超高效液相色谱法测定药用复合膜中7种水溶性荧光增白剂

建立了一种同时测定药用复合膜中7种水溶性荧光增白剂的超高效液相色谱(UPLC)分析方法。样品经40%乙腈水溶液(三乙胺调至pH 11.0)提取。采用Waters ACQUITY UPLC BEH C_(18)色谱柱(100 mm×2.1 mm,1.7μm)进行分离,以乙腈-甲醇混合溶液(2∶3)和含10 mmol/L四丁基溴化铵的甲醇-水溶液(5∶95)为流动相,调至pH 8.0后进行梯度洗脱,流速为0.2 mL/min,检测波长为350 nm,柱温为40℃。结果表明,7种水溶性荧光增白剂在相应的质量浓度范围内线性关系良好,相关系数(r)为0.998 6～0.999 7,方法检出限为0.17～1.29μg/mL,定量下限为0.55～3.85μg/mL,3个加标水平的平均回收率为83.2%～110%,相对标准偏差(RSD)为4.0%～9.7%。样品测定结果显示,聚酯/铝/聚乙烯药用复合膜和纸/铝/聚乙烯药用复合膜最多检出两种荧光增白剂,其他品种样品均未检出荧光增白剂。该方法操作简便、可靠、重复性好,可用于药用复合膜中水溶性荧光增白剂的测定。     

蘑菇包装纸中荧光增白剂的高效液相色谱分析方法的建立

本实验建立了同时测定蘑菇包装纸中3种荧光增白剂(VBL、CBS、CXT)的高效液相色谱-荧光检测法。样品用乙醇-水(V/V=1/2)溶液作提取剂,30℃条件下超声提取30min。采用Thermo Fisher Accucore C18(250mm×4.6mm,2.6μm)为分析柱,以20mmol·L~(-1)乙酸铵:乙腈(65%:35%)为流动相洗脱,激发波长为350nm,发射波长为430nm。3种荧光增白剂在0.005~10μg·m L~(-1)范围内线性关系良好,相关系数(r~2)均大于0.997;检出限(S/N=3)分别为0.0004、0.0001、0.0006μg·m L~(-1);回收率范围80.0%~102.7%。     

高效液相色谱-三重四极杆质谱法测定面粉中7种荧光增白剂

建立了高效液相色谱-三重四极杆质谱(HPLC-MS/MS)测定面粉中7种荧光增白剂(FWAs)的分析方法。在样品中加入30 mL乙酸乙酯,超声提取10 min,离心后在40℃下氮吹浓缩,用乙腈定容后,上机检测。选用Phenomenex Kinetex C18色谱柱(100 mm×2.1 mm,2.6μm)分离,以0.1%(v/v)甲酸-乙腈和水为流动相进行梯度洗脱,采用电喷雾离子(ESI)源,在正离子、多反应监测(MRM)模式下进行扫描,外标法定量。7种荧光增白剂在各自范围内线性关系良好,相关系数均大于0.99,检出限(S/N=3)为0.50~2.65μg/kg,定量限(S/N=10)为1.60~8.80μg/kg;在3个添加水平下的平均加标回收率为64.8%~117.5%,相对标准偏差(n=6)为0.9%~14.4%。该方法操作简单、回收率高、精密度好,适于面粉中7种荧光增白剂的测定。     

高效液相色谱-荧光检测法测定塑料儿童玩具中苯并■唑类荧光增白剂

建立了高效液相色谱-荧光检测法同时测定塑料儿童玩具中4种苯并■唑类荧光增白剂(FWA 135、FWA 367、FWA 368、FWA 184)的方法。样品经粉碎后,采用20 mL乙腈-三氯甲烷(6∶4,体积比)混合溶液一步溶剂提取法对样品进行前处理,40℃下超声提取30 min后,进行高效液相色谱分析。以乙腈和水作为流动相,Waters SunFire C_(18)色谱柱梯度洗脱,荧光激发波长(Ex)为360 nm,发射波长(Em)为430 nm。结果显示,FWA 135在1～100μg/L质量浓度范围内具有良好的线性关系,其他3种荧光增白剂在2～200μg/L质量浓度范围内线性关系良好,相关系数(r~2)均不小于0.999 3,检出限分别为0.5、1、1、1μg/L。加标水平为0.1、0.4、2.0 mg/kg时,4种荧光增白剂的回收率为84.2%～106%,相对标准偏差均小于10%。对市售10种儿童玩具进行检测,部分样品中4种苯并■唑类荧光增白剂均有检出。该方法操作简单,回收率好,精密度高,适用于各种类型塑料儿童玩具中上述荧光增白剂的测定。     

