Limit Of Determination Research Articles

Investigations on the amalgamation of gold nanorods by iodine and the detection of tetracycline

The morphological transformation process of gold nanorods (Au-NRs) resulting from the reaction between tetracycline and iodine was monitored by the plasmon resonance absorption (PRA) spectra and the scanning electron microscope (SEM) images. It was found that iodine could fuse Au-NRs into sphericity with the lower aspect ratio and blue shift of the longitudinal PRA band. It was found, however, that the presence of tetracycline, since it can react with I2, decreases the effective concentration of I2 and its fusion effect on Au-NRs. As a result, the longitudinal PRA of Au-NRs shifts to longer wavelength linearly with increasing the concentration of tetracycline. With that, tetracycline can be detected in the range of 5.0×10∮5- 5.0×10−4 mol·L−1, with a limit of determination (LOD) of 2.4×10−6 mol·L−1 (3σ). Most foreign substances in the samples did not interfere in the detection, and tetracycline in the synthetic samples could be detected with the recovery in the range of 92.8%–107.2%, and RSD lower than 4.3%. The concentration of tetracycline in milk detected with standard addition method was so low that it accorded with the safety regulation.

Atmospheric pressure glow discharge desorption mass spectrometry for rapid screening of pesticides in food

Flowing afterglow atmospheric pressure glow discharge tandem mass spectrometry (APGD-MS/MS) is used for the analysis of trace amounts of pesticides in fruit juices and on fruit peel. The APGD source was rebuilt after Andrade et al. (Andrade et al., Anal. Chem. 2008; 80: 2646-2653; 2654-2663) and mounted onto a hybrid quadrupole time-of-flight mass spectrometer. Apple, cranberry, grape and orange juices as well as fruit peel and salad leaves were spiked with aqueous solutions containing trace amounts of the pesticides alachlor, atrazine, carbendazim, carbofuran, dinoseb, isoproturon, metolachlor, metolcarb, propoxur and simazine. Best limits of determination (LODs) of pesticides in the fruit juices were achieved for metolcarb (1 microg/L in apple juice), carbofuran and dinoseb (2 microg/L in apple juice); for the analysis of apple skin best LODs were 10 pg/cm(2) of atrazine, metolcarb and propoxur which corresponds to an estimated concentration of 0.01 microg/kg apple, taking into account the surface area and the weight of the apple. The measured LODs were within or below the allowed maximum residue levels (MRLs) decreed by the European Union (1-500 microg/kg for pesticides in fruit juice and 0.01-5 microg/kg for apple skin). No sample pretreatment (extraction, pre-concentration, chromatographic separation) was necessary to analyze these pesticides by direct desorption/ionization using APGD-MS and to identify them using MS/MS. This makes APGD-MS a powerful high-throughput tool for the investigation of very low amounts of pesticides in fruit juices and on fruit peel/vegetable skin.

Microwave-irradiated synthesized platinum nanoparticles/carbon nanotubes for oxidative determination of trace arsenic(III)

Platinum nanoparticles/carbon nanotubes (Pt nano/CNTs) were rapidly synthesized by microwave radiation, and applied for the oxidative determination of arsenic(III). The transmission electron microscopy (TEM) revealed the size of synthesized Pt nanoparticles with nominal diameter of 15 ± 3 nm. Pt nano/CNTs modified glassy carbon electrode (Pt nano/CNTs/GCE) exhibited better performance for arsenic(III) analysis than that of Pt nanoparticles modified GCE (Pt nano/GCE) by electrochemical deposition or Pt foil electrode. Excellent reproducibility of the Pt nano/CNTs/GCE was obtained with the relative standard deviation (RSD) of 3.5% at 20 repeated analysis of 40 μM As(III), while the RSD was 9.8% for Pt nano/GCE under the same conditions. The limit of determination (LOD) of the Pt nano/CNTs/GCE was 0.12 ppb, which was 1–2 orders of magnitude lower than that of Pt nano/GCE or Pt foil electrode.

