New spot tests for vanadium(IV), silver,and molybdenum

Microchimica Acta - New spot tests for vanadium(IV), silver, and molybdenum are described. Vanadium(IV) can be detected by treating of Erioglaucine A and Eriogreen B, or of Ponceau 2 R and...     

New developments in particle-based tests and immunoassays.

Latex agglutination tests were invented in 1957. Thirty years later, new tests are still being devised and applied to new analytes. Reproducibility and readability continue to improve. Qualitative tests have now evolved to quantitative particle immunoassays: agglutination is detected by spectrophotometers or nephelometers, in tubes or 96-well plates. These same particles are now also being used in particle capture ELIST and ELISA (enzyme linked immunosorbent tests and assays) where particles are caught upon a filter and act as supports for sandwich tests (those "+/-" or "blue-dot" tests). These also can be quantified, as in the Abbott IM x assay system. Dyed microspheres now function as the color tags in over-the-counter sandwich-type pregnancy tests. In the future, results from assays using this technology could be read on reflectometers (strip readers). Currently, magnetic particles are used in solid phase radioimmunoassays and DNA probes.     

New specific spot tests for barbituric and thiobarbituric acids, malonic acid and urea

Barbituric and thiobarbituric acids may be detected with pyridyl pyridinium dichloride, giving, respectively, a reddish-blue and blue colour. The limit of identification is 0.5 μg in each case. Malonic acid can be converted to barbituric acid by heating with urea and is then detected in a similar manner. The limit of identification is 50 μg of malonic acid. Urea may be detected with a limit of identification of 200 μg by reversing the test for malonic acid. All four tests are specific.     

Simultaneous determination of different antibiotic residues in bovine and in porcine kidneys by solid-phase fluorescence immunoassay

Parallux, a solid-phase fluorescence immunoassay (SPFIA) developed for antibiotic residue detection in milk, was used for analysis of bovine and porcine kidney tissue. Four tetracyclines, 2 broad-spectrum cephalosporins, 3 beta-lactam antibiotics, and cephapirin were detected in one run after minimal sample preparation. This commercially available test system is designed as cartridges, each with a combination of 1-4 tests. One cartridge can be used to detect 4 analytes in the same sample, or 1 or 2 analytes in different samples. The cartridge with the combination tetracyclines-ceftiofur-penicillin-cephapirin was selected because tetracyclines, beta-lactam antibiotics as well as cephalosporins, are registered for oral or parenteral use in bovines and pigs in Europe. The test is qualitative and is recommended only for screening. Tetracycline, oxytetracycline, chlortetracycline, and doxycycline were easily detected at 300 ppb with the tetracyclines channel; ceftiofur at 1000 ppb and cefquinome at 200 ppb with the ceftiofur channel; penicillin G, ampicillin, and amoxicillin at 50 ppb with the penicillin channel; and cephapirin at 100 ppb with the cephapirin channel. These levels are equal to or lower than the corresponding maximal residue limits in kidney tissue. Cephalexin was not detected. The SPFIA test can be used as an alternative to classical inhibition tests and for post-screening inhibitor- positive kidneys, because it detects 3 specific groups of antibiotics, which enables selection of specific confirmatory methods for identification and quantification.     

Robust regression and outlier detection in the evaluation of robustness tests with different experimental designs

Robustness tests are usually based on an experimental design approach. As designed experiments generally lead to a large variability among the results, erroneous results are often not readily detected. As a consequence, the ordinary least squares (OLS) estimates of the effects of the robustness test can be biased. Here, two robustness tests are studied, which both contain a suspicious result. Moreover, simulated datasets are considered to examine the influence of the extent of the outlier as well as the influence of multiple outliers. On the one hand, different methods are applied to inspect the results of the experiments for outliers: the half-normal plot of the OLS residuals, the normal probability plot of the effects and a method, which is based on experimental design reconstruction. On the other hand, two robust regression methods are applied to calculate the effects with a minimum influence of possible outliers. The different methods are compared and it is evaluated under which circumstances they can be applied.     

Spot test detection of phenylhydrazine and arsonic acids

If phenylhydrazine or its salts are heated with arsenic acid or with one of its organic derivatives (aliphatic or aromatic arsonic acids) phenol results. The latter can easily be detected in the gas phase by the indophenol reaction with 2:6-dichloroquinone-4-chloroimine. This has been made the basis of characteristic tests for phenylhydrazine (also phenylhydrazones and osazones) as well as for arsonic acids. When conducted within the bounds of spot test analysis, the limits of detection are microanalytical.     