洗涤用品中5种荧光增白剂的高效液相色谱法检测及质谱确证

建立了同时测定洗涤用品中5种荧光增白剂类化合物(荧光增白剂393、荧光增白剂KCB、荧光增白剂CBS-127、荧光增白剂KSN和荧光增白剂OB)的高效液相色谱分析方法及质谱确证方法。洗涤样品以四氢呋喃为提取溶剂进行超声提取,提取液离心处理后,取上清液经微孔滤膜过滤后测定。采用Agilent Eclipse XDB-C18色谱柱(250 mm×4.6 mm,5μm)分离,以甲醇-水二元流动相梯度洗脱,流速1.0 mL/min,柱温25℃,荧光增白剂KCB和荧光增白剂CBS-127的检测波长为359 nm,荧光增白剂393、荧光增白剂KSN和荧光增白剂OB的检测波长为372 nm。荧光增白剂393的定量限为0.25 mg/kg,荧光增白剂KCB、荧光增白剂CBS-127、荧光增白剂KSN和荧光增白剂OB的定量限为0.5 mg/kg。在低、中、高3种加标水平下的平均回收率为87.8%~103.7%,相对标准偏差为1.5%~4.4%。方法的日内RSD均小于1%,日间RSD均小于2%。适用于洗涤用品中5种荧光增白剂类化合物的测定。     

分子荧光光谱法测定食品接触材料中荧光增白剂

建立了分子荧光光谱法对荧光增白剂的定性和定量测定方法。对14种荧光增白剂通过进行激发波长和发射波长的扫描确定了其最大激发波长和最大发射波长,可结合进行荧光增白剂定性判断,并以三种常用的二苯乙烯型荧光增白剂VBL、BA、CXT为例,通过其迁移建立了定量测定荧光增白剂含量的方法。结果表明,三种荧光增白剂在0~1.0μg/mL范围内线性关系良好(相关系数r^2>0.999),检出限均为2.3μg/g,加标回收率均为92.9%~106%,相对标准偏差均小于5%,方法能有效满足食品接触材料样品中荧光增白剂的测定。     

HPLC-DAD法测定环己烷氧化产物中的二元酸

建立了高效液相色谱法测定环己烷氧化产物中丁二酸、戊二酸和己二酸含量的方法。色谱柱为ZORBAX SAX 4.6 mm×250 mm 5μm,流动相为甲醇:50 mmol/L KH2PO4水溶液=5:95(V/V),柱温:25℃,流速:1.0 mL/min。结果丁二酸、戊二酸和己二酸在10~200μg/mL范围内线性关系良好(r=0.9998,0.9996,0.9997),3种二元酸的检出限均为1.50μg/mL,目标分析物不同级别加标回收率在89.8%~102.6%之间,相对标准偏差(RSD)在1.6%~4.5%之间(n=6)。方法已用于环己烷氧化产物中有机二元酸的定量分析。     

高效液相色谱法同时测定塑料和纸质包装材料中6种荧光增白剂

建立了同时测定塑料和纸质食品包装材料中6种脂溶性荧光增白剂(FWA 135、FWA 184、FWA 185、FWA199、FWA 378和FWA 393)的高效液相色谱方法。用三氯甲烷-乙腈(3∶7,v/v)混合溶液提取,经HLB小柱净化后用高效液相色谱-荧光检测法进行定性定量分析。采用Phenomenex C18色谱柱分离,以5 mmol/L的乙酸铵水溶液和乙腈为流动相,进行梯度洗脱。结果显示:FWA 393在15~1500μg/L范围内的线性关系良好,其余5种荧光增白剂在5~500μg/L范围内线性关系良好,相关系数均大于0.999;加标回收率为80.4%~125.0%;相对标准偏差(RSD,n=6)为1%~13%。应用该方法分析了市场销售的12个样品以验证方法的实用性。该方法前处理简单,回收率高,精密度好,适用于食品包装材料中6种荧光增白剂的检测。     