Determination of 4-Ethylphenol and 4-Ethylguaiacol in Wines by LC-MS-MS and HPLC-DAD-Fluorescence

Volatile phenols produced by Brettanomyces dekkera have been associate with off-flavors of wines. A versatile liquid chromatography-tandem mass spectrometry together with an HPLC-DAD-fluorescence methods were developed for the quantitation of two phenols, 4-ethylphenol (4EP) and 4-ethylguaiacol (4EG), in red and white wines. For LC-MS-MS analysis, fortified wines were directly injected after a dilution with methanol, and levels of phenols were measured by monitoring the multiple reaction (MRM) transitions of precursor ions mass charge (m/z) 121 --> 106 for 4EP and (m/z) 151 --> 136 for 4EG. Qualitative and quantitative confirmation data were acquired simultaneously by monitoring alternative MRM transitions following an external standard method. Calibration was linear over a working range of 10 and 5000 microg/L. Limit of determination (LOD) and limit of quantification (LOQ) were 10 and 50 microg/L for both 4EG and 4EP. HPLC analysis phenols were separated with a gradient system of acetonitrile-water and detected using a diode array detector (DAD) at 280 nm, and for the fluorescence analysis, excitation and emission wavelengths of 260 and 305 nm were used. Quantitative analysis of 4EP and 4EG was performed by the standard addition method to avoid matrix interferences. Calibration was linear over a concentration range from 10 to 5000 microg/L for HPLC-DAD, from 1 to 10,000 microg/L for 4EP, and from 10 to 10,000 for 4EG for fluorescence analysis. LOD and LOQ for the DAD analysis were 10 and 50 microg/L for both 4EG and 4EP. For fluorescence analysis, LOD and LOQ were 1 and 5 microg/L for 4EP and 10 and 50, respectively, for 4EG. The proposed methods can be easily used for the qualitative and quantitative determination of 4EP and 4EG in wines affected by microbial contamination with yeasts of the Brettanomyces genus.

Simultaneous Determination of 13 Phenoxy Acid Herbicide Residues in Soybean by GC‐ECD

In this study, a gas chromatography method for the multiresidue determination of 13 phenoxy acid herbicide residues (4‐CPA, 4‐CPP, phenoxy butyric acid, dicamba, MCPA, MCPP, MCPB, 2,4‐D, 3,4‐D, 2,4,5‐T, 2,4,5‐TP, 2,4‐DP, and 2,4‐DB) in soybean was developed. After the removal of fat using n‐hexane, the sample was extracted with acetonitrile‐50 mM HCl (v/v 7:3), and then followed by liquid‐liquid partition with n‐hexane (saturated by acetonitrile). The soybean extract was further cleaned up by anion exchange column. Then the residues were derived with pentafluorobenzyl bromide and the resulting pentafluorobenzyl (PFB) esters were analyzed by a gas chromatograph equipped with an electron capture detector (ECD), quantified by the external standard method. Recoveries of spiked samples at two fortified levels (0.01 and 0.1 mg/kg) are all above 70%. And the relative standard deviation was less than 20%. It shows that the limits of determination (LOD) of this method (S/N≥3) can meet the requirement of maximum residue analysis in import/export inspection for soybean.

Simultaneous determination of urinary dialkylphosphate metabolites of organophosphorus pesticides using gas chromatography–mass spectrometry

In this study, we developed a safe and sensitive method for the simultaneous determination of urinary dialkylphosphates (DAPs), metabolites of organophosphorus insecticides (OPs), including dimethylphosphate (DMP), diethylphosphate (DEP), dimethylthiophosphate (DMTP), and diethylthiophosphate (DETP), using a pentafluorobenzylbromide (PFBBr) derivatization and gas chromatography-mass spectrometry (GC-MS). Several parameters were investigated: pH on evaporation, reaction temperature and time for the derivatization, the use of an antioxidant for preventing oxidation, and a clean-up step. The pH was set at 6, adjusted with K2CO3, and the reaction temperature and time of derivatization were 80 degrees C and 30 min, respectively. Sodium disulfite was chosen as an antioxidant. The clean-up step was performed with a Florisil/PSE mini-column to remove the unreacted PFBBr and sample matrix. This established procedure markedly shortened the sample preparation time to only about 3 h, and completely inhibited the unwanted oxidization of dialkylthiophosphates. The limits of determination (LOD) were approximately 0.3 microg/L for DMP, and 0.1 microg/L for DEP, DMTP, and DETP in 5 mL of human urine. Within-series and between-day imprecision for the present method using pooled urine spiked with DAPs was less than 20.6% in the calibration range of 1-300 microg/L, and the mean recovery was 56.7-60.5% for DMP, 78.5-82.7% for DEP, 88.3-103.9% for DMTP, and 84.2-92.4% for DETP. This method detected geometric mean values of the urinary DAPs in Japanese with and without occupational exposure to OPs, 16.6 or 27.4 for DMP, 1.0 or 0.7 for DEP, 1.3 or 2.3 for DMTP, and 1.0 or 1.1 microg/L for DETP, respectively. The present method, which does not require special equipment except for GC-MS, is quick, safe, and sensitive enough to be adopted in routine biological monitoring of non-occupational as well as occupational exposure to OPs.

