Number Of Bromines Research Articles

Predicting the Gas Chromatographic Relative Retention Time of Polybrominated Diphenyl Ethers by MEDV-13 Descriptors

Polybrominated diphenyl ethers (PBDEs) have been used extensively over the past two decades as flame or fire retardants added into many products such as textiles, electronic equipment and insulation material. PBDEs are now ubiquitous environmental pollutants and have been detected in biotic and abiotic matrices that include fish, birds, sediments, air, marine mammals, and human plasma and milk. The purpose of the paper is to develop some models which can predict the gas chromatographic relative retention time of PBDEs on seven stationary phases. The molecular electronegativity distance vector based on 13 atomic types (MEDV-13) were employed to describe the structural changes of PBDEs. Using the variables selection and modeling based on the prediction (VSMP), some four-variable linear equations from 80 PBDEs in the training sets with the correlation coefficient (r2) >0.98 and the root mean square errors of estimation <0.029 (except for CP-Sil19) were established. The standard regression coefficient indicated that MEDV descriptor x91 (interaction between the substructure –Br and –Br) was the most important descriptor to affect the RRT values of PBDEs. At the same time, it was found that the number of the ortho-substituent bromines and the number of bromine atoms in PBDE molecule may improve the predictive quality.

Monofluorinated Analogues of Polybrominated Diphenyl Ethers as Analytical Standards: Synthesis, NMR, and GC-MS Characterization and Molecular Orbital Studies

Polybrominated diphenyl ethers (PBDEs), a group of 209 individual congeners distinguishable by the number and position of bromines, are produced for use as flame retardants in consumer goods. PBDEs have become ubiquitous environmental contaminants, present in increasing levels in the environment and humans. In the present study, 10 individual monofluorinated analogues of PBDEs (F-PBDEs) and one difluorinated PBDE (FF-PBDE) were synthesized and characterized, and their gas chromatographic (GC) and mass spectrometric (MS) characteristics determined. The synthesis method utilized a nucleophilic reaction of bromophenols with diphenyliodonium salts and the perbromination of fluorosubstituted diphenyl ethers. Reaction yields were between 10% and 59% with > or = 98% purity. Apart from the aromatic ring carrying the fluorine atom, only minor chemical nuclear magnetic resonance (NMR) shift changes were observed in comparison to the corresponding parent PBDEs, with the exception that the J(F,H) coupling was stronger. Our preliminary data show that F-PBDEs and PBDEs have comparable retention times in gas chromatography with F-PBDEs demonstrating in general shorter or identical retention times, depending on the pattern of fluorine substitution. We also calculated the torsion angles and the dipole moments for both and report that there is a good correlation between GC retention times and the torsion angles but not with dipole moments. In MS, the difference of the ion peaks of the F-PBDE/ PBDE pairs is m/z 19 (F), which allows a simultaneous MS detection without separation. On the basis of GC separation, simultaneous MS detection, and the stability of fluorine due to its generally resistance to nucleophilic displacement, we propose that F-PBDEs may function as valuable potential standards, markers, and tracers in environmental analysis.

Bromophenols, both present in marine organisms and in industrial flame retardants, disturb cellular Ca 2+ signaling in neuroendocrine cells (PC12)

Bromophenols are present in polychaetes as well as in algae in marine environments including the North Sea. They are thought to cause the typical sea-like taste and flavour. The ecological function of brominated phenols is not clear yet, but they may play a role in chemical defence and deterrence [Kicklighter, C.E., Kubaneck, J., Hay, M.E., 2004. Do brominated natural products defend marine worms from consumers? Some do, most don’t. Limnol. Oceanogr. 49, 430–441]. Some brominated phenols are commercially used as industrial flame retardants as, e.g., 2,4,6-tribromophenol and are suspected to disrupt the humoral system by showing tyroid hormone-like activity [Legler, I., Brouwer, A., 2003. Are brominated flame retardants endocrine disruptors? Environ. Int. 29, 879–885]. In this study 2-bromophenol (2-BP), 4-bromophenol (4-BP), 2,4-dibromophenol (2,4-DBP), 2,6-dibromophenol (2,6-DBP) and 2,4,6-tribromophenol (2,4,6-TBP), all of which are present in marine organisms, were tested. Especially 2,4-DBP and 2,4,6-TBP showed a significant effect on the Ca 2+ homeostasis in endocrine cells (PC 12). The reduction of depolarization induced Ca 2+ elevations by 2,4-DBP and 2,4,6-TBP and the increase of intracellular Ca 2+ by both substances, partly released from intracellular stores, may suggest a link to the disrupting effect of endocrine systems by brominated phenols. 2,4-DBP was the most potent substance we tested in respect to inhibition of voltage dependent Ca 2+ currents as revealed in whole cell patch clamp experiments. Brominated phenols disturb cellular Ca 2+ signaling with differential efficacy, depending on the number and position of bromine.