高效液相色谱法检测溴化丁基胶塞中11种抗氧剂及游离硫的浸出量及迁移量

采用Inertsil ODS-SP C18(250×4.6 mm,5μm)色谱柱,以0.1%乙酸水-甲醇-乙腈为流动相,进行梯度洗脱,流速为1.0 mL/min,检测波长为277 nm。胶塞提取溶剂分别为无水乙醇和模拟药液。11种抗氧剂及游离硫的分离度均大于1.5;在2.47~54.51μg/mL浓度范围内,线性关系良好(R^2均大于0.999);检出限为0.021~0.403μg/mL;以无水乙醇为提取溶剂时,加标回收率为82.8%~115.3%,相对标准偏差为1.1%~6.1%;以模拟药液为提取溶剂时,加标回收率为62.9%~103.2%,相对标准偏差为1.4%~5.6%。该方法可用于包材相容性试验中实际样品的检测。     

高效液相色谱法测定食用菌中10种荧光增白剂

采用高效液相色谱法同时测定食用菌中10种双三嗪氨基二苯乙烯型荧光增白剂的含量。色谱分离中,以Athena C18-WP色谱柱(4.6 mm×200 mm,5μm)为固定相,用乙腈和0.02mol·L-1乙酸铵溶液以不同比例混合的溶液为流动相进行梯度洗脱,用荧光检测器测定,激发波长为350nm,发射波长为430nm。10种荧光增白剂的质量浓度均在2.0~100μg·L-1范围内与其峰面积呈线性关系,方法的检出限(3S/N)在0.002~0.005mg·kg-1之间。以空白样品为基体进行加标回收试验,所得回收率在73.0%~121%之间,测定值的相对标准偏差(n=6)在0.90%~7.8%之间。     

Darstellung,Kristallstrukturen, Schwingungsspektren und Normalkoordinatenanalyse von vier bindungsisomeren Trichlorotrirhodanoosmaten(IV)

Preparation, Crystal Structures, Vibrational Spectra, and Normal Coordinate Analysis of four Linkage Isomeric Trichlorotrirhodanoosmates(IV) By treatment of fac-[OsCl₃I₃]^2? with (SCN)₂ in dichloromethane the linkage isomers fac-[OsCl₃(NCS)₃]^2? ( 1 ), mer-[OsCl₃(NCS)₂^c(SCN)]^2? ( 2 ), mer-[OsCl₃(NCS)(SCN)₂^t]^2? ( 3 ), and mer-[OsCl₃(NCS)(SCN)₂^c]^2? ( 4 ) are formed which have been separated by ion exchange chromatography on diethylaminoethyl cellulose. X-Ray structure determinations have been performed on single crystals of fac-(Ph₄As)₂[OsCl₃(NCS)₃] (triclinic, space group P1 , a = 12.142(5), b = 13.233(5), c = 19.300(5) Å, α = 98.642(5)º, β = 100.509(5)º, γ = 112.514(5)º, Z = 2), mer-(Ph₄As)₂[OsCl₃(NCS)₂^c (SCN)] · acetone (triclinic, space group P1 , a = 11.707(5), b = 13.238(5), c = 19.048(5) Å, α = 75.960(5)º, β = 88.981(5)º, γ = 69.999(5)º, Z = 2), mer-(Ph₄As)₂[OsCl₃(NCS)(SCN)₂ ^t] (triclinic, space group P1, a = 10.6861(12), b = 11.6587(5), c = 12.5232(5) Å, α = 112.069(8)º, β = 95.052(8)º, γ = 92.559(7)º, Z = 1) and mer-(Ph₄As)₂[OsCl₃(NCS)(SCN)₂ ^c] · 2acetone (triclinic, space group P1 , a = 11.444(5), b = 14.661(5), c = 15.830(5) Å, α = 75.790(5)º, β = 80.273(5)º, γ = 75.205(5)º, Z = 2). The complex anions are completely ordered. The via N or S coordinated thiocyanate groups are located nearly direct above one of the cis-positioned Cl ligands with Os? N? C angles of 169.1º, 171.5º, 175.7º ( 1 ), 175.6º, 178.6º ( 2 ), 172º ( 3 ), and 173.1º ( 4 ) and Os? S? C angles of 106.2º ( 2 ), 106.1º, 106.6º ( 3 ), 105.1º, and 108.2º ( 4 ). Using the molecular parameters of the X-Ray determinations the low temperature (10 K) IR and Raman spectra of the (n-Bu₄N) salts of all four linkage isomers have been assigned by normal coordinate analyses based on a modified valence force field. The valence force constants are f_d(OsN) = 1.71 ( 1 ), 1.46 and 1.62 ( 2 ), 1.69 ( 3 ), and 1.61 ( 4 ), f_d(OsS) = 1.27 ( 2 ), 1.36 ( 3 ), 1.32, and 1.49 mdyn/Å ( 4 ). Taking into account increments of the trans influence a good agreement between observed and calculated frequencies is achieved.     

