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.     

Development of an Ion-pair HPLC method for the determination of 2,4- and 2,6-toluendiamine in human plasma

Summary An ion-pair HPLC method is presented for the determination in plasma of 2,4- and 2,6-toluendiamine (TDA), known carcinogens. The chromatographic conditions consisted in isocratic elution on a reversed phase C₁₈ column with 5 mM octanesulfonic acid in methanol-water, 45∶55, as mobile phase. UV detection was performed at 235 nm. Samples were analyzed after a simple single step liquid-liquid extraction and the method was validated by measurement of precision (interassay and intraassay), sensitivity, specificity, linearity, and recovery. The detection limit for both TDAs in plasma was 20 ng mL⁻¹. The correlation coefficients based on the intrassay calibration curve were 0.998 and 0.997 for 2,6- and 2,4-TDA, respectively. The intraassay accuracy, expressed in terms of recovery, was found to be up to 89.91% and 97.05% for 2,6- and 2,4-TDA, respectively.     

Determination of tocopherols,tocopherolquinones and tocopherolhydroquinones by gas chromatography-mass spectrometry and preseparation with lipophilic gel chromatography

A method has been developed for the simultaneous determination of a range of aromatic amines using cation-exchange chromatography performed on a standard ion chromatography column using d.c. amperometric detection. The analytes separated were 2,4- and 2,6-toluenediamine (2,4- and 2,6-TDA), aniline, o-toluidine, benzidine, p-chloroaniline, 4,4'-diaminodiphenyl (4,4'-DDP), m-nitroaniline and 1-naphthylamine. A Dionex CS12 column was used with gradient elution from an initial eluent of 5% CH3CN+35 mM H2SO4 to 27% CH3CN+35 mM H2SO4 (at 35 min). Detection limits in the range 2.6-22.6 microg/l were observed for all analytes except m-nitroaniline, for which the detection limit was 201 microg/l. Linear calibrations and good precision were observed and the method was applied to the determination of benzidine, p-chloroaniline and 1-naphthylamine in wastewater samples. Further, the separation was also used (after some modification of the eluent conditions) for the determination of 2,4- and 2,6-toluene diisocyanate (2,4- and 2,6-TDI) and 4,4'-methylenediphenyl diisocyanate (4,4'-MDI) after their hydrolysis to 2,4-TDA, 2,6-TDA and 4,4'-DDP. Detection limits for 2,6- and 2,4-TDI and 4,4'-MDI were 3.8, 8.2, and 11.2 microg/l, respectively. The method was applied to the determination of diisocyanates in air.     

Extractable organic compounds in polyurethane foam with special reference to aromatic amines and derivatives thereof

Methods for determination of aromatic amines and related compounds in flexible toluene diisocyanate (TDI)-based polyurethane (PUR) foam were investigated. The foam was extracted using 0.1% (w/v) aqueous acetic acid (HAc). Extraction solutions were analysed and aromatic amines were determined as ethyl chloroformate (Et) and pentafluoropropionic acid anhydride (PFPA) derivatives. The determinations were performed using liquid chromatography (LC) and mass spectrometry (MS) detection with electrospray ionisation (ESI) or gas chromatography (GC)-MS with chemical ionisation monitoring negative ions (NCI). The Et derivatives were determined using LC-ESI⁺-MS with detection limit of 2 pg of toluenediamine (TDA). The PFPA derivatives were determined using LC-ESI⁻-MS or GC-NCI-MS with detection limits of 0.1 and 0.02 pg of TDA, respectively. Using trideuterium labelled TDA as internal standard, linear calibration curves were obtained in the range of 0.01-0.50 μg ml⁻¹ (n=7), with correlation coefficients >0.999. When plotting calibration curves for TDA-PFPA derivatives determined using LC-MS against TDA-PFPA using GC-MS and TDA-Et using LC-MS, linear curves were obtained. The relative standard deviation (R.S.D.) for determination of TDA in foam extraction solutions were 13%. LC-MS determination of PFPA derivatives was more selective, as compared to LC-MS of Et derivatives.In foam extraction solutions, 2,4- and 2,6-TDA, several isomers of methylenedianiline (MDA) and dimers of TDA/TDI were observed. 2,4-TDA and 4,4′-MDA are possible human carcinogens. Hydrolysis of the extraction solution revealed a large pool of TDA/TDI compounds and oligomers. The concentration of TDA in foam was affected by the extraction media, temperature and duration. The choice of derivatisation procedure also affected the determination of TDA. In extraction solutions from six different commercially available flexible foam qualities 2,4- and 2,6-TDA were found in the range of 0-7 and 0-6 μg g⁻¹ foam, respectively. When flexible foam was heated, considerable higher concentrations of TDA were observed.     

