Determination of 1-(2-methoxyphenyl)piperazine derivatives of isocyanates at low concentrations by temperature-programmed miniaturized liquid chromatography

Investigation of reagent distributions on glass fiber membrane filters used in air sampling

This project has arisen from the need to produce GFFs (glass fiber filters) bearing a thin and evenly distributed coating of a selected reagent in the equatorial plane for breakthrough studies. However, it has been discovered that today's two general techniques for coating GFFs (total immersion and application of reagent solution to GFFs) have usually produced unevenly distributed coatings of reagent in the equatorial plane. In addition, quantities of reagent on GFFs from commercial sources may vary widely in the same lot of coated GFFs. Consequences are variability in capacity of coated filters at the point of breakthrough and, perhaps, wasted reagent. Although today's reagent-coated filters may be satisfactory for routine air sampling, such filters may be unacceptable for precise breakthrough studies. Research has been conducted successfully to produce nearly evenly distributed coatings of reagents in the equatorial plane of GFFs by application of reagent solutions to the centers of GFFs which are resting on crisscrossing, fine, stainless-steel wire. Distributions of coatings have been determined by punching out twenty-one 5-mm circles from each GFF and analyzing each circle by flow-injection with a UV detector. Lowest achievable relative standard deviations of measurement (RSDs) for reagents in 5-mm circles have been 5 to 7%. Reagents studied have included 1-(2-pyridyl)piperazine (1-2PP), 2,4-dinitrophenylhydrazine (DNPH), and 1-(9-anthracenylmethyl)piperazine (MAP). Factors affecting the distribution of such coatings include choice of reagent and choice of solvent for the reagent solution.

Determination of airborne isocyanates

Isocyanates are important in industrial hygiene and workplace monitoring. Owing to their severe acute toxicity and sensitizing properties, analytical methods with high sampling efficiency and sensitivity in the low ppb to ppt range are required. The reactivity of isocyanates necessitates initial derivatization with nucleophilic agents--usually amines--for stabilization and enrichment; this is often followed by chromatographic separation with spectroscopic, electrochemical, or mass spectrometric detection. Sampling strategies for airborne isocyanates comprise active, i.e. pumped, or passive, i.e. diffusive, methods; the method selected depends on the application. Whereas active methods rely mainly on impingers, reagent-coated filters, or sampling tubes, passive samplers make use of reagent-coated filters, the surface of which is connected to the air sample by diffusion channels. Because airborne isocyanates are prone to occur in different forms, i.e. as vapors, as aerosols, or adsorbed on particulate matter, denuder sampling has been introduced, thus enabling simultaneous collection of gaseous and aerosol isocyanates. The first part of this review summarizes chemical methods and reagents which have been introduced for derivatization of airborne isocyanates. The advantages and drawbacks of the individual derivatization procedures and their combination with different detection principles are evaluated. In the second part, the most recent developments in air sampling for isocyanates, with special focus on diffusive sampling, are reviewed and critically discussed.

Validation of a diffusive sampling method for airborne low-molecular isocyanates using 4-nitro-7-piperazinobenzo-2-oxa-1,3-diazole-impregnated filters and liquid chromatography–tandem mass spectrometry

A diffusive sampling method for the determination of low-molecular isocyanates as their 4-nitro-7-piperazinobenzo-2-oxa-1,3-diazole (NBDPZ) derivatives using tandem mass spectrometry (MS/MS) after atmospheric pressure chemical ionisation (APCI) is presented. Isocyanic acid (ICA), methyl isocyanate (MIC), ethyl isocyanate (EIC) and phenyl isocyanate (PhIC) are collected on NBDPZ-impregnated polystyrene divinyl benzene (SDB) filter tapes. The method was validated for MIC, EIC and PhIC for concentrations between 0.5 and 50 ppb at relative humidity (RH) conditions from 10 up to 90%. Validation was carried out by active sampling using 1-(2-methoxyphenyl)piperazine (2-MP) as derivatising agent. Sampling periods applied were between 15 min and more than 8 h. The sampling rates were determined to be 21.0 mL/min for MIC with a relative standard deviation (RSD) of 9.0% for 184 samplers, 15.6 mL/min for EIC (RSD 11.6%; N = 154) and 11.5 mL/min for PhIC (RSD 8.4%; N = 87). The limits of quantification were 1.4 ppb for MIC and 1.3 ppb for EIC and PhIC applying 15 min sampling periods. Owing to high background signals, isocyanic acid could only be determined when it was present in concentrations in the high ppb range.