Polybrominated Diphenyl Ether (PBDE) Effects in Rat Neuronal Cultures: 14C-PBDE Accumulation, Biological Effects, and Structure-Activity Relationships

Polybrominated diphenyl ethers (PBDEs), widely used as flame-retardants, are now recognized as globally distributed pollutants, and are detected in most environmental and biological samples, including human blood, adipose tissue, and breast milk. Due to their wide use in commercial products and their persistent nature, long-term exposure to PBDEs may pose a human health risk, especially to children. Our previous reports showed that the commercial PBDE mixture, DE-71, affected protein kinase C (PKC) and calcium homeostasis in a similar way to those of a structurally-related polychlorinated biphenyl (PCB) mixture. These intracellular signaling events are associated with neuronal development and learning and memory function. The objectives of the present study were to test whether environmentally relevant PBDE congeners, with different position and number of bromines, affected PKC translocation in cerebellar granule neuronal cultures and compare the potency and efficacy of PBDE congeners with their 14C-accumulation. All the tested PBDE congeners increased 3H-phorbol ester (PDBu) binding, and a significant effect was seen as low as 10 microM. Among the congeners tested, 2,2',4,4'-tetrabromodiphenyl ether (PBDE 47) increased 3H-PDBu binding in a concentration-dependent manner and to a greater extent than other congeners. These effects were seen at concentrations and exposure times where no cytotoxicity was observed. The efficacy of PBDE congeners varied with their structural composition, and the effects seen on 3H-PDBu binding with some PBDE congeners are similar to those of PCB congeners. Cerebellar granule neurons accumulated all three PBDE congeners (PBDEs 47, 99, and 153) following exposure. At the lowest concentration (0.67 microM), about 13-18% of the total dose of 14C-PBDE congeners was accumulated by these neurons. There were distinct differences in the pattern of 14C-PBDE accumulation among the PBDE congeners. The 14C-PBDE accumulation, either represented as percent basis or nanomole basis, was much lower for the 30.69 microM PBDE 99 and 10.69-30.69 microM PBDE 153 than at the lower concentrations, which may be due to low solubility of these congeners. The accumulation pattern with PBDE 47 did not vary with concentration. On a nanomole accumulation basis, PBDEs 47, 99, and 153 accumulation was linear with time. While the nanomole accumulation was linear with concentration for PBDE 47, it is nonlinear for PBDEs 99 and 153. The pattern of PBDE accumulation seems to correlate with the effects on PKC translocation, with regression values of 0.773-0.991. These results indicate that PBDEs affected PKC translocation in neurons in a similar way to those of other organohalogens, some PBDE congeners are equally efficacious as the respective PCB congeners, and PBDE accumulation correlated well with PKC translocation, suggesting a common mode of action for this group of chemicals.

Theoretical Calculation of Thermodynamic Properties of Polybrominated Diphenyl Ethers

The thermodynamic properties of 39 polybrominated diphenyl ethers (PBDEs) in the ideal gas phase have been calculated using Gaussian 03 on the B3LYP/6-31G(d)//B3LYP/6-31G(d) level. Their thermodynamic and other physicochemical properties show a strong dependence on the bromine substitution pattern. The PBDE congeners' enthalpies of formation increase with an increasing number of bromines. The thermodynamic properties of congeners with the same number of bromines also show dependence on the bromine substitution pattern, especially for ortho-substituted congeners. PBDE congeners with one phenyl ring fully brominated, such as 2,3,4,5,6-PeBDE, 2,3,4,4‘,5,6-HxBDE, 2,2‘,3,4,4‘,5,6-HpBDE, and 2,3,3‘,4,4‘,5,6-HpBDE, were found to be the least stable among the analogues. The effects of bromine substitution pattern have been quantitatively studied by group additivity method (GAM) based on the output of the theoretical calculations. The results of the GAM were consistent with theoretical calculations, proving that t...