Chromofoams1 qualitative and semi-quantitative tests with chromogenic organic reagents immobilized in plasticized open-cell polyurethane foams

Polyurethane foams treated with organic reagents in a plasticizer solution can be used for simple, rapid, sensitive, and selective detection and semiquantitative determination of metal ions from dilute aqueous solutions. Batch techniques can be used for simple tests which provide sensitivity as good as, or better than, that attainable by normal spot tests. The application of reagent-treated foam columns for the detection and semiquantitative determination of metal ions from extremely dilute aqueous solutions is advantageous; ions in the p.p.b. range can be detected after passage of 1 l of solution at a fast rate. The use of these techniques for zinc(II) and lead(II) with dithizone, copper(II) with rubeanic acid, and cobalt(II) with thiocyanate-Amberlite LA-l, is described.     

Assuring trueness of analytical results

Summary A true analytical result presumes an analytical procedure without systematic errors. They can be detected by comparing the analytical results with the true value or with an accepted reference. Systematic errors are always superimposed by the random error, therefore such a comparison must include statistical tests. The paper describes suitable test-models for typical analytical problems, as e.g. the validation of an analytical procedure or the (current) control of analytical work. Furthermore, explanations will be given for the interpretation of the test results due to the trueness of analytical data and for the consequences concerning analytical work.     

A fiber-optic sensor system for monitoring chlorinated hydrocarbon pollutants

We have developed and field-tested a fiber-optic chemical sensor system for use in environmental monitoring and remediation. The system detects chlorinated hydrocarbon pollutants with colorimetry, and is based on an irreversible chemical reaction between the target compound and a specific reagent. The reaction products are detected by their absorption at 560 nm and can be monitored remotely with optical fibers. Continuous measurements are made possible by renewing the reagent from a reservoir with a miniature pumping system. The sensor has been evaluated against gas chromatography standards and has demonstrated accuracy and sensitivity (5 ppbw) sufficient for the environmental monitoring of trichloroethylene and chloroform. Successful preliminary field tests have been conducted in a variety of contamination monitoring scenarios.     

The analysis of counter performance by cusum techniques

It is necessary in most radiochemical studies to check periodically the efficiency of the detector with a standard or reference source to ensure its constancy. This can lead to a large number of readings which can best be analysed graphically by means of cumulative summation. Minor abrupt changes in counter performance can often be determined by retrospective examination of cusums. Alternatively in an on-going situation the reference source readings may be plotted as they are taken and a significant change detected comparatively rapidly with a V-mask. The standard deviation used in tests of significant change has in practice been found to be greater than that expected simply from the randomness of the disintegration process. The point of change can often be located precisely so that it should be possible if necessary to correct other measurements with the detector.     

A sensitive lateral flow biosensor for Escherichia coli O157:H7 detection based on aptamer mediated strand displacement amplification

Foodborne diseases caused by pathogens are one of the major problems in food safety. Convenient and sensitive point-of-care rapid diagnostic tests for food-borne pathogens have been a long-felt need of clinicians. Commonly used methods for pathogen detection rely on conventional culture-based tests, antibody-based assays and polymerase chain reaction (PCR)-based techniques. These methods are costly, laborious and time-consuming. Herein, we present a simple and sensitive aptamer based biosensor for rapid detection of Escherichia coli O157:H7 (E. coli O157:H7). In this assay, two different aptamers specific for the outmembrane of E. coli O157:H7 were used. One of the aptamers was used for magnetic bead enrichment, and the other was used as a signal reporter for this pathogen, which was amplified by isothermal strand displacement amplification (SDA) and further detected by a lateral flow biosensor. Only the captured aptamers on cell membrane were amplified, limitations of conventional DNA amplification based method such as false-positive can be largely reduced. The generated signals (red bands on the test zone of a lateral flow strip) can be unambiguously read out by the naked eye. As low as 10 colony forming units (CFU) of E. coli O157:H7 were detected in this study. Without DNA extraction, the reduced handling and simpler equipment requirement render this assay a simple and rapid alternative to conventional methods.     