Effect of temperature on the separation of chlorophenoxy acids and carbamates by capillary high-performance liquid chromatography and UV (or diode array) detection

In this work, the effect of temperature in isothermal and programmed modes on several chromatographic parameters such as retention factor, selectivity, resolution and plate number has been discussed. A critical comparison of isocratic/isothermal, gradient/isothermal and isocratic/program temperature modes has been made. Two representative families of pesticides have been selected for this study. One includes ionisable chlorophenoxy acids and two of their esters, some of which show similar polarities. The other one contains several weakly polar carbamates. Analysis was carried out using a reversed-phase capillary high-performance liquid chromatography (HPLC) system and focusing technique with UV or diode array detection (DAD).

Ferrocenoyl piperazide as derivatizing agent for the analysis of isocyanates and related compounds using liquid chromatography/electrochemistry/mass spectrometry (LC/EC/MS)

Ferrocenoyl piperazide is introduced as a new pre-column derivatizing agent for the analysis of various isocyanates in air samples using reversed-phase liquid chromatographic separation, electrochemical oxidation/ionization, and mass spectrometry. The nonpolar derivatives can be separated well using a phenyl-modified stationary phase and a formic acid/ammonium formate buffer of pH 3, which yields excellent separations, especially for one problematic group of isocyanates consisting of 2,4- and 2,6-toluylenediisocyanate (2,4- and 2,6-TDI) and hexamethylenediisocyanate (HDI). Electrochemical oxidation at low potentials (0.5 V versus Pd/H(2)) leads to formation of charged products, which are nebulized in a commercial atmospheric pressure chemical ionization (APCI) source, with the corona discharge operated only at low voltage. Limits of detection between 6 and 20 nmol/L are obtained for the isocyanate derivatives, and calibration is linear over at least two decades of concentration. The method is applied for the analysis of air after thermal degradation of a polyurethane foam, and it is demonstrated that it is suitable as well for the analysis of carboxylic acid chlorides and of isothiocyanates.

Temperature optimization for improved determination of phosphatidylserine species by micro liquid chromatography with electrospray tandem mass spectrometric detection

A sensitive method for determination of disaturated phosphatidylserine species in the presence of their monounsaturated analogs has been developed, using micro liquid chromatography coupled to electrospray ionization tandem mass spectrometry. The hydrophobic nature of the phosphatidylserine species required a combination of low-eluting sample solvents and sub-ambient temperatures in order to focus large sample volumes up to 20 microL. The samples were dissolved in 2-propanol:hexane:water (20:10:4, v/v/v) prior to 1:9 dilution with ammonium formate buffer:2-propanol:tetrahydrofuran (30:55:15, v/v/v) and final 1:4 dilution with ammonium formate buffer (10 mM):2-propanol: tetrahydrofuran (55:37.5:7.5, v/v/v). The analytical column was a 0.5 x 150 mm stainless steel column packed with 5 microm C30 particles, while the mobile phase contained ammonium formate buffer (10 mM): 2-propanol:tetrahydrofuran (30:55:15, v/v/v). A temperature program from 5 degrees C (hold for 3 minutes) to 75 degrees C at 8 K/min provided separation of the disaturated phosphatidylserine species from their monounsaturated analogs, making available a sensitive determination of the isobaric species. The mass limit of detection for dipalmitoyl phosphatidylserine was 100 pg, corresponding to a concentration limit of detection of 5 pg/microL when using an injection volume of 20 microL. This is an improvement by a factor of 20 as compared to previously reported numbers obtained with conventional LC columns. The within-assay precision of dipalmitoyl phosphatidylserine was 11.9% RSD (n = 3), while the retention time precision was 4.1% RSD (n = 6).

MMNTP—a new tailor-made modular derivatization agent for the selective determination of isocyanates and diisocyanates

The synthesis of a new tailor-made derivatization agent for the selective determination of (di)isocyanates is presented. Starting from cyanuric chloride, the reagent 4-methoxy-6-(4-methoxy-1-naphthyl)-1,3,5-triazine-2-(1-piperazine)(MMNTP) is synthesized by subsequent substitution of the three chlorine atoms. This new derivatization agent and the five urea derivatives of phenylisocyanate (PI), hexamethylene-diisocyanate (HDI), toluene-2,4-diisocyanate (2,4-TDI), toluene-2,6-diisocyanate (2,6-TDI) and methylenebisphenyl-4,4-diisocyanate (MDI) show good spectroscopic properties with small compound-to-compound variabilities (RSD([epsilon])= 5.3 %, RSD(relative fluorescence)= 9.4 %). Therefore, using UV detection, a single calibration is needed for the quantification of all diisocyanates and isocyanates respectively. For separation and analysis a HPLC method with a RP column and a binary gradient is presented. All derivatives are separated and show low limits of detection. In addition to the good spectroscopic properties and low limits of detection, good reactivity for the derivatizations at room temperature is observed. The aromatic diisocyanates can be measured immediately whereas aliphatic diisocyanates need 2 h incubation. These advantages make MMNTP a powerful and versatile derivatization agent for (di)isocyanates which is demonstrated by a real sample with solid phase sampling, where the reagent is coated on a sorbent.