Determination of lead in environmental water by a backward light scattering technique

An optical fiber assembly developed in our laboratory, which is based on detecting backward light scattering (BLS) signals, is now applied to detect the lead content in environmental samples. Due to effectively eliminating the interference of reflected light, this BLS signals based detection assembly can be used to determine analyte directly. In HAc–NaAc buffer medium (pH 4.8), the interaction of lead and sodium tetraphenylboron (TPB) in the presence of polyethylene glycol (PEG) yields large particles of ternary complex, resulting in strong enhanced backward light scattering (BLS) signals characterized at 371 nm. By measuring the BLS signals with the homemade optical fiber assembly coupled with a common spectrofluorometer, we found that the enhanced BLS intensity is proportional to lead content over the range of 0.03–1.0 μg ml −1 with the limit of determination (LOD) of 2.6 ng ml −1. Three artificial water samples containing various coexistent substances were detected with the recovery of 90.1–107.5%. Standard addition method was used to detect the lead content in drink tap water, and found that the lead is hardly to detect due to too low content. Prior enrichment should be made in order to detect river water samples, and it was found that the content of lead in Jialing River at Bebei Dock is about 14 ng ml −1, identical to the results using inductively coupled plasma atomic emission spectrometry (ICP-AES).

Systematic Investigations of Plastic Vials Concerning Their Suitability for Ultratrace Anion Analysis in High-Purity Industrial Applications

Ultratrace anion analysis in high-purity industrial applications is done using commercially available plastic vials to store the eluted liquid samples. Plastic vials are manufactured with materials containing several additives. Such additives might potentially release anionic contaminants, thus degrading the blank quality and determination limits (DL). The durability and thermal stability of several materials was found to be a function of anionic species. Fluorinated materials showed the best results for the majority of anions with the exception of fluoride. For the selective analysis of fluoride, polypropylene was found to be the best vial material, together with glass. Cold water extraction showed better results compared to hot water extraction. Over a long observation period, hot water extraction did not at all improve the performance, indicating that this type of supposedly efficient cleaning of the plastic containers to render them less prone to contaminant release does not hold true.

Determination of off-flavour compounds in apple juice caused by microorganisms using headspace solid phase microextraction–gas chromatography–mass spectrometry

In apple juice the presence of off-flavour is one of the most frequent causes for consumers rejections and, consequently, represents an important problem to apple juice producers. In this study, special emphasis was put on microbial caused off-flavours. Special attention is drawn to two bacteria species and their metabolites, Alicyclobacillus acidoterrestris and Actinomycetes. Both species produce aroma-active compounds (e.g. guaiacol, dibromophenol, geosmin, 2-methylisoborneol), which may lead to characteristic off-flavour in apple juice. They are described as musty/earthy or medicinal-like, even when they are present in very low concentrations. In this study, appropriate analytical methods were established to identify and quantify the compounds of interest. Gas chromatography–mass spectrometry was used after headspace solid phase microextraction (SPME) as sample preparation/extraction technique. The influence of the different parameters for headspace SPME (i.e. type of added salt, SPME fibre materials, time and temperature during thermostating of the sample and exposure of the fibre) on the sensitivity of the method are discussed. The final methods were fully validated. Limits of determination (LOD) and limits of quantification (LOQ) for the mentioned off-flavour compounds are located in the range of 0.08–7.7 μg L −1 for LOD and 0.27–25 μg L −1 for LOQ, depending on the compound. The presented analytical method provides a selective and sensitive technique to further investigate the off-flavour problem in apple juice.