Measurement of highly forbidden optical transitions by intracavity cw dye laser spectroscopy

Intracavity cw dye laser quenching has been used to observe extremely weak optical transitions near 6300 Å: the 2.0 band of the red atmospheric system of molecular oxygen and the 6,0 overtone band of HCl. Sensitivity tests indicate that band systems with oscillator strengths less than 10^?2 can be detected readily, thereby suggesting routine use for high-resolution optical spectroscopy of forbidden transitions.     

Spectroscopic insights into adhesion failure at the buried epoxy-metal interphase using AFM-IR

Local AFM-IR analysis is performed on the organic coating residues remaining on carbon steel substrates after pull-off adhesion tests. This approach provides unique spectral information, because scattering from these rough substrates has previously prohibited transflectance FTIR analysis of such regions. The AFM-IR spectra of epoxy-amine residues display characteristic oxidation bands, which can only be detected by ATR-FTIR spectroscopy of intact coatings after thermal aging. These oxidation bands are shown to be more intense for thinner coating remnants and dominate the spectra of residue left by coatings removed after thermal aging at 70°C for 4 weeks. This, alongside distinctive changes in the macroscopic adhesion behavior after thermal aging, provides direct evidence that rapid oxidation occurs in the buried polymer-metal interphase during thermal aging.     

Rapid assays based on immobilized bioluminescent enzymes and photographic detection of light-emission

Sensitive assays have been developed for adenosine 5'-triphosphate, the reduced form of nicotinamide adenine dinucleotide, cholyl glycine and alcohol, with immobilized and co-immobilized preparations of bacterial and firefly luciferase as reagents. With high-speed (ASA 20000) instant photographic film as detector, picomole amounts of the various analytes can be detected rapidly. The simplicity and convenience of the analytical combination of co-immobilized bioluminescent enzymes and photographic film for the detection of light make this an ideal technique for rapid screening tests.     

Improving the analysis of Y‐SNP haplogroups by a single highly informative 16 SNP multiplex PCR‐minisequencing assay

The SNP haplogroups of the Y‐chromosome are nonrandomly distributed among human populations. They are used for tracing the phylogeographical history of paternal lineages of male individuals and can be a useful tool for approaching the patrilineal bio‐geographic ancestry of unknown forensic evidences. With the aim of facilitating the inference of the principal informative worldwide Y‐SNP haplogroups, we have selected the minimum possible number of key Y‐SNPs to be amplified in a sensitive single multiplex PCR and detected by minisequencing. This assay, that includes 16 Y‐SNPs, was tested for male human specificity, sensitivity, and reproducibility. Its effectiveness was assessed in a set of degraded DNA samples and in a panel of male individuals from different worldwide populations. All these tests demonstrated the convenience of this assay for assigning the major Y haplogroups to forensic evidences by one single PCR‐minisequencing reaction.     

Investigating poly-(vinyl-chloride)-polyethylene blends by thermal methods

Poly-vinyl-chloride (PVC)-polyethylene (PE) alloys were prepared by melt blending using both low- and high-density polyethylene without applying a compatibilizer. The PVC and the PE are incompatible polymers; in spite of this fact stable microheterogeneous materials were obtained. Mechanical methods e.g. tensile tests generally (measured in the usual concentration range) do not support any compatibility. At higher concentrations, the incompatible parts mask the effect of molecular mixing, easily detected at low PE contents. Dynamic mechanical (DMA), differential scanning calorimetric tests were carried out. Glass transition temperatures were determined by both methods. DMA tests were made at four frequencies, and the energy of activation of PVC main transition was also calculated. The decrease of glass-transition temperatures and energy of activation show that there is a slight mixing of the polymers. Specimens were also investigated by infrared method. From the results of IR spectra, grafting reaction of PE can be assumed onto the PVC because of its dehydrochlorination.     

Simultaneous determination of 11 related impurities in propofol by gas chromatography/tandem mass spectrometry coupled with pulsed splitless injection technique

A variety of related impurities, including starting materials, process impurities, and degradation products, can be detected in propofol. In this article, a sensitive and selective GC‐MS/MS method using pulsed splitless injection technique for the determination of 11 main related impurities in propofol in one chromatogram is investigated. This method is extensively validated for its linearity, recovery, precision, LOD, and LOQ, and is able to detect trace‐level related impurities (LOD = 0.2–5.6 μg/g) in propofol bulk drug. Stressed tests proposed that oxidative degradation, photolytic degradation, and heat are the main causes for the formation of degradation products in propofol.     