Determination of unreacted 2,4-toluene diisocyanate (2,4TDI) and 2,6-toluene diisocyanate (2,6TDI) in foams at ultratrace level by using HPLC-CIS-MS-MS

Isocyanates can cause occupational asthma. By using available HPLC-UVF methods, isocyanates can be quantified only at levels above 1% of the Permissible Exposure Limits (PEL). Once sensitized, workers can react to concentrations below these limits of detection (LOD) making these methods insufficiently sensitive to adequately evaluate trace amounts of isocyanates present in air or in materials at safe levels for sensitized workers. This article describes a novel method for isocyanate analysis allowing the quantification of 2,4TDI and 2,6TDI monomers at very low concentrations using HPLC-CIS-MS-MS. The method's sensitivity increases with a decrease in the alkali radius. The LOD is 0.039 ng mL(-1) for 2,4TDI and 0.100 ng mL(-1) for 2,6TDI in solution when lithium is the alkali adduct, which is 20 times more sensitive than HPLC-UVF method. This new method allows determination in foam at levels of 0.078 ng g(-1) for 2,4TDI and 0.200 ng g(-1) for 2,6TDI respectively, for a 0.5 g foam sample. This is more than 100 times more sensitive than other methods for determining free monomers in solid materials. Analytical reproducibility and precision are better than 92% and 93% for both diisocyanate monomers. The use of HPLC-UVF conventional method failed to detect unreacted isocyanates in foam samples, but TDI monomers were quantified by HPLC-CIS-MS-MS.

High-temperature liquid chromatography

The present state of the active use of elevated temperatures in liquid chromatography is reviewed, including the effects on retention, selectivity and efficiency. Separations in aqueous mobile phases as well as non-aqueous media are discussed, with particular emphasis on narrow-bore columns.

Workplace monitoring of isocyanates using ion trap liquid chromatography/tandem mass spectrometry

A sensitive liquid chromatography/ion trap tandem mass spectrometry method was developed for the qualitative and quantitative detection of isocyanates in air. The method is based on derivatization of isocyanates with 1-(2-methoxyphenyl)piperazine during air sampling. The extracts are analyzed using an ion trap LC/MS system equipped with an electrospray (ESI) ion source. The method shows high linearity, specificity, accuracy and precision. The limits of detection are 40x to 55x lower than with UV-based methods.

4-Nitro-7-piperazino-2,1,3-benzoxadiazole as a reagent for monitoring of airborne isocyanates by liquid chromatography

4-Nitro-7-piperazino-2,1,3-benzoxadiazole (NBDPZ) is presented as a new reagent for the determination of mono- and diisocyanates in air samples. NBDPZ readily reacts with the airborne analytes, thus yielding the corresponding urea derivatives, which are subsequently separated by means of reversed-phase liquid chromatography. On a phenyl-modified stationary phase, excellent baseline separation for numerous mono- and diisocyanate derivatives is obtained. Both diode array and fluorescence detection are performed with limits of detection of 11-35 and 5-9 nmol/L for the individual derivatives, respectively. In contrast to established derivatizing agents for the analysis of isocyanates, NBDPZ provides for increased selectivity due to the favorable detection wavelengths in the visible range (UV/visible, absorption maximums approximately 480 nm; fluorescence, excitation maximums approximately 470 nm, emission maximums approximately 535 nm). In addition, the high molar absorptivities of the reagent and the derivatives provide excellent sensitivity that is superior to most literature-known methods. Finally, air sampling methods comprising both the use of impingers and test tubes are developed and successfully applied to the determination of isocyanates in gaseous samples. Excellent recovery reaching values of >90% is observed for each of the two techniques investigated.

Harmonized Nordic strategies for isocyanate monitoring in workroom atmospheres

The Nordic Network on Isocyanates (NORDNI) is financed by the Nordic Council of Ministers and is under the administration of Prof. Yngvar Thomassen and co-workers. National Institute of Occupational Health, Norway. The aim of NORDNI is to establish a broad network between the Nordic National Institutes of Occupational Health working within the field of isocyanate exposure and strategies for sampling and determination of isocyanates in workroom atmospheres. This viewpoint article summarizes the resolutions that were established at the 1st NORDNI consensus meeting arranged in Frøya, Norway, 31st August-2nd September, 2001. The consensus platform from the 1st NORDNI meeting was presented at the 4th International Symposium on Modern Principles of Air Monitoring, Lillehammer, Norway, 3-7 February, 2002.

