrane (polypropylene/n-undecane) into an acidic acceptor stream. This stream flows through a spectrophotometric detector allowing the measurement of nicotine absorbance at 260 nm. The influence of pH on the release of nicotine from aqueous nicotine solutions as well as from snuff has been studied. The method allows differentiating among different types of snuff depending on their nicotine content. The results of direct spectrophotometric measurements in the acceptor stream were checked against results obtained using gas chromatography.

The inherent difficulties of measurement in chemistry and biology have made it necessary to open discussion forums solely devoted to bench level work. This contribution summarises the conclusions of the Standards, Measurements and Testing Project (SMT4-CT96-6505) of the European Commission, devoted to the application of metrology in chemistry and biology. The objective of this project was to provide orientations and some recommendations which could partially satisfy end-users needs in the near future.

A new capillary zone electrophoretic (CZE) method has been developed for the simultaneous determination of carnitine, acetyl-carnitine, hexanoyl-carnitine, octanoyl-carnitine, decanoyl-carnitine and lauroyl-carnitine with indirect photometric detection. Two selected buffers were evaluated and optimized; the first one used copper sulfate and methanol, and the second used quinine as the principal constituent. Different chemical variables were evaluated and optimized in order to setup the most appropriate system for separating the acyl-carnitines. The robustness test showed that the quantitative responses (areas and heights) were affected mainly by pH and quinine concentration, while the migration times were influenced by quinine concentration, pH, voltage and temperature. The present method achieved times of separation of 20 min for six carnitine compounds with complete resolution of all compounds. The detection limits of the method were between 0.2 and 2.5 μg ml −1 using electrokinetic injection and reproducibility (RSD%) was between 2.1 and 7.7%. The proposed method was applied to determine carnitines in synthetic samples; the recoveries of the compounds were between 95 to 110% in different samples and the errors were lower than 10% in all cases.

A new sample-injection/sample-dilution system for the flow-injection analytical technique is proposed. The system is based on two variable-speed computer-controlled peristaltic pumps and a specially designed commutator located at the merging point. One of the pumps delivers a sample and the other a carrier solution. The pumps are run in such a way that the total flow rate after the merging point remains permanently constant. The volume of the injected sample is determined by the time the sample delivering pump is on, whilst the dilution of the sample is determined by relative flow rates of sample and carrier solutions. Two additional possibilities are offered by the proposed system. Firstly, the volume of the injected sample plug can be varied in a simple way, and secondly, for the first time, the injection of a sample plug having an exactly predetermined concentration profile for the measured analyte at the merging point can be carried out. By introducing a third pump delivering a standard solution of the measured species, the system is able to perform a quantitative determination of an analyte, either by the standard addition method or by forming a calibration curve using only one standard solution.

A flow injection system for the on-line preconcentration of ultratrace levels of cobalt by sorption with ammonium pyrrolidinedithiocarbamate on a C 60 fullerene column was developed. The eluate volume is reduced and dispersion minimized by using a nitrogen (or air) stream to carry the eluent (IBMK) for elution of the adsorbed chelate, which is collected in a 500 µl PTFE autosampler cup. The analytical figures of merit for the determination of cobalt are as follows: limit of detection (3σ), 8 ng l –1 ; precision (RSD), 4% for 0.2 ng ml –1 ; preconcentration factor, 40 (using 25 ml of sample and 500 µl of IBMK). Similar experiments involving C 18 -bonded silica as sorbent revealed ethanol to be the most suitable eluent under these conditions. The results obtained in the determination of cobalt in wheat flour testify to the usefulness of the proposed method.

The analysis and identification of structural isomers of mono-, di- and trichlorophenols is reported. The fragmentation of the phenols was examined by GC–MS in both electron impact (EI) and negative chemical ionization (NCI) modes, using methane as reagent gas. The ability of NCI to discriminate these isomeric compounds from differences in relative intensities for selected peaks is demonstrated. 3- and 4-chlorophenols have similar retention times; however, they can still be discriminated because their negative mass spectra are rather different. In dichlorophenols, the presence of one chlorine atom in the ortho position decreases their retention time and the relative intensity of the fragment ion at m / z 140. The NCI mass spectra for trichlorophenols are different from the rest, particularly for the m / z value corresponding to the chlorine atom. Tetra- and pentachlorophenols were also studied and sequential losses of Cl observed. An automatic solid-phase extraction system can optionally be used to preconcentrate chlorophenols in waters prior to determination at legally established toxic levels.

The implementation of quality programs in analytical laboratories and the plethora of guides and documents concerning ways to achieve quality objectives necessitate some clarification of particular metrological analytical terms and their hierarchical classification. This task is also important within the overall field of analytical chemistry. Concepts such as accuracy (involving trueness and precision in the newest definition), uncertainty and representativeness need to be systematically ranked and considered in the context of new developments in analytical science. Their relationship to the characteristics of analytical information is a key factor in the present view of the analytical laboratory-customer relationship.