RP-HPLC analysis of phenolic acids of selected Central European Carex L. (Cyperaceae) species and its implication for taxonomy

Eighteen species belonging to the Carex genus were checked for the presence and the amount of eight phenolic acids (p-hydroxybenzoic, vanillic, caffeic, syringic, protocatechuic, p-coumaric, sinapic, and ferulic) by means of HPLC. Both the free and bonded phenolic acids were analyzed. The majority of the analyzed acids occurred in the studied species in relatively high amounts. The highest concentrations found were caffeic acid and p-coumaric acid, for which the detected levels were negatively correlated. A very interesting feature was the occurrence of sinapic acid, a compound very rarely detected in plant tissues. Its distribution across the analyzed set of species can be hypothetically connected with the humidity of plants' habitats. Several attempted tests of aggregative cluster analysis showed no similarity to the real taxonomical structure of the genus Carex. Thus, the phenolic acids' composition cannot be considered as the major taxonomical feature for the genus Carex.     

Detection of antibiotics in muscle tissue with microbiological inhibition tests: effects of the matrix.

The effects of the tissue matrix on detection limits of antibiotics with microbiological inhibition tests, intended for muscle tissue, were measured. Pieces of frozen meat were laid directly on top of paper disks impregnated with aqueous antibiotic solutions. Inhibition zones were compared with those obtained by the same standard solution without tissue. Only tetracyclines were detected as efficiently with as without muscle tissue. Inhibition zones of the beta-lactam antibiotics ampicillin and penicillin G, and the fluoroquinolone antibiotics enrofloxacin and ciprofloxacin were smaller when muscle tissue was added to low levels of standard solution. At higher levels the differences were not substantial. Inhibition zones of tylosin were smaller and irregular or had disappeared completely, while ceftiofur, sulfadimidine, erythromycin, lincomycin, and streptomycin were not detected in spiked muscle tissue at concentrations fivefold higher than the detection limits without tissue. These results indicate that ceftiofur, sulfonamides, streptomycin and some macrolide antibiotics cannot be detected in intact meat with the plates and bacterial strains prescribed in the European Four Plate Test, a test which was initially intended as a multi-residue method for muscle tissue. Two plates of this system are not suitable for screening purposes; a third one detects tetracyclines and beta-lactam antibiotics in spiked tissue; the fourth one is sensitive for beta-lactam antibiotics and for some but not all macrolides. Samples spiked with the fluoroquinolones enrofloxacin and ciprofloxacin can be detected with an additional plate, not included in the Four Plate Test.     

Experiences with an identification and quantification program for inhibitor-positive milk samples

Beta-lactam antibiotics (penicillins, cephalosporins) are still the most commonly used antibiotics for dairy cows in Germany. In routine milk testing, according to the German milk quality regulation, a positive result obtained for bulk tank milk by microbiological inhibitor tests needs no further confirmation, but results in reduced milk payment of 0.05 euros kg(-1) for one month. In some cases, however, further identification of the causative agent can be of interest, either if antimicrobial drugs have not knowingly been used recently, or if improper use of such drugs is denied. As a service for milk producers, our laboratory offers further analyses of violative milk samples, aiming at the identification and quantification of the inhibitor(s). In this program, a panel of microbiological inhibitor tests, receptor tests, and enzyme immunoassays (EIA) is used in a step-by-step analysis, which primarily focusses on beta-lactams, but also includes other compounds such as sulfonamides or tetracyclines, respectively. Here we report results for violative milk samples (n=63) analysed between 2003 and 2005. In most cases (95%), beta-lactam antibiotics could be identified, although not always at levels exceeding the respective MRL values. Penicillin G (mostly together with benzylpenicilloyl metabolites) could be identified in 74.6% of all samples. Other compounds identified were, in decreasing order, ceftiofur (11%), ampicillin/amoxicillin (6.3%), isoxazolyl penicillins (3.2%), and sulfonamides (1.6%). The results indicate that penicillin G is still the predominant antibiotic responsible for violative bulk tank milk samples as detected during regulatory control.