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.     

2,4-Toluene diamines--their carcinogenicity, biodegradation, analytical techniques and an approach towards development of biosensors.

2,4-Toluene diamine (TDA), a class A carcinogen, is a major raw material for the production of toluene diisocyanate (TDI), which is one of the precursors for the production of polyurethane foams (PU). This review deals with 2,4-toluene diamine's (TDA) carcinogenicity, analytical techniques, biodegradation and use as a biosensor for biogenic and synthetic amines, emphasizing various carcinogenicity studies by 2,4-TDA on animals and humans. This review reports some publications of the analysis of body fluid samples of workers from a PU producing factory for presence of TDA and TDI, since TDI gets absorbed into the worker's body, getting metabolized into TDA. Biodegradations of 2,4-TDA by various researchers are reported and also our own research experience with biodegradation of 2,4-TDA using Aspergillus nidulans isolated from soil site at a polyurethane foam dumping site have been discussed in this review. Biosensors for various biogenic and synthetic amines are discussed.     

Determination of gas-phase produced ethyl parathion and toluene 2,4-diisocyanate by ion mobility spectrometry, gas chromatography and liquid chromatography

Ethyl parathion and toluene 2,4-diisocyanate (2,4-TDI) vapors were generated using a vapor generation system that was designed for the evaporation of liquid samples at known flow rates. The vapor generation of parathion and 2,4-TDI posed a challenge because of their low volatility and tendency to absorb into surfaces of the vapor generation system. Experimental concentration of parathion was determined using gas chromatography-mass spectrometry (GC-MS). 2,4-TDI was derivatized with 1-(2-pyridyl)piperazine to urea derivative which concentration was analyzed using high performance liquid chromatography (HPLC). In addition, in combination with vapor generator, aspiration IMS was used for monitoring ion mobility cell (IMCell) and semiconductor cell (SCCell) responses to parathion and 2,4-TDI vapors. The chromatographic results correlated well with the IMCell response data, showing high specificity of IMS to parathion and 2,4-TDI. The concentrations of parathion and 2,4-TDI at the detection limit of IMS were significantly lower than IDLH threshold values of parathion or 2,4-TDI, demonstrating high sensitivity of IMS to both compounds. The IMS patterns of both chemicals and the influence of humidity on IMCell and SCCell sensitivity were analyzed.     

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.     

2,4-/2,6-二氨基甲苯在D151树脂上的吸附分离

从10种树脂中筛选出D151树脂对2,4-二氨基甲苯和2,6-二氨基甲苯的吸附分离及其热力学性质进行了研究。 测定了吸附等温线,Freundlich模型对实验的拟合度大于Langmuir模型,其相关系数大于0.99。 热力学研究结果表明,在293～313 K条件下,初始质量浓度为60～80 g/L时,2,4-二氨基甲苯的吸附焓变为-4.3490～-5.7558 kJ/mol,自由能变为-0.2911～-1.0346 kJ/mol,吸附熵变为-12.965～-16.150 J/(mol·K);而2,6-二氨基甲苯的吸附焓变为-2.9645～-3.6054 kJ/mol,自由能变为-0.1610～-0.6384 kJ/mol,吸附熵变为-7.939～-11.005 J/(mol·K)。 进一步研究了D151树脂对二氨基甲苯的动态吸附分离,可以将2,6-二氨基甲苯含量从20%提高至99.93%,将2,4-二氨基甲苯含量从80%提高至99.42%。     

Determination of aromatic amines in aqueous extracts of polyurethane foam using hydrophilic interaction liquid chromatography and mass spectrometry

