Pd nitrate (Matrix modifier, Merck®)
with a Pd final concentration of 250 mg L−1 was used as chemicalmodifier.
Prior to use, all glassware and polypropylene flasks were washed
with soap, soaked in 10% (v/v) HNO3 for 24 h, rinsed with deionized
water and dried in such a manner to ensure that no contamination
occurred