ANALYST, DECEMBER 1991, VOL. 116 1369

Determination of Maleic Hydrazide in Onions and Potatoes Using Solid-phase Extraction and Anion-exchange High-performance Liquid Chromatography*

Naresh K. Vadukul Laboratory of the Government Chemist, Queens Road, Teddington, Middlesex TWI I OLY, UK

A simple method for the determination of maleic hydrazide in onions and potatoes using solid-phase extraction cartridges for clean-up and anion-exchange high-performance liquid chromatography is described. Solid-phase extraction cartridges f rom different manufacturers are also compared. Recoveries of maleic hydrazide added t o onions and potatoes at 1.5-15 m g kg-1 levels averaged between 81 and 107%. Keywords : Solid-p hase extraction; maleic h ydrazide; an ion-exc hang e h ig h-perfo rmance liquid ch roma tog rap h y

Maleic hydrazide is used as a growth regulator on certain foods such as onions and potatoes, where its main function is as a sprout inhibitor. Its toxicity is well documented and the Codex Alimentarius Commission have put forward recom- mended ‘maximum residue limits’ for onions and potatoes. 1

A number of methods for the determination of maleic hydrazide have been reported*-5 involving hydrolysis followed by distillation of hydrazine and then either formation of a hydrazone for spectrophotometric determination or forma- tion of a derivative for gas chromatography. A method for determining maleic hydrazide and maleic hydrazide glucoside in foods using ion-exchange clean-up has been reported,6 but it is susceptible to interferences and involves a time-consum- ing procedure.

Recently, the introduction of solid-phase extraction (SPE) cartridges for clean-up of analytes in different matrices has been reported.7-9 A number of these cartridges are available commercially offering good selectivity and reduction of clean-up time.

This paper describes a procedure for the determination of maleic hydrazide in onions and potatoes using ion-exchange SPE cartridges for clean-up followed by anion-exchange high-performance liquid chromatography (HPLC) . Recoveries of maleic hydrazide from different SPE cartridges are compared and the limits of detection reported.

Experimental Instrumentation

A Silverson blender was used for the blending of samples. The liquid chromatograph consisted of a Shimadzu LC 6A pump (Dyson Instruments), a Waters 490 programmable ultraviolet (UV) detector (Millipore) operating at 313nm and a Rheodyne 7125 sample injection valve with a 5 mm3 sample loop. The column was a 25 cm x 4.6 mm i.d. Nucleosil5 SNB (Technicol) with a 5 cm X 4.6 mm i.d. guard column, packed in-house with pellicular anion-exchange material (Alltech Associates, Stock No. 9264). The guard column was coupled to the analytical column1() and connected to the injection valve with 5 cm of 0.15 mm i.d. stainless-steel tubing. The column end was linked to the detector with a 5cm length of narrow-bore poly(tetrafluoroethy1ene) (PTFE) tubing. The chromatograms were recorded on a chart recorder and integrator. The mobile phase was 0.1 mol dm-3 acetic acid, adjusted to pH 4.8 with tetramethylammonium hydroxide.

An S5 ODs-1 cartridge-type column (25 cm x 4.6 mm i.d., Alltech Associates) was used for confirmation and the mobile

* Crown Copyright.

phase was acetonitrile-water ( 5 + 95) with 0.04% orthophos- phoric acid. Detection was monitored by UV absorption at 313 nm.

Reagents

Maleic hydrazide was obtained from Sigma. The solvents used in this work were methanol, acetonitrile (both HPLC grade, FSA), glacial acetic acid (Merck) , tetramethylammonium hydroxide (Merck) and orthophosphoric acid (FSA). Three SPE cartridges from different sources for sample clean-up were studied: Bond-Elut SCX (Anachem); Baker Bond SCX; and Worldwide Monitoring SCX (Technicol).

Procedure

The outer leaves and the roots of bulb onions were discarded and the remainder of the onion was cut into small cubes suitable for maceration and mixed thoroughly. The tubers of potatoes were rinsed in running water to remove adhering soil

Table 1 Comparison of SPE cartridges

Amount eluted

through Recovery cartridge*/

TY Pe Pg II Mean(%) SD(%) Bond-Elut 30 7 101 6 Baker Bond (SPE) 30 7 104 4 Worldwide Monitoring 30 7 101 7

* 30 yg of a 10 g sample corresponds to 3 mg kg- 1 .