A method is presented for the determination of aromatic amines in aqueous extracts of polyurethane (PUR) foam. The method is based on the extraction of PUR foam using aqueous acetic acid (0.1%, w/v) followed by determination of extracted aromatic amines using hydrophilic interaction liquid chromatography (HILIC) and tandem mass spectrometry (MS/MS) with positive electrospray ionisation. The injections of volumes up to 5 μL of aqueous solutions were made possible by on-column focusing with partially filled loop injections. The fragmentation patterns for 2,4- and 2,6-toluene diamine (TDA) and 4,4′-methylene dianiline (MDA) were clarified by performing a hydrogen-deuterium exchange study.TDA and MDA were determined using trideuterated 2,4- and 2,6-TDA and dideuterated 4,4′-MDA as internal standards. Linear calibration graphs were obtained over the range 0.025-0.5 μg mL⁻¹ with correlation coefficients >0.996 and the instrumental detection limit for each compound was <50 fmol. The stability of the amines was influenced by the matrix, so their concentrations decreased over time.Agreement was observed between the results of analyses of PUR foam extracts by HILIC-MS/MS and results obtained by ethyl chloroformate derivatisation and reversed phase (RP) liquid chromatography-mass spectrometry (LC-MS/MS).TDA was observed to be unstable in extracts of foam but not in pure solutions.     

Exposure to 4,4'-methylenediphenyl diisocyanate (MDI) during moulding of rigid polyurethane foam: determination of airborne MDI and urinary 4,4'-methylenedianiline (MDA)

Occupational exposure to 4,4'-methylenediphenyl diisocyanate (MDI) was measured during moulding of rigid polyurethane foam. The aim of the study was to find out whether an MDI-derived urinary amine metabolite could be detected in the urine of workers exposed to apparently low levels of MDI. Airborne MDI was sampled on 1-(2-methoxyphenyl)-piperazine (2MP)-impregnated glass fibre filters and determined by high-performance liquid chromatography (HPLC) using ultraviolet (UV) and electrochemical (EC) detection. The limit of detection of MDI was 3 ng ml-1 for a 20 microliters injection. The precision of sample preparation, expressed as relative standard deviation (RSD), was 1.3% with UV detection and 2.1% with EC detection at a concentration of 70 ng MDI ml-1 (n = 6). The 2MP-MDI derivative was stable at +4 degrees C up to eight weeks. The accuracy of the method was validated in an international quality control programme. Workers (n = 57) from three different factories participated in the study. Urinary 4,4'-methylenedianiline (MDA) metabolite was determined after acid hydrolysis as heptafluorobutyric anhydride derivatives by gas chromatography-mass spectrometry using chemical ionisation and monitoring negative ions. The limit of detection in urine was 0.2 nmol l-1. The precision of six analyses for a urine sample spiked to a concentration of 1 nmol l-1 was 29% (RSD). The MDI concentrations were below the limit of detection in most (64%) of the air samples collected in the worker's breathing zone. Still, detectable amounts of MDA were found in 97% of the urine samples. Monitoring of urinary MDA appears to be an appropriate method of assessing MDI exposure in work environments with low or undetectable MDI concentrations in the workplace air.     

Fire-resistant polyimides and copolyimides based on 1-[(dialkoxyphosphinyl)methyl]-2,4- and -2,6-diaminobenzenes

Various phosphorus-containing polyimides were prepared by the reaction of 1-[(dialkoxyphosphinyl)methyl]-2,4- and -2,6-diaminobenzenes (1) with a tetracarboxylic dianhydride like pyromellitic dianhydride (PMDA) and benzophenone tetracarboxylic dianhydride (BTDA). In addition, copolyimides that contained approximately 3% phosphorus were prepared by the reaction of 1 and m-phenylenediamine (MPD) with the aforementioned tetracarboxylic dianhydrides. Elemental analysis, inherent viscosity, infrared (IR) spectroscopy, differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA) studies were performed to characterize the polymers. Their thermal properties were compared with those of the corresponding common polyimides. It was shown that the molecular weight and thermal stability of the polymers were reduced as the concentration of the phosphorus moieties increased. The fire-resistance of the copolyimides was evaluated by determining their limiting oxygen index (LOI) value. Copolyimides that contained about 3% phosphorus showed an LOI value approximately 30% higher, than the value of the corresponding common polyimides. In addition, a model diamic acid and diimide was synthesized by the reaction of 1-[di(2-chloroethoxyphosphinyl)methyl]-2,4- and - 2,6-diaminobenzene (DCEPD) with phthalic anhydride and characterized by elemental analysis, IR, proton nuclear magnetic (¹H-NMR) spectroscopy, DSC, and TGA. The pyrolysis behavior of the model compounds was investigated by gas chromatography-mass spectrometry (GC-MS). A direct cleavage of the P? C bond and a possible rearrangement to diisocyanates occurred during their pyrolysis.     

