Trace determination of peptides in water samples using packed capillary liquid chromatography with UV and MS detection and characterization of peptide oxidation products by MS

A capillary liquid chromatographic column switching method has been developed for fast and sensitive determination of peptides in water samples. Sample volumes of 1 mL were loaded onto a (320 m I.D. ×30 mm) 10 m Kromasil C₁₈ pre-column, providing on-line analyte enrichment, prior to back-flushed elution onto a (320 m I.D. ×150 mm) 3.5 m Kromasil C₁₈ analytical column. Loading flow rates of 250 L/min and a mobile phase composition of acetonitrile/water/trifluoroacetic acid (22/77.9/0.1, v/v) provided a total analysis time of less than 25 minutes for the test peptides angiotensin II, bombesin, bradykinin, corazonin, neurotensin and substance P, using temperature programmed elution. In addition, solvent gradient elution and combined solvent gradient elution and temperature programming were explored. Using on-capillary UV detection at 210 nm resulted in a concentration limit of detection (cLOD) of about 1 ng/mL. The method was validated over the concentration range 1–100 ng/mL, yielding a coefficient of correlation of 0.997 or better. The within-assay (n=6) and between-assay (n=6) precisions of peak areas were on average 6% RSD and 5% RSD, respectively.When the method was applied to spiked chlorinated tap water samples, it was found that peptides containing methionine, tryptophan and cystine were oxidized. Identification of the oxidation products of the peptides in hypochlorite-treated water was done with positive electrospray ionization time-of-flight mass spectrometric detection.     

Intermediate oxygen-containing compounds in oxidative condensation of methane over sodium-manganese catalysts

CH₂O conversion over sodium-manganese oxide and oxychloride catalysts in methane dehydrodimerization have been studied under unsteady-state conditions at high temperatures (600–750 °C). It has been established that formaldehyde conversions produce deep oxidation (CO, CO₂), condensation (C₂H₄, C₂H₆) and methanation products through CH₃O^– formation and decomposition.

---

(600–750°C) CH₂O - . , (CO, CO₂) (C₂H₄, C₂H₆), , CH₃O^–.

     

Study of the absorption spectra of the 4f electron transition of the Nd and Er complexes with 2-isobutylformyl-1,3-dione-indane in the presence of TX-100 and its analytical application

The absorption spectra of 4f electron transitions of the systems of neodymium and erbium with 2-isobutylformyl-1,3-dione-indane and TX-100 have been studied by normal and derivative spectrophotometry. Their molar absorptivities at the maximum absorption bands are about 7.2 (at 571 nm) times greater for neodymium and 13.1 (at 519 nm) times greater for erbium than those in the absence of the complexing agents. Use of second derivative spectra both eliminates the interference from other rare earths and increases the sensitivity from neodymium and erbium. Beers law is obeyed from 020 g/ml for neodymium and 025 g/ml for erbium. The relative standard deviations are 1.2% and 1.6% for 5.0 g/ml of neodymium and 8.0 g/ml of erbium, respectively. The detection limits (signal-to-noise ratio=2) are 0.14 g/ml and 0.20 g/ml. A method for the direct determination of neodymium and erbium in rare earth mixtures with good accuracy and selectivity is proposed.     

Polypyrrole modified stainless steel frits for on-line micro solid phase extraction of ochratoxin A

Polypyrrole (PPy) was electrochemically synthesized on stainless steel frits as a sorbent for the micro solid phase extraction (SPE) of ochratoxin A (OTA). Using 20 l of standard solution under a fast flow rate of 0.5 ml/min, 80% recovery of OTA was achieved in the concentration range from 0.1–10 pg/l. This good recovery was achieved within a short residence time of 1.2 s. A binding capacity of 1 ng OTA was estimated for each PPy-modified frit, or 2 ng OTA for two frits in series. The bound OTA could be pulsed eluted (PE) with 20 l of 1% triethylamine in acetonitrile. On-line coupling of this PPy-on-a-frit and PE technique to high performance liquid chromatography (HPLC) was straightforward. On-line SPE-PE-HPLC results clearly demonstrated the capability of PPy-on-a-frit to bind OTA in the presence of red wine, beer, and orange juice components.     

Effect of Surfactants on the Immobilization of 4-(2-Pyridylazo)resorcinol on Silochroms

The effect of cationic surfactants (cetyltrimethylammonium bromide, cetylpyridinium bromide, and tetrabutylammonium perchlorate) and a nonionic surfactant (OP-7) on the conditions of the immobilization of 4-(2-pyridylazo)resorcinol (PAR) on three types of silica gel (Silochrom S-120 (200–350 m), Silochrom S-120 (315–500 m), and Silochrom S-80 (200–350 m)) was studied. It was found that OP-7 does not affect the adsorption of surfactants. The effect of cationic surfactants increases in the order tetrabutylammonium perchlorate < cetyltrimethylammonium bromide < cetylpyridinium bromide. The adsorption activity of silica gels increases in the order Silochrom S-120 (315–500 m) < Silochrom S-80 (200–350 m) < Silochrom S-120 (200–350 m). Cetylpyridinium bromide provides full immobilization of PAR on silica gel Silochrom S-120 (200–350 m) in the pH range 2–9.     