Reductive Debromination of Polybrominated Diphenyl Ethers by Zerovalent Iron

Polybrominated diphenyl ethers (PBDEs) are a new class of global, persistent, and toxic contaminants, which need proper remediation technologies. PBDE degradation in the environment is not well understood. In this study, degradation of PBDEs with zerovalent iron was investigated with six BDEs, substituted with one to 10 bromines. Within 40 days 92% of BDE congener 209 was transformed into lower bromo congeners. During the initial reaction period of BDE 209 (<5 days), hexa- to heptabromo BDEs were the most abundant products, but tetra- to pentabromo congeners were dominant after 2 weeks. The amount of mono- to tribromo BDEs was steadily increased during the experiments. BDEs 28, 47, 66, and 100 also showed a stepwise accumulation of lower bromo congeners. No oxidation products were detected in all experiments. The results showed that a stepwise debromination from n-bromoto (n-1)-bromodiphenyl ethers was the dominant reaction in all congeners. The reaction rate constants of lower bromo BDEs decreased as the number of bromines decreased. The initial reductive debromination rate constants were positively correlated with the heats of formation of BDEs. The preferential accumulation of specific congeners was observed in the experiment with BDEs 28, 47, 66, and 100, where the most abundant products were BDEs 15, 28, 37, and 47, respectively. Reactions proceeded to form more stable and less brominated products that have lower heats of formation. Almost all the possible isomers from a specific parent BDE were found in all the experiments, which was probably due to the small difference of heat of formation between the products (2-5 kcal/mol). Reactions of all congeners proceeded fast at the initial phase (<5 days) followed by a slow reaction. The rate of reductive debromination of BDE 209 was slower with environmentally relevant sulfide minerals (iron sulfide and sodium sulfide). However, the product congener pattern, produced by sulfide mineral catalysis, was nearly similar with that of zerovalent iron treatment. This may be a possible source of lower brominated BDEs in the environment. Debromination of PBDEs by zerovalent iron has high potential values for remediation of PBDEs in the environment.

Characteristic Substituent-Shift Models for Carbon 1s Ionization Energies and Mean Dipole-Moment Derivatives

Characteristic substituent-shift models for carbon mean dipole-moment derivatives are determined for the halomethanes, fluorochloroethanes, and some other small molecules. These models are analogous to those reported earlier for core ionization energies measured by X-ray photoelectron spectroscopy and are to be expected since Siegbahn's simple potential model relates these to mean dipole-moment derivatives obtained from infrared spectral data. Linear models relating carbon 1s ionization energies and mean dipole-moment derivatives to the number of fluorine, chlorine, bromine, and iodine atoms substituting hydrogen atoms in the halomethanes are reported. The regression coefficients in these models are similar to the coefficients for the fluorine and chlorine atoms found in linear models derived for the mean dipole-moment derivatives and carbon 1s ionization energies of the fluorochloroethanes. The signs of the coefficients in the fluorochloroethane model indicate that the a carbon becames more positive and the β carbon more negative upon fluorine substitution for hydrogen. Standard derivative values of -0.52 ′ 0.05, -0.25 ′ 0.05, -0.18 ′ 0.03, -0.17 ′ 0.03, and -0.01 ′ 0.01 e are proposed for the fluorine, chlorine, bromine, iodine, and hydrogen atoms of saturated fluorochlorohydrocarbons. Characteristic substituent shifts for Mulliken, CHELPG, and Bader charges of the carbon atoms in these molecules are also investigated.

Thermodynamic Properties of Polybrominated/chlorinated Dibenzo-p-dioxins Calculated by Density Functional Theory

Heat capacities, standard enthalpies of formation and entropies for 339 polybrominated/chlorinated dibenzo-p-dioxins (PXDDs) in the gas state were calculated using the density functional theory to construct a consistent set of thermodynamic values. The heat capacities and the entropies for PXDDs increase with increase in the substitute number of bromine and chlorine. As the degree of bromination increases, the standard enthalpies of formation and the Gibbs free energies of formation of PXDDs increase, while the degree of chlorination has only a small effect on their values compared with bromination. A much higher bromine potential than chlorine potential is needed for the formation of brominated dioxin congeners. However, the bromine-chlorine equilibrium potential for the formation of PXDDs suggested thermodynamically the possibility of their priority formation under the usual gaseous conditions where HBr and HCl are similar levels, because the bromine potential of the gas is much higher than the chlorine potential when the partial pressure of the two is similar.