High-performance liquid chromatography of 2,6- and 2,4-diaminotoluene, and its application to the determination of 2,4-diaminotoluene in urine and plasma

2,4-Diaminotoluene is used for the production of industrial dyes, and along with the 2,6-isomer, as an intermediate in the production of polyurethane foams. 2,6- and 2,4-diaminotoluene were resolved as sharp peaks by normal-phase high-performance liquid chromatography in 3 min by an acetonitrile-water-saturated chloroform elution solvent (8:2, v/v) with detection by ultraviolet absorbance at 250 nm. The relationship between peak height and amount injected was linear over a range of 0.025-2 microgram for both compounds. Retention times and peak heights were highly reproducible. Detection was very sensitive, allowing quantitation of 1-2 ng of either compound. Quantitative recovery of 2,4-diaminotoluene from spiked urine and plasma samples was obtained by extraction with methylene chloride.     

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.     

2,6-二[4-′(N,N-二苯基氨基)芪]苯并[1-2,4-5]二噁唑的合成与发光特性

通过对二苯氨基苯甲醛与2,6-二(4-氯甲基苯基)苯并[1-2,4-5]二唑之间的Wittig-Horner反应,设计并合成了一个2,6-二[4-′(N,N-二苯基氨基)芪]苯并[1-2,4-5]二唑新化合物,目的在于均二苯乙烯分子中同时引入空穴传输和电子传输结构单元,可望提高均二苯乙烯型发光材料的发光强度和光量子效率.采用UV-VisI、R1、HNMR和元素分析等分析方法对合成产物结构进行了确认,并考察了溶剂对其光致发光特性的影响.所合成化合物的相关分析数据表明:1)其分子中的两个均二苯乙烯基均为反式“芪”结构特征;2)随溶剂极性增高,其UV-Vis光谱和荧光光谱的λmax红移;3)可用作蓝色发光材料.     

Determination of airborne 2,4-toluenediisocyanate vapors

An accurate and convenient sampling and analytical method was developed for airborne 2,4-toluenediisocyanate (TDI). A chromophoric derivatizing reagent was used to convert the TDI to a stable urea derivative during collection for subsequent quantification by liquid chromatography. The overall accuracy (at the 95% confidence level) and precision of the method are +/- 7.9% and +/- 10.0% respectively under laboratory conditions. Long term stability was observed for both the reagent coated sorbent tube and the TDI urea derivative. A TDI concentration of 1 ppb can be detected by taking a 15-1 sample volume.     

Gold nanoparticles for enhanced chemiluminescence and determination of 2,4-dichlorophenol in environmental water samples

Gold nanoparticles (AuNPs) of different sizes were synthesized by the citrate reduction method. It was found that AuNPs could enhance the chemiluminescence (CL) of the luminal-NaOH system and 2,4-dichlorophenol (2,4-DCP) could inhibit AuNPs-luminal-NaOH CL signals in alkaline solution. CL spectra, UV-visible spectra, and transmission electron microscopy (TEM) were used to investigate the CL mechanism. On the basis of the inhibition, a flow-injection CL method has been established for determination of 2,4-DCP in water samples. Under the optimized conditions, the linear range for determination of the 2,4-DCP was 0.1 × 10(-6) to 20 × 10(-6) g mL(-1), LOD (limit of detection, S/N = 3) was 1.36 × 10(-8) g mL(-1), with RSD of 1.8% (n = 11). This method has been successfully used for analysis of 2,4-DCP in environmental water samples.     

Determination of toluene diisocyanate in synthetic-rubber track by ion chromatography with ultraviolet detection after alkaline suppressor

In the present work,a novel analytical method was proposed for the determination of toluene diisocyanate(TDI)in synthetic- rubber track by ion chromatography(IC)coupled with an ultraviolet detector setting at 212 nm.TDI can be hydrolyzed to toluene diamine(TDA)which can be separated by cation-exchange IC easily.The optimum IC separation was performed on an IonPac CS12A column(150 mm×4.0 mm)using 20 mmol L~(-1)sodium sulfate,10 mmol L~(-1)sulfuric acid and 10%acetonitrile as eluent. It was found that a hi...     