Determination of off-flavour compounds in apple juice caused by microorganisms using headspace solid phase microextraction?gas chromatography?mass spectrometry

In apple juice the presence of off-flavour is one of the most frequent causes for consumers rejections and, consequently, represents an important problem to apple juice producers. In this study, special emphasis was put on microbial caused off-flavours. Special attention is drawn to two bacteria species and their metabolites, Alicyclobacillus acidoterrestris and Actinomycetes. Both species produce aroma-active compounds (e.g. guaiacol, dibromophenol, geosmin, 2-methylisoborneol), which may lead to characteristic off-flavour in apple juice. They are described as musty/earthy or medicinal-like, even when they are present in very low concentrations. In this study, appropriate analytical methods were established to identify and quantify the compounds of interest. Gas chromatography–mass spectrometry was used after headspace solid phase microextraction (SPME) as sample preparation/extraction technique. The influence of the different parameters for headspace SPME (i.e. type of added salt, SPME fibre materials, time and temperature during thermostating of the sample and exposure of the fibre) on the sensitivity of the method are discussed. The final methods were fully validated. Limits of determination (LOD) and limits of quantification (LOQ) for the mentioned off-flavour compounds are located in the range of 0.08–7.7 μg L−1 for LOD and 0.27–25 μg L−1 for LOQ, depending on the compound. The presented analytical method provides a selective and sensitive technique to further investigate the off-flavour problem in apple juice.

Special new techniques of atomic spectrometric methods for trace analysis of high purity metals

How spectral interferences of analyte ions with polyatomic ions containing matrix atoms can be identified, reduced or eliminated was demonstrated for different pure metals using a double focussing ICP mass spectrometer in higher mass resolution. An in-situ coating procedure of the nickel inlet cones of the ICP mass spectrometer with a thin quartz glass film was developed in our laboratory. It leads to a drastic decrease of memory effects and blanks, especially for the analytes Na, Ni and Li. The limits of determination (LODs) of these analytes were decreased for more than one order of magnitude. The analytical performance of two atomic spectrometric techniques combined with electrothermal vaporization (ETV) of metallic microsamples was investigated using tungsten as an example. An ICP optical emission spectrometer equipped with ETV (ETV ICP OES) as well as a solid sampling atomic absorption spectrometer (SS-ET AAS) were used. Benefits and drawbacks of both method combinations were summarized and compared. The multielement capability of ETV ICP OES was much higher than the of SS-ET AAS. LODs of the less refractory analytes were lower with SS-ET AAS than with ETV ICP OES.

MTBE (methyl tertiary-butyl ether) in groundwaters: monitoring results from Germany.

In Germany information on the occurrence of MTBE in groundwaters is scarce. In order to assess the German situation, in 1999 a monitoring programme on MTBE in groundwater was set up. Within this survey 170 wells were examined, which are used as groundwater monitoring points or which are foreseen for drinking water extraction in emergency cases or for irrigation purposes. In rural areas MTBE was found only in 9% of all samples in concentrations above the limit of determination (LOD) of 0.05 microg L(-1). In urban areas MTBE was detected in 49% of all wells under investigation and the median concentration was calculated to 0.17 microg L(-1). In one case a maximum MTBE concentration of almost 700 microg L(-1) was detected. As a first result of this survey one can conclude, that MTBE is regularly present in German groundwaters under urban areas. Although investigations about the occurrence of MTBE in German groundwaters have to be extended in future, this first snapshot can lead to the assumption, that MTBE concentrations due to diffuse sources are lower than the ones found in the USA. Nevertheless, e.g. accidental spills can lead to elevated MTBE concentrations.

Comparison of denuder and impinger sampling for determination of gaseous toluene diisocyanate (TDI).