Table 2 Pesticide standards injected onto the system using 0.1 mol dm-3 acetic acid, pH 4.8, as the mobile phase

Pesticide Aldicarb Aldicarb sulphone Aldicarb sulphoxide Bromophos Carbar y 1 Carbendazim Carbofuran Chlorfenvinphos Chlorpropham Chlorpyrifos Diazinon

Concen- tration/ mg kg-I

1.6 1.6 1.6 0.7 1.2 2.5 1.9 1 3.2 0.8 0.8

Pesticide Dimethoate Fenitrothion Imazalil Iodofenphos Oxamyl Pirimiphos-methyl Prochloraz Tecnazene Thiabendazole Tolclofos-methyl Triazophos

Concen- tration/ mg kg-1

0.8 0.8 0.8 0.8

0.8 0.8 0.8 0.5 4 0.8

21

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1370 ANALYST, DECEMBER 1991, VOL. 116

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II I I 1 0 5 10

1 1 I I 0 5 10

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0 5 10

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Fig. 1 Typical chromatograms for maleic hydrazide in onions and potatoes: (a ) unfortified potato; (6) potato fortified at 3 rng kg-!; (c) unfortified onion; (d) onion fortified at 3 mg kg-1; and ( e ) 16.5 ng maleic hydrazide standard. Mobile phase, 0.1 mol dm- acetic acid, pH 4.8, at a flow rate of 1.0 ml min-1. Detector: UV at 313 nm, 0.008 a.u.f.s.

Table 3 Recoveries of maleic hydrazide from onions and potatoes

Recovery

Onion Potato

Fortification Mean Mean level/mgkg-l n (%) SD(Y0) n (Yo) SD(%)

1.5 5 92 10 5 81 9 3.0 5 79 8 6 95 10

15.0 3 93 - 1 107 - ~~~~~

and were then cut similarly to the onions and mixed thoroughly. A sample (10 g) was transferred into a beaker, 50cm3 of methanol were added and the mixture was left to stand for 1 h, The mixture was homogenized for 1 min and the homogenate was filtered through Whatman No. 541 filter- paper on a 9 cm Biichner funnel using a vacuum. The beaker was rinsed with lOcm3 of methanol, which was transferred into the filter-funnel in order to wash the residue. The residue was further rinsed with 5 cm3 of methanol and the combined filtrates were transferred into a 100cm3 rotary flask. The solution was concentrated to 2-3 cm3 on the rotary evaporator at 40 "C and then transferred quantitatively into a graduated 10 cm3 test-tube. The final volume was adjusted to 4 cm3. An aliquot of this solution (2cm3) was passed through an SCX cartridge and eluted with 2cm3 of water. The eluate was collected in a graduated test-tube and the volume made up to 4 cm3 with water. An aliquot of this solution ( 5 mm3) was injected onto the HPLC system.

Results and Discussion It was found that there was no significant difference between the recoveries of maleic hydrazide obtained with SPE car- tridges from Bond-Elut, Worldwide Monitoring or Baker Bond. The mean recoveries ranged from 101 to 104% with a standard deviation (SD) of 4 7 % (Table 1). The remainder of the work was carried out using cartridges from Baker Bond, Worldwide Monitoring or Bond-Elut , chosen randomly.

Chromatograms of sample extracts after clean-up showed no interferences in the maleic hydrazide area when run on any of the HPLC systems. There were no indications that any of the pesticides (Table 2) normally used on onions and potatoes were present at the retention time of maleic hydrazide. The recovery of maleic hydrazide from samples of onions and potatoes was checked by adding known volumes of a standard solution to l o g portions of the chopped sample, treated as described under Procedure. The results obtained are shown in Table 3. Typical chromatograms are shown in Fig. 1. The limit of detection for maleic hydrazide was 3 ng with a signal-to- noise ratio of 3 : 1.

Conclusion This work shows that SPE cartridges can be used effectively as a clean-up medium for the determination of maleic hydrazide in onions and potatoes. The method is simple to use and saves on lengthy clean-up times.

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References 1

2

3

4 5

Codex Alimentarius Commission, Food and Agriculture Organ- ization, Rome, 2nd edn., 1986, vol. XIII. Lane, J . R., Gullstrom, D. K. , and Newell, J. E., J. Agric. Food Chem., 1958, 6, 671. Inhat, M., Westerby, R. J., and Hoffman, I., J . Assoc. Off. Anal. Chem., 1973, 56, 1164. Lui. Y., and Hoffman, D., Anal. Chem.. 1973,45, 2270. Haeberer, A. F., and Chortyk, 0. T., J. Assoc. Off. Anal. Chem.. 1979, 62, 171.

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6 Newsome, W. H., J. Agric. Food Chem., 1980, 28, 270. 7 Lessage, S., LC-GC, 1989, 2, 54. 8 Marble, L. K., and Delfino, J. J., Znt. Lab., 1989, 19. 16. 9 Albeck, H., Woodfield, S., and Kreek, M. J., J. Chromatogr.,

1989, 488, 435. 10 Reed, G. D., and Loscombe, C. R., Chromatographia, 1982,

15, 15. Paper Ol05392I

Received November 29th, 1990 Accepted August 30th, 1991

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