Darstellung und Kristallstruktur von (n-Bu4N)3[Ir(NCS)(SCN)5]

Preparation and Crystal Structure of (n-Bu₄N)₃[Ir(NCS)(SCN)₅] The evaporated ethanolic extrakt of the reaction product of K₃[IrCl₆] and HNO₃, refluxed with an aqueous KSCN solution yields a mixture of the linkage isomers [Ir(NCS)_n(SCN)_6?-n]^3?, n = 0? 2, and small amounts of linkage isomeric chloropentarhodanoiridates(III), from which [Ir(NCS)(SCN)₅]^3? has been isolated by ion exchange chromatography on DEAE-cellulose. The X-Ray structure determination on a single crystal of (n-Bu₄N)₃[Ir(NCS)(SCN)₅] (monoclinic, space group P 2₁/a, a = 17.513(5), b = 32.607(5), c = 23.661(5) Å, β = 94.757(5)°, Z = 8) confirms the existance of a heteroleptic hexakis(thiocyanato(N)-thiocyanato(S))iridate(III) with an Ir? N distance of 2.03 Å and Ir? S bond lengths between 2.29 and 2.38 Å. The SCN groups with angles between 166 and 175° are nearly linear with Ir? S? C angles from 99.9 to 109.4°. The Ir? N? C angles of the two crystallographic independent anions are 166 and 174°.     

Darstellung,Kristallstrukturen, Schwingungsspektren und Normalkoordinatenanalyse von vier bindungsisomeren Tetrachlorodirhodanoosmaten(IV)

Preparation, Crystal Structures, Vibrational Spectra, and Normal Coordinate Analysis of Four Linkage Isomeric Tetrachlorodirhodanoosmates(IV) By treatment of cis- or trans-[OsCl₄I₂]^2? with (SCN)₂ in dichloromethane the linkage isomers cis-[OsCl₄(NCS)₂]^2? ( 1 ), trans-[OsCl₄(NCS)(SCN)]^2? ( 2 ), cis-[OsCl₄(NCS)(SCN)]^2? ( 3 ) and trans-[OsCl₄(SCN)₂]^2? ( 4 ) are formed which have been separated by ion exchange chromatography on diethylaminoethyl cellulose. The X-Ray structure determinations on single crystals of cis-(Ph₄As)₂[OsCl₄(NCS)₂] (triclinic, space group P1 , a = 10.019(5), b = 11.702(5), c = 21.922(5) Å, α = 83.602(5)°, β = 85.718(5)°, γ = 73.300(5)°, Z = 2), trans-(Ph₄As)₂[OsCl₄ · (NCS)(SCN)] (monoclinic, space group P2₁/c, a = 18.025(5), b = 11.445(5), c = 23.437(5) Å, β = 94.208(5)°, Z = 4), cis-(Ph₄As)₂[OsCl₄(NCS)(SCN)] (triclinic, space group P1 , a = 10.579(5), b = 11.682(5), c = 22.557(5) Å, α = 81.073(5)°, β = 85.807(5)°, γ = 87.677(5)°, Z = 2) and trans-(Ph₄As)₂ · [OsCl₄(SCN)₂] (triclinic, space group P1 , a = 10.615(5), b = 11.691(5), c = 11.907(5) Å, α = 111.314(5)°, β = 96.718(5)°, γ = 91.446(5)°, Z = 1) reveal the complete ordering of the complex anions. The via N or S coordinated thiocyanate groups are located nearly direct above one of the cis-positioned Cl ligands with Os? N? C angles of 171.2° and 174.3° ( 1 ), 162.3° ( 2 ), 172° ( 3 ) and Os? S? C angles of 108.3° ( 2 ), 105.7° ( 3 ) and 105.5° ( 4 ). Using the molecular parameters of the X-Ray determinations the low temperature (10 K) IR and Raman spectra of the (n-Bu₄N) salts of all four linkage isomers are assigned by normal coordinate analyses based on a modified valence force field. The valence force constants are f_d(OsN) = 1.59 ( 1 ), 1.67 ( 2 ), 1.60 ( 3 ) and f_d(OsS) = 1.27 ( 2 ), 1.31 ( 3 ) and 1.32 mdyn Å^?1 ( 4 ). Taking into account increments of the trans influence a good agreement between observed and calculated frequencies is achieved.     