Anwendung der Ringofenmethode zum Nachweis einiger Heteroelemente in organischen Verbindungen

Zusammenfassung Ein schnelles und einfaches Mikroverfahren zum Nachweis einiger Heteroatome organischer Verbindungen wurde entwickelt. Nach Aufschluß mit metallischem Kalium werden die entstehenden Ionen mit der Ringofenmethode getrennt und mit empfindlichen Reaktionen nachgewiesen. Nachweisgrenze: 0,5 bis 1g Stickstoff, 1 bis 2g Schwefel, 2 bis 3g Jod, 4 bis 5g Brom, 5 bis 10g Chlor in 0,5 bis 1 mg Einwaage.

---

Summary A rapid and simple micromethod was developed for the detection of several hetero-elements in organic compounds. After breaking down the sample with metallic potassium, the resulting ions are separated by the ring oven method and detected by means of sensitive reagents. Detection limits: 0.5 to 1g nitrogen, 1 to 2g sulfur, 2 to 3g iodine, 4 to 5g bromine, 5 to 10g chlorine in samples weighing 0.5 to 1 mg.

---

Résumé On a découvert un procédé à l'échelle micro, simple et rapide, pour rechercher certains hétéroéléments dans les composés organiques. Après mise en solution par le potassium métallique, on sépare les ions formés suivant la méthode du four annulaire et l'on effectue la recherche au moyen de réactions sensibles. Limite de dilution: 0,5 à 1g d'azote, 1 àg de soufre, 2 àg d'iode, 5 à 10g de chlore sur 0,5 à 1 mg de prise d'essai.

     

Quantum-Chemical Calculations of Palladium(II) Complexes and Clusters

The structural parameters of stable palladium(II) compounds, namely, [Pd(-OAc)₂]₃, Pd(OAc)₂ · 2NHEt₂, [Pd(OAc)(-OAc)(CH₃)₂SO]₂, [Pd(-OAc)(-SEt)]₄, and [Pd(-SEt)₂]₆, were determined by relativistic and nonrelativistic calculations using the density functional method with account taken of all electrons or with the use of pseudopotentials. The gradient functional (PBE) and local density functional (LSDA) ensure good agreement between the calculated structural parameters of the Pd(II) complexes and clusters under study and data of X-ray diffraction analysis.     

Simultaneous determination of copper,mercury and lead by first-order derivative spectrophotometry using dithizone as reagent

A first-order derivative spectrophotometric method has been developed for the simultaneous determination of copper, mercury and lead at g/L levels using dithizone as reagent. The procedure involves the simultaneous extraction of these elements by dithizone in chloroform from weakly alkaline solutions. Linear calibration curves were obtained in the ranges 0.5–10 (Cu), 1–10 (Hg) and 1–10 (Pb) g present in 40 ml of aqueous phase with detection limits of 5 g/L (Cu) and 20 g/L (Hg and Pb). The R.S.D.s for 100 g/L of copper, mercury and lead were 2.5, 2.6 and 3.1% respectively, for 5 determinations. The method is applicable for the determination of copper and lead in marine sediment samples with good precision and accuracy.     

Vacuum ultraviolet spectroscopic analysis of nitrogen in iron and steel with low-voltage condensed-spark discharge

Summary The determination of nitrogen in steels was investigated by low voltage condensed spark discharge and far ultraviolet vacuum spectroscopy. The excitation conditions were 1,000V, 193, 63 F and 50H in helium atmosphere of 700 mm Hg. Nitrogen contents from 20 ppm to 100 ppm in steel could be determined with the line pair of N I 1,745 Å/Fe I 1,876 Å or N I 1,742 Å/Fe I 1,876 Å.

---

Zusammenfassung Zur Bestimmung von Stickstoff (20–100 ppm) in Stählen wurde eine UV-vakuumspektrometrische Methode mit Niederspannungs-Funkenentladung benutzt. Die Entladungsbedingungen waren: 1000 V, 193 , 63 F und 50 H, unter Heliumatmosphäre von 700 mm Hg; verwendet wurden die Linienpaare N I 1,745 Å/Fe I 1,876 Å oder N I 1,742 Å/ Fe I 1,876 Å.