Fire- and heat-resistant adhesive resins based on maleimido and citraconimido substituted 1-[(dialkoxyphosphinyl)methyl]-2,4- and -2,6-diaminobenzenes

A novel class of fire- and heat-resistant bisimide resins was prepared by thermal polymerization of maleimido or citraconimido derivatives of 1-[(dialkoxyphosphinyl)methyl]-2,4- and -2,6-diaminobenzenes (1). The neat bisimide resin prepared by curing 1-[di(2-chloroethoxyphosphinyl)methyl]-2,4- and -2,6-bismaleimidobenzene exhibited a limiting oxygen index 75% higher and smoke evolution about 30 times lower compared with the parent polymer obtained by curing m-phenylenebismaleimide. The char yield of cured bisimide resins at 700°C was 58–70% in a nitrogen atmosphere and 35–60% in air. An increase in formula weight between the imide groups slightly reduced the char yield. The polymer precursors were synthesized by reacting the phosphorus-containing diamines (1) (1 mol) with maleic anhydride/citraconic anhydride (2 mol) or by reacting the monomaleimido derivative of (1) with benzophenone tetracarboxylic dianhydride/methylenebis(4-phenylisocyanate) in a 2:1 mole ratio. The monomers were characterized by elemental analysis, Fourier-transform–infrared (FT-IR), proton nuclear magnetic resonance (¹H-NMR) spectroscopy, and gas chromatography–mass spectroscopy (GC-MS). Direct cleavage of the P? C bond and inversion of the synthesis reaction may occur during their pyrolysis. The thermal polymerization of the monomers was investigated by differential scanning calorimetry (DSC). Biscitraconimides are thermally polymerized at a relatively lower temperature than the corresponding bismaleimides.     

Determination of airborne isocyanates as di-n-butylamine derivatives using liquid chromatography and tandem mass spectrometry

A method for the determination of isocyanates as di-n-butyl amine (DBA) derivatives using tandem mass spectrometry (MS/MS) and electrospray ionisation (ESI) is presented. Multiple-reaction monitoring (MRM) of the protonated molecular ions and corresponding deuterium-labelled d₉-DBA derivatives resulted in selective quantifications with correlation coefficients >0.998 for the DBA derivatives of isocyanic acid (ICA), methyl isocyanate (MIC), ethyl isocyanate (EIC), propyl isocyanate (PIC), phenyl isocyanate (PhI), 1,6-hexamethylene diisocyanate (HDI), 2,4-, 2,6-toluene diisocyanate (TDI), isophorone diisocyanate (IPDI), 4,4′-methylenediphenyl diisocyanate (MDI), 3-ring MDI, 4-ring MDI, HDI-isocyanurate, HDI-diisocyanurate, HDI-biuret and HDI-dibiuret. The instrumental precision for 10 repeated injections of a solution containing 0.1 μg ml⁻¹ of the studied derivatives was <2%. Performing MRM of the product ion [DBA + H]⁺ (m/z = 130) from the protonated molecular ion resulted in the lowest detection limits, down to 10 amol (for TDI). Quantification of concentrations below 10⁻⁶ of the occupational exposure limit (OEL) for TDI during 10 min of air sampling was made possible. In an effort to control the formation of alkali adducts, addition of lithium acetate to the mobile phase and monitoring of lithium adducts was evaluated. Having lithium present in the mobile phase resulted in complete domination of [M + Li]⁺ adducts, but detection limits for the studied compounds were not improved. Different deuterium-labelled derivatives as internal standards were evaluated. (1) DBA derivatives of deuterium-labelled isocyanates (d₄-HDI, d₃-2,4-TDI, d₃-2,6-TDI and d₂-MDI), (2) d₉-DBA derivatives of the corresponding isocyanates and (3) d₁₈-DBA derivatives of the corresponding isocyanates. An increase in number of deuterium in the molecule of the internal standard resulted in an increase in instrumental precision and a decrease in correlation within calibration series.