An air-sampling method employing denuders coated inside with a chemisorptive stationary phase has been evaluated for analysis of the hazardous gaseous 2,4 and 2,6 isomers of toluene diisocyanate (TDI). The denuder stationary phase consisted of polydimethylsiloxane (SE-30) to which dibutylamine (DBA) was added as a reagent for derivatization of TDI. The accuracy and precision of sampling by means of denuders were shown to differ only slightly from those of the established impinger method. The denuder method was, however, also shown to be suitable for long-term measurements (up to 8 h). The limit of determination (LOD) of the method, including LC-APCI-MS-MS analysis, was found to be 1.9 microg m(-3) and 1.2 microg m(-3) for 2,4- and 2,6-TDI, respectively, for short-term measurements (15 min). Significant lower LOD was obtained for long-term measurements. This is well below the Occupational Safety and Health Administration (OSHA) 8-h TWA (time-weighted average) exposure limit, which is 40 microg m(-3) for the sum of the TDI isomers. The denuder method was also found to be robust and easy to handle. The samplers can be prepared several days before sampling with no loss in performance. The contents of denuders should, on the other hand, be extracted immediately after sampling to prevent degradation of the isocyanate derivatives formed.

Occurrence of Antifouling Biocides in the Spanish Mediterranean Marine Environment

A compilation of the results of a monitoring program of the recently used antifouling pesticides diuron (3-(3,4-dichlorophenyl)-1,1-dimethylurea), Irgarol 1051 (2-methylthio-4-tertiary-butylamino-6-cyclopropylamino-s-teiazine), seanine 211 (4,5-dichloro-2-n-octyl-4-isothazolin-3-one), chlorothalonil (2,4,5,6-tetrachloro-isophthalonitrile), dichlofluanid (N′-dimethyl-N-phenylsulphanamide), TCMTB ((2-thiocyanomethylthio) benzothiazole), and three degradation products demethyldiuron (3-(3,4-dichlorophenyl)-1-methylurea), 3,4-dichlorophenylurea and 2-methylthio-4-tert-butylamino-s-triazine (Irgarol degradation product) that was carried out between April 1996 and February 2000 in enclosed seawaters from Catalonia and Almería (Spanish Mediterranean coast) is reported. Nine points were sampled along the Catalan coast: Barcelona Olympic port, Masnou, Blanes, Sant Carles de la Ràpita, Tarragona, Cambrils and Salou marinas as well as the Cambrils and Tarragona fishing harbors and in marinas and ports from Almeria: Aguadulce port, Almería port, Almerimar fishing harbour and Almerimar marina. The analytical methodologies were based on Solid Phase Extraction followed by liquid chromatography (LC) or gas chromatography (GC) coupled to a mass spectrometry (MS) or -Diode Array Detector. The main pollutants found in the sampled points were diuron and Irgarol 1051 that were detected at concentrations up to 2.19 µg l−1 and 0.33 µg l−1, respectively. On the other hand, seanine 211 was found at the highest concentration (up to 3.7 µg l−1) during the summer of 1999. Low concentrations of dichlofluanid and the above mentioned degradation products were detected for the first time in the Spanish coasts. Chlorothalonil, TCMTB were not found at concentrations higher than 1 and 20 ng l−1 respectively which were the limit of determination (LOD) of the method for these compounds. In general the contamination at the different marinas is higher at the end of spring and in summer where the boating activity is also higher. This paper shows for the first time that the contamination by the new antifouling pesticides in Spanish coastline, basically marinas and fishing harbours, is permanent along the whole calendar year. So, preventive actions by the harbour authorities will be needed in the near future in order to monitor and control the levels and effects of the new antifouling biocides in the marine environment.

Determination of the pesticide naptalam and its degradation products by positive and negative ion mass spectrometry.

N-1-Naphthylphtalamic acid (naptalam) and its degradation products, 1-naphthylamine and N-(1-naphthyl) phthalimide were simultaneously determined in river water by two independent mass spectrometric (MS) methods. These were negative ion MS (NIMS) and programmable temperature vaporizer gas chromatography mass spectrometry (PTV-GC MS) with electron impact ionization (positive ions). Prior to the NIMS analysis, the samples were preconcentrated by solid phase extraction (SPE) of C18 membrane discs. The PTV-GC MS studies were performed without any preconcentration procedure. Selected ion monitoring (SIM) and internal standardization with naphthalene were applied in both methods. The limits of determination (LOD) of NIMS studies were 230, 270 and 260 ng L-1 for naptalam, 1-naphthylamine and N-(1-naphthyl) phthalimide, respectively, with relative standard deviation (RSD) < 1% (n = 5) and of PTV-GC MS 17, 11 and 15 ng L-1 (RSD < 0.7%, n = 5). The LOD, linearity, RSD and time required for these methods are far better than for HPLC analyses.