Reactions of H3O+ with a number of bromine containing fully and partially halogenated hydrocarbons

The thermal bimolecular rate coefficients and product ion branching ratios for the reactions of H3O+ with the bromine containing molecules CH3Br, CH2Br2, CH2FBr, CHF2Br, CHFBr2, CH2BrCl, CHBrCl2, CHBr2Cl, CH3CH2Br, CH2BrCH2Cl, CH2BrCH2Br, CF3CF2Br and CF2BrCF2Br at 300K are reported. H3O+ reacts with an experimental rate coefficient (kexp) close to the collisional value (kc≈10−9cm3molecule−1s−1) with CHFBr2, CHBrCl2, CHBr2Cl, CH2BrCH2Cl, and CH2BrCH2Br, at a decreased efficiency with CH3CH2Br (kexp/kc≈0.3). The other neutral reactant molecules, CH3Br, CH2FBr, CHF2Br, CF3CF2Br, and CF2BrCF2Br react through a three-body associative process. There is no observable reaction with CH2Br2 and CH2BrCl. Mechanistic arguments are given that go some way to explaining the observed range in both reactivity and reaction pathways.

A selected ion flow tube investigation of the positive ion chemistry of a number of bromine containing fully and partially halogenated hydrocarbons

The thermal bimolecular rate coefficients and product ion branching ratios for the reactions of the positive ions (in order of increasing recombination energy) H2O+, N2O+, O+, CO2+, CO+, N+, and N2+ with the bromine containing molecules CF3Br, CF2Br2, CFBr3, CF2BrCl, CFBr2Cl, CBrCl3, CH3Br, CH2Br2, CH2FBr, CHF2Br, CHFBr2, CH2BrCl, CHBrCl2, CHBr2Cl, CF3CF2Br, and CF2BrCF2Br at 300K are reported. This represents the most comprehensive investigation of the positive ion chemistry of brominated molecules to date, with nearly all of the experimental data being presented here for the first time. Also reported in this paper are the reactions of H2O+ with CH3CH2Br, CH2BrCH2Cl, and CH2BrCH2Br. All the reactions are efficient, with the experimental reaction rate coefficients being greater than 10−9cm3molecule−1s−1. Dissociative charge transfer is considered to be the dominant reaction mechanism.

Vapor Pressures of the Polybrominated Diphenyl Ethers

The supercooled liquid vapor pressures PL of 23 polybrominated diphenyl ether congeners were determined as a function of temperature with a gas chromatographic retention time technique. PL at 298.15 K ranged from 0.1 Pa for monobrominated diphenyl ethers to 10-6 Pa for heptabrominated diphenyl ethers. The halogen substitution pattern was found to influence PBDE vapor pressure, indicating that congeners with bromine substitutions in the ortho positions to the ether-link have higher vapor pressures. The enthalpy of vaporization ΔvapH for the 23 PBDE congeners ranged from (−67 to −116) kJ/mol, decreasing with each additional bromine substitution by about (7 to 8) kJ·mol-1. ΔvapH was also found to be influenced by the number of ortho bromines. Using a Junge−Pankow approach, the fraction of chemical adsorbed to aerosols as a function of temperature was estimated for three congeners and used to speculate on the likely environmental behavior of these chemicals.

Emulsion polymerization of styrene using a new series of rigid rod-like cationic surfactants

A series of pyridinium salts (PCX) N-substituted with an ω-(4′-methoxy-4-biphenylyloxy)alkyl group has been synthesized and used as surfactants in the emulsion polymerization of styrene. These molecules have an alkyl chain with an even number (X = 6, 8, 10, or 12) of methylene groups and bromine as counterion. For these molecules a typical behavior of colloidal electrolytes has been observed by conductivity measurements on water solutions and the critical micelle concentrations (CMC) determined by this technique are 2.14, 1.47, 0.214, and 0.0097 mmol for PC6, PC8, PC10, and PC12, respectively. Latices prepared with three components (water/styrene/PCX) were fairly stable showing in all experiments a monodisperse particle size distribution (1.01 to 1.1) with particle diameters from 70 to 160 nm. These results are compared with those obtained using dodecylpyridinium bromide (DPB) as the surfactant.