Simultaneous determination of citalopram, fluoxetine, paroxetine and their metabolites in plasma by temperature-programmed packed capillary liquid chromatography with on-column focusing of large injection volumes

A miniaturized temperature-programmed packed capillary liquid chromatographic method with on-column large volume injection and UV detection for the simultaneous determination of the three selective serotonin reuptake inhibitors citalopram, fluoxetine, paroxetine and their metabolites in plasma is presented. An established reversed-phase C8 solid-phase extraction method was employed, and the separation was carried out on a 3.5-microm Kromasil C18 0.32x300 mm column with temperature-programming from 35 (3 min) to 100 degrees C (10 min) at 1.3 degrees C/min. The mobile phase consisted of acetonitrile-45 mM ammonium formate (pH 4.00) (25:75, v/v). The non-eluting sample focusing solvent composition acetonitrile-45 mM ammonium formate (pH 4.00) (3:97, v/v) allowed injection of 10 microl or more of the plasma extracts. The method was validated for the concentration range 0.05-5.0 microM, and the calibration curves were linear with coefficients of correlation >0.993. The limits of quantification for the antidepressants and their metabolites ranged from 0.05 to 0.26 microM. The within and between assay precision of relative peak height were in the range 2-22 and 2-15% relative standard deviation, respectively. The within and between assay recoveries were in the 61-99 and 54-92% range for the antidepressants, respectively, and between 52-102 and 51-102% for the metabolites.

Improved method for the simultaneous determination of d4T, 3TC and ddl intracellular phosphorylated anabolites in human peripheral-blood mononuclear cells using high-performance liquid chromatography/tandem mass spectrometry

There is still a need for direct determination (i.e. without dephosphorylation) of nucleoside reverse transcriptase inhibitor (NRTI) triphosphorylated nucleotides in the peripheral-blood mononuclear cells (PBMCs) of HIV-positive patients. The objective of this paper was first to improve our previously described direct liquid chromatography/tandem mass spectrometry (LC/MS/MS) assay for stavudine triphosphate (d4T-TP). Preparation of PBMCs was modified to reduce degradation of d4T-TP during cell preparation and to simplify this step for routine use in clinical units. The performance of several HPLC columns was compared in order to improve the stability of peak shape over time. The SMT C(18) column was replaced by a Supelcogel ODP-50, thereby reducing two-fold the concentration of the first standard. Various internal standards were compared to optimize peak shape and remove an interfering peak in LC. 2-Chloroadenosine 5prime prime or minute-triphosphate was chosen as the most appropriate internal standard. Substitution of the narrowbore column by a microbore column (150 x 0.32 mm) is also presented and discussed. Secondly, this improved method was successfully applied to the simultaneous determination of d4T-TP, dideoxyadenosine triphosphate (ddA-TP) and lamivudine triphosphate (3TC-TP) in PBMCs, which is useful in view of the common use of NRTI combinations. The method was subsequently applied to clinical samples from HIV-positive patients receiving antiretroviral therapy containing d4T, ddl and/or 3TC. This method can be used simply and routinely on approximately 200 samples per week, using commercially available instruments and with a simple cell lysis as sample treatment.

Separation of polyethylene glycol oligomers using inverse temperature programming in packed capillary liquid chromatography

Inverse temperature programming in packed capillary liquid chromatography coupled to evaporative light-scattering detection has been used to resolve native polyethylene glycol (PEG) oligomers. The model compound, PEG 1000, was separated on a 300 mm x 0.32 mm I.D. capillary column packed with 3 microm Hypersil ODS particles with acetonitrile-water (30:70, v/v) as mobile phase. The retention of the PEG oligomers increased with increasing temperature, different from what is commonly observed in liquid chromatography. The retention times of the oligomers were approximately doubled for each 25 degrees C increment of the column temperature in the temperature range 30-80 degrees C. The oligomers were almost unretained and co-eluted at a column temperature of 30 degrees C. At 80 degrees C a baseline separation of more than 22 peaks was obtained, but the last eluting peaks were severely broadened and all oligomers did not elute. When a negatively sloped temperature ramp from 80 to 25 degrees C at -1.5 degrees C/min was applied, the peak shapes were improved, additional peaks were detected and the analysis time was reduced by 48%. In the temperature programming mode, the intra-day precision of the retention times ranged from 0.5 to 5.8% (n=5).