     

Flow injection analysis at μl/min flow rates

The characteristics of knitted open tube (KOT) figure eight reactors and coil reactors at l/min flow rates were compared using plate height (H) calculations and peak height measurements. Peak broadening independent of flow rate was seen for the figure eight KOT but not the coil at flow rates of 150–300 l/min. Below 150 /min, the plate height values of both reactors were inversely proportional to flow rate. It was concluded that a 0.5-m KOT figure eight reactor is the most effective way to introduce delay time for a 1 1 injection size and tubing of 0.3 mm I.D. Enhancement of peak height response was particularly pronounced at flow rates less than 100 l/min.     

New cobalt trimethylacetate complexes with pyridine

The reaction of the tetranuclear trimethylacetate complex Co₄(₃-OH)₂(-OOCCMe₃)₄(²-OOCCMe₃)₂(EtOH)₆ with pyridine in acetonitrile was studied. Two new compounds, viz., the hexanuclear cobalt(ii) complex Co₆py₄(₃-OH)₂(-OOCCMe₃)₁₀ (25% yield) and the unusual ionic compound [Co₃py₃(₃-O)(-OOCCMe₃)₆]⁺[Co₄py(₄-O)(-OOCCMe₃)₇]^– (5% yield), were prepared. The structures of the new compounds were established by X-ray diffraction analysis.     

Bestimmung von Borspuren in Metallen durch Emissionsspektrometrie mit ICP-Anregung nach Abtrennung als Bors?ure-Ester

Zusammenfassung Zur Bestimmung von Borgehalten im ng/g- und unteren g/g-Bereich in Metallen (Mo, W, Zr, Al, Fe, Co) wurden Verbundverfahren ausgearbeitet, bei denen Bor nach geeignetem Probenaufschluß durch Destillation des Borsäuremethylesters oder durch Ausschütteln als 2-Ethyl-1,3-hexandiol-Komplex abgetrennt und emissionsspektrometrisch mit ICP-Anregung (ICP-OES) bestimmt wird. Mit einer neu entwickelten Kreislaufdestillationsapparatur aus Quarzglas lassen sich Bormengen zwischen 0,02 und 20 g innerhalb von 15 min aus schwefeloder schwefel-phosphorsauren Lösungen von Metallen (Einwaage1g) quantitativ als Methylester abtrennen und in wenigen Millilitern alkalischer Lösung konzentrieren. Das Verfahren ist für alle Metalle anzuwenden, für die man zum Lösen keine HF benötigt. Die Ethylhexandiol-Extraktion wurde für die Abtrennung von 0,02 bis 1 g Bor optimiert, wobei besonders die Matrices Mo, Fe, Zr und Al untersucht wurden. Die ICPOES ist für die Bestimmung von Gehalten an abgetrenntem Bor von 20 ng/ml geeignet. Je nach Matrix und Höhe der Einwaage können somit Nachweisgrenzen von 0,02 g/g erreicht werden.

---

Determination of traces of boron in metals by emission spectrometry with ICP after separation as boric acid ester

Summary Procedures for the determination of boron in the ng/g- and low g/g-range in metals (e.g. Mo, W, Zr, Al, Fe, Co) by emission spectrometry (OES) with inductively coupled hf-plasma (ICP) excitation have been investigated. The procedures involve the suitable dissolution of the samples and the separation of boron either by distillation of boric acid methyl ester with a new circulation distillation apparatus or by liquid extraction of the 2-ethyl-1,3-hexanediol complex. By distillation 0.02 to 20 g of boron are separated within 15 min from sulphuric or sulphuric-phosphoric acid solutions ( 1g of sample) and are concentrated in a few milliliters of NaOH. This separation is applicable to all metals which do not require hydrofluoric acid for dissolution. The ethylhexanediol extraction has been optimized for 0.02 to 1 g of boron in solutions of Mo, Fe, Zr, and Al. With ICP-OES concentrations of separated boron of 20 ng/ml can be determined, corresponding to limits of detection down to 0.02 g/g, depending on matrix and sample weight.

---

---

Herrn Professor Dr. W. Fresenius zum 70. Geburtstag gewidmet     

Determination of sulphathiazole in the presence of sulphametazine by first-derivative solid-phase spectrophotometry

Sulphathiazole in the presence of sulphametazine is determined by a method based on derivative solid-phase spectrophotometry. Both compounds are fixed on a dextran-type cation-exchange gel. The absorbance of the gel, packed in a 1-mm silica cell, is measured directly. The range of application is between 0.20 and 18.0 g/ml of sulphathiazole in the presence of up to 20 g/ml of sulphametazine, the relative standard deviation is 0.6% and the detection limit is 0.05 g/ml. The method has been applied to the determination of sulphathiazole in synthetic mixtures and pharmaceuticals, with recoveries of 95.0 to 102.5%     

Semiquantitative estimation of the mycotoxins citrinin, Ochratoxin A, Aflatoxin M1 and penicillic acid on thin-layer chromatograms with a grey scale

Summary Spots of citrinin, ochratoxin A, aflatoxin M₁ and penicillic acid on thin-layer chromatograms can be semi-quantitatively estimated by using a grey scale, commonly used in photo laboratories. The detection limits are 0.01 g for citrinin, 0.006 g for ochratoxin A, 0.002 g for aflatoxin M₁ and 0.01 g for penicillic acid. Standard curves for these mycotoxins are given.