Residues of Chlormequat and Mepiquat in Grain—Results from the Danish National Pesticide Survey

The objective of the present work was to establish information on chlormequat and mepiquat residues in grain for human consumption. Chlormequat (2-chloro-N,N,N-trimethylethylammonium, CAS RN 7003-89-6) and mepiquat (1,1-dimethylpiperidinium, CAS RN 15302-91-7) are plant growth regulators used to stabilize stalks in cereals. The study was part of the Danish National Pesticide Survey, managed by the Danish Veterinary and Food Administration. Samples were collected in autumn 1997. Residue contents were determined with a newly developed liquid chromatographic-tandem mass spectrometric (LC-MS/MS) method for chlormequat analysis. The method was extended to include mepiquat in the present study. Quantitation was done by the internal standards method, using mass chromatograms of the most intense daughter ions of mepiquat (m/z 98), chlormequat (m/z 58), and [13C]-chlormequat (m/z 61, internal standard). For chlormequat, the overall limit of detection (LD) was 6 micrograms/kg and the limit of determination (LOD) was 10 micrograms/kg. For mepiquat, LD was 2 micrograms/kg and LOD was 3 micrograms/kg. Of 77 samples analyzed, 51 contained chlormequat and 11 contained mepiquat. The highest levels of chlormequat were found in samples of oatmeal (3.76 mg/kg) and rye (1.08 mg/kg). In 9 rye grain samples containing chlormequat, 5 also contained mepiquat. However, in all samples analyzed, the residues of chlormequat and mepiquat were below maximum residue limits.

Immunochemical detection of aminoglycosides in milk and kidney.

In 1996, the European Union established provisional maximum residue limits (MRL) for gentamicin, neomycin, streptomycin and dihydrostreptomycin in milk and tissue (0.1-5 mg kg-1). For the detection of these four aminoglycosides, three enzyme linked immunosorbent assays (ELISA) for applications in milk and kidney were developed. The screening of defatted and diluted milk resulted in limits of determination (LDM) of < 0.01 mg l-1. Kidney samples were deproteinized with a trichloroacetic acid solution (3%) and after filtration and the addition of buffer, aliquots were used in the ELISA. The LDM of the four aminoglycosides in kidney were < 0.05 mg kg-1. The ELISA were found suitable for the semi-quantitative screening of milk and kidney for the presence of the four aminoglycosides far below the MRL levels. In randomly taken milk samples (n = 776) and in kidneys derived from healthy pigs (n = 124), the aminoglycoside residues found were far below their established MRL. In eight out of the 94 kidney samples obtained from diseased animals after emergency slaughter, aminoglycoside residues were above the MRL.

Determination of Formetanate Hydrochloride in Strawberries

A method was established for determining formetanate hydrochloride in strawberries by reversed-phase high-performance liquid chromatography (HPLC). Formetanate hydrochloride was extracted from strawberries with acidified organic solvents (acetonitrile:HCl:ethyl acetate), and the extract was purified with a solid-phase extraction (SPE) column followed by a strong cation-exchange (SCX) cartridge, and analyzed by HPLC with UV diode array detection at λm of 254 nm. The mobile phase was 0.01 M, pH 8 ammonium phosphate buffer:acetonitrile (70:30). Formetanate was quantitated by the internal standard method. The percent recovery averaged 87.4 ± 2.2 (0.167 mg kg-1), 89.0 ± 2.1 (1.67 mg kg-1), and 91.9 ± 3.2 (16.7 mg kg-1), the limit of determination (LD) was 0.018 mg kg-1, and the limit of quantitation (LQ) was 0.18 mg kg-1. Keywords: Formetanate hydrochloride; strawberries; residue; high-performance liquid chromatography (HPLC)

Limit of detection and limit of determination: Application of different statistical approaches to an illustrative example of residue analysis

For the analysis of organochlorine residues in sediments, sewage sludge and industrial waste water a new combination of well-known residue analytical steps has proved useful. Fortification experiments extensively performed should enable the estimation of limits of detection (LDC) and limits of determination (LDM) for 35 organochlorine compounds. The statistical evaluation of the analytical results showed, however, that with just 5 blank analyses and 5 analyses at a reasonable low fortification level, LDC and LDM estimates could be calculated which appeared to be exact enough for most purposes of daily residue analytical work.