Effect of HBr, HCl and Cl 2 on fullerene formation in benzene/oxygen/argon flames

Amounts between 2.5 and 5.9% of HBr, HCl and Cl 2 were added to fullerene forming benzene/oxygen/argon flat-flames burning at 75 mbar in an attempt to affect halogen substitutions in the carbon framework. The inhibition effect of HBr dramatically reduced the yield of fullerene, while it stayed in the same order of magnitude after addition of HCl or Cl 2. No formation of halogenated fullerenic compounds could be detected by mass spectrometry using chemical ionization with CH 4/N 2O or MALDI. The measurement of bromine- and chlorine-precursor mass spectra showed the formation of a great number of bromine or chlorine containing compounds, essentially polycyclic aromatic hydrocarbons (PAH). In the case of HBr addition, only relatively small molecules could be observed because reactions with bromine atoms are thermodynamically less favourable in regions far from the burner with relatively high temperatures.

Anti-AIDS (acquired immune deficiency syndrome) agents. 17. New brominated hexahydroxybiphenyl derivatives as potent anti-HIV agents.

Sixteen biphenyl derivatives were synthesized and evaluated for their inhibitory activity against HIV-1 replication in acutely infected H9 cells. 3-Bromo- (4) and 3,3'-dibromo-4,4'-dimethoxy-5,6,5',6'-bis(methylenedioxy)-2,2'- bis(methoxycarbonyl)biphenyl (5) demonstrated potent anti-HIV activity with EC50 values of 0.52 and 0.23 micrograms/mL and therapeutic index values of > 190 and > 480, respectively. A comparison of the anti-HIV activity of these biphenyl derivatives suggested that the types of substituents on the phenolic hydroxy groups rather than the number of bromine(s) on the aromatic rings are important to the enhanced anti-HIV activity. Compounds 4 and 5 also showed potent inhibitory activity against HIV-1 reverse transcriptase in a template-primer dependent manner. The site of inhibition of HIV could be related to inhibition of this enzyme. Compounds 4 and 5 did not induce virus expression from the chronic HIV-1-infected cell lines ACH-2 and U1. Furthermore, these two agents did not inhibit an increase in virus production from the chronic HIV-1-infected cell lines when the phorbol ester PMA was present.

Gas chromatographic identification of halogenated hydrocarbons by using the correlation between their retention and boiling points

The correlation between relative retention values of halogenated hydrocarbons (methanes, ethanes and ethenes with different halogen atoms in the molecule) and their boiling points at atmospheric pressure was found to be linear, and was used for identification purposes in gas chromatography. Absolute and relative retention values were measured on non-polar (OV-1) and polar (SP-1000) packed columns; the linear correlations found with the boiling points as a function of the number of hydrogen, chlorine, bromine and iodine atoms permits peak identification starting from known boiling points. Calculation of the boiling points of trace compounds starting from gas chromatographic data or linear interpolation to predict both the retentions and the boiling points of substances whose standards are not available are also possible.

The Production and Release to Atmosphere of Industrial Halocarbons

The available surveys of production and use carried out by the halocarbon industry for a number of important chlorine and bromine containing chemicals are summarised. The results of a new survey in which methyl chloroform production data were reconfigured into more detailed geographical regions for comparison with atmospheric measurements are presented.

Raman Spectra of ZnBr&lt;sub&gt;2&lt;/sub&gt;-KBr-PbBr&lt;sub&gt;2&lt;/sub&gt; Glasses

In Raman spectra of ZnBr2-KBr-PbBr2 glasses, the dominant bands are observed at about 60cm-1 and 155cm-1 or 174cm-1. The 60cm-1 band was assigned to the mode containing bending vibrations and the 155cm-1 or 174cm-1 band to the symmetric mode containing the stretching vibration between zinc and bridging or non-bridging bromine, respectively. The compositional dependence of the intensity of the 155cm-1 and 174cm-1 bands gives information about both the structural role of PbBr2 and the network structure from the viewpoint of bridging and non-bridging bromines. The introduction of PbBr2 increased the number of non-bridging bromine. This indicates that PbBr2 has the same role of glass modifier as that of KBr. On the other hand, the 155cm-1 band was observed even for a glass of the composition with 20mol% PbBr2, in which the atomic ratio, Br/Zn, is 4. This suggests that there are free bromide ions and/or zinc ions coordinated with more than four bromide ions.