---

Halbquantitative Bestimmung der Mycotoxine Citrinin, Ochratoxin A, Aflatoxin M₁ und Penicillinsäure auf Dünnschicht-Chromatogrammen mit Hilfe eines Graukeils

Zusammenfassung Mit Hilfe eines in Photolabors gebräuchlichen Graukeils können dünnschicht-chromatographische Flecke der obengenannten Mycotoxine halbquantitativ bestimmt werden. Die Nachweisgrenzen betragen 0,01 g für Citrinin, 0,006 g für Ochratoxin A, 0,002 g für Aflatoxin M₁ und 0,01 g für Penicillinsäure. Eichkurven werden angegeben.

     

Production of96Tc and95mTc via the93Nb(α, xn) Reactions

Relatively longer liver technetium tracers such as^95mTc (61 d) are useful for the development, evaluation and comparison of new technetium complexes for eventual development of^99mTc radiopharmaceuticals. The feasibility of producing⁹⁶Tc (4.35 d) and^95mTc (61 d) was studied by the alpha bombardment of pure Nb targets (⁹³Nb-100%).⁹⁶Tc was obtained in a yield of 30 Ci/Ah using 16 MeV alphas, but it contained significant activity of⁹⁵Tc (20 h) Relatively pure⁹⁶Tc and^95mTc was produced in yields of 18 Ci/Ah and about 1 Ci/Ah respectively with alphas of suitable energy and after allowing for suitable cooling periods after the end of bombardment (EOB).     

Nickel(II) xanthates with nitrogen heterocycles as bridging ligands

New homopolynuclear nickel(II) xanthate complexes with nitrogen donor heterocycles as bridging ligands have been prepared, namely [Ni(Rxa)2(-L)]n and [Ni2(Rxa)4(-L1)], where R=i-Pr,i-Am; xa=OCS2– L=1,2-bis(4- pyridyl)ethane (bpe), 4,4-dithiodipyridyl (dtp), 1,2-bis(4- pyridyl)ethylene (dpe), 4,4-trimethylene-dipyridine (tmd); L1=2,3-bis(2-pyridyl)pyrazine (bpp), 2,4-bis(5,6- diphenyl-1,2,4-triazine-3-yl)pyridine (bdt), or 2,4,6-tris(2- pyridyl)-1,3,5-triazine (tpt). The compounds have been characterized by elemental analyses, i.r. and electronic spectroscopies, magnetochemical and conductivity measurements. The results show that the [Ni(Rxa)2(-L)]n complexes are linear polymers in which the nitrogen heterocycles bridge between the nickel(II) ions, which are coordinated by four sulfur and two nitrogen atoms and have trans-octahedral geometry. The nearly constant values of the effective magnetic moment (3.36–3.34 eff/B) over the 77–295 K temperature range indicate that exchange interactions are lacking among the paramagnetic centres in the linear structure, [Ni(i-Amxa)2(dpe)]n. The variable- temperature magnetic susceptibilities of the [Ni2(i-Prxa)4(bpp)] (3.00–2.95eff/B per Ni atom), [Ni2(i-Prxa)4(bdt)] (2.72–2.63 eff/B per Ni atom), and [Ni2(i-Amxa)4(tpt)] (2.76–1.87 eff/B per Ni atom) were measured down to liquid nitrogen temperature. In the case of binuclear nickel(II) complexes with bdt or tpt, antiferromagnetic coupling between the nickel(II) ions was detected, giving the exchange integral J=–4.0cm–1 and –29.6cm–1, respectively.     

Hydrogen profiling in thin films using coincident ERD

By using the coincident measurement, an ERD method has been established and used for hydrogen profiling in thin foils. In the present study, 6 MeV has been used as incident particle, the scattered and the recoiled proton from one collision were coincidentally detected at 150 (proton) and 173.9 (). This method has been used for hydrogen profiling of 5.6 m Mylar and 8.6 m aluminium foils. Because of the coincident measurement, the background is largely reduced, and its minimum detection limit is about 0.5% (atomic), lower than the conventional ERD method. The measured depth resolution in 5.6 m Mylar is 0.6 m. It is possible to use this method for hydrogen profiling in thin foils of several micron thickness.