Comparative Thermogravimetric Studies of Poly(ether-ketone/sulfone) Imides and Their Parent Polymers: I. Poly(ether-ketone/sulfone) ethylimide

Thermogravimetry (TG) was employed to study the thermal degradation kinetics of poly(etherketone/sulfone)ethylimide (PEK-IE and PES-IE). The corresponding decomposition activation energies and reaction orders were obtained and the comparison was made with their parent polymerspoly(ether-ketone/sulfone) with Cardo group (PEK-C and PES-C). The results show that the degradation activation energies of PEK-IE and PES-IE were lower than that of PEK-C and PES-C; and two stages of the degradation process were found for all the four polymers. For PEK-IE and PES-IE, the activation energies in the first decomposition stage are much lower than that in the second stage and the two stages can be taken as slow induction and fast degradation, whereas for PEK-C and PES-C the activation energies in the first decomposition stage are larger than that in the second stage, and the two stages can both be taken as two fast degradation stages. The decomposition mechanism of the two stages was also speculated.This revised version was published online in November 2005 with corrections to the Cover Date.     

PMDA-BPDA-HAB聚苯并噁唑的合成及耐热性

PMDA-BPDA-HAB聚苯并噁唑的合成及耐热性;均苯四甲酸二酐;联苯四羧酸二酐;二羟基联苯胺;聚酰亚胺;聚苯并噁唑;耐热性     

SYNTHESIS AND CHARACTERIZATION OF METAL COMPLEXES WITH AMPICILLIN

Abstract

The reaction, in water, of Co(II), Ni(II), Cu(II), Zn(II) and Cd(II) ions with sodium ampicillinate at room temperature has allowed isolation of dimers with the following general formula [M(amp)Cl]₂ × nH₂O (n = 1.5?3.2). The complexes were characterized by elemental analyses, conductivity measurements, magnetic susceptibilities and spectroscopic methods (IR, Raman, EPR and UV-Visible). A dinuclear structure based on octahedrally coordinated metal ions is proposed.     

Thermal Degradation of Poly(ε-caprolactone), Poly(L-lactic acid) and their Blends with Poly(3-hydroxy-butyrate) Studied by TGA/FT-IR Spectroscopy

Summary: The thermal degradation behavior of poly(ε-caprolactone) (PCL) and poly(L-lactic acid) (PLA) have been studied in different environment. It was found that these polymers undergo completely different degradation processes in nitrogen and oxygen atmosphere. In oxygen environment PCL and PLA mainly decompose to CO₂, CO, water and short-chain acids. In nitrogen atmosphere PCL releases 5-hexenioc acid, CO₂, CO and ε-caprolactone, whereas PLA decomposes to acetaldehyde, CO₂, CO and lactide. The polymer blends of poly(3-hydroxybutyrate) (PHB) with PCL and PLA decompose similar to the individual homopolymers with crotonic acid as the initial decomposition product of PHB.     

Silica gel surface modified with sulfanilamide for selective solid-phase extraction of Cu(II), Zn(II) and Ni(II)

A new chelating matrix has been prepared by immobilising sulfanilamide (SA) on silica gel (SG) surface modified with 3-chloropropyltrimethoxysilane as a sorbent for the solid-phase extraction (SPE) Cu(II), Zn(II) and Ni(II). The determination of metal ions in aqueous solutions was carried out by inductively coupled plasma optical emission spectrometry (ICP-OES). Experimental conditions for effective sorption of trace levels of Cu(II), Zn(II) and Ni(II) were optimised with respect to different experimental parameters using the batch and column procedures. The presence of common coexisting ions does not affect the sorption capacities. The maximum sorption capacity of the sorbent at optimum conditions was found to be 34.91, 19.07 and 23.62 mg g^?1 for Cu(II), Zn(II) and Ni(II), respectively. The detection limit of the method defined by IUPAC was found to be 1.60, 0.50 and 0.61 µg L^?1 for Cu(II), Zn(II) and Ni(II), respectively. The relative standard deviation (RSD) of the method under optimum conditions was 4.0% (n = 8). The method was applied to the recovery of Cu(II), Zn(II) and Ni(II) from the certified reference material (GBW 08301, river sediment) and to the simultaneous determination of these cations in different water samples with satisfactory results.     