Studies on the Microsomal Metabolism and Binding of Polybrominated Biphenyls (PBBs)

The metabolism of polybrominated biphenyls (PBBs) was studied in vitro by using rat liver microsomes in the presence of NADPH and atmospheric O2. Quantitative recoveries of all PBBs were obtained after incubations with control or 3-methylcholanthrene (MC) induced microsomes. Of the twelve major components, losses of only peaks 1 (2,4,5,2',5'-pentabromobiphenyl) and 3 (a hexabromobiphenyl) were observed following incubations with microsomes from phenobarbital (PB)- or PBBS- pretreated rats. Of seven structurally identified PBB components, only peak 1 has a bromine-free para position. Peaks 1, 2, and 5 all have two adjacent unsubstituted carbons, yet only peak 1 is metabolized. Of two dibromobiphenyl model compounds studied, the 2,2'-congener was very rapidly metabolized by PB-induced microsomes whereas its 4,4'-isomer was not. These results suggest that the presence of a free para position is required for the metabolism of brominated biphenyls. Of lesser importance appears to be the number of bromines or the availability of two adjacent unsubstituted carbons. In vivo evidence for the metabolism of peaks 1 and 3 was also provided by their drastically diminished levels in liver and milk extracts. When a 14C-PBB mixture consisting almost exclusively of peaks 4 (2,4,5,2',4',5'-hexabromobiphenyl) and 8 (2,3,4,5,2',4',5'-heptabromobiphenyl) was incubated with PB- or PBBs- induced microsomes and NADPH, only traces of radioactivity remained with the microsomes after extensive extraction. However, less radioactivity was bound to microsomes from MC pretreated or especially control rats. No radioactivity was bound to exogenous DNA included in similar microsomal incubations, regardless of the type of microsomes used. Under the same conditions, [3H]-benzo[a]pyrene metabolites were bound to DNA, and PBB-induced microsomes enhanced this binding more than six-fold.

Studies on the microsomal metabolism and binding of polybrominated biphenyls (PBBs).

The metabolism of polybrominated biphenyls (PBBs) was studied in vitro by using rat liver microsomes in the presence of NADPH and atmospheric O2. Quantitative recoveries of all PBBs were obtained after incubations with control or 3-methylcholanthrene (MC) induced microsomes. Of the twelve major components, losses of only peaks 1 (2,4,5,2',5'-pentabromobiphenyl) and 3 (a hexabromobiphenyl) were observed following incubations with microsomes from phenobarbital (PB)- or PBBS- pretreated rats. Of seven structurally identified PBB components, only peak 1 has a bromine-free para position. Peaks 1, 2, and 5 all have two adjacent unsubstituted carbons, yet only peak 1 is metabolized. Of two dibromobiphenyl model compounds studied, the 2,2'-congener was very rapidly metabolized by PB-induced microsomes whereas its 4,4'-isomer was not. These results suggest that the presence of a free para position is required for the metabolism of brominated biphenyls. Of lesser importance appears to be the number of bromines or the availability of two adjacent unsubstituted carbons. In vivo evidence for the metabolism of peaks 1 and 3 was also provided by their drastically diminished levels in liver and milk extracts. When a 14C-PBB mixture consisting almost exclusively of peaks 4 (2,4,5,2',4',5'-hexabromobiphenyl) and 8 (2,3,4,5,2',4',5'-heptabromobiphenyl) was incubated with PB- or PBBs- induced microsomes and NADPH, only traces of radioactivity remained with the microsomes after extensive extraction. However, less radioactivity was bound to microsomes from MC pretreated or especially control rats. No radioactivity was bound to exogenous DNA included in similar microsomal incubations, regardless of the type of microsomes used. Under the same conditions, [3H]-benzo[a]pyrene metabolites were bound to DNA, and PBB-induced microsomes enhanced this binding more than six-fold.

Computer assignment of elemental compositions of mass spectral peaks from isotopic abundances

The Probability Based Matching (PBM) algorithm described previously has been extended to predict the number of bromine and chlorine atoms in ions of unknown mass spectra from the relative abundances of isotopic peaks. The theoretical isotopic patterns for 36 Br/Cl combinations are matched against peak ''clusters'' in the unknown spectrum with a modified PBM algorithm. The confidence values of the best Br/Cl assignments are further reinforced if they are consistent with the mass differences found for other peak clusters. In a test using the spectra of 2670 compounds in which 814 contained bromine and chlorine, 90 percent of the predictions were correct.