Anal. Chem. 1982, 5 4 , 557-559
55 7
Determination of Total N-Nitroso Content in Cutting Fluids Robert D. Cox' Department of Chemistry, The University of Iowa, Iowa City, Iowa 52242
C. W. Frank* Institute of Agricultural Medicine and Environmental Health, Environmental Chemistry Section, College of Medicine, The University of Iowa, Iowa City, Iowa 52242
Analytlcal methodology has been developed for the rapid determination of total N-nitroso group content In cutting fluids. The method Involves InItYal removal of nltrHe by Ion exchange, Iodide Ion, or sulfanllamlde. The nltrlte-free sample Is analyzed by denltrosatlon of N-nltroso compounds to produce nitric oxlde, which Is detected vla Its gas-phase chemllumlnescence reaction with ozone. The detectlon llmlt Is 5 X lo-'' mol on cuttlng fluid samples. Analysis tlme Is 5-15 mln.
Cutting fluidii are lubricants which are widely used in industrial machining operations. The composition of cutting fluids can vary widely from those which contain a hydrocarbon base and are not water soluble (cutting oils) to synthetic lubricants which are water soluble. Some typical formulations have been reported (1, 2). Recently, relatively high concentrations of N-nitrosodiethanolamine (NDELA) have been reported in synthetic cutting fluids (3,4). The presence of this compound is thought to result from reaction of nitrite ion, which is added to cutting fluids as a rust inhibitor, with diethanolamine and triethanolamine, which are used as lubricants or emulsifying agents. It has been demonstrated that diethanolamine and triethanolamine are readily nitrosated to form N-nitrosodiethanolamine (5). Formation of this compound by in vivo nitrosation has also been suggested (6). N-Nitrosodiethanolamine is of interest since this compound has demonstrated potent carcinogenic properties in animals (7). Individuals working with cutting fluids could be exposed to NDELA through skin contact and mist inhalation. Although no data concerning toxicity of this compound via these routes exist, daily exposrure of workers in combination with reported levels has provoked concern. The existing methodology for determination of N-nitrosodiethanolamine includes HPLC-TEA with confirmation by mass spectrometry (3). The thermal energy analyzer is a highly sensitive group specific detector for N-nitroso compounds. The basis of this detector is thermal cleavage of the N-nitroso nitrogen-nitrogen bond generating nitric oxide. The NO is determined in the gas phase via its chemiluminescence reaction with ozone. Since the exisiting analytical methodology is not entirely suitable for analyzing large numbers of samples at a reasonable cost, it was congidered advantageous to develop screening procedures for the deterimination of N-nitroso group content in complex samples. One such technique has already been developed but is only applicable to extractable N-nitroso compounds (8). Because of the polarity of N-nitrosodiethanolamine arid complexity of the matrix, low efficiencies for extracting this compound from the cutting fluids were obtained. Therefore, a method was developed for determiPresent addrelas: Radian Corp., Austin, TX 78766.
nation of total N-nitroso group content in cutting fluids. The technique is based on chemical cleavage of the nitrogen-nitrogen N-nitroso bond to generate nitric oxide. The nitiric oxide is determined via its chemiluminescence reaction with ozone. Nitrite interferes quantitatively; thus several techniques were investigated for complete removal of this speciles. EXPERIMENTAL SECTION Apparatus. A flow diagram of the system used is shown in Figure 1. The system is identical with one previously used for determination of nitrate and nitrite (9) with exception of the permanganate scrubber and associated valving. The scrubber consists of a small glass impinger filled with 10 mL of acidic permanganate solution. Gas flow from the scrubber was vented to the hood exhaust. Additional three-way stopcocks were required to allow air intake to the NO, analyzer while the scrubber was in use. Reagents and Chemicals. N-Nitrosodiethanolamine was obtained from the National Cancer Institue chemical repository at the Illinois Institute of Technology (chemical no. 208). Stock M were prepared in water and stored in the dark solutions of at -5 OC. Standard sohtions (la-6 M) were prepared by successive dilutions of the stock solution. Standard solutions of potassium nitrate and sodium nitrite (J. T. Baker Chemical Co.) were prepared in a similar manner. Reagents used for the denitrosation step were acetic acid aind sulfuric acid "suitable for mercury determination" (J. T. Baker Chemical Co.) and sodium iodide (Matheson, Coleman and Bell Chemical Co.). Sodium chloride, sodium bromide, and potassium thiocyanate were also investigated for use as denitrosatilon reagents. Dowex 1X-8 anion exchange resin (chloride form), sodium iodide, and sulfanilamide (J. T. Baker Chemical Co.) were investigated as reagenta for quantitativenitrite removal. High puriity water was obtained by passing distilled water through two IWT Research Model 1 ion exchange columns connected in series. Cutting fluid samples were supplied by industries in Iowa, Illinois, and Minnesota. Procedures. Initial