Energy relationship and the polarization of C_(60) cage in the endohedral complexes (X@C_(60))

In this paper, we carry out the calculation on the system (X@C60)(X=Li, Na, K, Kb, Cs; F, Cl, Br, I), where the position of X changes along 5 typical symmetry directions. For the calculation of quantum chemistry we use EHMO/ASED method, for the calculation of molecular mechanics we use Buckingham potential (exp-6-1) function, and for the calculation of thermo-chemical cycle we use individually isolating the processes such as the structure variation, charge transfer and charge distribution, and their interactions etc. The calculation results show that (1) In the region of radius r≈0.2 nm of the Ceo cage, the potential field is nearly spherical; (2) Except for Li and Na, the systems are the most stable with minimum energies at the center of C60 cage. For Li and Na, the systems are the most stable with minimum energies at r≈0.16 nm and r≈0.13 nm, respectively. In view of the interactive region of chemical bonds, the interactions between X and the C60 cage do not belong to the classical chemical bonds; (     

Drei stereoisomere quadratisch-pyramidale [Ma3b2]-Komplexe: Untersuchungen zur Existenz und zur Struktur kristalliner Dimethylsulfoxid-Komplexe von Antimon- und Bismuttrichlorid

Three Stereoisomeric Square-Pyramidal Complexes [Ma₃b₂]: Investigations of the Existence and the Structures of Crystalline Dimethyl Sulfoxide Complexes of Antimony and Bismuth Trichlorides The formation of solid complexes MCl₃ · n DMSO (M = Sb, Bi; n = 1–4) was reinvestigated. In each system, only two of four presumptive complexes could be isolated as crystalline solids: SbCl₃ · DMSO ( 1 a ) was prepared for the first time, SbCl₃ · 2 DMSO ( 1 b ), BiCl₃ · 2 DMSO ( 2 b ) and BiCl · 3 DMSO ( 2 c ) were reproduced according to literature data. Evidence is presented as to the non-existence of BiCl₃ · 4 DMSO, contrary to previous claims in the literature. A unit cell determination showed 2 c to be structurally identical with the monomeric fac-octahedral complex BiCl₃(DMSO)₃ obtained fortuitously and described elsewhere [Z. anorg. allg. Chem. 620 (1994) 1037]. The compounds 1 a (monoclinic, space group P2₁/c), 1 b (monoclinic, space group P2₁/n) and 2 b (monoclinic, space group C2) represent examples of each of the three possible geometric isomers of a square-pyramidal complex [Ma₃b₂]. In the formally 1/1 adduct 1 a , which is in fact [Sb(1)Cl₃(DMSO)₂ · Sb(2)Cl₃], the Sb(1) atom of the complex unit displays square-pyramidal geometry with the DMSO ligands situated in the apical and one of the basal positions. These units are linked into chains by SbCl₃ molecules acting as Cl-acceptors. Sb(2) forms two chelating chloro-bridges with cis-Cl atoms of one neighbouring complex and a third chloro-bridge with the remaining Cl of the symmetry-related second neighbour. The resulting Cl₆-geometry around Sb(2) is distorted octahedral. 1 b consists of square-pyramidal molecules, in which the DMSO ligands occupy two basal cis-positions; the monomeric units are loosely linked through the apical Cl atoms to form a chain of octahedra sharing trans-vertices. The asymmetric unit of 2b is a square pyramid with trans-basal DMSO ligands. The pyramids are connected by symmetry-equivalent basal chlorine atoms into chains of octahedra sharing cis-vertices. 1a displays remarkably short Sb? O dative bonds (204.7/212.9 pm); the M? O bond distances of 1b and 2b are 223.0/234.6 and 234.5/238.7 pm, respectively.