Cleanup. The first step of the procedure involved the removal of nitrite. If nitrate was present at levels exceeding 4 mg of N03-N/L, then removal of this species was also required. Ion exchange and several chemical methods were investigated for these purposes. Ion exchange was required when the nitrite or nitrate levels exceeded 4 mg of N/L. The resin was prepared by slurrying in 2 N HCl. A 5-mL bed was washed with two 25-mL portions of 2 N HCl and two 25-mL portions of distilled deionized water prior to sample application. A 10-mL aliquot of sample or diluted sample was applied to the column and eluted at a rate of 1 mL/min. The first 3 mL of eluate were discarded and the next 15 mL collected and retained for analysis. Because of high viscosity, dilution of many cuttiing fluid samples 1:2 to 1:5 with water was required before application to the ion exchange column. Following the removal of large amounts of nitrite and nitrate by ion exchange, a second treatment was required to remove lesser amounts of nitrite. Two methods for the chemical removal of small amounts of nitrite were investigated. The first involved reduction of nitrite by iodide ion in a weakly acidic medium. Oine milliliter of 1% sodium iodide and 1mL of 10% sulfuric acid were
0003-2700/82/0354-0557$01.25/00 lg82 American Chemical Society
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ANALYTICAL CHEMISTRY, VOL. 54, NO. 3, MARCH 1982
I-
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I
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h
F"=l
m
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A
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Figure 2. Effects of different halides on the denitrosation of NDELA.
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Flgure 1. Diagram of instrumentation: (A) helium carrier gas, (B) flow regulator, (C) denitrosation apparatus and reaction vessel, (D) permanganate scrubber, (E) cold trap, (F) vapor scrubber, (0)Teflon filter, (H) Bendix 8101-B NO, analyzer, (I) oxygen supply, (J) pump, (K) strip
Table I. Effect of Sulfanilamide Treatment on N-Nitrosodiethanolamine (NDELA) Determination NDELA concn, MIL
chart recorder, (L) electronic integrator. added to 20 mL of aqueous or cutting fluid sample. The sample was then outgassed and the flow vented through the permanganate scrubber (Figure 1). Nitrite removal was monitored by briefly routing the gas flow to the NO, analyzer by rotating the appropriate three-way stopcocks. Sulfanilamide was also investigated as a means of nitrite removal. A solution of 0.06 M sulfanilamide in 10% HC1 was prepared and 0.2 mL added to a 5-mL sample. The mixture was stirred, allowed to stand for 2 min, and then analyzed for N-nitroso content. Since many cutting fluids are alkaline in nature, the pH of the sample was monitored after addition of the sulfanilamide reagent. If the pH was above 3.5, excess 10% HC1 was added. Denitrosation and Chemiluminescence Detection. Denitrosation of N-nitroso compounds was brought about by mixing a 5-mL cutting fluid sample (or an aqueous solution of NDELA), 13 mL of acetic acid, and 3.5 mL of sulfuric acid in a reaction vessel. One milliliter of a 10% solution of sodium iodide was then added and the reaction vessel placed immediately on the outgassing apparatus. The sample was outgassed until no further NO evolution was observed. Peak areas were obtained by calculation from a strip-chart recorder or by electronic integration. Excessive foaming occurred during the denitrosation step for some cutting fluid samples. The addition of several drops of 2-octanol to the reaction solution served to control foaming and did not interfere in the method. RESULTS AND DISCUSSION Since N-niotrosdiethanolamine is the major compound of interest in cutting fluids, all developmental work was performed with this compound. However, the method discussed here is not specific for this compound, and was intended to estimate the total N-nitroso content in cutting fluids. Optimization of Conditions for t h e Denitrosation Reaction. Previous authors have recommended hydrogen bromide for the denitrosation of N-nitroso compounds (8,10, 11). In the present case, chloride, bromide, iodide, and thiocyanate were investigated as potential denitrosation reagents. The effects of chloride, bromide, and iodide on a lo+ M aqueous solution of NDELA are shown in Figure 2. Virtually no response was obtained for chloride. For bromide, a low broad peak was obtained which did not return to the base line. This is consistent with the findings of Drescher and Frank (8)concerning the use of HBr as a denitrosating agent in the presence of water. For iodide, a relatively sharp peak was obtained which returned to the base line. Thiocyanate produced a response similar to that of bromide. From the results obtained, iodide was used as the denitrosating agent. Concentrations of iodide, sulfuric acid, and water in the reaction medium were optimized for the denitrosation of NDELA. Initially, optimal conditions were considered to be those which produced the fastest reaction times while still
15.2 26.6 53.3 76.0
signal, counts before after treattreatment ment 250 1487 3854 5253 7966
313 1644 3854 5359 7939
%
difference 25 14
